speed controller for 775 motor

Hi folk, first I would like to thank you all for the advice given on running led strip from 18v battery. working well.
My project now is running a 775 motor taken from a 14v battery drill with a speed controller from an 18 v battery, again from a battery drill. I purchased a "DC 9-60V 12V 24V 36V 48V 20A PWM Motor Speed Controller CW CCW Reverse Switch" which worked well untill I put it under load with disasterous results . upon further reading I found the stall current can be 40A. so my question now is what what do I need to achieve my aim. ie, control the speed of my 775 motor ?