Spacecraft Robotics

LABORATORY

Spacecraft RoboticsLABORATORY

Project Manicopter:Multicopter-Based Robotic Arm

for Aerial Manipulation

March 7, 2016

Dr. Hyeongjun Park, NRC PostdocCapt. Bruno Tavora, Ph.D. Candidate (Brazilian AF)PIs: Prof. Marcello Romano (NPS-MAE)

Prof. Xiaoping Yun (NPS-ECE)

Spacecraft Robotics

LABORATORYContents

1. Introduction- Team - Motivation & Objectives

2. Multicopter model & parameter identification

3. Development of experimental platform- Robotic arm control through Pixhawk autopilot- Experimental setup

4. Summary

2

Spacecraft Robotics

LABORATORYTeam

• Staff– Dr. Marcello Romano, Professor (MAE)– Dr. Xiaoping Yun, Professor (ECE)– Dr. Hyeongjun Park, NRC Postdoc

• Student– Capt. Bruno Tavora, Ph.D. Candidate

• Collaborators– Dr. Yoonghyun Shin, ECEP visiting scholar at NPS, ADD, South Korea– Dr. Elisa Capello and Dr. Giorgio Guglieri, Politecnico di Torino, Italy

• Acknowledgement– CRUSER funding– Dr. Kevin Jones – Mr. Steven Kuznicki, Pilot Engineering Group, Mathworks

3

Spacecraft Robotics

LABORATORYMotivation & Background

• Motivation– Physical interaction with the environment enables to extend utilization

of UAVs to new type of missions• Grasping, object picking & assembly, data acquisition and inspection by

contact objects/surface– Robust and stable maneuvers for aerial manipulation are challenging

to achieve

• Background: Applications of aerial physical interacting

4

Type Approach Application

Aerialinteraction

Multiple UAVs connected to load Load transportationAir refueling & Device connecting two UAVs Refueling/Recharging

Air-groundinteraction

Perching & Docking Refueling/RechargingUAV with sampling device SamplingUAV with arm and gripper Picking/Assembly

Kondak et al., Unmanned aerial system physically interacting with the environment, 2015

Spacecraft Robotics

LABORATORYState of the Art

• Existing work by leading groups on aerial manipulation – University of Pennsylvania (UAS) led by Prof. Kumar– University of Seville (Spain) led by Prof. Ollero– Seoul National University (South Korea) led by Prof. Kim

– ETH Zurich (Switzerland ) led by Prof. Siegwart– University of Bologna (Italy) led by Prof. Marconi– University of Twente (Netherlands) led by Prof. Fumagalli

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- Pick & Place- Multi-UAV load

transportation- Assembly tasks - Mainly contact

with objects

- Contact with vertical surface

- Surface inspection

Spacecraft Robotics

LABORATORYResearch Objectives

• Investigation of the dynamics, guidance, and control of autonomous multicopters with robotic manipulation capability– Development of an experimental platform of a multicopter with a

robotic arm

– Analysis and experimentation for the system dynamics when the multicopter contacts with the environment

– Development of attitude controller and guidance algorithm for real-time path-planning to contact and avoid obstacles

– Implementation of mission scenarios• Picking & Assembly• Door/Drawer opening• Data acquisition on surface

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Spacecraft Robotics

LABORATORYScenario Simulation

• Video 1.

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Spacecraft Robotics

LABORATORYModel Description: Multicopter

• Hexacopter– Six motors and propellers– Six arms connected symmetrically

8

21

3

45

6

X"Y"

ZB

1,A

2,C

4,C

6,C

3,A

5,A

C: ClockwiseA: Anticlockwise

Part Description Weight [g]Autopilot 3DR Pixhawk 39Electric motor T-Motor KV 750 55 X 6Propeller E-Prop 254 X 120 12 X 6LiPo Battery & Power part Thunder power 1800 mAh 269

Total weight 1189Payload weight 2000

Spacecraft Robotics

LABORATORYModeling: Nonlinear Model

• Nonlinear model of the hexacopter

9

21

3

45

6

𝑋𝑋%𝑌𝑌%

𝑙𝑙(

Angles: 𝜙𝜙, 𝜗𝜗, 𝜓𝜓Angular velocity : 𝑝𝑝, 𝑞𝑞, 𝑟𝑟Translational velocity : 𝑢𝑢, 𝑣𝑣, 𝑤𝑤

