I'm just starting to look at electric bikes, and learning what some of the differences are among them...
I notice the energy from the disc brakes can be channeled back into charging. I also notice most of the hub-motor models will only have a drive unit on one wheel (I'm guessing to avoid overkill, and keep the other wheel available for a disc brake rotor).
Has anyone come up with alternators to fit in the non-motorized hub and/or the pedal assembly for channeling energy back into charging? After all, those parts are already in motion. I'm not familiar with the ins-and-outs of alternator design, but I'm wondering if a brushless alternator would have significantly less resistance, allowing it to give more energy than it takes?
Not that I've seen. The amount of regenerative energy generated in those systems that have it built in isn't that much, either. Hence the eternal quest for as much energy as you can pack into a battery while keeping the weight down. The most sophisticated e-bike is a German hybrid called the E-Rocket that will be beyond reach for most since it's price is over $40,000 USD. From an article here: http://www.cens.com/cens/html/en/new...ner_27291.html "The eROCKIT has a serial hybrid propulsion system that lets the rider control the motor speed through a crank assembly and an inter-connected generator. The generator monitors the rotation of the crank assembly and sends an output signal to the control electronics according to the rider`s peddling speed. The control electronics steers the electric motor with the received signal as a reference point. The faster you peddle, the faster the motor rotates the rear wheel. The generator thus has a double role of sending signals to the control electronics and transferring the peddling force into electricity to recharge the battery."
The E-Rocket doesn't have a throttle; you have to peddle to make it move and have power assist kick in, but its hybrid propulsion system can amplify the cyclist's pedaling power to reach speeds of 30-50 MPH.
Of course, there are existing hub motor systems that provide regenerative braking, like Bionx (and now Trek.) You don't need a separate generator, just a drive unit that doesn't freewheel and an appropriate controller.
The amount of energy recovered isn't huge, but the reduced wear on your brakes can be a plus.