Drivetrain Design 1

Unit 9

Drivetrain Turning• Most common type is a skid steer which is often called a tank drive. • Consists of 2 sets of wheels on each side of the chassis with each set

running at different speeds. • This allows the robot to steer in arcs and is also capable of a zero

radius turn.

Drivetrain Turning

• There are 2 properties of drivetrain turning:1. Turning torque2. Scrub torque

Turing Torque• the wheels on the left and the right of the robot are the drive wheels

and the wheels on the front and the back are used for stability.• When the right wheel moves forward, the left wheel moves in reverse.

This will cause the robot to move left. • The force of the wheels provides the torque at the center of the robot.

Scrub Torque• For a robot to turn, the front and rear wheels need to slide sideways

across the floor causing friction between the wheels and the ground.

• This friction opposes the turning of the robot and is called the scrub torque.

• If a robot is to turn, the turning torque needs to exceed the scrub torque.

How Can You Reduce the Scrub Torque?

1. Reduce the wheel friction with the ground. a. Change the normal force or the weight of the

robot.b. Change the coefficient of friction of the

wheel itself. 2. Reduce the size of the center of rotation. a. Change the configuration of the chassis.

How Can You Increase Turning Torque ?

1. Increase the turning force of the wheel.a. Increase the normal force.b. Increase the coefficient of friction.2. Increase the distance of the center of rotation

of the robot.a. Change the configuration of the chassis.

• This drivetrain is short and wide. This robot will have good turning because of its high turning torque and low scrub torque.

• This drivetrain is long and narrow. This robot will turn poorly because of its low turning torque and high scrub torque.

Summary

• To make a robot turn better, adjust:1. The chassis configuration.2. The difference in traction between the

various wheels (mainly the front and back wheels).

Unit 9 Tasks

• THINK Phase – lecture notes and keyterms• BUILD Phase – pp. 25-42• AMAZE Phase a. Challenge – p. 44b. Eng Notebook – p. 45c. STEM – Science #1, 2; Tech #1, 3; Eng #1-4

Unit 10 Tasks

1. THINK – keyterms. Read pp. 7-23. 2. BUILD – pp. 24-25. Use the Engineering Design

Process. Outline the 7 steps found in the Unit 3 lecture. This will be submitted as your Engineering Notebook.

3. AMAZE a. Challenge – p. 28b. Eng Notebook – Eng Design Process from BUILD

Phase.c. STEM – Science #1,2; Tech #1-3