Originally Posted by
General Geoff
Mista Sparkle:
If you had a bike equipped with regenerative braking, you could intentionally apply the brake moderately while going down a hill that you might otherwise coast down at top speed, in order to store a lot of the energy that is otherwise being wasted on overcoming drag at higher speed. Instead of going down a steep hill at, say, 40mph, if you use your regenerative brakes to maintain 20, you're storing a massive amount of energy for nothing lost except a bit of time, which is then made up for by using that energy to assist in the next hill climb.
It would make for a brilliant auto-brake feature on an e-bike, to be able to set your maximum speed at say, 20mph, and anything past that causes the regen brakes to kick in and keep you at 20 down hills, topping up the battery for the next climb automatically.
True, I can't see myself trying to go slow down a hill, but I don't have a lot of them around and they are all short and straight...
Trying to store any reasonable amount of energy in a flywheel though would be generally impractical on a bike, it either would have to be reasonably heavy(and therefore counterproductive) and/or go terrifyingly fast. Batteries are by far the better route as they should be able to handle the relatively low charge/discharge rate associated with moving a person on a bike at reasonable timescales without overheating.
Flywheels are "decent" in race cars because its a couple seconds of hard acceleration followed by hard braking etc etc and dumping that energy into a battery is difficult to do efficiently. They handle high peak power for short duration's well, but have generally poor energy density...