Letter of Transmittal

Gold Darr Hood

Senior Design 1 College of Engineering

University of Texas at San Antonio

One, UTSA Circle, San Antonio, TX 78249

Dear Professor Gold Darr Hood,

On behalf of Brobotics Inc., it is our pleasure to submit the Final Proposal. This report is

based upon the given parameters given by the professor, to design the final concept of a

quadrupedal robot for the Robotics and Motion Laboratory. Along with the final concept there

will be an in depth key specifications, proposed solution, justification as well as an earned value

analysis.

If any query or clarification about the Final Proposal is needed, feel free to contact the

team lead of Brobotics Inc.

Sincerely,

Brobotics Inc.

Signature of Team Lead

Signature of Sponsor

Final Proposal

Date: 12/10/2018

CREATED FOR:

ROBOTICS AND MOTION LABORATORY

CREATED BY:

MEMBERS:

Steven Farra zvo618@my.utsa.edu

zvo618 (210) 776-9117

Signature

Emiliano Rodriguez pyn109@my.utsa.edu

pyn109 (830) 462-1396

Signature:

John Carroll kor929@my.utsa.edu

kor929 (512) 229-7924

Signature:

Mario Navarro nmario597@gmail.com

rjr752 (210)232-4750

Signature:

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Executive Summary

Researchers in the RAM lab are currently interested in research relating to quadrupedal robots such as agile gait locomotion and climbing robots. The robot that is currently available to the researchers is expensive, some of its components are exclusively manufactured by the robot’s manufacturer, and its source code is not accessible. Building an open source robot with “off-shelf” components allows current and future researchers to find the necessary components while adjusting the robot’s design to suit their application. Customer discovery was performed for this project, to learn more about the problem at hand and how current solutions have addressed the problem. Interviews were conducted with researchers and hobbyists in the field of robotics. Following the interviews, the scope of the project was shifted from a two-legged, boom-supported to a four-legged, self-supported robot. Prior to the interviews, the targeted market included hobbyists and researchers in other laboratories. This changed after the interviews, only considering the researchers at the RAM lab as the targeted users.

The robot shall meet the following specifications:

● The robot shall be able to reach a speed of 0.2 m/s ● The robot shall be able to have a payload capacity of 25% ● The robot shall weigh less than 23 kg ● The robot shall be open source, with the source code licensed under GPL3

In the design process, examples of legged creatures from nature were examined for the

design of the legs of the robot. Two prevalent leg configurations were realized, which are the inward knee configuration, as seen in dogs, and the outward knee configuration, as seen in arachnids. A hybrid between the two configurations was then created, utilizing some advantages of both knee configurations. The legs are actuated using two motors at the hip, which will provide torque in parallel. The robot is comprised of a single board computer, four motor drivers, eight brushless DC motors, and four batteries. Python will be used to create algorithms for the operation of the robot, using closed loop control through position and orientation data that is used for tracking and correcting its motion.

To verify all specifications are met by the proposed solution, testing will be performed

for each requirement. The speed specification is verified through dynamic analysis, calculating the torque required by the motors to move the robot at the specified speed. To find the optimal motor to be used in the robot, the ratio of the torque provided by a motor to its weight is considered. The payload capacity specification is verified through a Finite Element Analysis of the most critical components in the system. The component which will undergo the greatest amount of loading and stress is the lower leg link fitted with the foot. By comparing the calculated stress at the critical location of the link to the endurance strength, the proposed design satisfies the required payload capacity. Once a functioning algorithm is established, all relevant documentation and files will be uploaded to an online repository, with source code licensed under GPL3.

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The calculated SPI and CPI indicate that the project is on schedule and the resources have been utilized effectively. Moving forward, the team will begin manufacturing and fabricating the parts, as well as creating the algorithm for the operation of the robot.

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TABLE OF CONTENTS

List of Figures 6

1. INTRODUCTION 7 1.1 Background 7 1.2 Customer Discovery 7 1.3 Problem Statement 7

2. KEY SPECIFICATIONS 7

3. PROPOSED SOLUTION 8 3.1 Overview 8 3.2 Leg Sub-assemblies 9

3.3.1 Components 9 3.2.2 Assembly Instructions 11

3.3 Body Sub-assembly, Electronics, And Electrical Schematic 11 3.3.1 Body and Electronics Overview 11 3.3.2 Electronics Breakdown 12 3.3.3 Electrical Overview 12 3.3.4 Wiring Description 13

3.3 Software Interface 13 3.3.1 Introduction 13 3.3.2 Use Case Diagram 13 3.3.3 Process Flowchart 13 3.3.4 Communication 14 3.3.5 Class Diagram 14 3.3.6 Hardware and Software Interface 15 3.3.7 GPL3 16 3.3.8 Conclusion 16

4. JUSTIFICATION 16 4.1 Structural Analysis 16 4.2 Motion Analysis 17

5. PROJECT MANAGEMENT 19 5.1 Bill of Materials 19

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5.2 Earned Value/Gantt Chart 20

6. CONCLUSION 21

7. APPENDICES 23 7.1 Referenced Figures and Images 23 7.2 Customer Discovery Report 34 7.3 Design Specifications 49 7.4 Drawings 57

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List of Figures

01. Lil’Bro Complete Assembly. 8 02. Leg sub-assembly. 9 03. Breakdown of components in leg sub-assembly. 9 04. Exploded view of body & electronic components 12 05. UML class diagram 15 06. User interface sequence 15 07. Angular velocity (deg/sec) vs. time (s) of one cycle 17 08. Symmetric five bar leg configuration model 18 09. Earned Value Management 21

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1. INTRODUCTION

1.1 Background Over the last three decades, robotics has emerged as a highly valuable field, gaining

interest by its potential for automation. Individuals from fields such as manufacturing and military/defense have taken note of this emergence, examining how it can be applied in their respective fields. The military has expressed interest in agile robotics, for applications such as scouts, search and rescue, and mules. While wheeled robots have been proposed for these applications, there are limitations to a rolling robot. Namely, uneven and highly variable terrain limits the locomotion of a wheel. To this regard, research on legged robots has served to solve some of the limitations on wheeled robots, especially autonomous legged robots. Researchers at the Robotics and Motion (RAM) laboratory at the University of Texas at San Antonio are interested in contributing to the field of agile locomotion for legged robots. The work they perform is heavily reliant on closed loop control through software manipulation, however, the currently available robot does not allow users to access its source code. This proves problematic for the research the RAM lab is interested in, coupled with the difficulty and price of maintenance. Brobotics Inc. is currently working with the RAM lab to provide an alternate solution to the researchers that allows them and future researchers to contribute to the field, ensuring all users can always access all relevant documentation of the robot.

1.2 Customer Discovery A customer discovery study was performed to learn more about the problem at hand and

how current solutions may have addressed these problems. Going into the interviews, the scope of the project was headed in the direction of an open source two-legged boom supported robot. The interviews were conducted with researchers and hobbyists in the field of robotics. The interviews results lead to one conclusion, that both hobbyists and researchers have more interest in a mobile quadrupedal robot. Hence the scope of the project shifted from the two-legged boom supported robot to a four-legged self-supported robot. Prior to the interviews, the main target users were researchers and hobbyists. This changed to only considering the researchers in the RAM lab as well as any other researchers from other universities interested in the field of robotics.

1.3 Problem Statement The robot being currently used in the RAM lab is difficult and expensive to maintain,

wherein all components are only sold by the manufacturer of the robot. Researchers also cannot access the available source code of the robot due to its encryption by the manufacturer. Researchers in the RAM lab are interested in varying gaits, leg design and sensory packages for their applications, and without the source code, it is not possible.

2. KEY SPECIFICATIONS The following are some key specifications for Lil’ Bro.

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● Open Source The robot shall have an online repository for its part files and source code.

● Minimum Speed The robot shall reach a minimum linear walking speed of 0.2 m/s.

● Carrying Capacity The robot shall have a carrying capacity of at least 25% of its own weight while standing.

● Profile Dimensions The robot’s profile dimensions shall be within a cubic meter box.

● Total Mass The robot’s mass shall not exceed 23 kg.

3. PROPOSED SOLUTION

3.1 Overview The overall design of Lil’Bro is shown in Figure 01.

Figure 01. Lil’Bro Complete Assembly.

There is a total of five sub-assemblies, two left leg sub-assemblies, two right leg sub-assemblies, and a body sub-assembly. The profile dimensions and approximated mass are shown below in Table 1. Table 1. Profile Dimensions and Mass of Lil’Bro.

Length 0.69 m

Width 0.57 m

Height 0.22 ± 0.08 m

Mass 9.5 kg

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The variation present in the height dimension is due to the extension and shortening of the legs.

3.2 Leg Sub-assemblies 3.3.1 Components Each of the four leg sub-assemblies consist of a motor mount, two motors with encoders

and motor hubs, two upper leg sections, and two lower leg sections. The upper legs will be fastened to the hubs using six fasteners each, while the lower leg sections will be connected to the upper sections and each other by using precision shoulder bolts that will act as pins and will rotate inside sleeve bearings that will be inserted into the legs. The assembly and a breakdown of the mentioned components can be seen below in Figures 02 & 03.

Figure 02. Leg sub-assembly.

Figure 03. Breakdown of components in leg sub-assembly.

