Safety Parachute System

School of Science, Engineering, and Technology

Department of Engineering

Safety Parachute System

by

Juan Luna Glaser (CE) and Sebastian Castro Ramos (ME)

Senior Design Project Presented to the Department of Engineering

In Partial Fulfillment of the Requirements

For the Degree of

Bachelor of Science

in

COMPUTER ENGINEERING

MECHANICAL ENGINEERING

San Antonio, Texas

April 2021

Supervising Advisors:

Dr. Juan Ocampo ASSOCIATE PROFESSOR OF MECHANICAL ENGINEERING

Dr. Ben Abbott INSTRUCTOR OF ELECTRICAL ENGINEERING

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ABSTRACT

The use of drones has risen steadily in recent years. Applications include surveillance,

filmmaking, photography, disaster relief, real estate, among others. This type of device, like any

other, is prone to fail for a variety of reasons; battery failure, environmental hazards,

communication error, structural failure, and pilot error are just a few of the common risks drones

possess. This project created an emergency-parachute system to safeguard drones of varying uses

and specifications from the aforementioned issues. When a drone exhibits erratic behavior, our

system provides a last resort that mitigates damage to surroundings and the drone itself.

This project involved two areas of engineering, computer engineering, and mechanical

engineering. We put into practice concepts in mechanical design, materials science, electronics,

microprocessors, and signals and systems. These concepts enabled us to theorize the proof of

concept, design, analyze, build, and test a parachute system for drones. Our combined efforts

formed an interdisciplinary project which met all requirements to improve upon existing

commercially available drone parachute systems and protect public safety.

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ACKNOWLEDGEMENTS

We would like to express our deep appreciation to all the people who helped us directly or

indirectly during this project. We are particularly grateful to Dr. Juan Ocampo and Dr. Ben Abbott,

who guided us throughout the project as our project advisors. We thank the St. Mary's Unmanned

Aerial Systems Lab and the SET Dean Erevelles’ Fund for sponsoring this project. We give our

special thanks to Dr. Dante Tezza and Dr. Bahman Rezaie, who provided their support and input.

We also extend our gratitude to Mr. Vernon Wier, who helped manufacture and test components.

We extend our thanks to Ms. Nicole Webb, who has aided us considerably in the lab. We thank

Ms. Gail Jascz for her help ordering the different parts we required on this project. Finally, we

would like to give thanks to our special friend, Gabriela Santos Bolanos, who coached us on our

presentations.

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Table of Contents ABSTRACT .................................................................................................................................................. 2

ACKNOWLEDGEMENTS .......................................................................................................................... 3

LIST OF FIGURES ...................................................................................................................................... 6

LIST OF TABLES ........................................................................................................................................ 8

LIST OF APPENDICES ............................................................................................................................... 9

1. INTRODUCTION .............................................................................................................................. 10

1.1 PROBLEM STATEMENT ......................................................................................................... 10

1.2 OBJECTIVES ............................................................................................................................. 10

1.3 DIVISION OF LABOR .............................................................................................................. 11

1.4 COMMERCIAL PRODUCT REVIEW ..................................................................................... 12

1.5 PROBLEM CONSTRAINTS, REQUIREMENTS, AND SPECIFICATIONS ......................... 14

1.6 PROPOSED SOLUTIONS ......................................................................................................... 15

2. OVERVIEW OF SYSTEM ................................................................................................................ 18

3. ITERATIVE DESIGN ........................................................................................................................ 19

3.1 ELECTRICAL DESIGN............................................................................................................. 19

3.2 SOFTWARE COMPONENTS ................................................................................................... 24

3.3 MECHANICAL DESIGN .......................................................................................................... 29

4. OVERVIEW OF FINAL DESIGN OF SYSTEM .............................................................................. 40

4.1 ELECTRICAL AND SOFTWARE .................................................................................................. 40

4.2 MECHANICAL ................................................................................................................................ 49

5. STANDARD DISCUSSION .................................................................................................................. 56

6. RESULTS ............................................................................................................................................... 58

7. PROTOTYPE FABRICATION AND TESTING .................................................................................. 60

7.1 CONTROLLED TABLET BURNING TEST .................................................................................. 60

7.2 CO2 LEAKAGE TEST ..................................................................................................................... 65

7.3 GROUND LAUNCH TEST 1 .......................................................................................................... 66

7.4 GROUND LAUNCH TEST 2 .......................................................................................................... 68

7.5 FLIGHT TERMINATION SYSTEM TEST .................................................................................... 69

8. ECONOMICAL, SAFETY, AND WELFARE ANALYSIS OF RESULTS ......................................... 71

9. FURTHER IMPLEMENTATION .......................................................................................................... 71

9.1 MECHANICAL DESIGN ................................................................................................................ 72

9.2 ELECTRICAL AND SOFTWARE .................................................................................................. 72

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10. REFERENCES ..................................................................................................................................... 74

11. APPENDICES ...................................................................................................................................... 75

12. SMC CAPSTONE REFLECTIONS ..................................................................................................... 96

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LIST OF FIGURES Figure 1 - Spring Deployment System Sketch ............................................................................................ 15

Figure 2 - CO2 Cartridge Deployment System Sketch ................................................................................ 16

Figure 3 - ESP32 Board to Replace the Raspberry Pi ................................................................................. 16

Figure 4 - Flow Diagram of the Safety Parachute System .......................................................................... 17

Figure 5 - Block Diagram ........................................................................................................................... 18

Figure 6 - Improved Block Diagram ........................................................................................................... 20

Figure 7 - Switching Module ...................................................................................................................... 21

Figure 8 - Breakout Boards Design............................................................................................................. 21

Figure 9 - Switching Module ...................................................................................................................... 22

Figure 10 - Second Iteration of the Power Management Prototyping Boards ............................................ 23

Figure 11 - Level 0 Context Diagram ......................................................................................................... 24

Figure 12 - Tools Used for the Website ...................................................................................................... 25


Figure 14 - Low Fidelity Prototype of the preflight parameters page ......................................................... 26

Figure 15 - Functioning Prototype 2 of the Website ................................................................................... 26

Figure 16 – Prototype 3 to test the verification of the BLE Connection Page ............................................ 27


Figure 18 - Level First Iteration of Spring-Loaded System ........................................................................ 29

Figure 19 - Spring-Loaded System Iteration 2 ............................................................................................ 30

Figure 20 - CO2 System Iteration 1 ............................................................................................................. 30




Figure 24 - Cross Section of CO2 System Iteration 4 ................................................................................. 33

Figure 25 - Flight Termination System Concept......................................................................................... 33


Figure 27 - Top Cross-Section of CO2 System Iteration 5 .......................................................................... 34


Figure 29 - Top View of CO2 System Iteration 6 ....................................................................................... 35


Figure 31 - Cross-Section of the Fusible Plug ............................................................................................ 37

Figure 32 - Cross-Section of Air Director Iteration 7 ................................................................................. 37

Figure 33 - System Eight Iteration .............................................................................................................. 38

Figure 34 - System Eight Iteration .............................................................................................................. 38

Figure 35 - Fusible Plug Eight Iteration...................................................................................................... 39

Figure 36 - Electronics Arrangement Eight Iteration .................................................................................. 39

Figure 37 - System Iteration Nine ............................................................................................................... 40

Figure 38 - ESP32 Microcontroller and its pinouts .................................................................................... 41

Figure 39 - Sensor and Alarm Board .......................................................................................................... 43

Figure 40 - ESP32 Microcontroller Pinout ................................................................................................. 44

Figure 41 - Power Sources and Power Management Boards ...................................................................... 45

Figure 42 - Surefire SF1234 Battery Discharge Rate ................................................................................. 46

Figure 43 - Switching Module .................................................................................................................... 47

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Figure 44 - Transfer Characteristics for the D4184 module ....................................................................... 48

Figure 45 – Important features .................................................................................................................... 48

Figure 46 - System Iteration Ten ................................................................................................................ 49

Figure 47 - Nichrome Wire Placement. ...................................................................................................... 50

Figure 48 - Piercing Block .......................................................................................................................... 51

Figure 49 - Cross-Sectional View CO2 Release System ............................................................................. 51

Figure 50 - CO2 Tube. ................................................................................................................................. 52

Figure 51 - Flight Termination System Flaps ............................................................................................. 53

Figure 52 - Disassembled Flight Termination System Flaps. .................................................................... 53

Figure 53 - Parachute Cage ......................................................................................................................... 54

Figure 54 - System Lid. .............................................................................................................................. 54

Figure 55 - Electronics Placement .............................................................................................................. 55

Figure 56 - Attachment System .................................................................................................................. 55

Figure 57 - Fruity Chutes Iris 36" Ultra Light Parachute [9]. ..................................................................... 56

Figure 58 - Danger Label. ........................................................................................................................... 58

Figure 59 - Sacrificial Tablet First Iteration ............................................................................................... 61

Figure 60 - Sacrificial Tablet Second Iteration ........................................................................................... 62

Figure 61 - Nichrome Wire Groove Designs .............................................................................................. 62

Figure 62 - Tablet Bottom Third Iteration .................................................................................................. 63

Figure 63 - Tablet Burning Box .................................................................................................................. 64

Figure 64 - Tablet Burn Test ....................................................................................................................... 64

Figure 65 - CO2 Leakage Test Setup .......................................................................................................... 65

Figure 66 - O-Ring Placement .................................................................................................................... 66

Figure 67 - Ground Launch Test 1 .............................................................................................................. 67

Figure 68 - Initial Balloon Test Setup ......................................................................................................... 68

Figure 69 - Second Balloon Test Setup ...................................................................................................... 69

Figure 70 - Third Balloon Test Setup ......................................................................................................... 69

Figure 71 - Flight Termination System Test Setup ..................................................................................... 70

Figure 72 - Flight Termination System Test Results .................................................................................. 71

Figure 73 - Home Page ............................................................................................................................... 91

Figure 74- Navigation Page Tab ................................................................................................................. 91

Figure 75 - Connect to BLE Tab ................................................................................................................. 91

Figure 76 - Plan Flight Tab ......................................................................................................................... 92

Figure 77 - Start Flight Tab ........................................................................................................................ 92

Figure 78 - Metrics & Emergency Deployment Tab .................................................................................. 92

Figure 79 - Report Tab ................................................................................................................................ 93

Figure 80 - Sample Generated Report ......................................................................................................... 93

Figure 81 - Documentation Page ................................................................................................................ 93

Figure 82 - Contact Page ............................................................................................................................. 94

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LIST OF TABLES Table 1 - Division of Labor ........................................................................................................................ 11

Table 2 - Details of Existing Parachute Systems ........................................................................................ 12

Table 3 - Images of Commercial Parachutes .............................................................................................. 13

Table 4 - BMP388 List of Key Features ..................................................................................................... 43

Table 5 - BMP388 List of Key Features ..................................................................................................... 45

Table 6 - Production Cost ........................................................................................................................... 58

Table 7 - ESP32 Power Modes ................................................................................................................... 77

Table 8 - Power Budget .............................................................................................................................. 78

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LIST OF APPENDICES Appendix A - Parachute Selection Calculations ......................................................................................... 75

Appendix B - Maximum Power Calculations ............................................................................................. 76

Appendix C - Power Budget ....................................................................................................................... 77

Appendix D - Center of Mass Calculations ................................................................................................ 80

Appendix E - Power Screw Calculations .................................................................................................... 84

Appendix F - Piercing Block Fastening Calculations ................................................................................. 88

Appendix G - Website Screenshots ............................................................................................................ 91

Appendix H - Datasheets of Electric Components and Links to Software Tools ....................................... 95

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1. INTRODUCTION

Drones are susceptible to failure, which can become a hazard. Drone failure could cause

damage to people, private property, animals, and the drone itself. We developed a modular

parachute system for drones that minimizes this hazard. To ensure adherence to engineering

standards, we considered a list of desired features set by the project sponsor and a set of standards

for drone parachute systems. Working under both lists of requirements, we developed a working

prototype that is thoroughly discussed in this report.

1.1 PROBLEM STATEMENT

A safety parachute system must be designed to detect a failure and deploy a parachute upon

detection of a failure or manual trigger. A parachute and mechanical deployment system are to

be developed for a drone, alongside an electronics system capable of detecting drone failure.

1.2 OBJECTIVES

The main objective of this project was to design and build a functioning safety parachute for

drones. To accomplish this, we identified the following sub-objectives:

• An onboard system is to be added to an existing drone system to detect a failure and deploy

the parachute.

