Hey, Intrigued, if only teachers could whoop students as if they were a red-headed step child, I would teach for free. If you are going to be excited about each post, I'll have to really make sure I actually have something interesting to report!
This is a modified version of Ian's "speedy"
controller. His was for a 24v trolley. This version is 72v, and powers the mosfets and the micro-controller with the 12v auxiliary battery (that powers the lights and blinkers and other stuff). It doesn't share a common ground with the battery pack.
Notice that the PWM output from the ATMega8 is the PWM input into the gate driver. The driver amplifies the PWM signal, and then opens the floodgates of all the mosfets at the same time!
By the way, if you have ever wondered why a pre-charge resistor is important, it's because there are TONS of huge capacitors inside the controller! They don't like to be short circuited! OOH, so we need just a little more stuff inside that schematic to have it pre-charge when the 12v battery power is applied.