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The motors chosen for use are dual shaft 270KV motors, that provide 2.14Nm of torque and are provided by O-Drive. The motor can be seen in Figure 19 in the appendix. The decision to go with these motors was based on their cost to torque and weight ratio. The encoders that were chosen are 8192 CPR encoders that have a maximum speed of 7500 RPM’s, and are provided by CUI Inc. The encoders were chosen based on the motor manufacturers recommendation.

To transfer the torque from the motor’s rotor to the upper leg sections an aluminum Mounting Hub with 8mm bore provided by Pololu were selected, the hubs can be seen in Figure 21, in the appendix. The decision to go with these motor hubs was based on the double set screw design and the price to weight ratio. To show that the chosen mounting hubs could support the amount of torque being transferred from the motor, finite element analysis was performed using SolidWorks simulation, the results provided a minimum safety factor or 7.2.

To connect the sections of legs together while also allowing them to freely rotate, a 5mm precision shoulder screw from McMaster-Carr was chosen, this screw would provide the smooth, rigid surface required to act as a pin. To ensure that the chosen screw would support the forces that would be applied to it, a finite element analysis was performed using SolidWorks simulation, the results provided a minimum safety factor or 200.

To allow the legs to rotate freely around the shoulder screw, a 5mm bore sleeve bearing provided by McMaster-Carr was chosen. The sleeve bearings outer diameter would provide an interference fit with the bores on the legs, and allow them to be inserted with minimal force. The sleeve bearings dynamic radial load capacity of 2224 N, and maximum supported angular velocity of 120 RPM’s meet the systems requirements. To allow an axial force to be applied to the joints without interfering with the free rotation, 5mm bore thrust bearings provided by McMaster-Carr were chosen for use, and can be seen in Figure 25, in the appendix. The thrust bearings dynamic load capacity of 89N will allow the shoulder screw to be sufficiently tightened, while their maximum rated angular velocity of 2500RPM’s meet the systems requirements.

The leg sections will be fabricated from 3D printed ABS. The decision to fabricate the legs out of 3D printed ABS was made based on the cost to weight ratio, and the sponsors desire to be able to produce and/or replace parts given access to a 3D printer. The material chosen (Acrylonitrile Butadiene Styrene) was found to have more strength, machinability, and higher temperature resistance when compared to the alternatives. While 3D printed ABS does not provide the same rigidity as metal material options, this was offset by the ability to add more material while still keeping the cost much lower than fabricating from metal alternatives.

To ensure that the legs can support the forces that will be applied to them, finite element analysis was performed using SolidWorks simulations in three different positions, forward, back , and center. The results provided a minimum safety factor of 1.53 when the leg is in the forward position. Due to the isotropic nature of the solidworks simulations, the lowest material properties of 3D printed ABS were used in the simulation along with doubling the forces that will be applied, this was done with the intention of making the simulations as accurate and conservative as possible.

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The motor mount will also be fabricated from 3D printed ABS and can be seen in Figure

07, below. To ensure that the motor mount can support the forces that will be applied to it, finite element analysis was performed using SolidWorks simulation. The results provided a minimum safety factor of 7.47. This solidworks simulation was also performed using the lowest material properties of 3D printed ABS along with doubling the forces that will be applied, this was done with the intention of making the simulations as accurate and conservative as possible due to the isotropic assumption of the simulation.

3.2.2 Assembly Instructions Locate all parts per bill of materials, assemble leg sub-assemblies by first inserting a

thrust bearing into each of the 7mm bores on the legs, then fasten the four sections of legs together by placing the leg-joint fastener first through a thrust bearing, then a leg section, another thrust bearing, and then the other leg section. use leg-joint lock nut to keep fasteners in place. (tighten to 0.8 in*lb). Place slip-on foot onto lower section of prime leg, use a desired epoxy to keep in place. Connect a motor hub to each upper leg using hub fasteners (tighten to a snug fit only using a flathead screwdriver) Place rotor of dc motors through the center bore of the right leg mount and into the motor hubs. Fasten motors to mount using motor fasteners tighten to a snug fit using a 3mm allen wrench. Tighten set screws on motor hubs using a 1.5mm allen wrench. Place motor housing over each dc motor, and fasten in place using motor housing fasteners. (tighten to a snug fit using a 2.5mm allen wrench). Fasten an encoder to each motor housing using encoder fastener. (tighten to a snug fit using a 2mm allen wrench) Place cable holders along the upper surface of the mount, and secure cables from encoders and motors. (run cables towards l-joint on mount) Secure each leg assembly to the body using leg mount fasteners, lock washers, and hex nuts. (tighten fasteners using a 4.5mm allen wrench, to no more than 8 in*lb. place two hex nuts on each fastener) Run cables from each leg assembly into the body, then to components, securing through cable holders.

3.3 Body Sub-assembly, Electronics, And Electrical Schematic 3.3.1 Body and Electronics Overview The body sub-assembly consists of a body shell, a single board computer (Raspberry Pi),

4 motor drivers, 4 batteries for motor drivers, 4 power resistors, an Inertial Measurement Unit (IMU), and a power bank. The exploded view of the body can be seen below in Figure 04. It should be noted that the IMU and power bank are not shown by the figure. The IMU is to be placed underneath the Raspberry Pi and centered with respect to the body. The power bank is placed underneath the body, attached using velcro with a wire placed through the body to power the Raspberry Pi.

The body shell will be fabricated from 3D printed ABS, which allows for increased customization capabilities such as extruded mounting holes from the body for the Raspberry Pi and the power resistors. By elevating these components, this increases the effective space available, and wires can be routed underneath the components. This also allowed for incorporation of lightening holes and ventilation holes such as the ones underneath the motor drivers. There are some disadvantages, however, of this method of fabrication. First, the rigidity

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of the body is limited due to the nature of 3D printed polymers. To compensate for this, the infill with which the body will be printed with will be no less than 70%. Secondly, the tolerances on bores created by the process are generally not as precise as other dimensions of the component, but it does vary based on the printer performing the fabrication.

Figure 04. Exploded view of the body and electronics.

3.3.2 Electronics Breakdown The electronics incorporated into the body are mentioned above in section 3.3.1, and in

this section a more detailed breakdown of the components is presented.

The first component is the Raspberry Pi 3 Model B+, which is a single board computer. This will serve as the brain of the robot, processing sensory information and sending commands to other components, by hosting a Python program that can be interfaced with the chosen motor drivers. The motor drivers are ODrive V3.5 motor drivers that can perform position, velocity, and current control. They are capable of real time communication via USB, with a minimum frequency of 4000 Hz. Each ODrive board is accompanied by a power resistor that is used for braking energy dissipation. A 1500 mAH 3 cell 11.1V rechargeable Turnigy LiPo battery is used for each motor driver, and a 5000 mAH rechargeable power bank powers the Raspberry Pi. The IMU used in the robot is a 3-axis accelerometer, a 3-axis gyroscope, and a 3-axis magnetometer that is also able to sense ambient temperature.

3.3.3 Electrical Overview Electronic schematics are special tools used as maps to understand and read circuits. Lil

Bro's wiring schematic is composed of “off the shelf” electronics, no printed circuit boards (PCB) were developed or created in order to support the connection between all electronic components, but rather all electronic components are in conjunction through the use of bullet connectors or soldering.

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3.3.4 Wiring Description The unit will prevent complete battery drainage via a battery gauge attached to its

corresponding battery. The alternating source of information derives from the raspberry pi, which gathers power from a 5,000 mAh power cell. The raspberry pi is connected to the IMU through the GPIO pins and all four Odrive motor driver via a USB cable. The Odrive motor drivers are powered from a 33.3V battery cell, a brake resistor is added to each motor driver to prevent any back emf spikes coming from the motors. All 8 motors are connected to a corresponding Odrive motor driver (2 per motor driver) along with its corresponding encoder (1 per motor).

3.3 Software Interface 3.3.1 Introduction

This section is intended to describe the software package and process flow of the embedded system. In addition, this chapter will exhibit the communication between the electronics and hardware being controlled. In order to validate the software interface, a use case diagram, process flow chart, sample rating, class diagram and user interface section are included in this report, and demonstrate all interfaces between the software and hardware of the system. The source code will be open source (under a general public license) and will be appended to an online repository (along with any executable files needed to run the program).

3.3.2 Use Case Diagram The use case diagram has three main actors (specifies a role played by a user or any other system that interacts with the subject) and extends or includes a process use case. A developer has the ability to develop the robot further by editing the source code directly; the developer can then create methods/functions that will be saved as processing commands in which any user of the robot can utilize at program execution. The user (controlling the robot) can start, or stop the system at any time and will have full access of controlling the robot by a remote controller. The rotational motor speed will be designated by a analog stick in the remote controller (variable resistor) which will ultimately set the robots velocity. The remote controller will send other processing commands to the robot which will read values (position, amperage, voltage) and adjust the robots position as indicated.

3.3.3 Process Flowchart The process flowchart represents the program’s algorithm or workflow. In the diagram

the execution of the program starts the sequence. The system then initializes all inputs and outputs required for the robot, calibrate all motors and set close loop control for the motors. Afterwards, the initial motor torques are applied for the starting (standing) position of the robot while simultaneously awaiting an input signal from the user. After the system is ready, a condition block decides whether an input signal was transmitted; if so, the robot will read the analog input from the controller while concurrently reading/writing a body position (via IMU sensor) and other significant values (current, voltage , battery level, motor velocity) and set the motor speed to move the robot. This process will loop through this sequence indefinitely until the user decides to terminate the program.

