Locomotion Exploiting Body Dynamics

- Semester Project -

Student: Matteo de GiacomiSupervisor: Jonas Buchli

INTRODUCTION

- Purpose of the project- The Puppy II robot- The CPG- Turning

Project objectives

Develop a stable and controllable galloping gait for a quadruped robot endowed with passive dynamics

Use of a CPG based on Hopf oscillators

Puppy II

4 hip motors 1 spring per knee

(passive dynamics) Sensors (inertia,

touch, tortion, IR) Parameters:

Amplitude Frequency Center of rotation

CPG

Fully connected system

Matrix describing a galloping in this system:

FL FR

RL RR

Turning

CPG: generates the basic galloping gait

Turn: modifies the basic rythm so that the robot can turn

Actuate:“translates“ the obtained values in values consistent with the robot architecture.

CPG

Turn

Actuate

basic rythm

feedback

Complete behaviour

Turning – Setpoint control

Idea: modify the basic position of each leg with a small value

FL FR

RL RR

+Δs

- Δs

+ Δs

- Δs

Turning – Amplitude Control

Idea: Increase the amplitude of movement of two ipsilateral legs and decrease the amplitude of their two opposites.

PERFORMED TESTS

- Introduction- Straight Locomotion- Setpoint Control- Amplitude Control

General Framework

Variables influencing PuppyII‘s behaviour: Amplitude Frequency Centers of oscillation

Centers of rotation have been fixed: PuppyII tilted 15° to the front

Test 1: Straight Locomotion (1)

Measure of linear speed depending on Amplitude and Frequency

1 measure: space covered over 5 sec 5 measures per test

Test 1: Straight Locomotion (2)

Under certain limits in amplitude and frequency, locomotion is stable

Amplitude seems a good way to control the robot‘s speed

Videos: Straight Locomotion

Tests on Turning Behaviour (1)

Fixed camera 2.45m over the robot Robot equipped with a red led on its back Robot behaviour filmed for various

parameters Tracking of the robot (red spot) Circle estimation in Matlab

Estimation of the turning radius of the robot depending on the used

parameters

Tests on turning behaviour (2) Example of circle estimation on tracked

trajectory

Video: Turning

Test 2: Setpoint Control

At almost every speed (amplitude) it‘s possible to obtain a good turning behaviour with a good variety of turning radius

Test 3: Amplitude Control

At high speed (amplitudes) the turning radius doesn‘t seem to be affected by the used parameter

At low speeds some localized peaks emerge: the robot CAN‘T turn there!

CONCLUSION

- Discussion- Further works

Discussion

Amplitude is a good way to control the robot‘s speed in a range of values contrained by the enviroment and by the robot itself.

Setpoint control is a good way to precisely control the turning radius of the robot

Amplitude control permits large turns at high speeds. At low speed shows a strange behaviour. Feature of the used springs?

Further Works

Feedback can improve the gait? Embed the turning part in the

oscillators themself may be useful? We fixed some parameters

(frequency and setpoints). What happens if we change them?

THE END

Thank you!Any Question?