Introduction to RoboticsLocomotion

CSCI 4830/7000January 11, 2010

Nikolaus Correll

What is locomotion?

• Latin: moving from place to place

Crawling Sliding Running

Jumping Walking Rolling

Other forms of locomotion

Gliding Flying Swimming

Propulsion

Locomotion relationships

• Swimming to walking• Walking to rolling• Gliding to flying• Running to jumping

A.J. Ijspeert, A. Crespi, D. Ryczko, and J.M. Cabelguen. From swimming to walking with a salamander robot driven by a spinal cord model. Science, 9 March 2007, Vol. 315. no. 5817, pp. 1416 - 1420, 2007.

Nature vs. Technology

• Robots become more and more capable of imitating natural locomotion schemes

• Nature did not evolve rotating shafts / rotational joints

Hinge joint Ball and socket joint

Walking vs. rolling

• If the terrain allows, rolling is more efficient

• Walking requires more– Structural complexity– Joints– Control

Characterization of locomotion

• Stability– Number of contact points– Center of gravity– Static/Dynamic Stabilization– Inclination of terrain

• Contact– Point vs. Area– Friction vs. grasp

3-Point rule

3 legs : static stability6 legs : static walking

Walking

2-DOF 4-DOF 6-DOF

How many DOF are needed?

Gait

• Sequence of event sequence

• Event: leg up or down• Possible number of

gaits N=(2k-1)!• Most efficient gait is a

function of speed!

Horse Gait (Gallop)

167 different gaits observed in a horse!

Industry

• 2-legged locomotion– popular because suited to

human environment– hardest to control– Commercial prototypes

• 4-legged locomotion– Not statically stable– Commercial prototypes

• 6-legged locomotion– Statically stable– Forestry

http://www.youtube.com/watch?v=CD2V8GFqk_Y

http://www.youtube.com/watch?v=FAcgSi6pzv4

Wheeled locomotion

• Most appropriate for most applications

• Stable with at least 3 wheels• Steered wheels make

control more complex pretty quickly

Stable zone

Wheel suspension

• Suspension consists of a spring and damper

• The damper absorbs shock

• The spring counteracts the shock

• Result: – wheel remains on ground– Better traction– Better control

Omni-Directional Drive

• Swedish Wheel– Rotation around wheel axle– Rotation around the rollers– Rotation around contact point

Uranus, CMU

Climbing with wheels

Friction-based Center-of-gravitybased

Suspension-based

Dynamic Stability

• The system has to move in order not to fall over

• Active balance• Inertia is used to

overcome unstable states

• Examples are– Running– Getting up

Inverted Pendulum

Part II: Practice

Brushed DC Motor

• Directly driven by DC current• Self-commutating• Speed regulated by voltage• Needs gear-box to generate useful speed/torque

Stepper Motor

• Requires dedicated circuitry to generate activation sequence

• Speed of sequence controls motor speed• Motor stops at precise increments

Brushless DC Motor

• Commutation done electronically• Requires speed controller• More efficient then brushed DC Motor

Encoders

• Required to estimate axis position

• Optical encoders– Differential– Quadrature– Absolute

• Hall-Effect

Servos

• Servo =motor + encoder + gearbox + controller

• Low-End:– Pulse-Width Modulation

(PWM):rate regulates position

• High-End:– Digital control allows

setting and querying position, speed and torque

Linear Actuators

• Rotation-based• Hydraulic / Pneumatic• Solenoid• Piezo-Electric• Shape-Memory Alloy

(SMA) wires

Design

• Lets design robots that– Crawl– Slide– Gallop– Jump– Walk– Roll

Crawling Sliding Running

Jumping Walking Rolling

Crawling

Mechanics of Soft Materials Laboratoryhttp://ase.tufts.edu/msml/researchInchBot.asp

Sliding

Hirose-Fukushima labhttp://www-robot.mes.titech.ac.jp/robot_e.html

Gavin Miller

Running

Scout II, McGill Universityhttp://www.youtube.com/watch?v=SRIU7PtyGOw

Jumping

Laboratory of Intelligent Systems, EPFLhttp://lis.epfl.ch/?content=research/projects/SelfDeployingMicroglider/

Rolling

http://modlabupenn.org

Homework

• Chapter 3– Required for next week’s exercise– Hints

• read the questions first• Skip: 3.2.3.4-5• Skim: 3.2.4-3.3.3• Understand what Maneuverability (Mobility and

Steerability is) conceptionally

• Goal: calculate the speed of your robot’s motors so that it can follow a desired trajectory

Next exercise

• Locomotion (1 week)• Play with different locomotion concepts in

Webots• Understand various gaits• Come up with a “stand-up-gait” for the Soccer

robot