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3.3.4 Communication The communication between the hardware and software of the robot will be done through

serial communication. This type of communication is the process of sending data one bit at a time, sequentially, over a communication channel. The sampling rate unit used is Hertz, which is the SI unit of frequency, equal to one cycle per second. The sample rate of the system is broken down and described by the communication between the hardware components below.

The raspberry pi communicates between the IMU, Odrive motor drivers and the six-axis

joystick controller at a sampling rate of 100 Hz. The Odrive motor drivers communicate with the encoders and motors at a sampling rate of 4000 Hz. This high-speed processing rate is enough for the robot to react to all inputs and execute the proper outputs.

3.3.5 Class Diagram The class Unified Modeling Language (UML) diagram is a type of structure that

describes the composition of a system by showing the system’s classes, attributes, methods and the relationships among objects in that system. Lil’Bro will contain several classes which will be refactored without affecting the program’s external behavior.The relationships among these classes include association, composition, and inheritance. Each class will have a certain role or function to assemble a working software model. The following classes are shown and listed below along with a descriptive role.

● Main - Establishes robot connectivity with computer, controller and other hardware. ● Robot - Takes in user input and sets speed according to that user input. Also

communicates with motor drivers. Motor drivers communicate with motors to set speed and position claimed by the robot class.

● Components - Gathers all hardware components and organizes the information obtained by them.

● Sensors - Individually takes in data input by measuring a physical property of its environment. These sensors include: six-axis joystick controller, battery gauge and IMU.

● Output - Writes values to a text file for data analysis.

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Figure 05. UML Class Diagram.

3.3.6 Hardware and Software Interface The user interface is the means by which the user and a computer system interact, in

particular the use of input devices and software. Lil’Bro’s user interface will be conducted through the six-axis joystick controller (DualShock 3) and will have various input signals which will command the robot to execute a corresponding command.

Figure 06. User Interface Sequence.

In the figure above, the sequence from off to walking stages are illustrated next to the corresponding joystick command. Figure (a) shows the robot in its initial “off” position, it can be

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seen that all motors and actuators are idle. Figure (b) demonstrates the output caused by the push of the start button on the controller, initiating the robots initial standing position. Figure (c) shows the left analog stick being push in an upward direction, setting the robots motion forward into its walking cycle (notice the joystick’s input is proportional the walking speed set on the robot). Similarly, figure (d) demonstrates the output caused by the left analog stick being pushed downward (speed increases as joystick increases its value). This is the main user interface and driving process behind Lil’Bro and its operation.

3.3.7 GPL3 Brobotics Inc. hereby disclaims all copyleft interest in the program for Lil’Bro’s

software and hardware operation and that it is under the GPL3 License. The GNU General Public License v3.0, is a free, copyleft license utilized for software. This license allows software to be cloned, modified, and distributed without any legal consequences. This allows Lil’Bro to exist as an open source project in which anybody can download and recreate the robot. The source code will be available through Github, an online repository.

3.3.8 Conclusion The software package for Lil’Bro will be open source under the GPL3 license. The

software will dictate all outputs based on user input and is structured by several classes which take care of specific tasks in the execution of the program. The interface can be used to control the robot over a wireless remote controller, and the processing control commands are performed by the hardware interface. The sensor readings such as voltage, amperage and body position will be available graphically to users through the medium of a single board computer (raspberry pi) integrated within the robot, and the remote control software is a useful tool for developing and testing new and existing features of the robot. This will extend decision making to the robot and will make the overall system more versatile. With the aid of the remote controller, there is no need for further modification to the hardware interface.

4. JUSTIFICATION

4.1 Structural Analysis To ensure that the overall structure could support the total calculated mass of 9.5Kg,

finite element analysis was performed on the critical components of the system, these components consist of the motor mount, legs, motor hub, and the precision shoulder screw. To ensure the structural integrity of these components the forces applied in the simulation were twice that of the predicted ones, the material properties of the 3D printed ABS were also set at a minimum value to account for the isotropic behavior of the material in the simulations. The table below shows the results of the finite element analysis simulations performed on the individual components.

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Table 2. Results of finite element analysis simulations in SolidWorks.

Critical Component and Location Factor of Safety

Leg in Forward Position 1.85

Leg in Central Position 3.36

Leg in Backwards Position 1.53

Leg Mount 7.47

Motor Hub 7.2

Precision Shoulder Screw 200

The lowest returned factor of safety was in the upper leg section when the legs were in the forward position. The results provided an area of concern that can be further investigated using laboratory experiments and actual tests, the dimension of the upper leg may also need to be changed based on the results of these tests.

4.2 Motion Analysis As stated by the specifications of this project, the robot is to reach a linear walking speed

of 0.2 m/s. To prove that the proposed design fulfills this specification, appropriate supporting analysis is performed. The motion analysis is split into two main parts, finding the required rotational speed and torque at the hip joint. Both parameters correspond to the motors of choice that are to be placed at the hip joint. To calculate the required rotational speed for the entire robot to have a linear walking speed of 0.2 m/s, a simulation in Solidworks is performed. The complete model of the robot is set to move at a speed of 0.2 m/s while setting the motion of the legs as intended. The rotational speed at the hip joint was tracked by observing the speed of the upper leg links, which rotate at the same speed of the motor’s shaft. A graph is then obtained of the rotational speed over one cycle, where a cycle is the robot taking a step, shown in Figure 07.

Figure 07. Angular Velocity (deg/sec) vs. Time (s) of One Cycle.

From the figure, the maximum angular velocity present in the cycle is approximately 128 deg/sec, which is equal to 21.3 RPM. The motor chosen enables the legs to rotate at more than

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100 times the specified speed, so the legs are able to travel at the specified speed. This analysis would be valid on its own if the robot was weightless since most motors are able to reach that RPM. To obtain a more accurate representation of the motor requirements for the specified speed, the torque of the robot alongside its estimated weight have to be taken into consideration.

A paper by Bhounsule, Pusey, and Moussouni[4] analyzes the symmetric five bar leg configuration, alongside two other configurations, however, they are not of interest for this robot. Figure 08 shows a schematic of the symmetric five bar leg configuration.

Figure 08. Symmetric Five Bar Leg Configuration Model.

From the figure, l1 is the upper leg link length, l2 is the lower leg link length, l is the length of the fifth imaginary leg link, 𝜃1 is the angle between the horizontal and rightmost upper leg link, 𝜃2 is the angle between the horizontal and the leftmost upper leg link, and alpha is the angle between the ground and the imaginary link. The point (x,y) is the hip joint, which in our case is the location of the two motors. One of the goals of the paper in question is finding an expression of the torque of each motor required to allow the leg to support itself, at various angles alpha. The Jacobian of forward kinematic of the symmetric five bar leg geometry is calculated in the paper, which is dependent on l1, l2, 𝜃1, and 𝜃2.

The next step is defining the acting force vector on the legs, which in the case of Lil’Bro is one fourth of its total weight. However, this is the case, assuming Lil’Bro was a static body that does not move. The paper in reference does not cover dynamic analysis of this leg geometry, so making an assumption about the difference between the static model and the dynamic model is required. By studying literature on the topic of walking force analysis, a solution presented itself in a paper by Rod Cross[5]. In this paper, the normal force exerted by standing is compared with that of slow pace walking and other gaits. In the context of Lil’Bro, the normal force due to standing and slow pace walking are the only two of relevance to the analysis, since the robot will be standing and walking at 0.2 m/s, which is considered to be slow pace walking. Results suggest that if the normal force (N) for standing is equal to the weight (mg), then for slow pace walking N is equal to approximately 1.33 times mg. With this in mind, the force exerted on the leg is considered to be one-fourth of the weight of Lil’Bro times the 1.33 walking factor. Given that the force is a vector, a value 0 is given to the horizontal component of the force since a walking multiplier is taken into consideration for the vertical component.

Now that both the Jacobian and the force vector of the leg are available, the following equation is used to obtain expressions for the required torque of the motors,

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FΓ = JT wherein is the torque, is the transpose of the Jacobian, and is the force vector. The Γ JT F calculated torque is a 2x1 matrix, representing the torque of each motor, and the expressions are in terms of l1, l2, 𝜃 1, and 𝜃2. l 1 and l 2 are then specified as constant values shown in Table 3 below. Table 3. Leg Geometry Parameters for Torque Calculations.

l1 0.1 m

l2 0.2 m

𝜃 1 [-𝜋/6, 𝜋/3] rads

𝜃 2 [-4𝜋/3, -5𝜋/6] rads

The angles are presented as ranges to demonstrate the range of angles the upper legs are anticipated to travel through. The exact torque values are now calculated at different angles 𝜃1 and 𝜃 2, shown in Figure 29, in section 7.1 of the appendices. Torque values are both positive and negative, indicating varying directions (clockwise vs. counter-clockwise). On the plot, the point at which the maximum torque occurs is specified and the torque value is shown as -2.124 Nm. When compared to the maximum torque the chosen motor is capable of reaching (2.14 Nm), the values appear to be relatively close. There are two things that are worth noting though. First, the total weight used for the calculation was a conservative estimate of 10 kg. The second being the combinations of angles the torque is calculated at are not all possible, that is only angles that result in a symmetrical geometry across the vertical axis will be utilized by the robot. The angles that result in the highest torques are those that result in an asymmetric geometry.