( )

( ) ( ) ( )[ ]

( )( ) ( )( ) ( ) ( )[ ]

( ) ( )[ ]yyxxzz

pxxzzyy

pzzyypxx

IIpqQQQQQQI

r

pIIIprdTTddTTddTTI

q

qIIIqrlTTdTTTTI

p

TTTTTTm

gqupvw

grupwvgrvqwu

rqrq

rqp

−+−+−+−=

Ω+−+++−+−++=

Ω−−+−+−−+=

+++++−−−=

−+=

+−=

+=

−=

++=

654321

35232433261

2513164

654321

1

,1

,1

,1coscos

,sincos,sin

,coscos

cossin

,sincos

,tancostansin

!

!

!

!

!!

!

!

!

φϑ

φϑ

ϑϑφ

ϑφ

ψ

φφϑ

ϑφϑφφ

Angular velocity of propellers

Moments of inertia

Thrust of motor

Motor reaction torque

Unknown parameters

Spacecraft Robotics

LABORATORYParameter Identification

• It is important to understand and obtain a precise model of a multicopter for advanced controllers – Direct computation of geometry [Chovancova et al. 2014; Elsamanty et al. 2013]

– Analysis from flight data [Stanculeanu et al. 2011; Chovancova et al. 2014]

• We devised and implemented an identification method: – Compound pendulum method [Gracey, NACA Technical Report, 1948]

• Evaluation of principal moments of inertia and engine thrust– Vicon motion capture system

• Infrared marker-tracking system with millimeter resolution for position and attitude of hexacopter

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Spacecraft Robotics

LABORATORYExperiment on Moments of Inertia

11

• Video 2.

Spacecraft Robotics

LABORATORYIdentification of Moments of Inertia

• Lagrangian approach

12

( )( )θθ

θ

cos)(1)cos1(

,)(21

,

111

221

211

dlmglgmV

IIdlmlmK

VKL

rod

+−+−=

++++=

−=

!

( )

( ) ( ) θθθθ

θθθ

θθ

BdlmgglmdlmgglmV

AIIdlmlmKdtd

VKdtd

rod

=++≈++=∂∂

=++++=∂∂

=∂∂

+∂∂

)(sin)(

,)(

,0

111111

21

211

!!!!!

!

IIdlmlmdlmgglm

ABBA

rodn ++++

++==

=+

21

211

1112

)()(

,0

ω

θθ!!

θ

l1

d

l

Yaw

Spacecraft Robotics

LABORATORYIdentification of Moments of Inertia

• Period of oscillation

– All known values except period 𝑇𝑇(– Period 𝑇𝑇( is measured by Vicon system

(analysis of time history)

• Principal moments of inertia

13

( ) rodp

np

IdlmlmdlmgglmT

I

ABT

−+−−++=

==

21

2111112

2

)()(4

,22

π

πωπ

𝐼𝐼55 0.0286 [𝑘𝑘𝑔𝑔𝑚𝑚?]

𝐼𝐼AA 0.0254[𝑘𝑘𝑔𝑔𝑚𝑚?]

𝐼𝐼EE 0.0418 [𝑘𝑘𝑔𝑔𝑚𝑚?]

Yaw angle

Pitch angle

Spacecraft Robotics

LABORATORYIdentification of Engine Thrust

• Thrust generated by a motor and propeller– Relation between PWM signal and

rotational speed of a rotor is known

• Thrust experiments: Thrust vs. PWM input to a motor– Use the compound pendulum

and Vicon system– One propeller

14

Thrust

RPMPWM

Spacecraft Robotics

LABORATORYExperiment on Thrust

15

• Video 3.

Spacecraft Robotics

LABORATORYIdentification of Engine Thrust

• Thrust experiments

– Different experiments are performedwith different PWM inputs 𝑃𝑃to a motor, 1100 ≤ 𝑃𝑃 ≤ 1900[𝜇𝜇𝑠𝑠].

