and a 9V battery for power. Even then, my battery lasted only for a few minutes.
So for 3 motors with seperate control circuits, I used a 12V 500mA wall wart with common power for all 3.
I read somewhere that TIP121 required large voltage because its a Darlington pair or something.
Wow! I looked up battery current capacity at http://www.techlib.com/reference/batteries.html and boy was I surprised. I naturally assumed they are bigger so must deliver more current. Guess size isnt everything.
So, I would expect that you could power the motors with 3V. I'd try 2 D cells per motor.
I'd tell you go to wikipedia - but for the next 24 hours it is down (in the USA) due to protest against SOPA/PIPA (look those up too, if you care about the internet - and if you are in the USA especially)...