5. PROJECT MANAGEMENT

5.1 Bill of Materials The total budget for the production of the quadrupedal robot Lil’Bro was $2000 dollars.

When deciding on the necessary components to construct the robot, the budget was always kept in mind, hence parts that met the specifications needed yet were relatively inexpensive were searched for. The components needed for were split into three categories, these categories being mechanical components, electrical components and lastly the 3D printed material. Down below in Table 4 , you can see the three categories on a table and the cost of each of them as well as the total cost.

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Table 4: Summarized Bill of Materials.

Table 4 summarizes the bill of materials into the three respective categories. The components that made up majority of the cost include the motors (mechanical), the driver motors(electrical), and the encoders (electrical). The total cost of all the components summed up to $1960.35 dollars, this price does include the shipping cost for a few of the components. Tax was exempted since Brobotics is working for the RAM lab and they fall under tax exemption provided by the University.

5.2 Earned Value/Gantt Chart The earned value provides a method for measuring the project's performance. It compares

the amount of work that was planned versus what was accomplished to determine if cost and schedule performance is as planned. Earned Value is separated into three different elements, Budgeted Cost of Work Scheduled (BCWS), Budgeted Cost of Work Performed (BCWP), and the Actual Cost of Work Scheduled (ACWS).

As for Brobotics Inc. the total number of hours that was considered to complete the project in the time frame of two semesters would be around 2,000 hours or 1,000 hours each semester. The hourly rate for each member of the group would be that of an engineer rate which is roughly about $100 per hour. The BAC was calculated to be $200,000, on top of this value the team added an additional two thousand dollars due to material cost as well as being the actual budget of the project. The next variable needed would that of the three key elements the BCWS. The total amount of hours spent was around 1,000 hours by the end of week 16. This BCWS was calculated to be 100,000($hr). The BCWP would be calculated using the variables of BAC multiplied by the percent of how much work had been completed by week 16. At this point it was determined that the team was in fact on schedule meaning that the percent of work completed would be that of 50%. The BCWP ended up having a value of 101,000($hr). The ACWP was calculated to be 95,050($hr). A chart using the BCWS, BCW and ACWP was created and helps give a better understanding and visualization of how the team is performing heading towards the end of the semester. Figure 19 represents the earned value analysis done to the reporting date.

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Figure 09: Earned Value Management.

After calculating the three key elements of an earned value management, they can be

used to calculate the CPI and SPI. The Cost Performance indicator was calculated using the Budgeted Cost of Work Performed over the Actual Cost of Work Performed, the value calculated was around 1.06. The value for SPI was roughly around 1.01. Both the CPI and SPI values were greater than 1, meaning that when it comes to CPI the team is using the resources allocated to the project efficiently. As for SPI the team is utilizing the time allocated towards the project very efficiently.

6. CONCLUSION From the analysis performed on this design, Brobotics Inc. is moving forward with this

proposed solution. The Earned Value Analysis indicates that the project is on schedule and will remain within budget. The team will continue to operate as efficiently as it did in the first sixteen weeks in order to complete the project on time and to satisfy the sponsor by meeting all the set specification requirements. Moving forward with the project, the next steps to be taken during the winter break include fabrication of the body parts, ordering both the mechanical and electrical components, as well as develop an algorithm for the operation of Lil’Bro.

The sponsor will be providing allen keys, small head screw drivers, crescent wrench, wire strippers, soldering gun, and the 3D printers necessary for the fabrication of the legs, motor housing, and body shell. The exact list of tools being provided by the sponsor can be seen in the references section. Brobotics Inc. will be asking the sponsor for the purchase of the mechanical, and electrical components as well as the 3D printed spool of material. The detailed list of mechanical and electrical components needed are stated in the bill of materials. The bill of materials can be found in the appendix, section 7.4.

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At the set date of completion, Brobotics Inc. will deliver Lil’Bro to the sponsor on time

while meeting all specifications set by the sponsor. Along with Lil’Bro and the controller, an operations manual will also be hand delivered. As for the programing software, there will be an online repository as mentioned in section 3.3.7, meaning that the sponsor and researchers will have full access to the code, and will be able to modify the code to the needs of their research.

References [1] Chilson, L. (2013) The Difference Between ABS and PLA for 3D Printing. [2] Cambridge Engineering Department (2003) Materials Databook. [3] Make It From (2015) Acrylonitrile Butadiene Styrene (ABS). [4] Bhounsule, Pranav A. Pusey, Jason. Moussouni, Chelsea. “A comparative study of leg geometry for energy-efficient locomotion”. [5] Cross, Rod. “Standing, walking, running, and jumping on a force plate”. Physics Department, University of Sydney, Sydney, New South Wales 2006, Australia Sponsor Provided Material: - Small flat head screwdriver - Small cross head screwdriver - Medium flat head screwdriver - Medium cross head screwdriver - T8 Torque head screwdriver - 1.5mm Allen key - 2mm Allen key - 2.5mm Allen key - 3mm Allen key - 4.5mm Allen key - 7mm Wrench - 13mm Wrench - Small crescent wrench - Wire cutters/strippers - Wire crimper - Solder gun - Solder

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7. APPENDICES

7.1 Referenced Figures and Images

Figure 10. Upper leg section, 3D printed ABS.

Figure 11. Leg section, 3D printed ABS.

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Figure 12. Leg section with foot, 3D printed ABS.

Figure 13. Motor mount, 3D printed ABS.

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Figure 14. Dual shaft 270KV Motor.

Figure 15. 8192 CPR Encoder.

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Figure 16. 8mm bore aluminum mounting hub.

Figure 17: Electrical Schematic For Lil’Bro

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Figure 18. Use Case Diagram of Main Actors, Roles and Actions

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Figure 19. Software Process Cycle.

Figure 20. Components Sampling Rate.

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Figure 21. FEA results on mounting hub using SolidWorks.

Figure 22. FEA results on shoulder screw using SolidWorks.

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Figure 23. 5mm Bore, sleeve bearing.

Figure 24. 5mm Bore, thrust bearing.

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Figure 25. FEA results of legs in back position, using SolidWorks. (Min FOS 1.85)

Figure 26. FEA results of legs in center position, using SolidWorks. (Min FOS 3.36)

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Figure 27. FEA results of legs in forward position, using SolidWorks. (Min FOS 1.53)

Figure 28. FEA results of motor mount, using SolidWorks. (Min FOS 7.47)

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Figure 29. Motor Torque vs. Upper Leg Angles 𝜃1 and 𝜃2.

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7.2 Customer Discovery Report Project Overview

Legged robotics is a relatively young field that has recently received increased attention. This is due to some of the limitations that wheel or track driven robots encounter such as movement over uneven and rough terrain. Quadrupedal robots, in particular, have seen interest from notable companies such as Boston Dynamics and Ghost Robotics. A quadrupedal robot is a four legged robot that moves using actuators due to an input. One common way of actuating robotic legs today is using an electric motor that receives an electrical signal, as an input, from a driver. A motor driver is a circuit board that receives power from a power source, such as a battery, and supplies controlled amounts of voltage and current to motors that are connected to it. Today, these components are seen in many dynamic systems that operate through electrical power and signals. In this project, a semi quadrupedal legged robot is to be built, consisting of a lateral half of a quadrupedal robot (one front leg, or fore leg, and one back leg, or hind leg), that is supported by a boom using electrical actuation driven by a motor driver and controlled by a microcontroller board. The boom support provides the robot with stability, however, the motion of the robot is restricted to the plane perpendicular to the boom arm. The project does not involve building the boom nor the boom arm for they will be provided by the sponsor. One goal of building this robot is to provide an open source robot, constructed using commercially available components. This robot can be used by researchers and students who are interested in developing controls and machine learning algorithms, and are not interested in designing and building a robot themselves. The sponsor of this project intends to use the robot for such purposes in his laboratory. Through the increased accessibility to legged robots that this project provides, more contributions to the field could be made from a greater number of people.

The intent of the project is also to minimize cost while maintaining a certain level of performance. This is achieved by using “off-the-shelf’ components that do not need customization, as well as choosing materials that are readily available and easy to fabricate parts from. Considering that the project is open source, those who are interested in acquiring the robot will only pay for the components and building materials.

Customer Discovery Approach (What types of people to interview and why) The approach we took was heavily dependent on the direction we intended to take the project

in. Most of the interviewees we spoke to were potential users because of the open source nature of the project. It was concluded that the project would be of most interest to researchers as well as some hobbyists when it comes to potential users. Researchers stand to benefit from this type of robot for two reasons. This robot would aid researchers who are primarily interested in developing control and machine learning algorithms for legged robots, especially if the researchers are not interested in designing a robot. Furthermore, if software is the main focus, then the price of this robot would deem it appealing since the intent is to make it as low cost as possible. The robotics hobbyist may also find it appealing due to its cost and accessibility.

