Life in the AtacamaCarnegie Mellon Hyperion Mobility Testing July 28, 2003 Dimi Apostolopoulos Michael Wagner Kevin Peterson James Teza Stuart Heys

Life in the Atacama Carnegie Mellon

Hyperion Mobility Testing

July 28, 2003Dimi Apostolopoulos

Michael WagnerKevin Peterson

James TezaStuart Heys


Mobility Characterization Project

Atacama, April 2003

Hard Surface, July 2003

Sand Simulant, July 2003


Mobility Approach

Atacama 2003 Hard Surface Soil Simulant

Drive/Steer/ClimbTorque/Power/Energy

Evaluate Performanceand Rethink Design-Locomotion-Mechanical Driveline-Traction/Steering Control-Mobility Sensing-Vehicle Electronics -Overall configuration-Payload accommodation


Weighing Hyperion

Scale placed under each wheelTotal weight in desert: 181.1

kgLab experiments: 140 kg

Hyperion

39.78 kg

40.00 kg

51.54 kg

49.78 kg


Mobility Studies

Driving

Steering

Slope Grading

Discrete Obstacle Climbing

Drawbar Pull

Combined Feature Negotiation


Measured & Computed Variables

Power is measured into amplifiers

Torque is calculated through the following equation:

T =

Torque measurements are most accurate when robot driving straight and at higher velocities

Compute consumed locomotion power as the product of resistive force (T/r) and vehicle speed

Compute losses due to soil work

I Viv / r

= 0.35-0.45 (total efficiency)


Atacama Flat Ground – Power

Peaks occur near moment of ~10 deg

pitch


Atacama Flat Ground – Torque

15 Nm

20 Nm


Atacama Flat Ground – Rolling Resistance


Flat Concrete Floor – Power


Flat Concrete Floor – Torque


Sandbox – Power


Sandbox – Torque


Flat Ground – Preliminary Summary

Max wheel power, considering only flat portions of terrain

Concrete floor: 40 W (rear right wheel)

Sandbox: 35 W (right wheels)

Atacama: 45 W (front right wheel)

Average wheel power

Concrete floor: 15 W

Sandbox: 20 W

Atacama: 30 W


Slope Climbing in the Atacama


Slope Climbing in the Atacama: 14 deg

25 Nm

35 Nm


Slope Climb Testing in Lab


Slope Climbing in the Lab: 30 deg

Entire robotclimbing ramp

Entire robotclimbing ramp

50 Nm

65 Nm


Slope Climbing – Preliminary SummaryMax wheel power

Ramp: 85 W (30-deg slope)

Atacama: 70 W (14-deg slope)

Average wheel power

Ramp: 70 W (30-deg slope)

Atacama: 50 W (14-deg slope)


Obstacle Climbing


Reconstructing Terrain Features

Twist = steering roll – body roll

Robot width x sin(twist) = height of object

Can be used to quantify surface roughness

Negative twist:Front left wheel

climbing

Positive twist:Rear left wheel

climbing

Vehicle length

Height: 20 cm


20-cm Obstacle on Concrete Floor

ba dc

a. Driving forward, front left wheel climbs obstacle

b. Driving forward, rear left wheel climbs obstacle

c. Driving backward, rear left wheel climbs obstacle

d. Driving backward, front left wheel climbs obstacle


20-cm Obstacle in Sandbox

a. Driving forward, front right wheel climbs obstacle

b. Driving forward, rear right wheel climbs obstacle

c. Driving backward, rear right wheel climbs obstacle

d. Driving backward, front right wheel climbs obstacle

ba dc


12-cm Obstacle in Atacama


12-cm Obstacle in the Atacama

a. Robot’s front left wheel climbs obstacle

b. Robot stops, fails to climb obstacle

c. After a second command, rear left wheel climbs obstacle

ba c


Obstacle Climbing - Preliminary SummaryMax instantaneous wheel power

Lab: 150 W (20-cm block)

Atacama: 120 W (14-cm rock)


Drawbar Pull Tests

Drawbar pull is the force a vehicle can pull on a given soil

The drawbar pull is measured by attaching the robot to a load cell and steel cableThe robot is driven until the cable is tensioned and its wheels begin to slip

The drawbar pull is the maximum force sensed by the load cell

Direction of travel

Steel cable

Load cell

Wall


Drawbar Pull Tests

Drawbar pull is a useful metric because it can be used to find the maximum climbable slope for a given soil type:

Max slope = atan(DP / weight)Performed tests in cohesionless sand

This soil provides very little traction, similar to regions of loose sand seen in the Atacama


Drawbar Pull Tests – Results

c

a

b

d

e

a. Robot driving normally

b. Cable tension rapidly increases

c. Wheels slipping

d. Motion controller fault, at least one wheel stops servoing

e. Robot reverses, cable goes slack

Max DP: 550 NMax slope: 22 deg


Discussion (1)

Key total locomotion power results

Driving power: 100-150 W

Steering: ~1.5 x Driving

Slope: 250-350 W to climb 20-25 sandy slope

Slope continuous; battery thermal limit

Obstacle: 150-200 W per wheel

Multiple obstacles is the worst case


Discussion (2)

Poor slope climbing and need for traction optimization motivate new locomotion system

Need for better and more payload accommodation, and new solar array layout motivate new chassis configuration

Must devise more precise/repeatable mobility to aid close-up science.

Documents

Life in the AtacamaCarnegie Mellon Hyperion Mobility Testing July 28, 2003 Dimi Apostolopoulos Michael Wagner Kevin Peterson James Teza Stuart Heys