• A parachute and a deployment mechanism are to be developed to work in conjunction with

the failure detection system.

• The parachute must be deployable by either machine decision or manual control from the

drone pilot.

• The communication protocols between the pilot and the drone should be improved to use

more communication lines in case of failure.

The minor objectives we have identified are the following:

• Implement a secondary parachute deployment trigger.

• Make the parachute system wholly or partially reusable.

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The system should allow the user to easily exchange the parachute or mechanical aspects to

one that fits better their purposes.

1.3 DIVISION OF LABOR

Division of labor is shown in Table 1, where an even distribution of work was ensured for

each member.

Team Member Task

Juan Luna • Design a modular kit for the electronics and onboard computer that

works for different drone models.

• Design the necessary circuitry to read the drone's vitals and relay this

data to the pilot.

• Implement wireless communications.

• Design and implement the algorithm used to detect critical points of

failure and scenarios that require parachute deployment.

• Design and implement a semi-autonomous computer which can

interpret the vitals and determine if the parachute should be deployed.

Sebastian Castro • Select a parachute of appropriate size for the drone that meets ASTM

F3322 standards.

• Design, build, and test a mechanical triggering system to deploy the

parachute rapidly and reliably.

• Design, build, and test a casing to house the electronic components,

parachute, and trigger system.

• Design, build, and test a modular attachment system compatible with a

set of different drone models.

Table 1 - Division of Labor

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1.4 COMMERCIAL PRODUCT REVIEW

A search for similar commercial products was conducted to set a standard of what is

currently available. The products listed are parachute systems that correspond to the size of the

drone used for this project. Table 2 gives an overview of current products' data, including price,

weight, and essential features.

Product Name Product Price Product

Weight

Product Features

Skycat X48 [1]

$519.15 0.250 kg Parachute system that operates via a fuse system.

Includes launcher, parachute, fuse set, and harness

kit. Bullet method deploys parachute. Dedicated

launch battery in case of power loss. Manually

triggered parachute that can be mounted on different

drone models.

MARS 58 V2

[2]

$389.00 0.278 kg An auto-deployment system which includes the

following: parachute system and mounting set; high

energy compression spring deployment, capable of

being mounted on different drone models; and servo

triggers.

Parazero

SafeAir

Mavic [3]

$2,499.00 0.165 kg Compliant with ASTM-3322 standards, compatible

with DJI Mavic 2 Series, automatic trigger, data logs

stored in black box device, includes mounting

equipment, easy to repack.

Parazero

SafeAir

Phantom [4]

$2,499.00 0.160 kg Compliant with ASTM-3322 standards, compatible

with DJI Phantom 4, automatic trigger, data logs

stored in black box device, includes mounting

equipment, easy to repack.

Table 2 - Details of Existing Parachute Systems

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Product Product Image

Skycat X48 [1]

`

MARS 58 V2 [2]

Parazero SafeAir Mavic

[3]

Parazero SafeAir Phantom [4]

Table 3 - Images of Commercial Parachutes

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The products' websites provided some valuable information. Firstly, there are two price

ranges, the Skycat and the Mars parachute systems lie between the $380-$520 price range, and the

Parazero parachute systems fall on the $2,500 price point. The most significant difference is that

the Parazero parachute systems follow compliance with ASTM F3322 parachute regulations, while

the others do not. Additionally, the Parazero parachute systems are designed for specific drone

models. The Skycat and Mars are designed to fit two different models within a size and weight

range. Three of the four products have automatic parachute deployment, and only the Skycat has

manual deployment. All the models come with a parachute and mounting devices. The parachute

systems are lightweight, ranging between 0.160 kg and 0.278 kg. The Parazero parachutes are the

lightest models.

1.5 PROBLEM CONSTRAINTS, REQUIREMENTS, AND SPECIFICATIONS

Our technical advisor helped to identify a set of constraints, requirements, and

specifications outlined below:

• The maximum weight allowed for the parachute system is 400g.

• The cost of producing one parachute system must be below $390.

• The parachute system must use the watchdog system to analyze for system failures.

• The drone's center of mass with the parachute system should not cause the motors' thrust

output to vary beyond 10% of each other.

• The parachute system should be easily modified for drones of various sizes.

• The overall drone must be capable of following the 2:1 ratio; the drone must be able to

carry twice its weight.

• The parachute system must be able to deploy effectively while the drone is tumbling.

• The parachute system must align with ASTM F3322 standards.

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1.6 PROPOSED SOLUTIONS

In the early stages of development, a series of possible solutions were brainstormed to set

forth the system's design. These considered the different constraints, requirements, and goals so

that the approaches could evolve to feasible final solutions. This section discusses the initial

proposed solutions for this project.

Two different options for the mechanical triggering system were identified: the first

involving a high compression spring, and the second a CO2 cartridge. Both are considered ballistic

ejection methods.

An early sketch of the first option, the springalternative , is shown in Figure 1. A spring

would be compressed inside the casing and a servo or actuator would hold the cap of the case in

place. When the parachute needs to be deployed, the servo would allow the spring to decompress,

which would then launch the parachute. The advantage of this method is that the parachute system

would entirely reusable. The parachute would need to be re-loaded each time the drone is used.

Figure 1 - Spring Deployment System Sketch

The second option, the alternative using CO2 cartridges, is shown in Figure 2. This option

would require a CO2 cartridge to eject the parachute. An onboard computer would send instructions

to a servo motor, which would control a valve to release the CO2. The servo would allow enough

air to push a pushing plate to deploy the parachute. Another alternative solution was a system that

would only puncture the cartridge when the parachute needed deployment.

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Figure 2 - CO2 Cartridge Deployment System Sketch

The electronics system incorporates an ESP32 microcontroller board, shown in Figure 3.

Commercial drones feature various sensors and communication protocols (accelerometer,

gyroscope, barometer, Global Positioning System (GPS), magnetometer, Radio Frequency (RF)

signals, and Bluetooth Low Energy (BLE)) used to track and 'talk' to the drone. Knowing this, the

electronics system in the Safety Parachute System includes electronics to communicate but not

interfere with the drone’s onboard system. BLE was chosen as the primary communication channel

to communicate with the onboard electronic systems of commercial drones. To detect a failure in

flight, sensors for altitude and acceleration were chosen. The sensors’ data is displayed to the drone

pilot, and if the ESP32 detected a flight error, a deployment signal is sent to the triggering

mechanism to deploy the parachute.

Figure 3 - ESP32 Board to Replace the Raspberry Pi

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Figure 4 shows the logical flow of the Safety Parachute System’s electronics. The user

inputs the altitude, acceleration, and flight time limits into the system before starting the flight.

Once the flight is initiated, the system continuously monitors the power remaining on the Safety

Parachute System, verifies that there is still communication of the onboard system with the pilot,

and checks the sensors’ data. If the system detects a failure and the flight is not yet completed, the

electronics send a deployment signal to the triggering mechanism.

Figure 4 - Flow Diagram of the Safety Parachute System

Figure 5 shows the block diagram skeleton used for the initial design of the electronics.

This schematic demonstrates which electric components are necessary to achieve the logical flow

presented in Figure 4: a microcontroller, power source, sensors, triggering mechanism, and a

communication block. The prototyping boards to accomplish these roles are discussed in the

following section

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Figure 5 - Block Diagram

2. OVERVIEW OF SYSTEM

The mechanical system considers two components: the ejection system that launches the

parachute upward, and the flight termination system that stops the drone propellers from spinning.

For the parachute ejection, we opted for the CO2 canister method because the burst of air

released by the cartridge can aid in the opening of the parachute. A CO2 canister is non-reusable,

so every time the parachute is deployed, the cartridge must be replaced, but the price of these

canisters is low and would not decrease product desirability. The cost of additional deployments

is discussed on a further section.

Different approaches were considered for the Flight Termination System, such as cutting

power from the motors and physically stopping the propellers from spinning. The problem of

attempting to cut off the motors' power is that it limits the parachute system's modularity.

Additionally, ASTM F3322-18 [5] standards warn that even if power is cut from motors, residual

energy may pose a hazard on pinwheeling propellers. For these reasons, it was decided to stop the

propellers physically. Some of the approaches considered were to shoot a net onto the propellers,

shoot a small string to each propeller, and shoot synthetic spiderweb to slow down the propellers.

Other solutions were to have the casing rotate so that a flap stops the propellers, to have extendable

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flaps, and to mount on each arm a mechanism to stop the propellers. Later in development, it was

finally decided to extend flaps out break the drone's propellers.

The system's software and electrical components, when in flight mode, checked for the

drone's status every 750ms. and communicated that information back to the user. The onboard

computer has an alarm and sensory system that consists of a speaker, accelerometer, gyroscope,

compass, and barometer. Finally, the system contains two power sources that consist of primary

and secondary batteries, each varying in power delivery.

The software was refined to the point that communication BLE protocols work. The user

can input data into the Safety Parachute System via a website containing a table which asks for

maximum acceleration, maximum altitude, and maximum flight time. The website delivers these

custom constraints via BLE.

3. ITERATIVE DESIGN

Throughout the development of this project, different components have undergone a series

of iterations, each improving upon the mistakes and aspects where the system falls short. A

description of the design process of the different components is outlined below.

3.1 ELECTRICAL DESIGN

The electrical components first drafted on block diagrams identified how many blocks are

needed to create a system capable of collecting and interpreting data, sending a deployment signal,

and preserving the system's life. After identifying the necessary components, they were transferred

to prototyping boards. Each test revealed some flaws in the initial drafting, which then changed in

later iterative design cycles. In this section, the electrical elements of the system are presented

from its iterative design cycles to the changes undergone before the final system design.

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ELECTRIC COMPONENTS

This project's electrical requirements are the following: a microcontroller responsible for

communication and decision-making; a sensor board to gather information used in deciding

whether a deployment is necessary or not; and a power management board that included Dynamic

Power Path Management that is used to toggle between the primary and secondary battery sourced.

Another vital component identified through iterative design was the triggering mechanism, and RF

communication was not deemed necessary.

BLOCK DIAGRAM

Figure 6 - Improved Block Diagram

Figure 6 identifies the components needed to create a datalogger. The I/O board is the

central device responsible for hosting the wireless communication via BLE technology and

interpreting the data gathered by the peripherals. The triangles represent the system power sources.

There are three distinct peripherals connected to the central device: receivers and peripheral

connectors to connect to the switching module, a board of several sensors that gather data in real-

time and report back to the central device and the power management block (Diode or Circuit)

used to preserve and guarantee the life of the system.

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Figure 7 - Switching Module

Figure 7 shows the block diagram for the switching module. A MOSFET is used as a switch

to drive a high current and voltage to the load. A switching module is necessary to protect the

ESP32 board from the power source. Another aspect considered is the MOSFET model used, as

the ESP32 board can only deliver 3.3V through its GPIO pins.

PHYSICAL DIAGRAMS OF EVALUATION BOARDS

Figure 8 - Breakout Boards Design

In Figure 8, the transition from Block Diagram to prototyping boards is shown. The

conceptual blocks were materialized into actual components that can be set up quickly and ready

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for rapid testing. For the initial iterative design, the power sources selected were two lithium coin

cell batteries in series to generate a total voltage of 6V with backup batteries connected nearby.

The Babysitter breakout board manages the switching of current delivered between the primary

and backup battery through its incorporated Dynamic Power Path Management. This breakout

board is responsible for communicating the batteries' status back to the central device and applying

a power-saving technique to prolong the complete system's lifeline. In the center of the schematic,

we have the central device, the ESP32 board. The ESP32 board was chosen for its ease of

managing wireless communication, compact size, and power consumption protocols. The ESP32

board was coded in the Arduino framework, and it communicates via BLE. To the right of the

schematic, lie the rest of the remaining peripheral devices. At the top is a speaker which sounds an

alarm, alerting bystanders that the drone is falling. The alarm's sound intensity reaches up to 120

dB. This level of intensity was chosen because it is a requirement from the National Fire Alarm and

Signaling Code. [6] Next are the LSM303DLHC and BMP388 sensors; these measure the altitude,

position, velocity, acceleration, and direction of the system. The sensors are responsible for the

collecting data used to determine a flight failure. The simple receiver is an alternative

communication protocol. Appendix H contains the various protoboards and components used in

this project.


Figure 9 illustrates the first version of the switching module that is not included in Figure 8.