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Hypotheses vs. Findings Hypotheses

Before attending any of the interviews, it was well known that there were already a few issues concerning the overall concept of the project. Going into the interviewing process we assumed that the concept of the semi quadrupedal robot supported by a boom had been solidified as our project. We thought that there would be several advantages of building the robot as a semi quadruped rather than a complete quadruped. First, fabricating the semi quadruped would be easier, faster, and lower in cost, simply because it requires less components and materials. Secondly, the boom would assist the robot in remaining stable by eliminating movement in the direction along the boom arm, which would in turn simplify controlling the robot. Lastly, the controller and motor drivers’ boards could be placed at the boom support rather than placing them on the robot’s body, reducing the weight that the robot has to bare. Having 3D printed components would make the robot lighter, and easier to alter per application since the design files will be available and adjusted parts can be reprinted. By minimizing the usage of non 3D printed materials, the cost can be reduced as well.

The initial goal of this project was to develop a legged robot intended for research purposes. Since the field of legged robotics itself hasn’t completely transitioned out of the research realm yet, we assumed the appeal to non-researchers would be very minimal. This could be due to current commercially available robots, of this nature, being relatively expensive. Since our project will be open sourced and mostly composed of low cost and readily available material, the price is drastically reduced; therefore, the convenience for hobbyists to purchase components for and build this type of robots is increased. Collecting information from graduate students to develop such a robot, in our case, was critical for clarifying which specifications and capabilities should be available.

As a minimum requirement, it is essential that robots of this nature are able to walk. Our intention was to provide two gaits, walking and a more agile gait, and additional gaits and modes of transport could be added by other users. Referring back to an issue mentioned earlier, due to only having one fore leg and one hind leg, locomotion is limited. A common issue with legged robots is the inability to switch between gaits while in motion, and research is currently being conducted by the sponsor and one of his students on finding a solution. Therefore, even if the robot only utilizes two gaits, being able to use it in that research would be beneficial. By attaining this capability, many doors open to other applications through the robot, such as agile locomotion gaits, adapting to different terrain and surfaces, and reducing energy consumption.

Findings

After beginning the customer discovery interviews, we concluded that our original idea of a half-quadruped robot supported by a boom, wouldn’t be ambitious enough. Half a robot would limit potential uses and consumers, while also limiting its use to the location of the boom. Once we finished our third interview, it was clear that the project was heading in a different direction. The initial intention of building half of a quadrupedal robot was to demonstrate that such a robot could be built using cheap “off-the-shelf” components. Some disadvantages noted during the interview process was the limited locomotion and number of gaits which could be generated by the bisected robot, due to the reduced number of legs. Since the motion of the robot

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with the boom is limited to one plane, only a pitch can be induced by the robot itself, while a roll is induced by the boom’s constraint on the robot. The pre-existing boom arm is also around four feet long, which means the robot would require at least four feet of clearance in all directions around it. This makes testing and operation difficult and time consuming, and even more so considering the weight of the boom. This insight led to a stretching conclusion of building a full quadrupedal robot.

Another assumption we held was to have the majority of the robot be based around 3D printed parts for accessibility, but as our project scope shifted we discovered through the customer discovery interviews that the weight would be a notable issue for any 3D printed parts, especially the leg fixtures. This would require multiple simulations to be performed in the design process for different iterations of leg designs, either with prototypes or using software. The increased weight of different materials would affect our initial objective of keeping the overall cost low, as more weight would require greater actuation, and therefore, more costly components and materials. The issue of extra weight and cost can be resolved, though, by reducing the final design size.

The overall cost of the project was also a factor in making it appealing to potential users. After considering the expansion of the half quadruped robot to a full one, it allowed us to include more users in our potential consumer base, however, this would increase the initial projected cost. The lower price was by far the largest concern for those who would consider building the robot, but the increased number of users would justify the increase in price. The quadrupedal robot could potentially be used as an educational tool for controls and software development. One example of this would be for robotics classes and clubs at schools.

Our hypothesis regarding us only having to provide two gaits stood true throughout the interviews. Whether the robot had two or four legs, it was necessary to include a gait other than walking. Including more than two would be desirable, however, it is time consuming and is unnecessary for our purpose.

Throughout the customer discovery interview process, our initial project plan and ideas morphed based on the insights of our interviewees. We were able to take the answers given by our interviewees, and make an alternative concept that could be used in a variety of different applications, and potentially reaching a greater number of users.

List of Interviewees (Names, Organization, Title) and Contact Information 1. Salvador Echeveste, Graduate student and researcher at UTSA

<salvador.echeveste@my.utsa.edu> 2. Pranav Bhounsule, Assistant professor at UTSA, mentor <pranav.bhounsule@utsa.edu> 3. Jason Pusey, Mechanical Engineer at U.S. Army Laboratory

<jason.l.pusey.civ@mail.mil> 4. Ali Zamani, Graduate student and researcher at UTSA

<alizamani.mecheng@gmail.com> 5. Eric Sanchez, Graduate student and researcher at UTSA <sbaz.93@gmail.com> 6. Michael Posa, Assistant professor at UPenn <posa@seas.upenn.edu>

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7. C. David Remy, Assistant professor at University of Michigan at Ann Arbor <cdremy@umich.edu>

8. Phil Umino, (Potential consumer)* 9. Elliot Martinez, (Potential consumer)* 10. Fernando Luna, (Potential consumer)* 11. Jeremy Krause, Graduate student and researcher at UTSA <robotics68@gmail.com>

*interviews conducted at hobbyist shop, contact info was not provided

Go/No-Go Checkpoint Did the interviews provide insight into a tractionable engineering problem? Or did they show that this project is unsuitable?

The interviewees were able to provide an abundance of insight, which influenced the group into taking a different approach. They gave us the knowledge that building a half lateral quadruped was not going to be ambitious enough. Many recommended that we move away from the half lateral quadruped and lean towards a full quadrupedal robot. The interviewees stated that the quadrupedal would be of more interest, especially if it were made with 3D printed parts as well as being easy to assemble. They also recommended having at least one more gait other than just walking. Lastly a cheap open source quadrupedal could benefit users in its potential for educational use. An example mentioned to us by interviewees were high school students in robotics clubs who do not have a big budget for an expensive quadruped. The insight from the interviews was the desire for a full quadruped robot that is cheap while also unique due to having more than one gait, which provided a tractionable engineering problem. Application to Design Specifications If the project is a Go at the Checkpoint, how will the interview findings shape your initial draft of design specifications?

After acquiring the go at the checkpoint, the notes that we received from the interviewees clearly showed that the change in approach would affect the design specifications drastically. By this we mean that going from a half quadruped to a full quadruped does not seem as a great feat, but it does add more work as well as components and weight that was originally supported by the boom. With this in mind, the design of the legs is going to be very important in order to support the weight of the robot.

What aspects of this problem do you not yet understand?

The type of actuation (motors) we’ll be using is still not clear, as it will influence the leg design that will be suitable for the weight of the components. Since motors are the most expensive component in the project and we are attempting to make this an inexpensive project, it is still unclear what type of motor we’ll be utilizing. The leg design is also uncertain at this point, given that it will be 3D printed, several designs are needed to test for yield and fracture strengths. Something previously mentioned is the overall project scope changed due to the interviews, going from a half quadruped to a full size will be complicated and is uncertain whether or not time will allow for this change. Who or what do you need to follow up with to address the above gaps?

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The entire group plans to meet with the mentor of the project to explain to him our findings from conducting these interviews. His feedback on the new approach that the group wants to take would be very beneficial. His prior knowledge and experience in building these types of robotic machines will allow him to tell us whether building the full quadrupedal is feasible due to the constricted time frame we have to actually build it and test it.

Appendix

Interview #1

Time and location: 31 August 2018 / 1:00 PM / BSE Lounge

Interviewee: Salvador Echeveste, Grad student (vds202@my.utsa.edu)

Noted Q&A, and advice Q: Source of experience with quadruped robots A: Never purchased a unit or kit, experience came from lab work. Intends to build a project that involves the refinement of the locomotion of a quadrupedal robot. Q: Capabilities desired in a quadruped robot A: Speed & agility(for all terrain). Mentioned current project has Gazelle rear legs & Gorilla front legs. Legs should be easy to replace.

Q: Manufacturing conveniences and inconveniences

A: Scaling down prototypes will save time and materials, it will also reveal unpredicted issues. Weight needs to always be considered and accounted for.(use metal parts if needed for extra weight)

Q: Would an operational quadruped robot help in the lab, and how

A: Would allow attention to be focused on controller/programing. Would allow for leg design refining. Also, The preparation time of desired robot would be cut given the available design.

Q: What controller would be convenient

A: Raspberry Pi. This would allow the system to be modular, and the usage of Python is convenient for most users. Q: What would be the ideal interaction with the software? For example, would you rather have pre-written classes and methods to call, or write the classes and methods to be used yourself

A: Having pre-written classes is preferable, however, the code would need to be very clearly documented and comments should be provided about the structure. The code is likely to be changed anyways depending on the application.

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Advice: Too many concept ideas does not leave enough time for design refinement. Scale down prototypes for testing. Use as many purchased or 3D-printed parts as possible, as it will save time.

Interview #2

Time and location: 31 August 2018 / 2:00 PM / BSE Lounge

Interviewee: Pranav Bhounsule, Mentor

Noted Q&A, and advice

Q: How could a 3D printed quadruped robot benefit you?

