Here is another video by using Lego. In this demo notice that when the person rotates a tire the other tire rotates in apposite
direction. I wanted to demonstrate this by using buttons RF and RB
In this video when the motor is running both wheel rotates in the same direction. However when the man holds one tire the other
tire rotates much faster. This is demonstrated in our animation as S (Slip) button. Have you ever stuck in the mud or snow whit
your car. One tire rotates but your car is going no where. This is because in one tire there is less resistance and it rotates
by engine while the other one hold by ground.