The switching module was created after identifying how the triggering mechanism worked. The

MOSFET IRF520 was chosen for initial testing due to its easy wiring that allowed for quick

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prototyping. This module aims to deliver a high current to burn the load. For the power source, a

battery of 9V discharging at 6 A was chosen. The load is the Nichrome wire with a resistance of

1Ω. Through testing, the Nichrome wire required 3-5 seconds to reach a minimum temperature of

56 C°. This is the required temperature to melt the sacrificial tablet that the system uses.

Figure 10 - Second Iteration of the Power Management Prototyping Boards

Figure 10 shows the second iteration of the power management prototyping boards.

Through tests conducted, that the Babysitter can only manage a 3V battery for the primary source

and 6V for the secondary battery. Adding more voltage damages the Babysitter board and could

potentially damage the rest of the components. To solve this, the primary source was instead

connected in parallel. In connecting the Lithium coin cells in parallel, the voltage remained at 3V

and capacitance of 0.8mA. Doing this solved the problem voltage issue but gave light to another

problem.

Powering the system through the coin cells did not deliver enough current to the ESP32

board. A poor understanding of the current draw from the various power modes in the ESP32

boards caused this mistake. Regardless of which operating mode the ESP32 is in, the BLE

communication protocol requires a minimum of 80mA in Modem-sleep mode. The primary battery

source delivered 0.8mA, ten times less than the required amount. The final design of the system

solves this problem by replacing the primary battery with one that has a higher discharge rate.

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3.2 SOFTWARE COMPONENTS

The software components were initially drafted at an abstract level which identified critical

functionalities to comply with the requirements. These functionalities were mapped in a context-

level diagram that breaks down the problem into two levels: Level 1 defines the GUIs used with

the user, and Level 2 defines the algorithms implemented in the ESP32 board to identify an error

in the flight and trigger the deployment mechanism. Level 0 of the context diagram identifies the

general system interaction.

CONTEXT DIAGRAM LEVEL 0

Figure 11 - Level 0 Context Diagram

Figure 11 describes the Level 0 context diagram of the project, which houses the systems

and user interactions of the overall system. The primary interactions take place between the flight

controller and the onboard computer. They interact in a constant loop, feeding back information

on the drone's status and if deployment is necessary. If the system detects that at any point,

deployment is needed, then an alert is sent to the parachute system to deploy. If deployment is

made, the decision and report of why the parachute launched is sent back to the user. The user can

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toggle between manual/autonomous mode and override the system’s automatic triggering

mechanism by pressing a button, bypassing the decision-making step of the two main systems.

Figure 12 - Tools Used for the Website

Figure 12 illustrates the tools used to host the graphical interface. This project uses an LLP

configuration: Linux, Lighttpd, and PHP. Lighttpd was chosen for its speed in hosting light

websites. No database is needed currently, as we are not required to save the user's input data.

Finally, PHP adds the functionalities onto the header file and transmits data, alongside scripts

written in JavaScript. The links to the sources can be found in Appendix H.

CONTEXT DIAGRAM LEVEL 1 (INPUT AND COMMUNICATION)


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Figure 13 shows the level 1 Context diagram of the graphical interface and flight controller.

The user inputs information through a graphical interface (a website in this instance) , from which

the preflight parameters are obtained. Then a receiving process receives the data and sends it to

the emergency parachute system via a BLE communication protocol; the protocol communicates

the parameters to the rest of the peripherals. A status process compiles the report and encodes it

into a readable document for the user. A low-fidelity prototype of the website is shown in Figure

14, demonstrating how the website will collect data from the user.

Figure 14 - Low Fidelity Prototype of the preflight parameters page

The low-fidelity prototype in Figure 14 was demonstrated to the client; they demonstrated

satisfaction with the design and said that the website aligned with their vision for the graphical

interface. The client then requested a functioning prototype of the website to advance to the testing

phases of the project.

Figure 15 - Functioning Prototype 2 of the Website

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Figure 15 shows the functioning prototype created from the low-fidelity prototype from

Figure 14. As the client requested, a website was quickly created through Bootstrap to make a

table capable of receiving numbers, which are then downloaded in a header file through the

download button. The client was satisfied with the website's functionality, so it was then requested

that the next prototype must include the color scheme, layout, functionality, and communication

with the user.

Figure 16 – Prototype 3 to test the verification of the BLE Connection Page

Figure 16 shows the third prototype of the website. As the client requested, this prototype

shows one of the color schemes used in the latest version of the website and contains a functional

button that can connect with the Safety Parachute System via BLE. The clients were satisfied with

the color selection and functionality but were displeased with the lack of GUIs and lack of content.

Clients suggested that for the next iteration, the website should include colorful GUIs that users

could navigate easily and contain more instruction. All the user’s requests were noted and included

in the latest version of the website, which will be discussed in the final overview of the system.

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CONTEXT DIAGRAM LEVEL 2 (STATUS, SECURITY, AND DEPLOYMENT)


The Level 2 context diagram shown in Figure 17 explains the communication protocol

between the central device and the Safety Parachute System. The process starts with the status

interface, in which the peripheral sensors mine and gather data used to pinpoint the drone's

location. The raw data is then packaged for interpretation in the status process. Although initially

considered to be implemented, it was deemed unnecessary to write any security protocols that are

not already included in the ESP32. The status process decides if a deployment is necessary. If the

deployment is required, a signal is sent to the parachute emergency system to deploy. The status

confirmation verifies the successful deployment of the parachute. This flag is triggered again if

deployment failed, or if in the case that it was successful, alert the user and send a report detailing

what transpired.

The previously mentioned protocols were written in C++ under the Arduino framework.

The code flashed in the ESP32 houses three files, which are parameter.h, functions.h, and

main.cpp. In parameter.h, the preflight parameters are stored and read by main.cpp as for

deployment criteria. Functions.h houses the various BLE communications protocols, switching

module, and data collection done by the sensors. The documentation and code can be found at the

GitHub repository (the url can be found in Appendix H).

https://github.com/juanluna97/Safety_Parachute_System

29

3.3 MECHANICAL DESIGN

The mechanical components of the system have undergone some changes from the initial

designs. This section presents the distinct phases of the mechanical elements of the system. These

changes stemmed from suggestions and redesign proposals discussed during weekly meetings with

the sponsor and our advisors.

The initial design of the deployment system used a compressed spring for parachute ejection:

shown in Figure 18.

Figure 18 - Level First Iteration of Spring-Loaded System

This system was envisioned to work with two torsional springs, held down by the blue tabs.

Those tabs would be each pulled by an actuator or solenoid. A problem with this system is that

two actuators would add significant mass to the system, increasing the cost and having a high-

power requirement.

30

Figure 19 - Spring-Loaded System Iteration 2

The second iteration of the spring-loaded system modified the placement of the tabs. This

system added a piece to act as a pin that keeps the blue tabs together, as seen in Figure 19. This

design would have one extension spring at the end of each blue tab. When the red pin is moved

downwards, the blue tabs would move back, and the torsional springs would be allowed to

decompress, colliding with a small cage holding the parachute. The mass problem has been solved,

but now having a single actuator moving vertically requires the complete system to be taller. A

taller system would bring some difficulties when creating the flight termination system, so this

design was abandoned.

Figure 20 - CO2 System Iteration 1

Simultaneously, as the spring-loaded system was being designed, the first iterations of the

CO2 system were developed. The first iteration of the CO2 system can be observed in Figure 20.

The most distinctive characteristic of this system is that it uses a valve to control the release of

CO2 from the cartridge. Screwing the cartridge would puncture it. The valve would then release

the CO2 whenever the parachute needed deployment.

31

A problem with this design is that the valves capable to operate with the involved pressure

are expensive and heavy. Another issue is that a cartridge would be used every flight; it would be

preferable to use a cartridge only when the parachute needed deployment.


On the second design iteration, the valve was removed, and it was decided that the cartridge

would be punctured only when the parachute needs to be deployed. As seen in Figure 22, the

second iteration features a linear actuator, to which a puncturing needle is attached. The actuator

would move the puncturing pin forward to deploy the parachute. A complication is that the actuator

must provide the necessary force to puncture the cartridge. Such actuators are expensive, heavy,

and bulky, so this approach was discarded. This iteration also includes a piece called the air

director, which would allow the CO2 to flow in the right direction towards the parachute.

The third iteration is similar to the second, the difference being the puncturing device. As

seen in Figure 22, this iteration would use a rotary actuator or a DC motor to puncture the cap of

the CO2 cartridge. Still, like iteration two, this would require a bulky device capable of delivering

the required force.

32


The third iteration would have a similar pin that would rotate and hit the cap of the CO2

cartridge.


On the fourth iteration of the CO2 system, various changes were implemented. The casing

for this iteration is shown in Figure 23. Firstly, this system has an altered positioning of the CO2

cartridge; the previous versions' positioning would significantly shift the system's center of mass.

Placing it on the side would reduce the effect of the cartridge's mass on the shift of the center of

mass. This design also includes a section of the casing for the electronics and a funnel-shaped air

director. Additionally, the system now features a spring-loaded firing pin that punctures the

canister. The firing pin can be observed in Figure 24.

33

Figure 24 - Cross Section of CO2 System Iteration 4

The pin would be spring-loaded and held in place by some mechanism. This idea of having

a spring deliver the impact allows for less expensive and specialized electromechanical

components.

Another feature that this iteration adds is the flaps at the top of the casing. The flaps would

act as the flight termination system.

Figure 25 - Flight Termination System Concept

The flight termination system would activate simultaneously with the CO2 cartridge

puncturing. The system would be positioned on the drone as seen on the left diagram in Figure 25;

when the system is deployed, the system would rotate 45°, where the flaps would interfere with

the propellers, causing them to stop. A problem with this system is that the size of the flaps would

34

not be universal. Drones of specific sizes would require a set of flaps with a certain length. This

issue reduces the modularity of the system, and so this idea was modified.


On the fifth iteration of the system, modified components were added to the previous

iteration, as seen in Figure 26. This system made the funnel removable so that parts inside the

system were easily accessible. Similarly, the electronics would be mounted onto a removable plate

that would allow for easy access. This iteration also includes a safety pin that the user can place

so that the system would not fire under any circumstance. This iteration also contains a pin that

would connect to an electromechanical component, as seen in Figure 27.

Figure 27 - Top Cross-Section of CO2 System Iteration 5

35

As seen in the figure above, this design features two pins, one that the user places while

the system is not to be deployed, and the second on the inside that would retract for system

deployment.


Figure 28 shows the sixth iteration of the system, which is a modification of the previous

iteration. This version features a cap which would stop the firing pin after deployment. This system

also has the safety pin placed vertically.

Figure 29 - Top View of CO2 System Iteration 6

This iteration also features a flight termination system of extendable flaps. As seen in

Figure 29, this system has flaps that extend whenever the system is deployed. The released CO2

from the cartridge would push the flaps. This version also has the electronics placed on the outside

of the case to allow a larger funnel. The electronics would be further away from any metal

components used; this helps to balance the center of mass of the complete system more effectively.

36

This system featured a power screw system paired with a DC motor to drive the internal

deployment pin connected to the firing pin. Calculations were made to determine the necessary

torque output from a motor to use the power screw system. The calculations in Appendix E show

that the required torque of 1.07 Nm. From this calculation, it was decided that the puncturing

approach would not be optimal since the DC motors capable of this torque output are too large and

too heavy. One of the requirements set by the sponsor was for the mass to be less than 400g; a DC

motor would take up much of the total system mass.


Figure 30 shows the seventh iteration of the system. The two main changes between this

and the previous iteration are the deployment method of CO2 and the air director. This iteration

uses a fusible plug. As seen in Figure 31, the fusible plug has a needle which would pierce the CO2

as is screws in. The blue tablet would stop the pressurized CO2 from escaping. When the parachute

needs deployment, the Nichrome wire which passes in front of the tablet heats up, melting the

tablet and releasing the CO2.

37

Figure 31 - Cross-Section of the Fusible Plug

Figure 32 shows the air director of the seventh iteration. This director features an upper

part to assist CO2 flow along the bottom part. The parachute is placed above the director and held

in place using a rubber band along the grooves from the exterior part. This design would make the

parachute inflate like a balloon and would speed up its opening.

Figure 32 - Cross-Section of Air Director Iteration 7

The eighth iteration of the system had a few changes because of fabrication constraints.

