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I am making a homemade mid drive ebike. This bike will have the motor driving the front cassette which is modified with a freewheel so the pedals are stationary. However, since the freewheel is one way, when I pedal manually with motor shut off the motor will turn. The friction is not noticeable so I want to take advantage of this by welding the rear freehub, so the motor is constantly spinning. Before I do this I want to know if this is a good idea or not.

Basically I want to take advantage of the motor's spin for regenerative braking, but am unsure it is feasible. The drivetrain from motor to rear wheel is 8.3 times speed reduction to increase torque, so if the motor could be driven by the rear wheel when it is unpowered, it would spin 8.3 times as fast as the rear wheel and generate a lot of electricity (theoretically). With the current set up the only time the motor will spin unpowered is if I pedal. But if I welded the freehub at the rear wheel, the entire drivetrain (and motor) will constantly be spinning as long as the bike is moving but freewheel at front cassette will ensure pedals remain stationary.

Has anyone else tried this? And is regeneration feasible for ebikes?

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  • $\begingroup$ You might want an additional guard on the front sprocket so that your toe can't get pulled into the teeth. $\endgroup$
    – Drew
    Commented Dec 28, 2022 at 7:19
  • $\begingroup$ Many e-bikes have regeneration, so what’s the problem? $\endgroup$
    – Solar Mike
    Commented Dec 28, 2022 at 8:56
  • $\begingroup$ correct but I am unsure if they accomplish this by having the motor in a state of constant spin. In this design as soon as the motor turns off it turns into a generator. For regen on normal bikes it may only activate when the brake or dedicated switch is pressed but in this design the motor has no "downtime". My goal is to make regen occur automatically as soon as motor shuts off without any switches. If there are no electrical or mechanical issues posed by having the motor constantly spinning then ill weld the rear freehub $\endgroup$
    – MechEboss
    Commented Dec 28, 2022 at 12:01
  • $\begingroup$ Also there are efficiency concerns, would a regen braking system be effective if it was constantly stealing momentum from the bike to generate charge versus if it was only activated for braking? For example with my proposed design when the motor is shut off it will immediately turn into a generator and steal back the momentum it just worked to produce. But if I input extra energy into the system by manually pedaling or by going downhill, would it be efficient to steal back this momentum since energy was added to the system? $\endgroup$
    – MechEboss
    Commented Dec 28, 2022 at 12:36

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