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Objectives
Autonomous Systems Lab http://www.asl.ethz.ch
Thomas Thüer ([email protected])Ambroise Krebs ([email protected])Roland Siegwart ([email protected])
ETH ZentrumTannenstrasse 3, CLA
8092 Zurich, Switzerland
System Overview
To support the design of planetary rovers in Europe, a set of tools is being prepared to allow for accurate predictions and characterisations of rover performances as related to the locomotion subsystem. This infrastructure, referred to as RCET, will consist of both S/W and H/W elements that are interwoven to result in a complete and user-friendly environment.
The tool developed by the ASL is the Performance Optimization Tool (POT) which aims at providing a means to perform a quick evaluation of the obstacle negotiation capabilities of rough-terrain rovers. It is based on a static, 2D model including a wheel torque optimization because the systems are over actuated.
Consortium (partners):• Customer: European Space Agency (ESA)• Project Leader: Oerlikon space• Sub-Contractors
• Autonomous Systems Lab (ASL)• Deutsches Zentrum für Luft-und Raumfahrt (DLR)• Surrey Space Centre• EADS Space Transportation
Data Flow Main Modules
Single Wheel Testbed: soil channels attempt to operate a wheel under controlled loading and controlled soil conditions to obtain reproducible measurements.
3DS is a 3D simulator based on the SimPackdynamic multibody simulation tool with strongly integrated coupling betweenvehicle and wheel-soil dynamics.
The POT is based on static 2D rover models and optimizes torques such that minimal friction occurs.
Main modules of POT:
- 2D Rover Design Interface - 2D Batch Creator and Launcher- 2D Simulator (engine) - 2D Player
System architecture:
POT Framework
Locomotion performance metrics: Friction coefficient, wheel torque (contact forces).
Info
Rove
r: C
RAB,
RCL
-E,
MER
(w
eigh
t =
35kg
; w
heel
dia
met
er =
260
mm
)O
bsta
cle:
Ste
p (h
eigh
t =
260
mm
)
POT Output
Model ValidationThe degrees of freedom (DoF) of the rover model are checked. The Grübler criterion states for the 2D case:
A statically determined mechanism must have f=1.
3*( )iB G G
i
f n n f= − +∑: number of bodies; : number of joints: DoF depending on joint typei
B G
G
n nf
Optimization• Under-determined equation system (all wheels of the rover motorized)
• Optimization in order to find the minimum static friction coefficient
• Heuristic:
))min(max(i
i
NT : wheel torque
: contact normal forcei
i
TN
2D Simulator
2D Rover Design I/F
2D Batch Creator
2D Batch Launcher
1. Rover State Generation
RCET DB 2D Player
2. Calculation / Optimization (MATLAB)
Visualization (MATLAB)
POT Features
AAUTONOMOUS UTONOMOUS SSYSTEMS YSTEMS LLABAB
Rover Chassis Evaluation Tools (RCET)