The fusible plug system of this iteration would require equipment not available at St. Mary's

University’s Laboratories. For this reason, instead of fabricating the parts, it was decided that to

re-purpose the piercing device of a commercial CO2 bike pump.

38

Figure 33 - System Eight Iteration

Additionally, two hinged doors were added to the top of the casing and the parachute box;

these would secure the inside components from coming out. The parachute box holds the parachute

inside the system. There is a small hole for CO2 to pass through and push out the parachute.

Figure 34 - System Eight Iteration

Figure 35 shows the fusible plug system of the eighth iteration. The cartridge screwing in

place punctures the seal. The blue sacrificial tablet stops the CO2 from flowing out. When the

system decides to deploy the parachute, a Nichrome wire (shown in green in Figure 35) heats the

39

tablet enough to allow the pressure of the CO2 to break a hole in the tablet. This allows the CO2

to flow.

Figure 35 - Fusible Plug Eight Iteration

Figure 36 shows the placement of the different electronic components between three

categories. The yellow section was designated for the system's onboard computer, power

management, and sensors. The blue area was established for the power supplies that the system

requires. Finally, the red section was designated for the switching module that provides power to

the Nichrome wire.

Figure 36 - Electronics Arrangement Eight Iteration

40

The next iteration of the system came after a seies of tests thoroughly discussed in a

different section. System Iteration Nine, seen in Figure 37 below, changed how the parachute

ejects and the flaps extend. The Ground Deployment Test 1 determined that the CO2 did not

provide enough pressure to push out the flaps. To fix this, instead of having pressure build up

inside the tubing system, a balloon fills and pushes itself against all the components.

Figure 37 - System Iteration Nine

4. OVERVIEW OF FINAL DESIGN OF SYSTEM

The work described in the previous section led to the final version of our system. The final

iteration of the parachute system is described in this section.

4.1 ELECTRICAL AND SOFTWARE

The final iteration of the electrical components features the various connections and

stripboards placed in the final iteration of the mechanical components. The electrical components

are divided into the following four sections: microcontroller, sensors & alarm, power source &

41

power management, and switching module. Due to sizing constraints from the mechanical

components, the various breakout boards and stripboards are spread throughout the system. Some

components were removed from the original physical diagram of the prototyping board through

testing and wiring from prior iterative designs. These changes will be seen with the components

that remained in final design.

MICROCONTROLLER

Figure 38 - ESP32 Microcontroller and its pinouts

Figure 38 shows the ESP32 and its respective connections. The ESP32 microcontroller

operates on various low-power modes and has numerous wireless communications protocols. The

final design uses BLE as the chosen wireless communication protocol. Four distinct operating state

modes were written to differentiate between the various power consumption modes to preserve

power: sleep, stand-by, flight, and emergency. Appendix C shows the power budget of the ESP32

board and the power consumption used by each mode.

The ESP32 starts in ‘sleep’ mode and waits for user input (touching pin GPIO 0) to enter

‘stand-by mode’. Once in ‘stand-by’ mode, the ESP32 activates its BLE communications to

receive parameters from the website. ‘Stand-by’ mode is only used to receive preflight parameters

from the user. After the user has input the necessary parameters, the user then clicks the ‘Start

42

Flight’ button on the website, which will switch from ‘stand-by’ mode to ‘flight mode’. In 'flight

mode,' the ESP32 activates its sensors to collect data and determine is the system has exceeded the

set maximum altitude, acceleration, or flight time. If the system detects awry flight, the Safety

Parachute System will enter 'emergency’ mode. In this mode, BLE and sensors are switched off

and all power is redirected to the DL4184 module to burn the Nichrome wire. After 4 seconds have

passed, the DL4184 shuts off, and the alarm begins to sound. Once the drone has landed safely

with the parachute, or if the drone completes its flight successfully, the user needs to press the RST

(reset) button in the ESP32 to return to ‘sleep’ mode. If another flight is to be made with the same

parameters, the user needs to input the same information again as the information is deleted with

the RST button press.

Moving to the pinout of the ESP32 board, pins are used as data lines, power supply, and I/O

decisions. As seen in Figure 38, the ESP32 takes 3.3V and features two separate ground pins. One

ground pin is used for the PWR source and the other for peripherals. GPIO 22 and GPIO 21 are

reserved as SCL and SDA respectively. These data lines handle all system communication. GPIO

18 is used as the I/O for the alarm; this PWM pin sends the power needed for the buzzer to reach

120 dB and the sound frequency to be heard. The ESP32 sends a frequency of 5kHz an audible

sound for human ears. GPIO 5 is used to activate the switching module; this pin output pin delivers

a high signal of 3.3V once the ESP32 enters 'emergency’ mode. The GPIO touch sensor is used to

switch between 'sleep’ and 'stand-by' mode.

For the final design of the electronics system, the RF receiver is not included. Flying the system

is beyond of the scope of this project due to licensing and permits to fly. Adding the RF receiver

was unnecessary in this iteration since the BLE can trigger the deployment signal for testing inside

the Drone Lab.

43

SENSORS & ALARM

Figure 39 - Sensor and Alarm Board

Figure 39 displays the wiring of the sensor and alarm boards; these are powered by a 3V

input to the Vin pin and grounded by a GND pin. Due to the 𝐼2C connection for the data lines,

only SDA and SCL pins are necessary to send the sensory data back to the ESP32 board. An I/O

sends a signal flag to turn on/off the alarm buzzer. All these pins trace back to the ESP32 board as

seen in Figure 39.

Table 4 - BMP388 List of Key Features

44

The BMP388 is a precision barometric pressure digital sensor used to collect its

surroundings' altitude and temperature. This chip is built explicitly for drones and flying gadgets,

ideal for the Safety Parachute System. Table 4 reveals that the BMP388 requires a voltage input

of 3.3V and consumes 3.4 µA at 1Hz pressure and temperature. The datasheet also states that the

maximum current drawn from the component is 900µA. The electronics system must be mindful

of its current consumption, so it does not become underpower during flight time. This chip was

also chosen due to its absolute accuracy of 50 Pa since our system relies on extreme measurements

to detect if the system has gone strayed its flight path. This IIR filter is an added benefit, which

can reduce external interference caused by short-term changes (strong winds, doors slamming).

The BMP388 breakout board is a successful component in indicating if the drone has flown too

high from its intended flight.

The LSM303DLHC features linear acceleration and magnetic sensors used to obtain the

orientation of the drone and its distance. These sensors are used to measure the acceleration of the

drone accurately and warn the Safety Parachute System if the drone strays from its intended flight.

The sensors collect the distance traveled from the drone’s origin in the X,Y, and Z-axes; as seen

in Figure 40 below.

Figure 40 - ESP32 Microcontroller Pinout

The LSM303DLHC was also chosen for its low power consumption. Table 5 states that

the LSM303DLHC requires an input of 3.3V and typically consumes 110 µA during regular

operation. This is ideal for the Safety Parachute System and guarantees the lifetime of the

electronics system.

45

Table 5 - BMP388 List of Key Features

The onboard buzzer is used to alert bystanders that the parachute has been deployed. The

buzzer can reach sound intensities up to 120 dB if 200mA is delivered to its I/O pin. To power the

buzzer, 3.3V volts are required at a current consumption of 0.2mA. Due to its current consumption,

the alarm will only be turned on once the Nichrome wire has been burned. During operation, the

buzzer can sound between 100-120 dB, which is the same intensity that standard fire alarms output.

This is loud enough to guarantee that people below will notice and allow them time to move to a

safe area.

POWER SOURCE & POWER MANAGEMENT

Figure 41 - Power Sources and Power Management Boards

46

Figure 41 displays the power sources and two power management boards that deliver power

to the ESP32 and its sensors. For the final iterative design, the primary power source was replaced

by a Surefire SF1234 3V battery. This was done to solve the issue of the board being underpowered

when the ESP32 turns on its BLE protocols. The Surefire was chosen because, as shown in figure

42, it discharges 1.50A. This is more than the system requires but will ensure that the ESP32 will

carry out all its functionalities without power issues in ‘flight’ mode. The drawback of this design

is that it shortens the system's life and requires changing batteries more frequently; albeit this is

counteracted by the fact that the system is not in ‘flight’ mode often. Besides the replacement of

the primary battery, the other components are preserved.

Figure 42 - Surefire SF1234 Battery Discharge Rate

Moving on to the remaining components, the Babysitter breakout board features Dynamic

Power Path Management (DPPM) that can alternate between the primary and secondary battery to

guarantee that the system will still function with insufficient power delivery. The secondary battery

consists of two lithium cell coins connected in series, delivering 6V at 230 mAh. The dip switches

set the Babysitter's DPPM. When both dip switches are ON, the DPPM is set to a limit of 100mA,

meaning that the primary battery continuously delivers 1.5A, and the secondary battery delivers

0.4 mAh. This ensures that the system can deliver enough power to burn the Nichrome wire

through the implementation of the Watchdog Timer, although no report will be generated due to

the lack of power.

47

To further extend the system's battery life, a power nano timer TPL 5110 is used to decrease

the current consumption of the ESP32 further to 35nA while in sleep mode down. The pins PWR-

OUT and PWR-GND represent the power going to the ESP32. The I/O pin is the 'wake up' call the

power nano timer uses to reactivate the ESP32 board from sleep mode. The I/O pin used for the

'wake up' signal is the GPIO 0 with its touch sensor.

The results of the overall power consumption can be found in Appendix C. As seen from the

calculations, the system has an overall life of approximately 1 year, and it can be continuously

used in flight mode for 3 hours. Appendix C highlights the current consumption of each mode and

why it is necessary to use that amount of power.

SWITCHING MODULE


Figure 43 displays the switching module of the D4184 MOSFET used to burn the sacrificial

tablet. After testing and research, the IRF520 was deemed inadequate for burning the Nichrome

wire, as it requires a voltage of 5V at the gate for the module to burn the tablet effectively. The

IRF 520 MOSFET required 3-5 seconds to burn the Nichrome wire; alternately the switching

D4184 module required ~1 second to burn the sacrificial tablet. The necessary calculations can be

found below.

48

Figure 44 - Transfer Characteristics for the D4184 module

The D4184 is preferred for its ability to deliver 10 A – 40 A at a voltage gate of 3.0V – 3.5V,

as seen in Figure 44. The ESP32 board can only deliver a maximum of 3.3V from its I/O pins.

After applying 3.3V to the gate, the D4184 module activates, delivering 4.3V from the Li-Po

battery to the load of the Nichrome wire. This Li-Po battery was chosen for its compact size and

its effectiveness in burning the Nichrome wire. The battery's effectiveness is ~98%, calculated

through the maximum power theorem found in Appendix B.

SOFTWARE

Figure 45 – Important features

Figure 45 shows the client’s most requested functionalities from inspecting the third software

prototype. The most notable change was the inclusion of the color scheme which matches the St.

Mary’s University colors (the color code for blue is RBG 28,54,100 and for gold is RGB

242,191,72). On top of that, an instructions page was added to indicate to the user what steps are

necessary to conduct a flight. Then, a parameters table was modified so that input data is

transmitted via BLE. Finally, the most important request was to collect metrics and use a

49

deployment button to test remotely if the electronics work without powering the ESP32 via a

Laptop. The rest of the screenshot can be seen in Appendix G, and the code is also found in the

GitHub repository (the url can be found in Appendix H.)

Some GUIs were created in Inkspace; others and the timer visual were downloaded with a free

license for use and are referenced in the GitHub repository. The BLE communication is possible

thanks to a JavaScript library called Web Bluetooth (authored by Google engineer Reilly Grant)

[7].

The constraint of this website is that it only supports the Google Chrome Browser. Any other

browser will display the wrong font and give an error if any functionalities are attempted.

Regardless of this, the client was satisfied with the improvements made from prototype three, and

the project once again aligned with the client's vision.

4.2 MECHANICAL

The final iteration of the system is the culmination of an iterative design, prototype, and

test process. The tenth and final iteration of the system is shown in Figure 46. Similar to iteration

the ninth iteration, the system uses a balloon to eject the parachute and extend the flaps of the flight

termination system.

Figure 46 - System Iteration Ten


https://webbluetoothcg.github.io/web-bluetooth/

50

The different components of this system will be discussed in the same sequence used in

the system's deployment. The first component is the CO2 release system. As seen in Figure 47, the

bottom piece of the sacrificial tablet is inserted into the system. The piece has the appropriate shape

to fit in position relative to two male connectors of breadboard jumper cables. A piece of Nichrome

wire of a 4.5 cm length is pre-formed and connected to the jumper cable connector. Then, the cap

of the sacrificial tablet is inserted.

