I am ona project of making a robocar and I want it to turn. After my first attempt I realized that it should be a three wheel car with a ball bearing in the front as the third wheel. But I want to make it a four wheel drive and the problem is: I use simple motors and they are free to rotate in both directions.So Even if I stop motors on one sid's set of the wheels tehy continue to move in the forward direction. Any suggestions??????