Speed controller used to slow down the performance of our baby bikes after they were converted to run on 18v Milwaukee batteries. The running time is amazing for those who are interested. With the speed controller we were able to adjust the speed of the motors back to the appropriate level, first we slowed them down so that our child could drive the car comfortably, and then we increased them a little. No problems with heat build-up or slipping of the adjustment knob. The motors and speed controller stayed cool even after prolonged use. The adjustment knob turns easily but doesn't move even when the drive wheels bounce in the grass. Good product!