Simulate MER Opportunity Rover Real Maneuver in Adams Solverpages.mscsoftware.com/rs/mscsoftware/images/Simulate MER... · Maneuver in Adams Solver 2012 International Ground Vehicle

MSC Software Confidential 2012 International Ground Vehicle Users Symposium

Simulate MER Opportunity Rover Real

Maneuver in Adams Solver 2012 International Ground Vehicle Users Symposium

Presented By: Feng Zhou

Co-Authors: Ray Arvidson, Brian Trease, Randel Lindemann, Paolo Bellutta, Scott

Maxwell, Karl Iagnemma, Keith Bennett, Carmine Senatore

October 19, 2012


Background: Spirit and Opportunity Rovers

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•Six wheel drive

with rigid wheels

•Outer four wheels

able to turn

•Rocker-bogie

suspension system

•Navigation and

hazard avoidance

Systems


Background: Spirit and Opportunity Rovers status

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Spirit Opportunity

•Right front wheel drive actuator

failed on sol 779 so subsequent drives

caused rotations about that wheel

•Embedded in sands of Troy after

breaking through soil crust

•Extrication stopped on Sol 2169 to

prepare for winter

•Last communication March 2010 and

mission over May 2011

•Right front wheel left rotated ~8 deg

inward when azimuthal actuator failed

•Shoulder IDD actuator failed so driving

uses “fishing stow” and have limited

Deployment work space

•Mini-TES no longer responding

•Already exceeds 35 kilometers of

driving

•Still working at Cape York on the rim

of Endeavour Crater

Note: Information from http://marsrovers.jpl.nasa.gov/mission/status.html


Terramechanics effort to MER rovers

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A lot of efforts have been put to free Spirit from embedding sand. One effort is to

form a multidisciplinary team from WUSTL, JPL, MIT to help MER rover planners

on:

Minimize risk of high sinkage and slippage during drives;

Better understand soil properties and rover terramechanics from drive data;

Diagnose rover mobility issues.

The team developed and utilized dynamic computer-based models for rover drives

over realistic terrains. The tool, named ARTEMIS (Adams-based Rover

Terramechanics and Mobility Interaction Simulator), is a dynamic modeling tool to

simulate the movement of a rigid wheeled rover over planetary surfaces:

•A dynamic rover model is created in Adams/View with 200-element, 428

degrees of freedom, associated with 85 individual parts or rigid bodies;

•It is based on the classical terramechanics expressions to model the wheel-

soil interaction.

•Surface modeling is based on digital elevation model derived from stereo

Navcam and Pancam images taken by Opportunity rover.


ARTEMIS structure

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Key component of ARTEMIS is

an external solver library which

contains:

• rover motion control;

• wheel-soil Terramechanics;

• terrain deformation.


Opportunity’s real drive

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Opportunity has three standard drive commands:

• straight drive;

• arc-turn;

• turn-in-place.

Also Opportunity has two basic types of drives:

• Blind drive;

• Autonav with visodom;


Visodom

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What: Visodom is the way the rover makes use of camera-based Visual Odometry

(visodom) to correct the errors in the initial wheel odometry based estimate that

occur when the wheels lose traction on large rocks and steep slopes. In other word,

rover odometry data needs to be corrected to remove the effect of rover slippage.

How: The rover visual odometry system computes rover pose (x,y,z, roll, pitch,

yaw) by tracking the motion of “interesting’’ terrain features between two pairs of

stereo images in both two-dimensional (2-D) pixel coordinates and three

dimensional (3-D) world coordinates. A maximum likelihood estimator applied to the

computed 3-D offsets produces the final motion estimate.

Why: Visodom not only improves rover safety but also increases science return.

Ref: Cheng, Y., Maimone, M., Matthies, L. (2006). Visual Odometry on the Mars Exploration Rovers. IEEE Robotics and Automation

Magazine 13 (2): 54–62. doi:10.1109/MRA.2006.1638016.

Maimone, M., Biesiadecki, J., Tunstel, E., Cheng, Y., Leger C. (2006). Surface navigation and mobility intelligence on the Mars

Exploration Rovers. Intelligence for Space Robotics, TSI Press, San Antonio, TX, USA, chapter 3, 2006, march 2006, 45-69


How to simulate these drives?

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The key step is to implement the arc-turn drive.

Straight drive is a special

arc-turn with the infinite

turning radius and turn-in-

place is a special arc-turn

with the turning center at

rover center.

Ackermann Calculation


How to implement in ARTEMIS?

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loop

Drive command simulation is implemented through the customized MOTSUB

in Adams/Solver.


Sample drives simulation

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Simulating forward, 5m, and 30 deg arc-turn in ARTEMIS



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Simulating blind drive with 50cm step size, backward, 5m, and 30 deg arc-turn



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Simulating visodom drive with 50cm step size, backward, 5m, and 30 deg arc-turn


Opportunity Sol 2143 drive simulation: overview

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vertical exaggeration =5.0

A:

2m backup straight;

B:

6 steps arc-turn, 15

deg and 0.2m each

step;

C:

visodom backward to

waypoint (13 steps,

50cm step size).


Opportunity Sol 2143 drive simulation

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Soil region determination:

multiple soil regions for terramechanics calculation



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3D slip comparison between telemetry report and simulated results



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Rover pitch comparison



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Edge profile line

Rut profile line

Note: The elevation is based on Opportunity site

frame. Its positive direction is pointing down.

Sinkage comparison

Digital elevation model


Opportunity Sol 2808~2816 diagnosis simulation

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•Turn-in-place on sol 2808 stopped because of high current (high

torque) on RF wheel drive actuator. To diagnose this situation, an

Artemis dynamical model for Opportunity with stick-slip rheology for

irregular bedrock was used to simulate this drive.

•Sol 2808 modeled as straight drive followed by turn-in-place with fixed

8 deg in-board rotated RF wheel using drive commands sent to

Opportunity.

•Topography was modeled from digital elevation model derived from

NavCam images.

•To continue this diagnosis, Sol 2816 backwards drives (15 cm 10°arc

and 5 cm straight drive segments) also modeled as a comparison.


Opportunity Sol 2808 diagnosis simulation

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Opportunity Sol 2816 simulation

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Simulate MER Opportunity Rover Real Maneuver in Adams Solverpages.mscsoftware.com/rs/mscsoftware/images/Simulate MER... · Maneuver in Adams Solver 2012 International Ground Vehicle