# Regenerative braking mode exist?



## Francis Cebedo (Aug 1, 1996)

When I had Trek ebike 8 years ago with a Bionx motor, it had regenerative braking. Basically, it would recharge the battery if used the hub motor to slow down on a big downhill.

Does this exist today on any system? Or is the concept dead?

How much power can we gain back by recharging the battery by braking?

It seems like most electric cars have this to optimize range. Too complex and heavy and for cars only or is it part of the ebike future? I saw a crazy version at Sea Otter this year.


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## Mudguard (Apr 14, 2009)

I don't have a foot in the e-bike camp, but if a wheel dynamo for a light was anything to go by, I imagine the drag would be pretty bad?
NB I was contemplating the shuttle truck we used on the weekend (old V8 Land Rover) and was wondering how efficient a fully electric version would be, I mean it went straight up, and straight back down, it wouldn't need to brake (conventionally) the whole way down.


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## Francis Cebedo (Aug 1, 1996)

Mudguard said:


> I don't have a foot in the e-bike camp, but if a wheel dynamo for a light was anything to go by, I imagine the drag would be pretty bad?
> NB I was contemplating the shuttle truck we used on the weekend (old V8 Land Rover) and was wondering how efficient a fully electric version would be, I mean it went straight up, and straight back down, it wouldn't need to brake (conventionally) the whole way down.


Yup. it's all about the drag. It is what is used to stop the rider/bike. It has to be so variable though that it can be modulated.


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## Jake January (Sep 12, 2014)

Yep, I had the same question while drooling on the new Surly Big Easy with the Bosch Performance CX center drive.
All the write ups do not mention regen brake effect.


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## Joules (Oct 12, 2005)

I'm not really in the ebike scene, but I do have a bit of e-car experience. Rule of thumb is 20% improved range, but that can vary a lot with braking patterns. 

Actually, as I think through this even if you were to accept a hub motor (or that ridiculous sea otter contraption) and design a compatible brake lever, I don't see regen working on bikes. Here's why: front wheel drive doesn't exist on bikes. So even if 100% of your rear braking were regen (and it wouldn't be), that would amount to almost nothing since almost all the braking energy goes to the front. So unless you limited your riding to situations where you didn't use the front brake, I don't see it. And in those situations, how much are you braking really?


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## Joules (Oct 12, 2005)

craigsj said:


> There are no variable regeneration brake levers available. The hardest is part of doing regen is what mounts on the handlebar.


Nothing like that exists currently, but it would be trivially easy to design. Just do something like the old Magura BAT levers, where the lever has free stroke before the master cylinder starts moving; put a pot on the lever pivot, and feed that to the motor controller, so you have an electric brake stage, then the friction brake takes over. That's how the brake pedal in electric and hybrid cars work.

Bigger problem is, unless your motor is on the front wheel, there's not much energy to be had.


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## Francis Cebedo (Aug 1, 1996)

Joules said:


> Nothing like that exists currently, but it would be trivially easy to design. Just do something like the old Magura BAT levers, where the lever has free stroke before the master cylinder starts moving; put a pot on the lever pivot, and feed that to the motor controller, so you have an electric brake stage, then the friction brake takes over. That's how the brake pedal in electric and hybrid cars work.
> 
> Bigger problem is, unless your motor is on the front wheel, there's not much energy to be had.


"trivially easy". I smile. Now to get that to ride well on a trail is a whole nother level.

Good point on the front wheel. That's where most of the braking energy is.


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## hikerdave (Mar 8, 2006)

Joules said:


> I'm not really in the ebike scene, but I do have a bit of e-car experience. Rule of thumb is 20% improved range, but that can vary a lot with braking patterns.
> 
> Actually, as I think through this even if you were to accept a hub motor (or that ridiculous sea otter contraption) and design a compatible brake lever, I don't see regen working on bikes. Here's why: front wheel drive doesn't exist on bikes. So even if 100% of your rear braking were regen (and it wouldn't be), that would amount to almost nothing since almost all the braking energy goes to the front. So unless you limited your riding to situations where you didn't use the front brake, I don't see it. And in those situations, how much are you braking really?


Joules knows joules. That makes sense.


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## Bigwheel (Jan 12, 2004)

Actually front wheel drive does exist on bikes. Direct Drive hub motors have been used for years to just that effect. Direct drive motors, such as the BionX which only came in rear drive, can be configured to apply regen mode by a switch that basically reverses the flow of energy.

I have a few drop bar bikes set up with front DD motors and find the regen very effective as an aid to front braking. It does not come on super strong and at the most will show -350w on my display. I use it when coming to a stop and as a drag brake on hills mainly. To that effect it does save on brake pads. The amount of energy return is fairly minimal but can extend range a few miles depending. But if it is there to use why not use it.

Just to the right of my left, front brake, brifter I have a momentary switch, the red button, that I can push that activates the regen plus I can also apply the lever at the same time.









Cars get much more benefit out of regen because they weigh much more and the motors have more copper and magnets to release the energy.

Any geared type system, including geared hub motors, are not capable of regen unless as that bike from Sea Otter demonstrates is willing to frankenstein. As far as mtb use goes it will never really be a functional option but for road bikes it can be.


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## Francis Cebedo (Aug 1, 1996)

Good points everyone. 

Since mid-drive motors dominate mountain biking, the fundamental problem is the motor does not spin when one is coasting and braking.

I think a solution in the future will be to have a dynamo in the rear and the front hubs to brake and produce energy to recharge the battery.


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## Francis Cebedo (Aug 1, 1996)

found the sea otter regen.


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## Joules (Oct 12, 2005)

Bigwheel said:


> Actually front wheel drive does exist on bikes. Direct Drive hub motors have been used for years to just that effect. Direct drive motors, such as the BionX which only came in rear drive, can be configured to apply regen mode by a switch that basically reverses the flow of energy.


That is pretty cool! What is the watage of that motor?
I would bet if you could come up with a... "anti-throttle" rather than an on/off control, you could probably get a lot more out of it. Of course having software control your front brake could be a little nerve wracking... I've had some scary moments in cars, and it was with software I wrote.


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## Bigwheel (Jan 12, 2004)

Joules said:


> That is pretty cool! What is the watage of that motor?
> I would bet if you could come up with a... "anti-throttle" rather than an on/off control, you could probably get a lot more out of it. Of course having software control your front brake could be a little nerve wracking... I've had some scary moments in cars, and it was with software I wrote.


To better understand what is going on I would suggest you take a look at this: https://www.ebikes.ca/product-info/cycle-analyst-3.html

The CA has been around for a long time and is the most comprehensive display available in regards to functions that control the parameters of e motor systems. So while the button provides an on/off function through the CA it is regulated.

As far as what wattage my motors are that is a product of the 52v batteries I use and the amount of Amps I set for the controller. I use 20A as a limit so a little over 1000w peak capable which in OR where I live is legal. However via the CA I can set voltage limits in increments that another button control allows me to adjust and I have that set to 250w/500w/750w/1000w. I ride to maximize range value so I mostly stay in the 250w/500w modes but if I am on a short ride and feeling like more speed I will up it to 750w but rarely if ever go to 1000w.

Why I use a 52v battery is to maximize the wh capacity onboard. The 52v 15ah 14s3p Samsung 50E 21700 cell battery I use is 780wh's. If I ran a 15ah 48v battery I would lose 60wh's which as my usual average of 15wh/mi is 4 miles. Not much but enough to make it worthwhile.

And Francis adding the weight of a dynamo, especially with your obvious concern about it and how it affects bike handling, to the hubs in order to get minimal braking and range benefits probably won't be happening anytime soon.


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