Regenerative Braking?

Let me elaborate a little bit @kahn.

Regenerative braking requires a motor/generator which is a Direct Drive hub motor. DD e-bike motors are very heavy, rare, and the regenerative braking control must be complicated because you would rather like to be coasting when not pedalling instead of be slowed down by the generator. I have only heard of only one well known brand that tells you they can do it, and that's Stromer. We might ask @jodi2 how the regenerative braking works in his Stromer. (What I hear is regenerative braking makes very little sense for e-bikes as the moving mass of the object here (bike + biker + cargo) is relatively small, bikes operate at relatively slow speed, and very little of the kinetic energy could be recovered, especially with the low efficiency of the generator).

No, no normal e-bike (including geared hub motors and mid-drives) has any regenerative braking capability. Your e-bike hubs are just hubs, and the motor doesn't work when you're not pedalling. All the kinetic energy of braking is converted into heat, and that can be checked by moving your hand close to the brake rotor after intensive downhill braking: its hot.
 
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yes, as @Stefan Mikes says, there is zero chance that any current specialized bike has regenerative braking. the motor, with it's magnets and windings, is not connected to any moving parts when you're braking.

that said - for many types of ebikes, i actually disagree with the notion that there isn't enough kinetic energy to matter. the available energy is proportional to the energy needed to accelerate the object, particularly when high speeds and high wind resistance aren't such a big factor. i have an e-scooter with dual direct drive motors in the wheels, and it's only slightly heavier than many ebikes, and it recovers a significant amount of energy through regenerative braking. the "single finger" driving is also very interesting, like driving an electric car using primarily your right foot and only braking in emergency.

the drag of this system is VERY noticeable when pushing with the throttle completely off - but one could even charge the battery in this way - the drag is translating to energy added to the battery.

if someone developed a relatively light (and certainly low power!) direct drive motor with a clutch assembly, and the rider was willing to use the electronic "brake" as much as possible including descending at very slow speeds with maximal braking, excellent range could be achieved. unfortunately that's no fun, it's much more fun to go super fast right up until you have to stop, and then stop faster than the battery/motor system could accept a charge. and of course, it's NO FUN going downhill at 10mph, converting all that gained energy from climbing a hill back into electrical potential in the battery.

in my experiments with the scooter. riding up a long continuous grade of 8-10% at 15mph and then DOWN it at 10mph recovers a sizable fraction of the spent energy. the exact amount is hard to say since the battery meter isn't all that precise, but it's at least a quarter. on the other hand, descend at full speed until the last block and then hit the brakes hard and you get virtually nothing back.
 
mschwett said:
if someone developed a relatively light (and certainly low power!) direct drive motor with a clutch assembly
Click to expand...
I'm afraid that is not doable.
Besides, did you know the most powerful of Stromer DD motors only developed 48 Nm @ 820 W while the most powerful Specialized mid-drive offered torque of 90 Nm @ 550 W?
I think all that regenerative braking certainly makes meaning in heavier vehicles such as cars but e-bikes?

Waiting for anyone with Stromer for their experiences! I would also like to know what the weight of the rear wheel of a Stromer is, and what total weight it is. (A neighbour here -- a disabled person -- rides a DD motor e-trike, and he told me his motor was 11 kg alone. And his batteries were 12 kg).
 
My 2014/2015 Turbo S has a regenerative mode using the hub motor. I think they dropped it in the last Turbo S models as it was of very limited value. I used it a couple of times when something happened in the charge cycle and I was trying to get home by using it on the downhills, conserving power on the flats and only using some power on the hills. The savings was very small and you had to switch to the regen mode for every possible downhill but it would save a few per cent or just enough so I didn't have to try and pedal it un-powered all the way home. Unlike a Creo or Vado SL there is substantial drag without the motor.
 
Stefan Mikes said:
Let me elaborate a little bit @kahn.

Regenerative braking requires a motor/generator which is a Direct Drive hub motor. DD e-bike motors are very heavy, rare, and the regenerative braking control must be complicated because you would rather like to be coasting when not pedalling instead of be slowed down by the generator. I have only heard of only one well known brand that tells you they can do it, and that's Stromer. We might ask @jodi2 how the regenerative braking works in his Stromer. (What I hear is regenerative braking makes very little sense for e-bikes as the moving mass of the object here (bike + biker + cargo) is relatively small, bikes operate at relatively slow speed, and very little of the kinetic energy could be recovered, especially with the low efficiency of the generator).

