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. Figure 11.13 illustrates this:

Figure 11.13 – Illustrating wheel movement when turning through an arc

The inner wheel drives a shorter 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. Figure 11.14 shows how the wheels and the turn relate to each other:

Figure 11.14 – Relating wheels to turn radiuses

If we consider the turn radius as setting where the middle of the robot is, an inner wheel's turn radius is the difference between the turn radius and half the distance between the wheels:

The outer wheel's turn radius is the turn radius added to half the distance:

We convert our angle to turn into...