Figure 47 - Nichrome Wire Placement.

After the sacrificial tablet and Nichrome wire are in place, the piercing block is connected

to the system. This piece is fastened using four M5 screws. The heads of the screws are placed on

the countersunk holes of the piercing block. The calculations for the safety factor of these screws

are shown in Appendix F.

51

Figure 48 - Piercing Block

Figure 49 shows a cross-sectional view of the entire CO2 Release System. This cross-

section shows the different components that make up this system. The two yellow components are

metal parts re-used from a commercial CO2 cartridge [8]. The left yellow component is a threaded

piercing device. When the CO2 cartridge is screwed into this piece, the seal of the cartridge is

punctured. This part is attached to the block with epoxy resin. The resin also helps create a seal

between the parts. The yellow piece at the right is the part that holds the bottom of the sacrificial

tablet. This part is also held in place using an epoxy resin. On the two sides of the top part of the

sacrificial tablet, two O-rings were placed to ensure a good seal. These rings prevent any CO2 from

escaping the system. The rings are 14x2.5 mm NBR O-rings. The two horizontal back parts are

the male connectors of breadboard jumper cables. Epoxy resin also holds these in place.

Figure 49 - Cross-Sectional View CO2 Release System

52

The CO2 release system is designed to burn the top part of the sacrificial tablet. When the

tablet has melted enough, the pressure of the CO2 can break a small hole through the tablet,

allowing all the CO2 to flow.

Once released, the CO2 flows through a tube shown in Figure 50. The tube ends at the

center of the case, where the balloon can be connected. The end of the tube has a change in

thickness to allow a zip tie to hold the balloon in place. The zip tie also holds the CO2 inside the

balloon as it inflates.

Figure 50 - CO2 Tube.

The inflating balloon pushes out the flight termination system flaps, as shown in Figure 51.

The round end of the flaps was found to be effective experimentally during a set of tests of the

flight termination system. These flaps can be easily modified to be the appropriate length for

different drones of different sizes.

53

Figure 51 - Flight Termination System Flaps

The flaps are made of two different pieces, as shown in Figure 52. The pieces are joined

together using epoxy resin.

Figure 52 - Disassembled Flight Termination System Flaps.

The parachute is placed on the parachute cage shown in Figure 53. This cage was made

using a lattice structure to reduce the mass of the system. The cage sits on top of the balloon, and

when the balloon inflates, the cage is ejected.

54

Figure 53 - Parachute Cage

The lid of the system was changed from flat to a curved. Figure 54 shows the lids of the

system. When the balloon inflates, the lids prop open, allowing the parachute cage and parachute

to be ejected.

Figure 54 - System Lid.

The system's electronics were classified into four different categories and placed into

different places within the casing. The color-coded sections can be seen in Figure 55. The red

section was designated for the MOSFET that supplies power to the Nichrome wire. The green

section was designated for the power management boards. The blue section was designated for the

system's power sources. Finally, the yellows section was designated for the system's onboard

computer and the system's sensors.

55

Figure 55 - Electronics Placement

Four different sets of holes were made at the bottom of the casing to attach the system to a

drone. The holes can be seen at the bottom of the case in Figure 56. A set of four zip ties, one for

each hole, attaches the case to the drone. This provides four attachment points that make the system

more stable on top of a drone. The circular hole at the bottom was made to pass the parachute

risers. The parachute attaches directly to the frame of the drone.

Figure 56 - Attachment System

56

The parachute chosen for the St. Mary's Drone was the Fruity Chutes Iris 36" Ultra-

Light Parachute [9]. Based on calculations shown in Appendix A, this parachute complies with

ASTM standards. The chosen parachute will make the system compact and have a descent rate of

4.78 m/s, impact energy of 22.8J, a drag coefficient of 2.2. Figure 57 - Fruity Chutes Iris 36" Ultra

Light Parachute. shows the parachute.

Figure 57 - Fruity Chutes Iris 36" Ultra Light Parachute [9].

This system uses several 3D printed parts printed with Vero [10] material from a Stratasys

Object 260 printer. The complexity of the case’s tube system requires support material that would

have been impossible to remove with other commercial printers. The Stratasys Object 260’s

support material can be easily removed using a pressure washer.

5. STANDARD DISCUSSION

The standards followed in this project are the ASTM F3322-18, Standard Specification for

Small Unmanned Aircraft System (sUAS) Parachutes. This section discusses key design

parameters used in the development of this project. These standards are required by the Federal

Administration Agency (FAA) to fly our system over people.

57

The standards give specifications for the parachute design or selection. The calculations

for the parachute selection are attached on Appendix A. For a load of 2 kg, the parachute produces

a decent rate of 4.78 m/s and impact energy of 22.84 J. At the time the ASTM F3322-18 standard

was published, there was no defined maximum impact energy. However, on December 28, 2020,

the FAA published a rule regarding impact energy [11]. This rule provides four drone categories.

The parachute system designed on this project fits in for a Category 3 drone, for which the drone

cannot cause injury or damage due to an energy transfer greater than 25 𝑓𝑡 ∗ 𝑙𝑏 (or 33.9 𝐽). The

selected parachute meets the impact energy criterion.

The standard states that a ballistic ejection system may release the parachute if specific

criteria are met. Firstly, the ejection system must be controlled in a manner to not cause a fire on

the drone. The Nichrome wire that melts the tablet heats up only for a short time to meet this

requirement. When the CO2 is released at high pressure, any burning components are extinguished.

A second requirement for the ballistic ejection is that the system's electronic signaling should not

interfere with the drone's primary electronics system.

The standard requires placing labels outside the system to provide a visual warning that the

system is equipped with a ballistic ejection system. The operator of the system holds responsibility

for the visual placement of the labels. A triangular danger label must be placed on the largest

projected surface, and the size must be 80% of the diameter of the largest circle encompassed. This

label shall be placed adjacent to the ejection point of the parachute. A QR code may be added that

directs to a website with information about the system. The label should include the word

"DANGER" and provide contact information to seek help from the manufacturer. The danger label

should be printed with a red border and white letters. Figure 58 below shows the danger label

designed for this project.

58

Figure 58 - Danger Label.

6. RESULTS

By the end of the academic year, a functioning prototype was completed. To gauge the

success of our work, this section reviews the requirements and constraints set by the sponsor and

verifies their compliance.

The system was required to have a mass no larger than 400 g. in total. The delivered system

has a mass of 409.0g. However, this delivered system used protoboards that add more mass than

the

The production cost of our system unit must be lower than $390. Table 6 itemizes all the

components that make up the system and provides a cost for each. The total cost for manufacturing

our system unit is $194.03. The cost of each additional deployment is $3.44. The items shaded in

blue are a one-time cost, and the items shaded in yellow are a cost for each additional deployment.

Table 6 - Production Cost

Item Units Cost per Unit Cost

59

ESP 32 Board -

WROOM-32D

1 10 $ 10.00

Adafruit BMP388 1 9.95 $ 9.95

Adafruit LSM303DLHC 1 14.95 $ 14.95

Lithium CR 2032 3V Coin

Cell Battery

4 1.37 $ 5.48

Lithium CR 2032 3V Coin

Cell Battery holder

4 2.50 $ 10.00

Babysitter Breakout Board 1 19.95 $ 19.95

Nano Power Timer TPL

5110

1 6.5 $ 6.50

D4184 Module 1 1.25 $ 1.25

LiPo Battery 4.35V 1 10 $ 10.00

12 in Zip Ties 4 $ 0.1199 $ 0.4796

3 in Zip Ties 1 $ 0.0662 $ 0.0662

Latex Balloon 1 $ 0.0839 $ 0.0839

4.5 cm length of

Nichrome Wire

1 $0.00958 $0.00958

12 g CO2 Cartridge 1 $ 2.80 $ 2.80

Genuine Innovations

Commercial Bike Pump

1 $19.99 $19.99

14x2.5 mm NBR O-Rings 2 $ 0.121 $ 0.242

M5 Screws 4 $ 0.1386 $ 0.5543

Components 3D Print 1 $ 81.72 $81.72

Total Fixed Cost $ 194.03

Total Additional Deployment Cost $ 3.44

A Watchdog system is included in the ESP32 board to catch system errors and unexpected

failures. To activate the watchdog, the main.cpp code utilizes the interrupt Watchdog flag and task

watchdog timer library. This reboots the ESP32 if an erroneous input or corrupted data makes the

system faulty.

The center of mass of the system had to be positioned so that the thrust output of the drone

motors did not have a percent difference greater than 10%. For the size and mass of the St. Mary's

60

Drone and the design mass of the system, the parachute system can be placed anywhere on the

drone. The calculations to determine this are in Appendix D.

The delivered system can be easily modified to be used on drones of different sizes. The

size of the flaps on the flight termination system can be modified in SolidWorks. The lid can also

be modified to fit a larger parachute within the system. The case can be scaled larger if necessary.

The system took different design parameters from the ASTM F3322-18 standards used in

its development. The design parameters discussed in section 5 were used. Some examples of how

the Safety Parachute System complies with the ASTM F3322-18 standards include the inclusion

of a failure report and print of the exact time, velocity, and position at which the parachute was

deployed.

7. PROTOTYPE FABRICATION AND TESTING

A series of prototypes were constructed throughout this project's development, and tests

were conducted to develop a successful final working prototype. This section discusses the

different tests performed.

7.1 CONTROLLED TABLET BURNING TEST

A series of prototypes were constructed throughout this project's development, and tests

were conducted to develop a successful final working prototype. This section discusses the

different tests performed.

The first version of the tablet, seen in Figure 59, had a groove at one end, where a single

line of Nichrome wire would cross. During testing, it was determined that this design was sub-

optimal because the amount of Nichrome wire in contact with the sacrificial tablet was not at large

as it could be. Being a circular tablet, perhaps a circular pattern of Nichrome wire would make

61

better use of the available space. Additionally, the placement of wire on the casing would not be

accessible if the wire ran across the tablet. This was another problem to tackle.

Figure 59 - Sacrificial Tablet First Iteration

The first tablet iteration was a single piece made of two joined cylinders. The top part

would stop the flow of CO2, and the smaller bottom part would take the force exerted by the CO2

pressure. For the second tablet iteration, shown in Figure 60, the two cylinders separated into two

parts to form a small groove for the Nichrome wire placement. The bottom part of the tablet has a

hole in the middle for the CO2 to flow through when the upper thinner part was melted. The bottom

part also has two square holes through which breadboard jumper cables would pass through. The

jumper cables would connect one side to the Nichrome wire and a MOSFET to the other.

62

Figure 60 - Sacrificial Tablet Second Iteration

Three different wire groove designs were made, as seen in Figure 61 The first two designs

have groove patterns that follow a circular path. The third design has a parallel line pattern that

travels from one end of the tablet to another. Another difference between the designs is the duct

for the vent for the CO2. Two of the designs had a single large hole, while the other had an

arrangement of five small holes.

Figure 61 - Nichrome Wire Groove Designs

Testing the second iteration of tablets revealed a problem with this design. Although the

grooves' diameter was double the wire's diameter, placing the wire onto the tablet was difficult.

The turns the track follows are narrow, so bending the wire to fit was difficult. It was easier to pre-

63

make the curves on the wire before placing it on the tablet, but forming the correct shape was still

complicated. The third iteration of the tablet has changes to address this.

The third iteration of the tablet retained the upper part but allocated a small area for the

wire in the lower part, instead of following a predetermined path. The user has the freedom of

forming the wire into any desired shape that will fit in the designated space. Figure 62 shows the

bottom part of the tablet.

Figure 62 - Tablet Bottom Third Iteration

To test said tablets, a small box was designed, and 3D printed. This box was the same as

the section on the system for the tablet, shown in Figure 63. The tablet was inserted into the box,

and the Nichrome wire was placed and connected to the MOSFET.

64

Figure 63 - Tablet Burning Box

The tablets were then burned under three conditions. First, the tablet was burned without

any pressure source connected to the box. Second, a new tablet was burned connected to

pressurized air at 95 psi. The tablet burning released the pressurized air. Third, the system was

tested similarly but using a CO2 cartridge. A new tablet was placed, the CO2 cartridge was inserted

into the box, and the CO2 was successfully released when the tablet was burnt. Figure 64 shows

the results of burning the tablets with the Nichrome wire using pressurized CO2. The force of the

pressurized CO2 punched a small hole on the tablet top part large enough to release the CO2.

