I'm developing a better "small circuit" which will also place a shunt on the battery -ve lead and have a speed sensor input. This will make my arrangement legal in both speed and power. By tempering the demand to the ESC by the measured speed I can avoid the synch loss events and massive uncontrolled torques that make my present bike hard to ride. The battery current feeds back electric power usage and I can make that 250W (+ a bit for inefficiency) over the speed range (say) 4 to 15.6mph - i.e. I effectively have an electrical CVT. The "small circuit" design at present looks as though it will cost about £1 (2 active components, a single opamp and a ATtiny5 micro).
It should be an attractive package - suitable motors cost ~£25, an ESC ~£10. If it works well I'll make the design infomation available & get a few PCBs made (BTW the PCB is 2cm square & is simply supprted bythe wiring) and knock them out at cost to home constructors.
PCB design is done & I'm talking to a guy who'll develop the software tonight: should have results reasonably quickly.
