what size speed control
 

just wondering if someone can help me. just bought a 970 size motor off ebay.6-14voltsand runs at about 14000 rpm. the noload speed at 12 volts is 12.0.at 6v the rpm is 5600. has a 7 pole armature for good tq.has built in internal fan. was wondering if someone out there could tell me whatsize speed control i need to use thanks much