Are You Wondering How to Hook Up a Motor Driver IC chip (such as an L293D) ?
**Click the picture to show it bigger, and then click that picture again to make it big enough to read the fine print**
ADDED (06MAY2012) This is the motor drive circuit exactly as I built it for my newest lttle SHR-like robot.
The above configuration using the L293D is a good way to prevent shorting out the power supply as can happen in the circuit below if you make inputs A and B high at the same time. The Integrated circuit can supply 600 mA current per channel (and twice that in a non-repetitive peak). It also contains internal protection against reverse spikes such as are generated when driving an inductive load.
With this configuration, in adding the extra transistors I have changed the function of the inputs. Power to the motor is turned on or off with one lead and You set forward or reverse with the second one. While this feature is not essential, some people may like this better. It is still the same 2 wires per motor (as below), but their functions have changed. Some of my older drawings using the L293D just tied the Enable leads to +V (always enabled), but by using the enable leads you can switch the output to a high-impedance state when the on/off lead is low.
Below is a common driver circuit I pulled )almost at random) off the internet. (If anyone is upset that I posted something I did not draw myself, I will remove it; there are many more examples.) I have even seen a video for that particular 6-transistor circuit showing how to put it together, but I do not remember them saying, "Oh by the way, don't turn both inputs on at the same time or you could burn down your house." (Ok, it may not be THAT bad, but the transistors *will* burn up if the battery does not go dead first.)
This does work but there is always the danger of accidentally turning both inputs on at the same time, and *P*O*O*F*.