I got the disc brake to work decently well by watching this http://www.youtube.com/watch?v=Gt3XRYiFsqg
This is a Windsor Cliff 4700 26" mountain bike with a Yescomusa 1kW motor, Hua Tong 40A 1.5kW controller, 20s2p Turnigy Lipos 10Ah, new rear tire (Maxxis 2" Larsen TT) and Kenda heavy duty...