Bezalel

Another thread on this forum regarding electric hubs got me thinking. Would it be feasible to create a hub with regenerative braking? I'm thinking something to replace drum brakes that automatically activates when the wheel approaches a user defined top speed or when the primary brake is engaged.

ironhanglider

You mean like this?

https://www.youtube.com/watch?v=gbCshB3eSCc

Need to work out how to include really wide gear ratios for tandem use, but it doesn't seem like it is far away.

Cheers,

Cameron

Bezalel

My goal is for braking, I don't care about electric assist. I'd provide some power to the user if they choose to charge a battery pack, the rest of the energy I'd waste as heat but away from the wheel.

Chris_W

What's wrong with controlling a drum brake manually?

Abram

The simplest system would use a permanent magnet rotor, but I'm not sure it would generate enough power to be useful in a reasonable size. Consider that generator hubs only generate <10W, and you probably want 100W+. Add a field winding with brushes and you can make more power but with more complexity.

Probably much more reliable to accomplish the same effect with a regular mechanical brake (drum or disk).

StephenH

I've just always heard the term "regenerative braking" used with the assumption that the power would be stored or transferred into overhead catenaries for use in getting up the hill.

The issue with your plan is you need a generator good for several hundred watts (basically, what two strong riders can do uphill, you need the brake to do downhill), which makes it big and heavy. If you get rid of that power as heat, you're going to have a toaster element or something similar sticking off the back of your bike somewhere.

My idea is a fan enclosed in a tube with roller that rolls on the tire when engaged, with the tube acting as a brake drum and the fan part blowing enough air through to keep the brake cool, and also using a lot of that energy for blowing the air. But I think the market would be too small for it.

Leisesturm

What you have described is an electronic drag brake. You would 'waste' any energy recovered by the system since you don't intend to use the "electrical assist" function of the hub motor. Why bother then? Conventional brake technologiies are way better at 'wasting' excess delta vee as heat than any hub motor/electronic controller combination existing. Our 2005 Raleigh Coupe has dual Avid BB7's with 160mm rotors. We've been riding it till the present time without any other kind of supplemental drag braking. 180mm or 203mm rotors have even more capacity to absorb heat and I simply cannot imagine a scenario where dual 203mm rotors would not be sufficient. Not even loaded touring.

H

nfmisso

If you go to the heaviest of land based transport systems (freight railroads), you will find "Dynamic Brakes"; which use the traction motors as generators dumping electrical power into resistor grids (toaster wires), generating MegaWatts of heat and drag. Why do railroads use this technology - overall it is cheaper than totally relying on friction brakes.

There are other ways to electro-magnetically create drag than motors/generators. Take a look at the North American Eagle land speed record car - its high speed brakes work just like the magnetic damper on a postal scale - drag is proportional to velocity.

prathmann

Sure, but that's because of the magnitude of the energy they need to disperse - spreading out the heat to a large area with a resister grid is an efficient way to do that.

But, as already mentioned by Leisesturm, there are reasonable mechanical methods available that do an adequate job handling the heat generated by bicycle (either single or tandem) brakes and these have the advantage of being simpler (more reliable), lighter, and less expensive than an electrical regenerative system.

StephenH

On a typical diesel-electric locomotive, they already have the traction motors there for power anyway, plus they aren't concerned about weight- I understand they have to add weight in the frame to get the traction they need- so altogether totally different from bicycle needs.

Team Fab

I have mentioned before on other threads. Magnetic brakes. Like the expensive spin bikes. Place a magnet beside a spinning aluminum disk. The closer you put the magnet the more force applied to stop.

Leisesturm

Aluminum you say. Really? Hmmmm. You don't by any chance have a dual career in Stem Cell research do you?

rahill

Yes, aluminum - or something else non-ferromagnetic (e.g., copper).

Eddy current brake - Wikipedia, the free encyclopedia

SJX426 

The article describes controling circular eddy current brakes with electro-magnets. Where does the energy come from to control the electro-magnets? You can't be referring to linear eddy current brakes because they are useless at low speeds.

rahill

Except for the bit that refers to: "Adjustable permanent magnet eddy current brake"

In any case, I wasn't suggesting it was or wasn't practical, just that the mention of aluminum in Team Fab's posting was not a mistake.

Perhaps it's time to dissect a magnetic resistance bike trainer and check out the internals...

Team Fab

I do not think it needs to be an electro magnet just a magnet(maybe one of those new rare earth magnets).

Easy to test. Get aluminum disk, spin it, bring magnet close, if disk slows faster with magnet than without it works.

this could be a job for chojn1

would be a great replacement for drum brakes if it works

I was thinking maybe aluminum rim may substitute for a disk, or just one of the Stan's Aluminum rotors

qspencer

I remember a demonstration of this concept in an undergraduate electrical engineering class. The class demonstration featured two aluminum pendulums. One of them had a solid flat sheet of aluminum at the bottom, and the second was in the same shape but with slots going through it, making them look more or less like solid and slotted spatulas that have been flattened. When a strong magnetic field is applied (permanent magnets in this case), a strong braking force on the solid pendulum results, while minimal braking force results on the slotted pendulum. The idea is that the movement of the conducting metal through the magnetic field induces an internal electric current (the "eddy" current), which essentially converts the kinetic energy of the pendulum to heat. The continuous sheet of aluminum experiences much stronger braking force because the internal electric currents are unrestricted, while the slots in the other sheet of metal limit the eddy current and therefore reduce the braking force.

To use this concept on a bicycle, magnetic rim brakes may not be feasible because I don't know if the magnets would be close enough together to get a strong enough magnetic field, and I don't know if spoke holes are likely to cause problems by breaking up the eddy currents. Magnetic disk brakes seem more plausible, but there may still be challenges posed by putting strong magnets right next to the spokes, and you definitely need a solid aluminum disk, so existing brake discs wouldn't work.