veganbikes

E-bikes DO NOT have regenerative braking, it is a gimmick they try to sell you on but it does not work and cannot work on something so light and weak in the brakes. Granted lifting an e-bike even the nicer ones and stopping some of the nicer ones will be light and quick but compared to a car it is nothing. If you want some extra power, I would suggest a nice hub Dynamo such as SON or Shutter Precision paired with a E-Werk from Busch and Muller if you want a battery storage solution. Brian Chapman from Chapman Cycles has built at least two Di2 bikes that use a hub dynamo to keep batteries topped up and I was initially going to do that and ending up steering in a different direction. You could also use the dynamo to power lights and charge USB devices Sinewave cycles, Cinq 5/The Plug and Busch and Muller make some great solutions for this from lights with charging built in to just top cap mounted chargers.

If you couldn't tell I love dynamos and wish I had gone for one much sooner. I had looked at them when I first started at a shop and was going back and forth and eventually decided not too but then as I was building up my Single Speed/Fixed Gear RandoCross Fun Time Machine and knew I had a sort of rando vibe going on I said I have to go dynamo and I am so glad I did.

Reynolds 

A flywheel would be very heavy. Since the motor is your body, maybe using the braking energy to synthetise glucose?

Mista Sparkle

This might be on to something, put a dynamo on on an E-bike, use the dynamo to charge the batteries! A perpetual motion machine!

veganbikes

I actually had thought about doing that on my Redux but mainly for lights and usb charger but glad I am going with wired in lights. I don't think the dynamo would generate enough to charge the e-bike enough to do that but it would be fun to try.

RGMN

Having worked on several HHVs this would be wildly impractical for a bike. The HP accumulator likely would weigh more than most people's bikes. And 3000 psi components can only be made so light, heavier than one would want on a bicycle. Hybrid technology works most efficiently when there is a lot of stop-and-go, like a delivery vehicle, mail carrier vehicle, or refuse collection vehicle. Over steady-state speed conditions (driving down the highway or riding on a long flat section) hybrid hardware is just additional weight that needs to be carried around.

UniChris

This is meaningless nonsense.

Regenerative braking utilizes the motor, not the conventional brakes, so your argument that something "light and weak in the brakes" cannot have it is meaningless.

There are in fact hub-motor personal transports lighter than e-bikes that have regenerative braking as their *only* means of braking.

If a given e-bike does or does not have regenerative braking is a legitimate question. But if the motor is bidirectionally coupled to the wheel (for example, a hub motor rather than something driving a freewheel through a chain), then it is fully possible for it to. And there is essentially no increase in weight to provide it.

The biggest issue would be the control to actuate it - if that would be distinct, or some sort of dead zone on a conventional brake lever where regeneration is electronically active but backup mechanical braking has not yet started, or if the front wheel has conventional braking but the rear only regeneration.

woodcraft

My idea was to use the frame- already a pretty good pressure vessel,

to store compressed air during braking that could later be released to help power the bike.

prathmann

Don't think I'd feel very comfortable on a mountain descent to know that my frame is being stressed more and more as the internal pressure builds up at every turn. I suggest you make a rough estimate of the pressure that would be required to hold a significant amount of energy that would help on the following climb. I note that I can pump up my tires to 100+ psi with fairly easy arm power in a couple minutes vs. the hour or more of continuous leg power that I use on a substantial climb.

Road Fan

The braking electronics needs to handle the kinetic energy of the bike/rider/cargo combination, in as brief a time as possible for an emergency stop - very high power. The kinetic energy at 10 m/s is about 14 kJ. To brake that in 10 seconds, requires the motor to convert motion to current at 14,000 joules in 10 seconds, or 1400 watts. The electronics needs to process that power and deliver it to the battery, which is now the energy sink. The wheel motor has to generate that much electricity and the electronics must transfer it to the battery, without roasting the braking electronics. But to accelerate up to that speed without pedal operation should take maybe 30 seconds, so the energy transfer is only 460 watts. I can't say the electronics box will weigh three times what the non-braking one does, but the battery also has to be rated to charge up 1400 watts in 10 seconds many times in its lifetime.

The electronics will also be more complex to control the power in two directions, braking energy transfer and propulsion energy transfer.

This is completely do-able and is within the laws of physics, but I don't know if it's practical and advantageous compared to a pair of rim or disk brakes.

Road Fan

What kind of electric motors do e-bikes usually have?

MikeyMK

Yes, its pretty good once you're used to it and adapt to get the best out of it.

its taken me a while. For starters, it only works whilst pedalling (so i can push harder to generate more), i have a 2-stage back brake lever. So the technique is to touch the lever to kill the power and activate the regen. If i pull the lever beyond the first stage then the pads will grip the disc - something i only do when regen isn't slowing me enough.

If i stop pedalling, the computer lets go altogether and it just coasts like a normal bike.

So i have three levels of braking really - regen, regen plus back brake, or regen and both brakes. I only need one finger for each lever, so holding a pinkie on the rear lever has got comfortable, and so i regen all the time, as soon as i don't need assistance - as a result, i can cruise around for several hours on a charge.

Whilst i'm still honing my skills, fast riding can be a bit of a handful to harness well, but whatever the pace it's very involving and fun as a result.

MikeyMK

The small hubs typically house a couple of chordless drill motors in them, the inside of the drum being a big cog.

The large motors are actually a motor, with a big coil-wound wheel inside, and magnets all around the inside of the drum.

JonathanGennick 

So you're basically engaging the regenerative braking on purpose to recharge your battery from your pedaling efforts?

RGMN

Your analysis is accurate except you made an error in your assumption that you would use regen during an emergency braking event. The usual action for a regen system is to shutoff or disengage IMMEDIATELY when an abnormal braking event (much greater than normal deceleration, anti-lock triggered) is detected. The primary concern is to stop safely. Recovering energy is a much, much lower priority. BTW, your mixing of power, time, and energy makes your analysis a little hard to follow, although most are going to be confused by power and energy...


Adding the electronics to a motor controller to allow regen is pretty easy. It can be as simple as an additional FET, but the real challenge isn't trying to dump the energy in to the battery, it is knowing how much energy is currently in the battery, and then only dumping the enough energy to bring the battery to no more the 100% charge to prevent damaging the battery. State of Charge (SOC) monitoring is a big issue in electric vehicles, and most methods come down to some version of coulomb counting. Over-sizing the battery to handle peak regen currents is very expensive, limiting the current in the controller is easier and safer.

clengman

Nothing new under the sun...

https://www.wired.com/2011/08/regene...wered-bicycle/

I note that there's no clutch to engage/disengage the flywheel so when starting from a complete stop, you need to spin that sucker up. I guess once you're moving it wouldn't be that bad. It would take a while for me to get the hang of managing the CVT to get best use from the flywheel.

Elvo

https://www.stromerbike.com/en_US/e-bikes/st1.html

MikeyMK

It pays to make the best of it, as with anything, yes. You don't have to push it down a hill but why not..? I cycle for exercise amongst other ressons - means it helps me up more hills in return. Of course, you dont have to, it's easy to be lazy with an e-bike.., but being savvy with it, get good at it, and get more out of it as a result.. yeah it's worth having if you want that option.

Doug5150

The Bionx e-bike motors has/had a regenerative braking option that could be engaged. Bionx is out of business now however.... I don't know of any others that have it but I'm not really into e-bikes.

I asked once and users said that the regen option rarely added more than 5% to the run time. It was only useful if you were basically coasting down a mountain.