An H-Bridge circuit has a control circuit, usually PWM, which then determines the switching of high-voltage supply to drive a current. Typical embedded H-Bridges can drive about 5A of current. In the case, of the Freescale Cup car the motors can sustain much more current resulting in more toque and faster speeds.
Performance Tuning Tips
1. You can place H-Bridges in parallel to balance the current load. For example, if you place two 5A (peak) H-Bridge outputs in parallel, the system can support up to 10A current.
2. Keep it Cool. H-Bridge's dissipate A LOT of heat. Heat = increases inefficiency of a semiconductor, so the better job you do keeping it cool, the better (and longer) it will work for you.
This is the simplest H-bridge, where the four gates represent for transistors. By manipulating these gates and connecting the upper and lower terminals to a voltage supply, you can control the motor in all the behaviors as below.