Adding a magnetic encoder to a GM3 Gearmotor

You may want to add a rotation encoder to your wheel motor. Optical encoders are popular because of the very high resolution (counts per rev) you can obtain.

Here we will add a magnetic encoder, which has advantages of low cost and dirt insensitivity. The resolution is only 1 count per revolution of the motor, but because of the gearing (transmission ratio) it is many counts per revolution of the wheel.

Shown here is the Hobby Engineering Gearmotor-3 with traction wheel, which has a 224:1 transmission ratio

You can also add a magnetic encoder to the Gearmotor-9, which has a 143:1 transmission ratio