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As opposed to electric regenerative brakes on eBikes or flywheel KERS (flywheel = lots of weight)

Why is a mechanical solution not feasible?

For example:

  1. Pull brake lever
  2. Clutch on rear wheel engages a wire that winds some spring or elastomer
  3. Release lever. Ratchet prevents unwinding, conserving the energy gathered.
  4. Pull some other lever to release the energy
  5. Wire transmits unwinding energy into gears that reverse rotation, so the wheel can move forward not backward

Would be useful for start-stop traffic during city commuting. Many cyclists are weary of losing the momentum they have put effort into building, which can result in more reckless riding behavior. If you can get a mechanical assist boost when you pick back up you've more incentive to stay behind a stopping vehicle instead of dangerously overtaking it.

To qualify, the mechanical solution would have to come in lighter than an eBike conversion with regenerative braking.

  • A quick google for "flywheel bicycle" throws up an awful lot of articles dated from around 2011 for a feller who'd come up with a prototype. I can't find anything more recent that follows up from that. It's an interesting idea, but a couple of articles have mentioned the first thing about that kind of solution which came to my mind - a whacking great big flywheel is going to have interesting gyroscopic effects why you try turning.. – Jerb Jul 20 '18 at 15:00
  • @Jerb Sorry forgot to exclude flywheels from the question. While they would be a mechanical energy recovery system, they rely on lots of weight to work. Bad for bicycles. – Leeroy Jul 20 '18 at 15:07
  • A spring that could store a decent amount of energy and release it in a controlled fashion would also be fairly heavy, especially once you take into account the need for it to not injure someone in a crash. I've seen a design using a compressor (and the frame as a cylinder for compressed air): heavy again. – Chris H Jul 20 '18 at 15:46
  • All it takes is a very large spring! – Daniel R Hicks Jul 20 '18 at 17:07
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    This was all examined starting maybe 40-50 years ago, when fuel prices began to be an issue for buses, and when it became camp to try to break MPG records for cars. The first few attempts used springs, then flywheels, then compressed air. But then batteries got cheap and light and most other technologies were abandoned. And these were vehicles where the added weight wasn't such a big deal, whereas with a bicycle weight is still a major concern. – Daniel R Hicks Jul 20 '18 at 18:57

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