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Monday, August 24, 2009

Regen vs Freewheeling

Now that I am adding a freewheel to the pedal cranks, I'm seriously considering disabling the freewheel in the rear wheel cassette, so that I can get regen on the motor, and use the motor itself to help brake the bike, as well as recover a small amount of power.

I would probably also want to put a kind of clutch into the motor drivetrain, so that I could still coast on flats or down slight grades without running the motor but also without triggering regen braking. It'd be of a type that is electrically controlled, and on all the time except when I trigger the "cruise" mode to free it up.

I considered the clutch from the air conditioner compressor in the parts Ford LTD, but that operates the opposite way I want it to--only engaged when power is applied. Maybe I can reverse that, but I'd have to take it apart first to see how it works as-is.

Disabling the freewheel shouldn't be that hard, but I don't want to do it in a permanent way if I can avoid it; most likely I will have to simply sacrifice the freewheel permanently to the experiment, and weld it together.

I have a number of them around, but only the one on the bike has 7 chainrings on it (except for the free*hub* that's on the DayGlo Avenger) , and I don't think they'll fit on any of the others that have 5 or 6. So for the experiment I would have to use one of the 6-ring units, and simply not have all the available gears I've got now. Not too big a deal with the motor on there, but having more gear ratio choices is certainly helpful for pedalling should I need to do solely that at some point.


  1. Hi Mike. I was thinking along the same lines for that old JCPenny that already has the non-freewheel rear cassette on it. I originally thought that I would want a freewheel type on the rear wheel. Regen is something to consider if there are a lot of hills around, I think.

  2. If you want regen I don't think you're going to be able to use multiple gears... Regen would be putting tension on the lower half of the chain, and might break the derailleur. Could set it up as a fixie though.

    I've been disappointed with the regen numbers on a bike though. Of the energy put into forward motion, so much of it is dissipated by wind resistance, the amount you can reclaim on the downhills is miniscule in comparison. In a heavier, more aerodynamic vehicle it makes more sense because it takes so much more energy just to get the vehicle up the hill, it's definitely worth collecting it again on the way back down the hill. You might get 5% efficiency increase or more, instead of a fraction of one percent.

    I wouldn't bother with regen on a bike.

  3. I am looking at the regen much more for it's braking ability than I am for it's recapture of energy. I seriously need better braking for this heavy a vehicle, especially on downhill slopes (even low-grade slopes can be much harder to stop quickly on because of the extra weight, which is something on the order of FOUR TIMES the weight of even a heavy bike, and so what a typical bike rim brake is expected to stop (not including rider for either specs or reality)).

    The energy return is just a bonus, if I get any back. As long as it doesn't *cost* more energy, I'm happy. :)

    I am aware of the problem with the derailer/chain and am pondering solutions.

    The easiest solution is an internally geared hub, even if I don't use it in the wheel itself but rather built into the drivetrain somewhere else (to make it easier to fix bad flats on the road, as I could just swap wheels instead of having to fix the tire on the wheel).

    Unfortunately that solution is too expensive, and I have not run into any used ones with at least 7 ratios (preferably 8, 9, or more) equivalent to my existing cassette that I could afford any more than the new ones. I'd have to get lucky and come across a scrapped bike or bike wheel that has one still in it, which is a pretty unlikely thing to happen. I might as well wish for a wallet full of $100 bills to turn up on the roadside with no ID or way to get it back to it's owner. ;-)

    I am looking into designs of belt-based CVTs, which I could use instead, but haven't yet got a design that could be made with parts I already have *and* would fit on the bike and be light enough (under 5 pounds, if possible).

  4. DOH! I've been doing some more research on regen. Someone posted some believable data which indicated they were getting a 10% efficiency boost using regen in a hilly environment. So it looks like I've been spreading misinformation. Sorry! Mea culpa.

  5. Not necessarily--it depends on how the regen works in a particular controller and motor combination, the vehicle, it's aerodynamics if running it at higher speeds, and how much it's used at higher speeds vs stop/start riding/driving.

    The more it's used at long high speed stretches, especially if like most bikes highly unaero, the less efficient regen will be (total percentagewise) because so much power is permanently lost trying to push against air to keep the vehicle at speed.

    As an example of aeroness, when I ride sitting up, it fairly consistently takes around a tenth of an amp MORE than when I'm sitting back in the seat (leaning back more at an angle) to keep me at the same fairly low speed of ~15MPH. That's in an otherwise windless condition. With headwinds, it's worse.


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