Figure 64 - Tablet Burn Test

65

Having successfully released the CO2, this series of tests was concluded. A working CO2

release system was ready to be integrated into our emergency parachute system.

7.2 CO2 LEAKAGE TEST

Another important aspect to consider for the Safety Parachute System design is CO2

leakage. A series of tests were conducted to determine if the system was preventing the CO2 from

leaking. These tests were conducted simultaneously with the controlled burning tablet tests, using

the same 3D printed box of Figure 63. However, as a precaution, the system was placed inside a

metal electrical box. This was a safety measure in case the pressure of the CO2 caused the box to

shatter. The testing setup for the CO2 leakage test is shown in Figure 65.

Figure 65 - CO2 Leakage Test Setup

To prevent any type of leaks, a set of three O-rings was placed on the system. The o-rings

can be seen in Figure 66. These O-rings were placed in this arrangement to prevent CO2 from

flowing out of the system.

66

Figure 66 - O-Ring Placement

The first test conducted was done using pressurized air. A hose with air at 95 psi was

connected to the system. At first, some air leaked out of the point of connection between the hose

and the piercing device. This was solved by wrapping Teflon tape around the threads of the hose.

No further pressurized air leaked from the device.

After testing the box using pressurized air, a CO2 cartridge was used. Similarly, the

cartridge threads were wrapped by Teflon tape to avoid leaks from that connection point. The box

was tested for leaks by placing soapy water at possible leaking points, and no leaks were found.

Through these tests, it was determined that the system had no leaks over a short period.

To test leaks over an extended time, a CO2 cartridge was connected to the box, and the

setup's mass was recorded. Then, the mass was re-measured over two hours in twenty-minute

intervals. Over that period, the mass of the testing setup did not change. The testing setup was then

left overnight, and after 17 hours, 10 g of CO2 was lost. With this series of tests, it was determined

that the system would hold CO2 within periods appropriate for flight but would not have extended

shelf life. This means that every flight requires a new CO2 cartridge.

7.3 GROUND LAUNCH TEST 1

After the CO2 release system was proven to work effectively, the next series of tests

involved extending the flight termination system's flaps and ejecting the parachute. These tests

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determined that the approach for extending the flaps and ejecting the parachute of this iteration

would not be functional.

For this test, the eighth iteration of the system was 3D printed. The piercing device was

connected, and a CO2 cartridge was screwed into the system. There was no tablet placed on the

system to allow the CO2 to flow through the tube system right away. Figure 67 shows the test

setup. The expected outcome was for the flaps to extend and the parachute cage to be launched

into the air. However, the actual result was that the flaps did not move, nor did the parachute cage.

Figure 67 - Ground Launch Test 1

To solve this, one possible solution was to reduce the diameter of the rods. This would

reduce the friction between the rod and the tube where it sits. A new CO2 cartridge was then tested,

and again the flaps did not move, nor was the parachute cage ejected. The CO2 flowed around the

rod instead of building pressure to push it. It was then determined that the approach of the eighth

iteration was not effective.

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7.4 GROUND LAUNCH TEST 2

After the first ground launch test results, the idea of having a balloon inflate to deploy the

flaps and the parachute was proposed. The first series of tests were conducted by modifying the

existing 3D print of the eighth iteration. The inside tube system was removed using a Dremel tool.

A hole on the bottom of the case was drilled to pass a balloon through. The balloon was then

inflated using pressurized air. This first test setup is shown in Figure 68.

Figure 68 - Initial Balloon Test Setup

Each time the balloon was inflated, at least one of the flaps would extend, but the balloon

would always explode before all flaps were pushed out. The balloon would pop before all flaps

were extended because the rod's surface area in contact with the balloon was small and subject to

significant pressure. A set of cardboard hemispheres, shown in Figure 53, were attached to the flap

rods' ends to fix this problem. Using this setup, it was possible to effectively extend all four flaps

without popping the balloon.

69

Figure 69 - Second Balloon Test Setup

Through this modified case test, it was determined that the balloon approach could be

feasible. A system was designed, and 3D printed using this concept for making further tests. Figure

70 shows the printed version of the ninth iteration of the system being tested. During this series of

tests, the balloon effectively pushed the flight termination system flaps out and ejected the

parachute cage.

Figure 70 - Third Balloon Test Setup

7.5 FLIGHT TERMINATION SYSTEM TEST

70

With the ground deployment tests were concluded, the flight termination system's

deployment method was finally set. The next step in the development process was to test the

effectiveness of the flight termination system. A testing rig was set up, as seen in Figure 71. A

drone was strapped onto a platform, and our system was attached to the drone. The drone’s motors

were powered one by one, and the flight termination system was triggered to test if each flap could

stop the propellers from spinning.

Figure 71 - Flight Termination System Test Setup

As seen in Figure 72, the flight termination system was capable of successfully breaking

the propeller of a drone. The propeller broke enough to prevent flight from happening. Advanced

drone systems will automatically stop the motors from spinning if it detects the propellers have

been compromised.

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Figure 72 - Flight Termination System Test Results

8. ECONOMICAL, SAFETY, AND WELFARE ANALYSIS OF

RESULTS

One of the biggest fears people have about drones is having one fall on someone or

something important. A drone falling out of the sky can have significant descent rates and high

impact energies. The damage a drone is capable of is considerable and justly frightening. For this

reason, it is an important task to make drones more reliable and take necessary precautions when

flying them.

From the beginning of this project's development, one of the most important goals has been

making a parachute system that provides a safety feature to drones. We believe that the prototype

we have developed manages to minimize the hazard posed by a falling drone. A drone utilizing

our system will minimize the impact energy to a reasonable amount established by ASTM. Our

system will also alert bystanders in the form of an alarm that a drone is falling.

9. FURTHER IMPLEMENTATION

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The development of this project was carried out successfully. A final working prototype

was delivered to the project sponsor that meets the set requirements and constraints. However,

some improvements can be made to upgrade it. This section discusses possible improvements in

the project's mechanical, electrical, and software areas.

9.1 MECHANICAL DESIGN

One of the most significant setbacks this system has is requiring new CO2 cartridges for

each flight. This requirement elevates the cost of operating our system. We would suggest a future

project implementing a CO2 release system that can either considerably extend the system's shelf

life or release the CO2 from the cartridge only when the parachute needs deployment.

Another improvement that the system would highly benefit from is reducing the total

system mass. Although this system meets the sponsor's mass requirement, any mass optimization

would further the system's applications.

The systems' modularity is limited to quadcopter use. Drones with other quantities of

propellers do not readily fit the system designed in this project. To make the system usable on

drones of any number of propellers, new tubes for holding the flight termination flaps should be

added. The inflating balloon will push all flaps out. The biggest challenge of this modification

would be the re-arrangement of all electronic components.

The final suggestion for the system's mechanical aspects is to give the user the ability to

detach the parachute from the system quickly. In the case that the parachute is activated, there is a

possibility that the parachute could entangle on a tree, lamp post, or similar tall object. Access to

the drone in any of these situations may not always be attainable. A quick-release system that can

be activated remotely would be a good feature for easy recovery.

9.2 ELECTRICAL AND SOFTWARE

There can be various implementations added to the electronics and software components.

The purpose of adding more components to the design would be to make the system "smarter" or

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more straightforward for the user to interact with. On top of that, if something were to be added or

implemented, future designers must be cognizant of security, power consumption, and cost

constraints.

For the electronics, improvements can be made in the quality and quantity of sensors. The

current system only houses two sensors, which might prove insufficient for particular flights.

Future designs could implement a GPS, but be aware that a GPS can interfere with other signals

and have inaccuracy, which is undesirable for an emergency parachute system. Improvements can

also be made to the triggering system. A MOSFET or switching module capable of driving higher

currents at a voltage gate of 3.3V would reduce the amount of time wasted in heating the Nichrome

wire.

For the software, improvements can be made in the algorithms implemented in the GUI,

as well as adding machine learning. Currently, the algorithm for detecting errors is rudimentary

and relies solely on user input. The flaw in this design is it invites unexpected failures from user

input. Hence, algorithms for detecting crashes that rely more on collective data than on user input

are desirable. Another way to achieve this is through machine learning. The onboard device can

learn what a typical erroneous flight is like and autonomously decide without the need for the user

to have much knowledge. The only constraint to be wary of is the power consumption of the ESP32

board’s processors.

The website could also be improved by adding more functionalities and testing for a wider

audience. The website currently requires that the pilot using the website is knowledgeable in

drones and knows their precise flight path. Improvements can be made so that the different

parameters are thoroughly understood and allow specific flight paths to be saved. Another

improvement would be to flash instructions to the ESP32 without the need of BLE, although doing

so opens the risk for security breaches.

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10. REFERENCES

[1] Skycat, "X48 PRO SERIES," [Online]. Available: https://www.skycat.pro/shop/skycat-x48.

[2] Mars Parachutes, "MARS 58 V2," [Online]. Available:

https://www.marsparachutes.com/product/mars-58-v2/.

[3] Parazero Drone Safety Systems, "SafeAir Mavic," [Online]. Available:

https://parazero.com/products/safeair-for-dji-mavic/#features-functionality.

[4] Parazero Drone Safety System , "SafeAirTM Phantom 4," [Online]. Available:

https://parazero.com/products/safeair-for-dji-phantom/.

[5] ASTM, Standard Specification for Small Unmanned Aircraft System (sUAS) Parachutes, 2018.

[6] National Fire Protection Association, National Fire Alarm and Signaling Code, 2013.

[7] R. Grant, Web Bluetooth, 2020.

[8] Genuine Innovations, "Microflate Nano," [Online]. Available:

https://www.genuineinnovations.com/collections/bicycle-co2-tire-inflators/products/microflate-

nano-co2-bike-tire-inflator.

[9] Fruity Chutes Professional Aerospace Recovery Solutions, "Parachute Descent Rate Calculator,"

Fruity Chutes, [Online]. Available: https://fruitychutes.com/help_for_parachutes/parachute-

descent-rate-calculator?term=IFC-36-SUL&weight=4. [Accessed 8 April 2021].

[10] Stratasys, "Vero," [Online]. Available: https://www.stratasys.com/materials/search/vero.

[11] Federal Aviation Administration, "Operations Over People General Overview," 28 December 2020.

[Online]. Available:

https://www.faa.gov/news/media/attachments/OOP_Executive_Summary.pdf.

[12] R. G. Budynas and J. K. Nisbett, "Diameters and Areas of Coarse-Pitch and Fine-Pitch Metric

Threads," in Mechanical Engineering Design, Shigley, p. 404.

[13] W. D. Callister, Jr. and D. G. Rethwisch, "Room-Temperature Mechanical Characteristics of Some of

the More Common Polymers," in Materials Science and Engineering, An Introduction, Wiley, 2014,

p. 583.

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11. APPENDICES

Appendix A - Parachute Selection Calculations

Main Canopy Nominal Diameter Equation:

𝐷0 = √𝑆0

𝜋

where 𝑆0 is the parachute surface area. The surface area for the selected parachute is

𝑆0 = 0.6363 𝑚2 according to the manufacturer. [9]

𝐷0 = √0.6363 𝑚2

𝜋

𝐷0 = 0.4500 𝑚

Canopy Descent Rate at Sea Level:

𝑣𝑐𝑜 = √2∗𝑊𝑇

𝑆𝑜∗𝐶(𝐷0)∗𝜌0

where 𝑊𝑇 = 19.62 𝑁 is the design weight of the load, 𝐶(𝐷0) = 2.2 [9] is the drag coefficient for the

parachute, and 𝜌0 = 1.225 𝑘𝑔/𝑚3 is the air density at Sea Level.

𝑣𝑐𝑜 = √2∗19.62𝑁

0.6363𝑚2∗2.2∗1.225 𝑘𝑔/𝑚^3

𝑣𝑐𝑜 = 4.78 𝑚/𝑠

Impact Energy:

𝐸 =1

2∗ 𝑚𝑇 ∗ 𝑣𝑐𝑜

2

where 𝑚𝑇 is the design load.

