If its for near exact control (inc Torque) try "electronize" products
www.electronize.co.uk
Microprocessor speed controllers..
Selectable mode processor system, high, low or variable frequency control.
DSP for smooth operation
can run motors up to 30 amp DC
90 Amp short term stall rating (short time)
low loss power MOSFET switching
screwdriver speed adjustment range
runs from 6 to 24V DC supply
standard RX RC input
no servos required.
can be bought in kit form or pre built (kit is cheaper) and have various types available from £20.45 to £41.55.
I use an FR30HX (specs above) which gives near perfect speed control.