Heat-sinks wont be a problem becaus I have four of them laying here. (I have 3 rc-cars)

But the reason I want to overvolt the motors instaid of geting a 12V valve is becaus you will get more power from the drive and you need bigger batterys for the same amount of Amps on 12V then on 24V. (weight)

And the screw on the speedo sets how much Volt gows to the motor om maximum rotation of the joystick.

I was also thingking about a resistor or something like that between the speedo and the motor to lower the voltage.
But I dont know mutch about resistors and stuf so maby someone can help me on this area.
Like how much Ohm the resistor should be if I want half the voltage.

I found a circuit on http://www.circuitsonline.nlwww.circuitsonline.nl that lowers the voltage from everything that has a higher voltage than 12 volt.
But that only works up to 5A and thats to less for a drill motor.