Making a specific turn

The next task we can use our encoders for is to make a specific turn. When turning a robot, each wheel is going through an arc. The following diagram illustrates this:

Illustrating wheel movement when turning through an arc

The inner wheel clearly drives a smaller distance than the outer wheel, and from the basics of differential steering, this is how we make the turn. To make an exact turn, we need to calculate these two distances, or the ratio between them. The following diagram shows how the wheels and the turn relate to each other:

Relating wheels to turn radiuses

If we consider the turn radius as setting where the middle of the robot would be, an inner wheels turn radius will be the difference between the turn radius and half the distance between the wheels. The outer wheel's turn radius would be the turn radius added to half the distance.

We...