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.