CS 102B Robot Design Tuesday, 111604

1
CS 102B Robot DesignTuesday, 11/16/04

• Todays Class
• Differential gears and drives
• Questions about project
• Lab work
• Time to work on Project 4
• Reading
• Ferrari pp. 36-39, Chap. 8

2
Differential Gear

• Differential Gear houses three 12T bevel gears
• Wheels turn independently
• Computing total angular velocity (signed!) from
  velocity of each wheel
• (V1 V2) / 2 Vtotal

3
Differential Drive

• Differential Drives
• Two parallel wheels on opposite side of robot
• Each wheel powered independently
• Extra pivoting wheels (casters) used to support
  weight.
• Similar idea to setup in Chap. 2, using
  differential gear, but that gear need not be used
  in a differential drive.
• Our robot drives so far have not been
  differential drives, because each motor powers
  two wheels on each side.
• Running the powered wheels at varying speeds in
  same or opposite directions makes robot move
  straight, rotate, or turn.

4
Steering Drives

• Steering Drive used in Car
• Front wheel used for steering
• Rear wheels fixed
• Drive (motor) can be attached to front, rear, or
  all 4 wheels.
• Hence the names front wheel drive, 4-wheel
  drive
• In Lego, it can be built using one motor to steer
  front wheels, and one motor, plus differential
  gear, to drive the rear wheels.
• Simplest design turns front wheels, keeping them
  parallel, to make turns

5
Ackerman Steering

• Ackermann Steering uses geometry to compute the
  individual turning ratios for each front wheel.
• Idea is that in real turns the inside and outside
  wheels are traveling along smaller and bigger
  circles inner wheel must make a sharper turn
  than outer

6
Ackerman Drive Angles

• In first picture, front tires are parallel, so
• How are these angles related in second picture,
  in terms of x, W, and L?

7
Implementing Differential and Steering Drives

• Both models use rack and pinion mechanisms, as
  shown in picture.
• A round (here 8T) gear is meshed with a rack
  a plate with gear teeth

8
Other kinds of drives

• Tricycle Drive
• Single steering front wheel
• Works best with power on front wheel
• Synchro Drive
• Uses 3 or more wheels, all steering and drive
  wheels
• Picture shows a synchro drive with 4 wheels