donn said:
Sure, that's a fair point if the proposition is to eliminate physical brakes and rely solely on regen. I think his point, however, was not that we should follow the lead of that scooter maker and do that, but that inasmuch as they can get away with that and it works, then it's a testament to the usefulness of regen braking. Considering that people sweat over the difference between various kinds of disk brakes etc.
It's a shame that no one has figured out how to clutch the freewheel in geared hubs, so the only choice here is between "no regen" (most) and "no freewheel" (GMAX.)
Well, there are motorcycle manual clutches. It can be combined a fixed gear left-sided middrive, so you can have both.
Problem is, they are an overkill for a bicycle - where 'intermittent assist' (accelerations, hills - and regen braking, right) makes most sense.
Admittedly, 'virtual freewheel' (very low power assist to compensate for cogging/iron losses) most does make sense and actually regen braking DOES make up for it - usually, when riding in city and with hills.
However, during long-distance riding on mostly pedal power - no, it does not, especially if your motor is particularly powerful.
There are two options here:
A really *low* power DD motor or one stage reduction fixed gear middrive using RC motor, just enough for 'low assist level when pedalling' and scrubbing speed to decelerate with conventional brakes to come to a complete stop, and very low cogging losses combined with conventional geared motor. In fact, a rear geared motor with left-sided midddrive replacing rear cog seems like the best solution. You can have very considerable assist and regen with 700gr e-board motor and 24v battery at medium to high (think ~50 kmh) speeds, while allowing very brisk accelerations and hill climbing from low to mid speeds when using a combination of two motors and pedalling.
However, if you need efficiency AND high braking power, there is possibility of combinting a middrive e-board motor with a 50cc moped centrifugal clutch (it also serves as a gearbox).
You *will* take a considerable hit to efficiency when using it for high-torque starts, but when fully engaged it should be as efficient any other middirve, and as long as you don't use it to brake to a complete stop and within torque range nessesary for engagement - you can use it both AS assist AND regen (most centrifugal clutches dont care one way or the other), but by overcoming engagement static friction with a brief, but powerful burst of regen braking you can force disengagement and go into 'fully freewheeling' mode.
You just need smart torque-controller like VESC and very simple MC like arduino to handle the logic.