16

θl1

l2l m1g

mg T

0sinsin 211 =−+ Tlmglglm θθ

9266.50052.0 −= PT

Thrust vs. PWM RPM vs. PWM

Spacecraft Robotics

LABORATORYIdentification of Torque

• Relation of aerodynamic torque produced by motors and propellers

• Ad hoc method using a floating test bed & robots– The robot with the hexacopter is floating on the granite rig– Three propellers rotating in the same direction are mounted

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Dimension 4𝑚𝑚×4𝑚𝑚×0.3𝑚𝑚

Surface precision AAA

Leveling precision < 0.01𝑑𝑑𝑒𝑒𝑔𝑔Planar accuracy ±0.00127𝑚𝑚𝑚𝑚- Linux Real-Time workstation- Ad-Hoc WiFi internal network

Spacecraft Robotics

LABORATORYExperiments on Torque

18

• Video 4.

Spacecraft Robotics

LABORATORYIdentification of Torque

• Experiments on the floating test bed– Two cases and comparison (torque is assumed to be constant)

• Case 1: No propellers on & 4 thrusters of the floating robot on for 5 s• Case 2: Three propellers on & No thrusters of the floating robot on

– Torque 𝜏𝜏 = 𝐼𝐼U�̇�𝜔E

– In Case 1, 𝜏𝜏 is known and equal to 0.003[𝑁𝑁𝑚𝑚] and �̇�𝜔E is measured from Vicon. Hence, 𝐼𝐼E is obtained

• Relation between PWM and torque:

19

0520.00001.0 −= PτMeasured yaw angle Torque vs. PWM

Spacecraft Robotics

LABORATORYValidation by Flight Data

• Flight experiments to validate the results of parameter identification

• Initially, the hexacopter hovers on a desired position, and performs accelerating movement

• Verify the nonlinear model and parameters

• Experimental setup

20

Spacecraft Robotics

LABORATORYFlight Experiment for Validation

21

• Video 5.

Spacecraft Robotics

LABORATORYExperimental Results

• Generation of angular acceleration– Hexacopter hovers– Impulsive inputs are applied to generate pitch acceleration at 10.2 s

and 22.2 sec – Estimation is overall well-correlated to measured values

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Pitch acceleration Yaw acceleration

Spacecraft Robotics

LABORATORYImprovement of Test Platform

23

• Mission planner – APM firmware– Embeded PID attitude controller– Limitations

Spacecraft Robotics

LABORATORYPrevious Experimental Setup

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• Mission planner – APM firmware

Ground Station

HexacopterVicon System HexacopterVicon System

Spacecraft Robotics

LABORATORYPrevious Experimental Setup: Issues

• Delay of 0.4 sec

• Resolution: Each command can be quantized among 153 different values only

• APM firmware can only run a specific PID controller, whose gains are the only parameters that can be changed

• No capability of sending and receiving raw data through serial ports. However, it’s essential to get access to the serial ports to have communication between Pixhawk and Arbotix-M, the robotic arm controller board.

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Spacecraft Robotics

LABORATORYSimulink Pixhawk Support Package

26

• Opensource • Customized communication blocks provided by Pilot

Engineering Group, Mathworks

Spacecraft Robotics

LABORATORYNew Experimental Setup with Simulink

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Ground Station

Robotic ArmVicon System

Hexacopter

Spacecraft Robotics

LABORATORYNew Experimental Setup with Simulink

• Small delay and better resolution

• More flexibility to attitude controller design, not more restricted to a PID controller

• Pixhawk and Arbotix-M can be connected through a serial cable

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Spacecraft Robotics

LABORATORYControl Robotic Arm through Pixhawk

• Video 6.

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Spacecraft Robotics

LABORATORYSummary

• Development of an experimental platform for a multicopter with a robotic arm (achievement since May, 2015) – Modeling and parameter identification via compound pendulum and

Vicon system– Improvement for communication and attitude control algorithm

development – Robotic arm controlled by Simulink Package for Pixhawk

• Future work– Flight experiments with the robotic arm– Development of attitude controllers – Study on collision detection/response using the robotic arm– Real-time path-planning to avoid obstacles

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Spacecraft Robotics

LABORATORY

Spacecraft RoboticsLABORATORY

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