A: Mainly because we have multiple 3D printers, if it breaks it will be easy to fix because you can give the file to a student to print another one. If the design needs to change it will be easy since you can 3D print it. Q: What are the advantages/disadvantages of a quadrupedal vs bipedal?

A: Quadrupedal’s are more stable, can carry more weight since it has more supports (more legs). Bipedal’s are more maneuverable and can go into smaller spaces than quadrupeds. Q: Have you had any issues in the past with legged robots?

A: Yes they are bulky, pricey, difficult to fix if they break, don't have copyrights to many of them which means you can not modify them, as well as many parts of the code are hidden so one can not change them. Q: If given the option between a controller based quadruped vs an algorithm based quadruped, which would benefit you the most and why?

A: If I were a consumer and just wanted a robot that would fetch something from here or take something there then an algorithm quadruped would be better. Since I am conducting research the controller based one would be a much better option. Q: Is there a minimum battery capacity required or time frame that you would need it to work?

A: I believe an hour and a half is pretty good, if you are only walking at average speed.

Q: What would you use this type of robot for?

A: Research, teaching and to possibly sell in the future. Q: Is there an ideal size for you?

A: I think anything under 10 kg would be good. Anything lighter is better, and size wise i would say for a quadruped would be between 1m to 2m. Preferably 1 meter. Also the lighter it is the better it is because it'll have more usability and will be cheaper because you will have less motors.

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Q: Have you worked on something similar to this?

A: A bipedal, I was trying to make it walk energy efficiently. Q: For research what would be the ideal amount you would like to spend?

A: At this point you would try to make it as cheap as possible. A reasonable budget, well if you have eight motors each one costs one hundred dollars that's eight hundred dollars, you have four drives and each is one hundred dollars, if you can keep it between $1600-2000 would be ideal. The current robots are very expensive, the cheapest one when I purchased it was $10,000 but they are no longer selling it, instead they are selling their $50,000 model.

Advice: Your success will come from your number of iterations, if you do 5 iterations you'll be more successful than if you do one iteration. No simulations will be required for your type of project. The key is to make one good leg design and the other three will be easy. Also two people should work on the design and building aspect while the other two work on the controls. Find ways that you can make each part independent so that one doesn't have to wait for another members part to continue working.

 

 

 

Interview #3 Time and location: 4 September 2018 / 2:00 PM / Electronic (phone call) Interviewee: Jason Pusey, Mechanical engineer at US Army Lab (Jason.l.pusey.civ@mail.mil) Noted Q&A, and advice Q: Source of experience with 3D printed material in robotics? A: It’s pretty extensive, if entire structure is 3D printed it will be very flexible, which can alter gait manipulation. You want something light and rigid, something like aluminum. Q: Advantages/Disadvantages between quadrupedal vs. bipedal robots?

A: Bipeds are very unstable and don’t have many gaits. Quadrupeds are more stable can produce more gaits, can be faster than a bipedal robot. Q: Issues with legged robots?

A: Try to make the mass of the legs as light as possible and the body as well. If there is a flight phase you would have to propel all of the weight to the space. Pay attention to the torque of the motors since they are responsible for pushing all of the mass. Q: What controller would be convenient?

A: Look into Arduino, raspberry pi might have slower refresh rates. It depends on the size of the processor in the microcontroller. Q: What type of gaits and how many should be incorporated?

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A: At least one other gait, other than walking. Should definitely have Walking, but you can add trotting or bounding. Q: other Application where this robot could be used?

A: 5Kg quad could be used as a scout, larger ones could be used to pick up an object by adding an end effector.

Q: Battery capacity required?

A: From the moment its powered on, it should last at minimum 15 minutes in operation. But it will depend on the type of operation being performed.

Advice: Too many concept ideas does not leave enough time for design refinement. Scale down prototypes for testing. Use as many purchased or 3D-printed parts as possible, will save time.

 

 

Interview #4 Time and location: 4 September 2018 / 2:30 PM / BSE Lounge Interviewee: Ali Zamani, Grad student (alizamani.mecheng@gmail.com) Noted Q&A, and advice Q: Source of experience with quadruped robots

A: Experience came from lab work and research. Q: Problems encountered in quadruped robots design.

A: Legs require non linear motion, but the controller requires the most time and attention. Q: Leg design and manufacturing.

A: Quad linked legs are high strength and low weight but the kinematics are complex. Humanoid legs have simple kinematics but are bulky Q: Ideal size?

A: Base size on desired cost of unit. Q: What good motors have you encountered?

A: Maxon. Q: What’s an important step in design before manufacturing?

A: Run multiple simulations. (recommended Atom software for simulations) Q: What prep/research would you consider for the design process?

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A: Read published papers and journals. (Recommended readings by Mart Raybert, and IGRR)

Advice: Try to keep legs massless. Avoid in operation gait change due to complexity.

 

 

Interview #5 Time and location: 4 September 2018 / 2:30 PM / BSE Lounge Interviewee: Eric Sanchez, Grad student (sbaz.93@gmail.com) Noted Q&A, and advice Q: Source of experience with quadruped robots

A: Senior design project (robotic leg prototype) converting rotary motion to linear motion. Research lab, rimless wheel robot. Q: Problems encountered in quadruped robots design.

A: cost for these types of robots are always an issue. Also, the lack of sensors make it difficult to obtain valuable data. Q: Leg design and manufacturing.

A: Quad linked legs are high strength and low weight but the kinematics are complex. Humanoid legs have simple kinematics but are bulky Q: Open source quadruped robot expectations?

A: the robot should at minimum be able to walk or run (contain slow or fast gaits). Q: What type of motors would be used for this application?

A: Gear D.C. motors will work but they’re expensive. Pancake motors might be best option.

Q: Battery power issues?

A: usually not a problem for research purposes as it will more than likely be tethered or will be observed under short periods of time. Q: Potential uses for this robot?

A: this robot could be used to testing controllers, most changes will only come from software (i.e. used to implement machine learning navigation). Q: Drawbacks to this design (3D printed robot)?

A: Strength capacity is an issue with 3D printed robots, but it is cheaper and can be prototyped more frequently, whereas aluminum based robots are stronger but manufacturing takes time and is more expensive.

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Advice: Time and cost are always an issue for robotic projects, try to develop a design which will work with your motors based on your specifications. Time management will be very important due to the demands and deadline of this project.

 

 

Interview #6 Time and location: 5 September 2018 / 1:15 PM / Phone Call Interviewee: Michael Posa, Mechanical Engineering, University of Pennsylvania Noted Q&A, and advice Q: Are there any issues with commercially available legged robots?

A: Some robots such as Ghost Robotics Minitaur lack sufficient sensing capabilities for my desired applications. Some robots have knee linkage designs that limits the motion of the robot. Q: What are some of your desired capabilities for this kind of robot?

A: A good sensing capability for the motors’ parameters and in the legs. The robot also needs to be easily adjustable to the needs of the user. This includes the design and the software. Q: What kind of motors would you use on legged robot?

A: Pancake motors are the ideal motors for this type of usage. They provide high torque at low speeds and they are relatively light compared to other motors with similar performance. The drawback is the price, so you can use a different type of motor, but gearing may be necessary. This would be done to provide higher torque at lower speeds. Q: What is your experience with boom supported robots?

A: Boom supported robots are mainly made in the process of making a quadrupedal. First a monoped robot is created, then a boom supported robot based on the monoped and lastly the full quadrupedal. Q: Have you used 3D printed materials with a legged robot before? A: Only for prototyping. 3D printing parts can be time consuming and for some parts may be more expensive than using aluminum. Not to mention the compromise in strength that results from using them.

 

 

Interview #7 Time and location: 6 September 2018 / 7:40 AM / Electronic (Video Call) Interviewee: C. David Remy, Robotics and Motion Laboratory, University of Michigan at Ann Arbor Important Q&A, and advice

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Q: Is there a need for a cheap opened source quadrupedal robot?

A: Depends on what the robot is supposed to do. I believe your main audience would be more towards something educational or for hobbyists. Something educational would be where some students in a high school robotics club can build with ease. There will be a similar scenario with hobbyists who would want to build a robot. Q: What are some improvements that can be made in commercially available robots such as the minotaur?

A: I think minotaur is a really nice robot, bringing down the price, and making it into something that people can manufacture themselves. Manufacturing im referring to making a design that's fully 3D printed do not mix and match different types of parts which would have to be printed on a different type of printer. Q: Are there any other types of motors that can be used other than pancake motors?

A: RC motors are one option. They would have to provide high torque at low speeds. They could potentially not require any gearing. Dynamex motors would be a step up but are quite pricey. Q: What should the robot be able to do once someone acquires the robot?

A: You should always be ambitious, you are trying to make this available as an open source, and our expectations as a user is that it works. If i download your instructions, your rapid prototyping file that I am able to build a machine that way. Make it easy to change so one can start playing with it and make their own change to it. Q: What are some of the possible drawbacks you may encounter with a 3D printed Quadrupedal robot/RC? A: A legged robot has a lot of motion, each leg will have 2 joints, how would you 3D print the joints and that move well. How do you add non printed components. The size may be an issue, especially with cheap 3D printers. Ensuring to make your system modular. Components will be one of the main issues.

