Carnegie Mellon

Zoë Vehicle Controller Design

Design Review

December 19, 2003

Michael Wagner (mwagner@cmu.edu)

Carnegie Mellon

Aspects of Controller Design

Chassis redesign

Evaluate Hyperion controller design in terms of:

Changing algorithms, exposing variables

Ease of use

Power consumption of hardware

Integrating instrument deployment

Reliability for multi-day operation

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Chassis Redesign

Tu

rn R

ad

ius

2 passive steering pivots2 roll pivots

Kinematics similar to Hyperion

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How to Control It?

Initial tests show that the chassis naturally tends towards an incorrect configuration

not…

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Controller Performance

Robot stopped, axles both

angled to the right

Front wheel over block

Rear wheel over block

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Controller Performance

Robotstopped

Front wheel over block

Rear wheel over block

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Controller Architecture

PIController

GalilMotion

ControllerRobot

KinematicModel

VehicleController,

Pendant

d

vd

inner,front

++

ticks/s

a

+Erad+

–

–

+ +

+

a

c

PID

= Kp(d – a) + KI (d – a)

outer,front

outer,rear

inner,rear

PIController

++

ticks/s+

E

rad

+

–

–

+

+

+

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Slip Control

Idea is to control slip ratio [Yoshida03]

s = r – v / r

Slip ratio should be small to travel over terrains

Slip ratio of 1 means the wheels are just spinning on the soil

Must reliably measure both and v

Angular wheel velocity is easy to measure with encoders

Rover velocity is trickier without GPS

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Instrument Controllers

Software blocks to interface with the science “instruments”:

SPI cameras

Spectrometer

Fluorescence camera

SPI pan/tilt

Underbelly deployment mechanism

Each component must:

Reliably carry out command

Know when failures occur, report this to executive

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Instrument Controllers

Blocks must be split up to allow complex science operations, for instance:

Stop robot

Deploy fluorescence imager to (x0,z0)

Take fluorescence image

Move robot ahead by y0 (NOTE: how do we check that this is safe?)

Take fluorescence image

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Control Hardware

Several instrument controllers must interface with motion control hardware

8 axes to control:

4 drive motors (w/o sinusoidal commutation)

2 SPI pan/tilt motors

2 underbelly deployment mechanism (x / z)

But also some simpler motions that may not require sophisticated control hardware

Plow deployment

Calibration target deployment

Shroud deployment

Filter wheels, dust covers, …

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Next Steps

Test Hyperion’s motion controller with Zoe amplifiers and drive motors

Tune steering controllers for rough terrain

Analyze failure modes

See if control / power performance is as expected

Improve reliability of Vehicle Controller process• Handle “odd” motion controller conditions (amps, limit switches, etc.)

• Instrument more variables for State Observer and Health Monitor

Implement chassis self-calibration

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Next Steps

Prototype instrument controllers:

Pan/tilt

Underbelly deployment (in conjunction with safe driving)

Design “control” for simple actions (shroud, plow, etc.)

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That’s it

Muchas gracias

¿Preguntas?

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Goals of Redesigned Chassis

Support science payload under chassis

Create overlapping fields of view

Support “recover maneuver” to autonomously back out of non-traversable regions

Provide maneuverability to approach targets in the morning within panorama from Sol N-1

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Double Passive-Steered Chassis

MetricMetric Double Passive-SteeredDouble Passive-Steered

Mechanical Complexity Extra complexity to couple steering motions.

Turning Radius Much tighter turning radii possible.

Controller Modifications Modifications required to vehicle controller.

Stability Less stable in tight turns.

Expected Mass Extra mass required for steering motion coupler.

Expected Power Draw Smaller stresses on frame should reduce power draw.

Ease of Science Instrument Integration No fixed rear axle to attach science instruments.

Dead Reckoning Accuracy Less wheel slip should provide better information about vehicle state.

Symmetry of Fwd and Reverse Driving Motion should be symmetric

Failure Modes Hard stops needed to avoid collapse.

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Controller Performance

Robotstopped

Front wheel over block

Rear wheel over block