Tonight I spent some time playing around with a Victor 884 speed controller that I interfaced to my Vex Robotics controller. The speed controller was tested with several motors and the results were fantastic. It ran well with a Dewert motor as well as to a surplus windshield washer motor that I had recently purchased.
The speed controller allows you to use any voltage motor with your robotic controller. The signal from the controller talks to the speed controller which does the interface with the actual motor. You supply the correct voltage to the speed controller which powers the motor.
I would like to use Vex to power my R2D2. That way I could not only use the radio controlled motion for it, I could also program the R2 to randomly move his dome back and forth as well as pop the periscope up and down periodically. I'm sure I can do all of that with what I have now. The speed controllers aren't cheap and are a little more than $100.00 apiece. But ... they sure do open doors with robotics when you need more power.