I'm building a car. It has mecanum wheels. The weight of the car is 1.5kg, the weight of each wheel is 250grams, the diameter of each wheel is 10cm. wheels are printed on 3D printer. I;m also using two drive shields Pololu DRV8835 (http://www.pololu.com/product/2511). I have four Pololu micro metal motor reductors 50:1. The car goes forward and backward when the speed is set to maximum. At the half of the max speed the car doesnt move but there is a sound from the motors that show that they are trying to do that. I can turn the car as a non-mecanum wheel car (to wheels forward, two wheels backward when the speed is maximum). But mecanum wheels allow the can to move aside. This my motors can't do even when the speed is max. I'm thinking of buying Pololu2214 (http://www.pololu.com/product/2214). But I don't know will it be enough. How can I calculate that? I tried different suffaces at home.