Problems with Robot Turning

With the IFI traction wheels, our robot is having difficulty turning. What can I do to make it turn better?

**When using tank style steering, there is often a large amount of scrub (frictional forces which oppose turning) in the system. To increase turning, one needs reduce the scrub in a given drive configuration.

There are many ways of accomplishing this.
For more information on turning physics, please consult the following whitepaper by Chris Hibner:

To understand scrub, think of the robot with a point fixed between the 2 front wheels. The front wheels will rotate the robot about this point. The rear wheels, will slide sideways across the ground, around this point. The frictional force of these wheels sliding sideways across the ground, acts as a brake on the robot turning; this is turning scrub.

Methods for Reducing Scrub:

With 4-wheels touching the ground:
Decrease traction on 2 of the wheels (the 2 front, or 2 back), the robot will turn about the point between the high-traction wheels.

To greatly reduce scrub, try using 2 omni directional wheels. These wheels have high traction in the forward direction, but not a lot of lateral traction.

Alternately, use casters, or other super-low friction wheels. The downside of this is, these wheels will not provide forward pushing force.

Shorten** the drivebase length.
Increase the drivebase width.

To shorten the drivebase length, without losing footprint (stability) try using a 6WD configuration, where the middle 2 wheels are lowered 3/16" (the kitbot chassis has this option). This way, only 4 wheels touch the ground at a given time. The robot will rock back and forth between the front or rear wheels. This results in a wheelbase at any given time, being 1/2 as long as the robot.