mtbkym01 wrote:You'd need pretty strong servos to shift the rear I'd reckon..
Actually it's the front derailleur that requires the substantially more powerful servo. It takes quite a bit of grunt to mash the chain across such a large size difference between the two rings. Shimano's battery life (single charge) figures estimate 35,000 rear shifts, but only 7,500 front shifts, due to the greater power needs at the front. When the battery gets low, front shifting stops first, to reduce the drain on the system, allowing you a better chance to get home with at least some range of gears.