Christopher Vaughan ✭✭✭✭✭
So this is interesting, The H-Bridge not only reverses the direction of the motor, but you can pulse width modulate the Arduino and the motor has wonderful torque characteristics. I think that if I included a rotary encoder on the system I could achieve a high torque bi-directional 360 degree servo.
Datasheet for IC: http://www.ti.com/lit/ds/symlink/l293d.pdf
You can pick up prebuilt Arduino motor drive shields off of Ebay for about $5 each!
They're really easy to program for and can handle up to about an amp at anything up to 36V.
If you get a cheap rotary encoder, you can build a pretty reasonable servo / PID control system yourself - but at a certain point it becomes cheaper and more sensible to just use an open-loop (no feedback/sensors) system like a stepper motor, or just bite the bullet and buy a $20 servo from Hobby King that's stronger than you are!