𝐸 =1

2∗ 2 𝑘𝑔 ∗ (4.78

𝑚

𝑠)

2

𝐸 = 22.84 𝐽

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Appendix B - Maximum Power Calculations

Maximum Power Theorem Calculation:

For this calculation, the voltage drop between an open circuit and a 10Ω resistor is used to find

the current flowing in the diagram. Once that value is found, the internal resistance of the

battery is calculated. With the internal resistance found, the ratio of power dissipated is used to

define the battery's efficiency.

Variable Names and Components:

𝑉𝐿(𝑉𝑜𝑙𝑡𝑎𝑔𝑒 𝑜𝑓 𝑙𝑜𝑎𝑑)

𝑉𝑂𝐶(𝑉𝑜𝑙𝑡𝑎𝑔𝑒 𝑜𝑓 𝑂𝑝𝑒𝑛 𝐶𝑖𝑟𝑐𝑢𝑖𝑡)

𝑉𝐼(𝑉𝑜𝑙𝑡𝑎𝑔𝑒 𝐷𝑟𝑜𝑝 𝑎𝑐𝑟𝑜𝑠𝑠 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒) 𝑅𝐼(𝐼𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒)

𝑅𝐿(𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓 𝑙𝑜𝑎𝑑)

𝑛(𝑅𝑎𝑡𝑖𝑜 𝑜𝑓 𝑃𝑜𝑤𝑒𝑟 𝐷𝑖𝑠𝑠𝑖𝑝𝑎𝑡𝑒𝑑)

Schematic:

Variable Values:

𝑉𝑂𝐶 = 4.32𝑉

𝑉𝐿 = 4.21𝑉

𝑅𝐿 = 10.1Ω

Calculation:

𝑉𝑂𝐶 = 𝑉𝐼 + 𝑉𝐿

4.32𝑉 = 𝑉𝐼 + 4.21𝑉

𝑉𝐼 = 0.11𝑉

𝑉𝐿 = 𝐼 ∗ 𝑅𝐿

7.81𝑉 = 𝐼 ∗ 10.1Ω

𝐼 =7.81

10.1𝐴

𝐼 ≈ 0.77𝐴

77

𝑉𝐼 = 𝐼 ∗ 𝑅𝐼

0.11𝑉 = 0.77𝐴 ∗ 𝑅𝐼

𝑅𝐼 ≈ 0.14Ω

𝑛 =𝑅𝐿

𝑅𝐿 + 𝑅𝐼

𝑛 =10.1Ω

10.1Ω + 0.14Ω

𝑛 = 0.986

Appendix C - Power Budget

This section highlights the power consumption of the electronic component throughout the

various stages of flight. The system doesn’t house a switch to turn the system ‘ON’ or ‘OFF’.

Instead, the system is always on, but utilizes various techniques talked in this section to

guarantee the life of the system. The system can toggle between four operating states, which

are the following: 'sleep mode', 'stand-by mode', 'flight mode', and' emergency mode.' The

table below is used as reference for power consumed during the various power modes.

Table 7 - ESP32 Power Modes

In sleep mode:

The ESP32 is put into 'deep-sleep' mode. In this state, the power nano timer continuously

switches the ESP32 board on and off every 10 seconds. While the ESP32 board is 'off' due to

the TPL 5110, 35nA is consumed from its power. When the ESP32 board is 'on', the ESP32

board is put into 'deep-sleep.' In this state, the low co-processor, RTC timer, RTC memory,

and touch sensors are available- consuming a total of 150 µA. The ESP32 will not toggle to

the next state until a user touch triggers a wake-up call to GPIO 0. The ESP32 waits 10

seconds for a touch; if none is received, the nano power timer again switches off the ESP32.

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In stand-by mode:

The ESP32 wakes from 'deep-sleep'. In this state, the BLE functionalities can be turned on to

receive information. This consumes a total of 200mA. In stand-by mode, the ESP32 connects

to the webserver via BLE and receives the parameters from the website. Once parameters have

been sent, the user needs to click the button on the website that says, "Flight mode". Once

pressed, a flag will be set to toggle 'stand-by' to 'flight mode'.

In flight mode:

The ESP32 remains awake. In this state, approximately 500mA is consumed to power the

sensors and the BLE communication. This is necessary to accurately collect and interpret data

from the sensors and send a deployment signal without much delay. As the sensors are low

power, the current consumption is not altered significantly. If the flight is completed without

error, the user will need to press the RST button on the ESP32 to return to 'sleep' mode. In the

unfortunate event of an error in the flight, a deployment signal will trigger the state change to

'emergency' mode.

In emergency mode:

The processor sends the voltage input to the MOSFET gate to activate, and it remains on for 5

seconds. After the Nichrome wire burns the sacrificial tablet, the MOSFET I/O is turned to a

digital signal LOW, and the rest of the power available is directed for the speaker. The speaker

consumes a minimum of 20mA to achieve an audible level of 120dB. BLE capabilities are

switched off, reducing the current consumption to 100mA. This prevents the BLE from

draining the battery.

Final power budget:

Table 8 - Power Budget

Operating Mode Current Drawn Hours of Operation Calculations

(t = time in hours)

Deep Sleep 150µA 10333 hours 1.55𝐴

150 ∗ 10−6𝐴= 𝑡

Stand-by 200mA 7.75 hours 1.55𝐴

200 ∗ 10−3𝐴= 𝑡

Flight 500mA 3.1 hours 1.55𝐴

500 ∗ 10−3𝐴= 𝑡

Emergency 200mA 7.75 hours 1.55𝐴

200 ∗ 10−3𝐴= 𝑡

Overall, the system lasts roughly 1 year before needing to change the batteries. While in use,

the system can endure a continuous flight of 3 hours before draining the batteries.

80

Appendix D - Center of Mass Calculations

𝑚1 is the point of the center of mass of the St. Mary's Drone.

𝑚2 is the point of the center of mass of the Safety Parachute System.

𝐹𝐴, 𝐹𝐵, 𝐹𝐶 , 𝑎𝑛𝑑 𝐹𝐷 are the forces exerted by the motors.

𝑊𝐷 = 1.6 𝑘𝑔 ∗ 9.81 𝑚𝑠2⁄ = 15.68 𝑁 is the weight of the St. Mary's Drone.

𝑊𝑆 = 0.4 𝑘𝑔 ∗ 9.8 𝑚𝑠2⁄ = 3.92 𝑁 is the weight of the Safety Parachute System.

𝐿 = 0.33𝑚 is the distance in the x-axis between the points A, B, C, and D and the origin.

n is the maximum distance in the x-axis allowed for the center of mass of the Safety Parachute

System to be placed on to meet the requirement.

Assumption: 𝐹𝐴 = 𝐹𝐷 and 𝐹𝐵 = 𝐹𝐶 due to symmetry on the x-axis.

Σ𝐹𝑧 = 0

0 = 𝐹𝐴 + 𝐹𝐵 + 𝐹𝐶 + 𝐹𝐷 − 𝑊𝑆 − 𝑊𝐷

0 = 2𝐹𝐴 + 2𝐹𝐵 − 𝑊𝑆 − 𝑊𝐷

−2𝐹𝐴 = 2𝐹𝐵 − 𝑊𝑆 − 𝑊𝐷

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Σ𝑀𝑦 = 0

0 = −𝐿 ∗ 𝐹𝐴 + 𝐿 ∗ 𝐹𝐵 + 𝐿 ∗ 𝐹𝐶 − 𝐿 ∗ 𝐹𝐷 − 𝑊𝑆 ∗ 𝑛

0 = 2𝐿 ∗ 𝐹𝐵 − 2𝐿 ∗ 𝐹𝐴 − 𝑊𝑆 ∗ 𝑛

0 = 2𝐿 ∗ 𝐹𝐵 + 𝐿 ∗ (2𝐹𝐵 − 𝑊𝑆 − 𝑊𝐷) − 𝑊𝑆 ∗ 𝑛

0 = 2𝐿 ∗ 𝐹𝐵 + 2𝐿 ∗ 𝐹𝐵 − 𝑊𝑆(𝐿 + 𝑛) − 𝐿 ∗ 𝑊𝐷

0 = 4𝐿 ∗ 𝐹𝐵 − 𝑊𝑆(𝐿 + 𝑛) − 𝐿 ∗ 𝑊𝐷

4𝐿 ∗ 𝐹𝐵 = 𝑊𝑆(𝐿 + 𝑛) + 𝐿 ∗ 𝑊𝐷

𝐹𝐵 =𝑊𝑆 ∗ (𝐿 + 𝑛) + 𝐿 ∗ 𝑊𝐷

4𝐿

𝐹𝐵 = 𝑊𝑆 ∗ (0.25 +𝑛

4𝐿) +

𝑊𝐷

4

−2𝐹𝐴 = 2𝐹𝐵 − 𝑊𝑆 − 𝑊𝐷

𝐹𝐴 =−2𝐹𝐵 + 𝑊𝑆 + 𝑊𝐷

2

𝐹𝐴 =−2 (𝑊𝑆 (0.25 +

𝑛4𝐿) +

𝑊𝐷

4 ) + 𝑊𝑆 + 𝑊𝐷

2

𝐹𝐴 = −𝑊𝑆 (0.25 +𝑛

4𝐿) −

𝑊𝐷

4+

𝑊𝑆

2+

𝑊𝐷

2

𝐹𝐴 = −𝑊𝑆 (0.75 +𝑛

4𝐿) +

𝑊𝐷

4

The requirement states that the thrust output between the different motors should not exceed a

10% percent difference. From this relationship, the maximum allowed n value can be

determined.

82

|𝐹𝐴 − 𝐹𝐵|

(𝐹𝐴 + 𝐹𝐵

2 )≤ 0.1

| [−𝑊𝑆 (0.75 +𝑛

4𝐿) +𝑊𝐷

4 ] − [𝑊𝑆 ∗ (0.25 +𝑛

4𝐿) +𝑊𝐷

4 ] |

([−𝑊𝑆 (0.75 +

𝑛4𝐿) +

𝑊𝐷

4 ] + [𝑊𝑆 ∗ (0.25 +𝑛

4𝐿) +𝑊𝐷

4 ]

2)

≤ 0.1

|−𝑊𝑆 −𝑊𝑆 ∗ 𝑛

2𝐿 |

(0.5𝑊𝑆 +

𝑊𝐷

22

)

≤ 0.1


2𝐿 | ≤ 0.1 ∗ (

0.5𝑊𝑆 +𝑊𝐷

22

)


2𝐿 | ≤ 0.025 𝑊𝑆 + 0.025𝑊𝐷

−0.025 𝑊𝑆 − 0.025𝑊𝐷 ≤ −𝑊𝑆 −𝑊𝑆 ∗ 𝑛

2𝐿 ≤ 0.025 𝑊𝑆 + 0.025𝑊𝐷

−0.025 𝑊𝑆 − 0.025𝑊𝐷 ≤ 𝑊𝑆 +𝑊𝑆 ∗ 𝑛

2𝐿 ≤ 0.025 𝑊𝑆 + 0.025𝑊𝐷

−0.025 𝑊𝑆 − 0.025𝑊𝐷 ≤ 𝑊𝑆 +𝑊𝑆 ∗ 𝑛

2𝐿 ≤ 0.025 𝑊𝑆 + 0.025𝑊𝐷

−0.025 𝑊𝑆 − 0.025𝑊𝐷 − 𝑊𝑆 ≤𝑊𝑆 ∗ 𝑛

2𝐿 ≤ 0.025 𝑊𝑆 + 0.025𝑊𝐷 − 𝑊𝑆

−1.025 𝑊𝑆 − 0.025𝑊𝐷 ≤ 𝑊𝑆 ∗ 𝑛

2𝐿 ≤ −0.975 𝑊𝑆 + 0.025𝑊𝐷

83

(−1.025 𝑊𝑆 − 0.025𝑊𝐷) (2𝐿

𝑊𝑆) ≤ 𝑛 ≤ (−0.975 𝑊𝑆 + 0.025𝑊𝐷) (

2𝐿

𝑊𝑆)

[(1.025 ∗ (3.92𝑁) − 0.025 ∗ (15.68𝑁)] (2 ∗ 0.33𝑚

3.92𝑁) ≤ 𝑛 ≤ [(0.975 ∗ (3.92𝑁) + 0.025 ∗ (15.68𝑁)] (

2 ∗ 0.33𝑚

3.92𝑁)

−0.7425𝑚 ≤ 𝑛 ≤ 0.7095𝑚

To meet the center of mass requirement, the center of mass of the Safety Parachute System

must not be placed at a distance in the x-axis greater than 0.7095 m.

