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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
5
- 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
6
Spacecraft Robotics
LABORATORYScenario Simulation
• Video 1.
7
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
10
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
17
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
22
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
24
• 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.
25
Spacecraft Robotics
LABORATORYSimulink Pixhawk Support Package
26
• Opensource • Customized communication blocks provided by Pilot
Engineering Group, Mathworks
Spacecraft Robotics
LABORATORYNew Experimental Setup with Simulink
27
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
28
Spacecraft Robotics
LABORATORYControl Robotic Arm through Pixhawk
• Video 6.
29
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
30
Spacecraft Robotics
LABORATORY
Spacecraft RoboticsLABORATORY
Thank you