Advice: As Mechanical Engineering students do not underestimate the controls aspect of the project. Make one demo that works, doesn't have to be spectacular but just make sure that it works and can be easily changed.

 

 

Interview #8 Time and location: 6 September 2018 / 10:00 AM / R.C Headquarters Interviewee: Phil Umino, Sales Rep. Noted Q&A, and advice Q: Do you know what a quadruped robot is, and if so do you have previous experience with one?

A: Yes, a four legged robot. And no previous experience.

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Q: If given the option between a controller based Quadrupedal robot vs an algorithm based one, which would you prefer and why?

A: A controller based one, with algorithms for walking and running. Controller based for fun. Q: If given the option, what size quadruped RC/robot would be ideal for you?

A: 1.5 cubic ft Q: What Quadrupedal robot/RC capabilities would interest you?

A: Jumping, running, and picking up objects. Q: Would you like a Quadrupedal RC/robot design to allow for customizations, and what would you do to it?

A: Add camera and lights. Q: If you owned a Quadrupedal RC/robot, would you like to test your own code on it, and what would it be?

A: No, I don’t know how to code.

Q: Given the opportunity to purchase a fully operational (and customizable) Quadrupedal robot/RC, what price range would you feel comfortable paying?

A: $300 to $500

Advice: Design the unit for a specific task to get people interested in it.  

 

Interview #9 Time and location: 6 September 2018 / 10:30 AM / R.C Headquarters Interviewee: Eliott Martinez, Technician Noted Q&A, and advice Q: Do you know what a quadruped robot is, and if so do you have previous experience with one?

A: No, and no previous experience. Q: If given the option between a controller based Quadrupedal robot vs an algorithm based one, which would you prefer and why?

A: Unknown, no previous experience, so no preference. Q: If given the option, what size quadruped RC/robot would be ideal for you?

A: 1-2 cubic ft Q: What Quadrupedal robot/RC capabilities would interest you?

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A: Just walking would be interesting. Q: Would you like a Quadrupedal RC/robot design to allow for customizations, and what would you do to it?

A: Yes, different skins. Q: If you owned a Quadrupedal RC/robot, would you like to test your own code on it, and what would it be?

A: No, I don’t know how to code.

Q: Given the opportunity to purchase a fully operational (and customizable) Quadrupedal robot/RC, what price range would you feel comfortable paying?

A: $200 to $500

Advice: Design a unit that would allow for easy access you replace/modify working parts.  

 

Interview #10 Time and location: 6 September 2018 / 11:30 AM / HobbyKing USA Interviewee: Fernando Luna, Technician Important Q&A, and advice Q: Do you know what a quadruped robot is, and if so do you have previous experience with one?

A: Yes, and no previous experience. Q: If given the option between a controller based Quadrupedal robot vs an algorithm based one, which would you prefer and why?

A: Would prefer a pre programmed robot. Not that into RC’s Q: If given the option, what size quadruped RC/robot would be ideal for you?

A: 2 cubic ft Q: What Quadrupedal robot/RC capabilities would interest you?

A: Being able to run and jump over obstacles, and offer user a first person view. Q: Would you like a Quadrupedal RC/robot design to allow for customizations, and what would you do to it?

A: Yes, unique legs and other performance parts. Q: If you owned a Quadrupedal RC/robot, would you like to test your own code on it, and what would it be?

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A: Yes, program it to do stuff around the house.

Q: Given the opportunity to purchase a fully operational (and customizable) Quadrupedal robot/RC, what price range would you feel comfortable paying?

A: $1,200 to $3,000

Advice: Beat opposition to pricing unit at under $1,000 each.  

 

Interview #11 Time and location: 6 September 2018 / 8:00 PM / Electronic communication Interviewee: Jeremy Krause, Mechanical engineer Grad student (robotics68@gmail.com) Noted Q&A, and advice Q: Source of experience with quadrupedal robots?

A: I have not worked with quadruped robots. My focus has been on monoped robots (one legged) robots, as well as 3d printing. I have been working with Dr. Bhounsule on actuator design for a few semesters. We published a journal on pneumatic 3d printed actuator design this past semester. I also designed and built the test platform that is in the lab now. Q: Problems encountered in quadrupedal robot design?

A: The biggest problem encountered in most robot design processes is working with a power to weight ratio that lets the robot move as required while having a usable battery life. More recently, I have encountered issues with the power supply requirements for motor based actuators. Specifically, steady state current specs are almost useless in certain situations as you will encounter spikes in motor current draw during movement operations that exceed the stated current. See inrush current. This is important because it will cause heating in conductors and can ultimately cause component failure even if the average current is at allowable levels. Q: Are there manufacturing conveniences and inconveniences?

A: The biggest single inconvenience you will find is the construction medium, 3d printed plastic. You will find that it is difficult to perform an accurate analysis on the part models because the strength of the material is dependent on the printing conditions (temperature, print orientation, etc). The best process I have found is to print test parts and test them to confirm they meet spec before doing a final print. Leg design, in an of itself, is not overly difficult as it has been greatly explored.

Q: Is there an ideal size for this type of robot?

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A: 8-12" height. Smaller and you will have trouble printing linkages/gearing because of the resolution of the 3d printers, larger and you will have excessively high motor power requirements and material cost. Q: Important steps in design before commencing manufacturing process?

A: Determining your requirements, design your parts, computer based analysis of designed parts, experimental verification of computer based analysis via physical test prints. Q: Most practical controller for this application in your opinion?

A: The raspberry pi offers a much higher speed than the arduino and teensy, but requires programming in a language you may not be familiar with and does not have an onboard ADC. The teensy is much faster than an arduino and can be programmed in the same language. The teensy also has the benefit of having the smallest footprint, with everything on a single chip package. If possible I would use a raspberry pi, but a teensy would work alright for you guys as well, cost is comparable. Q: Have you had any issues in the past working with legged robots?

A: Think of a possibility and I have probably addressed it. I have dealt with parts that were weaker than intended, deforming under stress. I have had to deal with fabrication issues where excess heat would cause the plastic to deform unless it was water cooled during processing. I have dealt with leakage issues through the 3d printed plastic. I have had to experimentally determine the proper tolerances for a press fit into 3d printed plastic for linear bearings. I have addressed power issues in motors and solenoids. Programming issues in the onboard controller, specifically working around response nonlinearities that formed due to minor variations in post production. Q: What are some alternative applications or uses for this type of robot?

A: To put it bluntly, the money is with the defense department, but you could probably find interest with other parts of the scientific community, especially the ones that man remote research outposts. 3D printing could, in theory, make such a robot easy to transport.

Advice: Set realistic goals. It will take time to create a functional robot and even more time to configure it to walk. I would try not to go much further than that, especially for senior design.

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7.3 Design Specifications

1. SCOPE

1.1. Scope This Specifications document includes both the performance, and design specifications for an open source quadrupedal robot. The robot will be optimized for a minimal cost, and operate on four independently actuated legs. The robot will assist in research performed at the University of Texas at San Antonio’s Robotics and Motion Laboratory, in the area of agile locomotion gaits. Quadrupedal robots are currently of interest due to their ability to traverse rough terrain, and operate in environments considered inaccessible to humans.

2. APPLICABLE DOCUMENTS 2.1. General

This section contains documentation regarding design, operation and testing, that will not be referenced elsewhere in this document. Document users are required to meet all applicable requirements and specifications listed.

2.2. Open Source Documentation This section contains information about the classification of Free Open Source Software (FOSS) licenses. Free software can be categorized into Copylefted, GPL’ed and Public domain software, which excludes any proprietary software or Closed software.

2.2.1. GNU General Public License FOSS is an inclusive term generally synonymous with both free software and Open Source Software (OSS). It is liberally licensed to grant the right of users to study, change and improve its design through the availability of its source code (FOSS, 2008).

● The freedom to run the program, for any purpose. ● The freedom to study how the program works and adapt it to

users’ needs. Access to the source code is a precondition for this. ● The freedom to improve the program and release the

improvements to the public, so that the whole community benefits. Access to the source code is a precondition for this.

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2.3. Institute Documents (UTSA)

2.3.1. Training Documentation This list of specified institutional laboratory training requirements are mandatory under applicable conditions, before any design, operation and testing may take place in a University of Texas at San Antonio laboratory. All document users must comply with the training mandated.

● Hazardous Waste Generator Training (SA 401)—for personnel who work in laboratories which generate chemical or biological waste.

● Radiation Safety Training (SA 433)—for personnel who work in laboratories which use radioactive materials or radiation producing machines.

● Hazard Communication and Laboratory Safety (SA 443.01)—for personnel who work in laboratories where chemicals are used or stored.

● Laser Safety Training (SA 465)—for personnel who work in laboratories where lasers are used.

● Biosafety and Bloodborne Pathogens for Researchers (SA 483)—for personnel who work in laboratories where biological agents, recombinant DNA, cell or tissue culture are used.

● Hazard Communication & the Arts (SA 488)— identify and understand hazards of the chemicals that are handled in the art studio.

● Workers Compensation Insurance Supervisors Training (SA 542)—for all personnel who supervise others.