84

Appendix E - Power Screw Calculations

The required force to puncture a CO2 canister is 300N. This value was determined by

correspondence with a manufacturer of commercial CO2 cartridges. To puncture the cartridge,

the spring must be able to deliver this force. The diagram below shows the free body diagram

of the pin that would hold the spring in place before deployment.

In the diagram,

𝑓 is the frictional force

𝐹𝑁 is the normal force

𝐹𝑃 is the required force to pull the pin out

𝜇 = 0.33 is the friction coefficient of the material

ΣFy = 0

0 = 𝐹𝑁 − 300 𝑁

𝐹𝑁 = 300𝑁

Σ𝐹𝑥 = 0

0 = 𝐹𝑃 − 𝑓

𝐹𝑝 = 𝑓

𝐹𝑃 = 𝐹𝑁 ∗ 𝜇

𝐹𝑃 = 300 𝑁 ∗ 0.33

𝐹𝑃 = 99 𝑁

85

A power screw system, shown on the diagram below, would be used to pull the pin.

Σ𝐹𝑥 = 0

0 = 𝑃𝑅 − 𝑁 ∗ 𝑠𝑖𝑛(𝜆) − 𝑓 ∗ cos(𝜆)

0 = 𝑃𝑅 − 𝑁 ∗ 𝑠𝑖𝑛(𝜆) − 𝑁 ∗ 𝜇 ∗ cos(𝜆)

𝑃𝑅 = 𝑁(sin(𝜆) + 𝜇 ∗ cos(𝜆))

Σ𝐹𝑦 = 0

0 = −𝐹𝑃 − 𝑓 ∗ sin(𝜆) + 𝑁 ∗ cos(𝜆)

𝐹𝑃 = −𝑁 ∗ 𝜇 ∗ sin(𝜆) + 𝑁 ∗ cos(𝜆)

𝐹𝑃 = 𝑁(cos(𝜆) − 𝜇 ∗ sin(𝜆))

𝑁 =𝐹𝑃

(cos(𝜆) − 𝜇 ∗ sin(𝜆))

86

𝑃𝑅 = 𝑁(sin(𝜆) + cos (𝜆)

𝑃𝑅 = (𝐹𝑃

(cos(𝜆) − 𝜇 ∗ sin(𝜆))) (sin(𝜆) + 𝜇 ∗ cos(𝜆))

𝑃𝑅 =sin(𝜆) + 𝜇 ∗ cos (𝜆)

cos(𝜆) − 𝜇 ∗ sin(𝜆)∗ 𝐹𝑃

𝑃𝑅 =sin(𝜆) + 𝜇 ∗ cos (𝜆)

cos(𝜆) − 𝜇 ∗ sin(𝜆)∗

1cos(𝜆)

1cos(𝜆)

∗ 𝐹𝑃

𝑃𝑅 =tan(𝜆) + 𝜇

1 − 𝜇 ∗ tan(𝜆)∗ 𝐹𝑃

tan(𝜆) =𝐿

𝜋𝑑𝑚

𝑃𝑅 =

𝐿𝜋𝑑𝑚

+ 𝜇

1 −𝜇𝐿

𝜋𝑑𝑚

∗ 𝐹𝑃

𝑇 =𝑑𝑚

2∗ 𝑃𝑅

𝑇 =𝑑𝑚

2∗ (

𝐿𝜋𝑑𝑚

+ 𝜇

1 −𝜇𝐿

𝜋𝑑𝑚

) ∗ 𝐹𝑃

𝑇 =𝐹𝑃

2∗ (

𝐿 + 𝜇 ∗ 𝜋𝑑𝑚

𝜋𝑑𝑚 − 𝜇𝐿)

87

For ACME threads,

𝑇 =𝐹𝑃

2∗ (

𝐿 + 𝜇 ∗ 𝜋𝑑𝑚 ∗ sec (𝛼)

𝜋𝑑𝑚 − 𝜇𝐿 ∗ sec(𝛼))

The possible threads to be used in this power screw system are shown in the table below, along

with their size parameters. Using the relationship above, the necessary torque has been

calculated.

𝑑𝑚 (m) L (m) α (°) T (Nm)

1/4-16

ACME 0.0635 0.015875 29 1.06848

5/16-14

ACME 0.079375 0.018143 29 1.30806

3/8-12

ACME 0.09525 0.021167 29 1.559905

The smallest necessary torque to pull the pin out is 1.068 Nm with the 1/4-16 ACME thread.

88

Appendix F - Piercing Block Fastening Calculations

The piercing block is fastened to the rest of the case using four screws. The positions of the

screws are shown in the diagram below.

The four different screws are arranged symmetrically across the block, so each holds the same

load. The diagram below is a free-body diagram of the connection.

Where

𝐹𝑆 is the force of each screw

𝐹𝐶𝑂2 is the force due to the pressure of the pressurized CO2

89

The pressure of the CO2 is 800 psi. This is equal to 5,515.8 kPa

The force exerted by the CO2 on the block is

𝑃 =𝐹𝐶𝑂2

𝐴

𝐹𝑆 = 𝑃 ∗ 𝐴

𝐹𝐶𝑂2 = 5,515.8 𝑘𝑃𝐴 ∗ (𝜋

4) ∗ (0.01𝑚)2

𝐹𝐶𝑂2 = 433.2 𝑁

Σ𝐹𝑥 = 0

0 = 4𝐹𝑆 − 𝐹𝐶𝑂2

𝐹𝑆 =𝐹𝐶𝑂2

4

𝐹𝑆 =433.2 𝑁

4

𝐹𝑆 = 108.3 𝑁

The load on every screw is 𝐹𝑆 = 108.3 𝑁

The stress on the bolt is

𝜎 =𝐹𝑆

𝐴𝑡

Where 𝐴𝑡 is the Tensile-Stress Area. For an M5 bolt, 𝐴𝑡 = 14.2 𝑚𝑚2 [12]

𝜎 =108.3 𝑁

1.42 ∗ 10−5 𝑚2

𝜎 = 7.627 𝑀𝑃𝑎

The safety factor for the screws is

𝑛 =𝜎𝑦𝑖𝑒𝑙𝑑

𝜎

90

The lowest yield stress for Nylon is 𝜎𝑦𝑖𝑒𝑙𝑑 = 44.8 𝑀𝑃𝑎 [13]

The safety factor for the screws is

𝑛 =44.8 𝑀𝑃𝑎

7.627 𝑀𝑃𝑎

𝑛 = 5.874

91

Appendix G - Website Screenshots

Figure 73 - Home Page

Figure 74- Navigation Page Tab

Figure 75 - Connect to BLE Tab

92

Figure 76 - Plan Flight Tab

Figure 77 - Start Flight Tab

Figure 78 - Metrics & Emergency Deployment Tab

93

Figure 79 - Report Tab

Figure 80 - Sample Generated Report

Figure 81 - Documentation Page

94

Figure 82 - Contact Page

95

Appendix H - Datasheets of Electric Components and Links to Software Tools

Components & Software

ESP32-WROOM-32D

BMP388

LSM303DLHC

Babysitter

Nano Power Timer 5110

LiPo Battery

DL4184 Module

PHP 7.4.13

Lighttpd 1.4.55

Ubuntu 20.04.1

CR2032 Coin Cell Battery

Link for url:


https://www.espressif.com/sites/default/files/documentation/esp32-wroom-32d_esp32-wroom-32u_datasheet_en.pdf

https://cdn-learn.adafruit.com/downloads/pdf/adafruit-bmp388.pdf?timestamp=1600143854

https://cdn-learn.adafruit.com/downloads/pdf/lsm303-accelerometer-slash-compass-breakout.pdf

https://cdn.sparkfun.com/assets/learn_tutorials/5/3/0/bq24075.pdf

https://www.ti.com/lit/ds/symlink/tpl5110.pdf?ts=1619379439068&ref_url=https%253A%252F%252Fwww.google.com%252F

http://www.farnell.com/datasheets/1666647.pdf

http://www.aosmd.com/pdfs/datasheet/AOD4184A.pdf

https://www.php.net/

https://www.lighttpd.net/

https://ubuntu.com/

https://data.energizer.com/pdfs/cr2032.pdf


96

12. SMC CAPSTONE REFLECTIONS

Sebastian Castro Ramos

In my last semester at St. Mary's University, I have reflected on the journey I have taken

in my time here. When I was about to graduate from high school, I had great expectations about

my future as an engineer. However, at that time, my idea of an engineer was a guy who was good

at math and built cool stuff. My engineering vision was limited to building gadgets in the garage

for myself, my family, and my friends and working at a big company. Now, at the end of my

studies as an engineer, I understand that there is more to engineering than simply building cool

gadgets.

Every student at St. Mary's University must take a series of classes, the core SMC's, that

provide students important values every professional should have. Each of the SMC classes I have

taken has been an integral part of my Marianist education. One of the classes I enjoyed most and

is readily the most applicable SMC for my professional life was SMC 2301 Ethics. In this course,

we discussed different ethical theories and their applications. The best part came during the lab, in

which we were given engineering ethics case studies, and we would have to use the theories

learned in class to determine the best course of action for every case. Practice makes perfect and

having this opportunity to strengthen our ethical compasses was an excellent exercise. Another

SMC course I hold dear is HO 1301, The Human Quest for Meaning. As a young adult,

determining the right path to follow in life is not an easy task. It can be challenging to find a

meaningful goal in life to drive us. In this class, I found a desire to help others with my work as an

engineer. Partially for this reason, I chose to work on a Senior Project that involved parachute

system safety. As mentioned before in this report, drones are prone to failure and can cause

physical damages. Using my knowledge to develop a system that can make drones safer goes

alongside this goal of helping others that St. Mary's has instilled in me.

Now that I am graduating, I strive to be an engineer who can make cool gadgets for myself

but also who uses his knowledge for the benefit and advancement of others.

97

Juan Luna Glaser

I was first unsure what a Marianist education would do to benefit me. I graduated from

Escuela Americana in El Salvador 5 years ago as the 25th best student in a class of 102 students.

As seen in my involvement in the school's math club and technology club as an officer, I was

passionate about technology and mathematics. I would also challenge myself by enrolling in

various AP classes and helping in community centers during the weekends. However, I felt that

something was missing; my actions were not meaningful at a grand level. I knew I would find my

answer in college, but this is easier said than done. There are over 25,000 universities globally,

with every university catering to great engineering curriculums that would prepare me for a future

as an engineer. My biggest challenge back then was to decide which institution would give me the

best education overall. I probably read and navigated over 100 university web portals, deciding

which institution would cater me the best. Out of the 100 universities I considered, St. Mary's

University was definitely in the top ten. I was moved by its mission statement and personally

related to its 5 Marianist characteristics. I knew at that moment that what I was looking for in

college education was quality education with an overall understanding of the impact an individual

can do in a community.

I knew I made the right decision once I arrived at St. Mary's University. My first year is

marked as a year of self-growth and intrigue, where I learned how to perform well in STEM classes

that were of greater difficulty. I struggled at first, but thanks to the personal connections I made

with faculty members and the help of various students here at St. Mary's University, I overcame

the challenges and gained self-confidence in my abilities to learn. On top of that, I made friends

with a couple of upperclassmen who oriented me and inspired me to be involved in campus. With

their help, I was able to get a job as a resident assistant here at St. Mary's University. As an RA, I

helped students every day with their struggles and volunteered in surrounding communities.

Without realizing it, my actions were driven by core lessons taught here in St. Mary's University

SMC classes- specifically, SMC Self, SMC Ethics, and SMC God.

In SMC Self, I learned about the meaning of the "self." Self that was taught to me traces its

origin to the phrase coined "I think; therefore, I am." This phrase taught me that a fundamental

element of humanity is its ability to think. Recognizing this, human thought can be destructive or

restorative; it depends on the meaningful intention attached to it. This is where SMC God and

98

SMC Ethics come into play. SMC Ethics teaches the necessary tools to recognize unethical issues

in society, which is essential to an engineer constantly making thoughtful decisions that can impact

the lives of millions with the technology they create. On the other hand, SMC God teaches that an

action is meaningful if it springs from love. When all the classes are grouped, I learned that I must

make conscient decisions, as it is my nature as an engineer and a person. Those thoughts must be

filled with the love that God preaches and be ethical under the eyes of society so that my actions

have the meaningful impact that I have ever yearned for since high school.

Safety Parachute System

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