I know everyone is putting brushless on theirs, but we have found a cheap alternative that works great for indoors. We run a GWS dual IPS 4.8V B gear box set-up. We wire the motors in series and run 3 cells. So far a 12x6 works the best. We hover at 1/2 throttle or a little less. Climb out is good. We get about 25 minutes with 640's. The motors barely get warm. I was going to put brushless in it because it is the cool thing to do, then I saw this set-up fly. I also fly mine outside with no problem. A couple of guys I fly with have over two months with this set up and flying two nights a week without burning up the motors.