2.3.2. Hazardous Waste Management This section contains the references for the proper disposal of material considered hazardous, at all University of Texas San Antonio facilities. Document users must comply with the listed disposal standards on University of Texas San Antonio owned property.

● Chemical waste is regulated by 40 CFR 261 and the Texas rules 30 TAC 335

● Universal waste is managed under 40 CFR 273 and 30 TAC 335.262.

● Biological waste is regulated by the Texas Department of State Health Services. All waste generated at UTSA facilities will be collected and managed under the EHSRM Hazardous Waste and Biological Management Safety Plans.

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● Radiation waste is also managed by EHSRM and is regulated by the US Nuclear Regulatory Commission.

2.3.3. Fire and Life Safety This section contains recommended action and reactions, with regard to safety, provided by the UTSA Fire Prevention and Life Safety team, part of the Risk Management & Life Safety Division of EHSRM. All document users are strongly recommended to read the following section.

● Maintain all exit doors clear of any storage; regularly ensure that they are fully functional.

● Maintain 44" of clear, walkable space in all hallways, preferably in direct line with egress doors. Avoid storing items of any kind in hallways.

● Ensure all stairwell doors remain closed. Do not prop open stairwell or fire rated doors.

● Control your storage. Do not block fire extinguishers, pull stations, alarm devices, exit signage, emergency lights, and sprinkler heads. Keep storage below 18” of the ceiling or of fire sprinkler heads in sprinkled buildings.

● Limit fuel load. Reduce quantities of flammable and combustible liquids, and limit accumulation of loose paper and cardboard.

● Connect electrical devices, plug strips and extension cords directly into wall outlets. Do not plug extension cords and plug strips in to one another. Inspect all electrical cords prior to use, and unplug then coil extension cords at the end of every work shift.

● Check your heat generating devices (portable heaters, hot pots, coffee pots, irons, etc.) They should draw no more than 15 amps, be UL listed, and have automatic shut-off and/or tip-over detection features.

● Participate fully in fire drills; evacuate and assemble at rally points 150 feet from the building.

● In case of fire think – RACE Remove people from the location Alert others by sounding the alarm system, calling 911, or through verbal warnings Contain the fire by closing doors Evacuate the area using the nearest safe exit.

● Have an exit strategy everywhere you go. Always know two ways out!

3. REQUIREMENTS

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3.1. Performance Requirements

The following specifications pertain to the minimum acceptable parameters for the performance of the robot. The parameters are to be approved by the sponsor, but are not limited to those listed below. Later in this document are a set of desired specifications that can be added to the project after the completion of all the requirements.

3.1.1. Input/Output Interface The user will be able to control the robot’s motion through a handheld device. Inter-process communication will be executed by a single-board computer, which will transmit the commands between the motor driver and sensors. The motor driver will then send the appropriate signal, controlling the motor’s position, speed and torque. The single-board computer will allow for enough bandwidth expenditure over a traditional micro-controller board. A micro-controller board may be added to the interface, however, to assist the single board computer with data and signal processing if necessary.

3.1.2. Operation The robot will stand and operate without any assistance or support from a boom or other weight bearing supports. This will allow the unit to operate and be tested in an uncontrolled environment, which is one of the primary uses for robots. A hand-held tether may be attached to the robot as a mechanical mean for direct in-operation handling.

3.1.3. Locomotion The robot will use self propulsion as its method of transport, without any external forces assisting it. Independent locomotion capabilities, without external assistance would allow the unit to operate for periods of time in remote locations.

3.1.4. Leg Strength

The robot will be able to support its own weight while in motion. The robot shall also support an additional 25% of its total weight while it is standing in place.

3.1.5. Data Collection

The data for the following parameters shall be collected, and stored by the system’s memory: motor position, motor speed, motor current draw, and center of mass position. The data could then be viewed through the robot’s computer for

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performance monitoring. The data will be utilized to configure the robot’s source code for program optimization.

3.1.6. Data Processing

The robot’s computer shall be capable of processing data at a frequency of no less than 16 MHz. The computer shall also be able to process data from multiple sources, such as motor drivers and sensors.

3.1.7. Rate of Motion

The robot will be able to move in the forward direction at a minimum rate between 0.2 and 0.4 meters per second (m/s), as specified by the sponsor. This minimum requirement for the maximum rate of speed will ensure the unit is useful in the research taking place in the Robotics and Motion Lab.

3.1.8. Battery

The power source of the system will support 10 minutes of continuous operation, at a speed in the range set forth by Section 3.1.7. The robot’s ability to operate on its own power source would allow it to operate in remote locations for a period of time, and grant it access to uncontrolled environments.

3.2. Design Requirements The following specifications pertain to the minimum acceptable parameters for the performance of the robot. The parameters are set and to be approved by the sponsor, but are not limited to those listed below. Later in this document are a set of desired specifications that can be added to the project.

3.2.1. Size

The unit will be no larger than one cubic meter, or 35 cubic feet. The required size would allow the unit access to small areas while also allowing the unit enough size to carry a potential load. The required size will also be convenient for a single person to handle comfortably.

3.2.2. Weight The robot will have a total mass of no more than 23 kilograms, or equivalent to 51 pounds. The required weight will allow the robot to be light enough for a single handler to lift, based on the Occupational Safety and Health Administration’s

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(OSHA) recommendations. The weight requirement will also allow for additional weight to be placed on the unit as potential loads.

3.2.3. Open Source The robot will be open sourced, or available for public access. All technical drawings and their respective part files, as well as source code are licensed under GPL3, these files will be available through an online repository. The repository shall also include the list of commercially available parts used in the robot, with vendor information.

3.2.4. Interchangeability Each leg of the robot must be identical to the other legs, allowing them to fit into an assembly of the same type. The legs must be easily accessible and interchangeable in the event of damage with the use of simple hand tools.

4. DESIRED SPECIFICATIONS

4.1. Desired Performance Specifications

The following specifications pertain to performance parameters of the robot to be included if all specifications listed in Section 3 are fulfilled. The addition of the parameters outlined below shall be approved by the sponsor, upon the availability of time and resources.

4.1.1. Operation Power source of the robot will support 15 minutes of continuous operation, at a speed between 0.2 and 0.4 m/s. The unit will be operable from a remotely controlled device, with no wires to be attached to the robot. The remote controller will have a range of transmission of up to 15 feet away from the robot. This is beneficial to the user, not having to walk alongside the robot if the controller were to be attached to the robot.

4.1.2. Rate of Motion

The robot will be able to move in the forward direction at a speed between 0.8 and 1.0 m/s.

4.1.3. Leg Strength The robot shall be able to lift or elevate an additional 50% of its own weight while standing in place. The robot shall also be able to move with a payload of weight equal to 25% of its own weight.

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4.2. Desired Design Specifications

The following specifications pertain to the design parameters of the robot to be included if time and resources permit.

4.2.1. Size The robot’s dimensions shall be within the following ranges, 0.3 to 0.8 meters in length, 0.2 to 0.6 meters in height, and 0.2 to 0.5 meters in width.

4.2.2. Weight The robot’s weight shall be equal to 10 kilograms or less.

5. VERIFICATION

5.1. Measurement or Test Data

The following sections detail how some requirements outlined in Section 3 will be tested and validated for completion. The validation will be executed through the measurement of certain parameters, and the examination of applicable data.

5.1.1. Leg Strength Validation

The strength of the robot’s legs shall be validated by measuring the amount of weight it can support statically and dynamically. External weight will be used for the static test.

5.1.2. Size Validation The dimensions of the robot shall be measured using a distance-measuring tool, and validated in accordance with Section 3.2.1.

5.1.3. Weight Validation

The total weight of the robot shall be measured using a weight scale. Validation may be carried out through the measurement of the sum of all individual components’ weights, or through the measurement of the weight of the assembled robot if a scale for such size is accessible.

5.1.4. Rate of Motion The speed of the robot set forth by Section 3.1.7 will be tested on a treadmill. For example, the treadmill could be operating at 0.7 miles per

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hour which is approximately equal to 0.3 m/s. The robot’s instantaneous position, relative to the treadmill and its starting position, will indicate whether or not its speed is 0.3 m/s or greater.

5.1.5. Battery The power consumption rate will be verified using the procedure described in Section 5.1.4, wherein, the robot will move at a speed in the range of 0.2 to 0.4 m/s for a time period of 10 consecutive minutes.

5.2. Visual Verification

The following sections detail how some other requirements outlined in Section 3, and not referred to in Section 5.1, will be tested and validated for completion. The validation will be executed through the visual inspection of the parameters.

5.2.1. Operation The validation of the lack of weight bearing supports will be done by visual inspection of the robot.

5.2.2. Locomotion The robot’s intended method of locomotion, described in Section 3.1.3, will be verified through visual observation of it in motion.

5.2.3. Data Collection Data collected for the parameters of interest, stated in Section 3.1.5, will be verified through accessing the storage in which the data was stored, and observing and validating the data for the parameters.

5.2.4. Input/Output Interface

Control by single-board computer will be seen through motion of motors due to a user’s input, as well as viewing the source code of the robot, validating the described flow of logic throughout the system.

5.2.5. Data Processing The requirement set forth by Section 3.1.6 shall be validated by observing the processor of the robot’s computer and its available specifications. Most manufacturers of commercially available processors provide the processing capability.

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7.4 Drawings

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