Gearmotor + encoder for "Dagu Wild Thumper" or similar?

The “Dagu Wild Thumper” pololu.com/product/1564 looks like what I need for my robot project, except that there are no shaft encoders on the wheels or motors. That page notes:

If I want a chassis with encoders, I am out of luck? Is there anything similar offered that does have encoders? How much modification would be needed to shoehorn an encoder-type gearmotor onto some existing Pololu chassis? I want to command a wheel rotation speed, not just a motor voltage or current, because the wheel speed will also depend on the applied torque, which my controller does not know.

Hello.

While the motors with encoders do not directly work with the Wild Thumper chassis, the motor housings can be modified to use the motors with encoders. One of our customers documented the process in the “Modifying the Wild Thumper to use motors with encoders” PDF guide, which can be found under the Resources tab of the product page. The guide walks through the steps they took to do this modification.

Please note, we consider this to be an advanced modification, so we can only offer limited support for it.

- Grant