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

Life in the AtacamaCarnegie Mellon Mobility Characterization Project Atacama, April 2003 Hard Surface, July 2003 Sand Simulant, July 2003

Life in the AtacamaCarnegie Mellon Mobility Approach Atacama 2003 Hard Surface Soil Simulant Drive/Steer/Climb Torque/Power/Energy Evaluate Performance and Rethink Design -Locomotion -Mechanical Driveline -Traction/Steering Control -Mobility Sensing -Vehicle Electronics -Overall configuration -Payload accommodation

Life in the AtacamaCarnegie Mellon Weighing Hyperion Scale placed under each wheel Total weight in desert: kg Lab experiments: 140 kg Hyperion kg kg kg kg

Life in the AtacamaCarnegie Mellon Mobility Studies Driving Steering Slope Grading Discrete Obstacle Climbing Drawbar Pull Combined Feature Negotiation

Life in the AtacamaCarnegie Mellon 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 V iv / r  = (total efficiency)

Life in the AtacamaCarnegie Mellon Atacama Flat Ground – Power Peaks occur near moment of ~10 deg pitch

Life in the AtacamaCarnegie Mellon Atacama Flat Ground – Torque 15 Nm 20 Nm

Life in the AtacamaCarnegie Mellon Atacama Flat Ground – Rolling Resistance

Life in the AtacamaCarnegie Mellon Flat Concrete Floor – Power

Life in the AtacamaCarnegie Mellon Flat Concrete Floor – Torque

Life in the AtacamaCarnegie Mellon Sandbox – Power

Life in the AtacamaCarnegie Mellon Sandbox – Torque

Life in the AtacamaCarnegie Mellon 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

Life in the AtacamaCarnegie Mellon Slope Climbing in the Atacama

Life in the AtacamaCarnegie Mellon Slope Climbing in the Atacama: 14 deg 25 Nm 35 Nm

Life in the AtacamaCarnegie Mellon Slope Climb Testing in Lab

Life in the AtacamaCarnegie Mellon Slope Climbing in the Lab: 30 deg Entire robot climbing ramp Entire robot climbing ramp 50 Nm 65 Nm

Life in the AtacamaCarnegie Mellon Slope Climbing – Preliminary Summary Max 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)

Life in the AtacamaCarnegie Mellon Obstacle Climbing

Life in the AtacamaCarnegie Mellon 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

Life in the AtacamaCarnegie Mellon 20-cm Obstacle on Concrete Floor b a d c 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

Life in the AtacamaCarnegie Mellon 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 b a d c

Life in the AtacamaCarnegie Mellon 12-cm Obstacle in Atacama

Life in the AtacamaCarnegie Mellon 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 b ac

Life in the AtacamaCarnegie Mellon Obstacle Climbing - Preliminary Summary Max instantaneous wheel power Lab: 150 W (20-cm block) Atacama: 120 W (14-cm rock)

Life in the AtacamaCarnegie Mellon 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 cable The 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

Life in the AtacamaCarnegie Mellon 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

Life in the AtacamaCarnegie Mellon 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 N Max slope: 22 deg

Life in the AtacamaCarnegie Mellon Discussion (1) Key total locomotion power results Driving power: W Steering: ~1.5 x Driving Slope: W to climb sandy slope Slope continuous; battery thermal limit Obstacle: W per wheel Multiple obstacles is the worst case

Life in the AtacamaCarnegie Mellon 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.