Half a croissant, on a plate, with a sign in front of it saying '50c'
h a l f b a k e r y
You could have thought of that.

idea: add, search, annotate, link, view, overview, recent, by name, random

meta: news, help, about, links, report a problem

account: browse anonymously, or get an account and write.



Speed limiting, extended range bike

Go the distance - but slowly …
  [vote for,

Regenerative braking usually isn’t helpful on unfaired bicycles <EDIT: or supercapacitor, per bs0u0155 suggestion>, because if you’re going fast most of your work is pushing air out of the way - not enough left to make it worth trying to recover braking energy. When it comes time to slow down, the energy recoverable to go from 15MPH to 0 is much, much less than what it took to get you up to 15 originally.

This could be adjustable, but by way of example let’s set an arbitrary limit of 12 MPH. That’s enough to cover a 100 miles in an easy day and not so fast that aero is too big a deal. Have a speed limiter that could cap your speed to 12MPH (perhaps via a generator that imposes a load at the pedals or rear wheel), even if you were putting enough ergs on the pedals to go faster - instead of letting that go to the wheels, dump it into a battery. Similarly, if you were braking, or coasting downhill, recover all that energy. Then use it feed an assist motor when you need to start up from a stop, or slog up a hill, or in any circumstance where you’re putting a lot of ergs to the pedals and NOT even making 12 MPH.

I thought of this idea today while I was blasting down a hill at over 40 MPH after slogging UP the approach to it at around 6 MPH. Enjoyed the payback but lamented that it really didn’t balance because aero drag increases as a cube function of velocity.

a1, Jun 19 2021

https://stealthelec...r-an-electric-bike/ Example of a bike with regenerative braking [pocmloc, Jun 20 2021]

https://www.cycling...rge-when-you-pedal/ Explanations of why regen is a stupid idea [pocmloc, Jun 20 2021]

https://www.cycling...bikes-uk-law-234973 Explanation of the law [pocmloc, Jun 20 2021]

https://solar.lowte...biles-part-two.html Discussion of legal issues [pocmloc, Jun 20 2021]

bicycle with speed governor Shameless self promotion [xaviergisz, Jun 21 2021]


       I think there are lots of legal issues with electric bikes in general, mainly because they don't fit into established categories (pedestrian or motor-vehicle)   

       In the UK, electric assist is limited to 15.5mph.   

       Some machines do have regenerative braking, but not many - for general city use I think it is considered an unnecessary additional expense and complexity for very little gain.   

       Many manufacturers use powered bottom brackets rather than powered hubs (connected perhaps to legal issues to do with "pedal assist" being the only permitted form of motorisation) which obviously is not suited to regenerative braking at all.
pocmloc, Jun 20 2021

       [pocmloc], thanks for the links. I thumb my nose at legalisms but they cover some good tech points. I’ve also looked at the Stealth (covered in your first link) and dismissed it as a bad implementation. They need my speed limiting idea to automate how/when to capture braking & downhill energy - not relying on the rider to push a button at specific times.
a1, Jun 20 2021

       //limited to 15.5mph//
There are electric scooters here (stand-on style) that will happily keep up with 50km/h traffic. Not sure about "normal" bicycles with electric assist (definitely more than 15mph though...).
neutrinos_shadow, Jun 20 2021

       Oh yes those things are here as well, there's a slight mismatch between what vehicles are popular and practical, and what vehicles are permitted under road and vehicle legislation. But I'm sure in about 100 years time the laws will have been updated...
pocmloc, Jun 21 2021

       //Some machines do have regenerative braking,//   

       There is a little complexity, but not much. It's all in the electronic speed control and is available for not too much money, Benjamin Vedder's VESC for example. The problem occurs with the battery. Lithium cells of all chemistries are picky about charging. I have some cells of 5500mAh that are rated for 100c, that is 550A continuous draw, amazing really, but they are only rated for a 1c charge rate. So there is always a limit to how fast you can put energy back. Supercapacitors would help here.
bs0u0155, Jun 21 2021

       // supercapacitor //   

       Thanks, edited writeup to include that possibility.
a1, Jun 21 2021


back: main index

business  computer  culture  fashion  food  halfbakery  home  other  product  public  science  sport  vehicle