No, no normal e-bike (including geared hub motors and mid-drives) has any regenerative braking capability. Your e-bike hubs are just hubs, and the motor doesn't work when you're not pedalling. All the kinetic energy of braking is converted into heat, and that can be checked by moving your hand close to the brake rotor after intensive downhill braking: its hot.
Click to expand...
Pretty good summary!
mschwett notwithstanding, others have run the numbers, so to speak, and found little gain, for exactly the reasons stefan mikes points out - there isn't enough mass or speed with a bike and rider to make for much energy to be recovered, especially given the efficiencies of the system. The use cycle of a bike is different from a car, too. We tend to coast more, brake less. Overall ride distances are less too.

Many of us think of the high mileage reported by Prius car owners, but few realize that much of the mileage gain is due to the use of a Stirling cycle engine, not regen braking.
 
What brought this subject up was a friend who just returned from a six day trip on a bike path in Pennsylvania. I watched their slide show the other day. I gather he met some engineer along the way and they discussed, you guessed it, Regenerative Braking. I recalled, I think, some Dutch motor/wheel where there was a large disc battery and it had regenerative braking, too. I went on a Google (well, Duck Duck) search and found that article. The mention in the article of so many Specialized models brought me to YOU FOLKS.
 
Stefan Mikes said:
I'm afraid that is not doable.
Besides, did you know the most powerful of Stromer DD motors only developed 48 Nm @ 820 W while the most powerful Specialized mid-drive offered torque of 90 Nm @ 550 W?
I think all that regenerative braking certainly makes meaning in heavier vehicles such as cars but e-bikes?

Waiting for anyone with Stromer for their experiences! I would also like to know what the weight of the rear wheel of a Stromer is, and what total weight it is. (A neighbour here -- a disabled person -- rides a DD motor e-trike, and he told me his motor was 11 kg alone. And his batteries were 12 kg).
Click to expand...
well, not doable at all / with current products technology isn’t the same as not ever doable! it’s not hard to imagine a direct drive motor with a tiny electronic clutch which disengages when both the motor and the brake are off. if either brake or motor are on, it’s engaged.

weight is certainly the biggest issue, given the lack of gearing for the motor, but 11kg is pretty absurd - the entire tire/wheel/motor assembly of a boosted rev scooter weighs less than 10lb; call it 4.5kg, and obviously less than that for the motor. this is a 750w motor that does regenerative braking. a pair of them have no problem propelling me up 15% grades at speed, and reaching a top speed of 25 without any leg input and about the worst aerodynamics you could imagine! clearly an 11kg motor is not required.

the much smaller wheel size may be part of why this works - direct drive is more feasible with the inherently different torque requirements of a small wheel.
 
On my DD hub motor bikes I get the most value out of regen, which I activate via a momentary button located on my left brake hood, as a drag brake that helps me keep speed under check on downhills and the first thing I do when wanting to slow down in any situation without actually using, and wearing the pads, on my brakes. I've found that they last much longer as a result. Any energy it puts back into the battery extending my range no matter how much is just gravy.
 
Guys that have used regen in hilly areas can tell you it's WAY more about the braking power offered than it will ever be about charging the battery. Noteworthy is the fact that this regen works by charging the battery. If the battery is fully charged, as in encountering a big down hill section as you leave the house, there can be all sorts of problems in the electonics, as the battery is going to refuse any further charge....
 
Stefan Mikes said:
Regenerative braking requires a motor/generator which is a Direct Drive hub motor. DD e-bike motors are very heavy, rare, and the regenerative braking control must be complicated because you would rather like to be coasting when not pedalling instead of be slowed down by the generator. I have only heard of only one well known brand that tells you they can do it, and that's Stromer. We might ask @jodi2 how the regenerative braking works in his Stromer. (What I hear is regenerative braking makes very little sense for e-bikes as the moving mass of the object here (bike + biker + cargo) is relatively small, bikes operate at relatively slow speed, and very little of the kinetic energy could be recovered, especially with the low efficiency of the generator).
Click to expand...
I agree to your last sentence in brackets. But as I wrote this this year somewhere in a forum (but I don't remember where...), let me ask, was it somewhere here and you now repeat my phrases or do you get this arguments from somewhere else? That we know how many independent "sources" we have... I'm not sure if It's clear what I want to say in my bad english. If not, never mind... ;-)

I'm not completely sure why there is no/never reg. braking in geared (middle) ebike motors and only in a few hub motors. But it needs a relatively big motor (for a bicycle) to produce some braking and charging power and also a big battery to stand the currents during regeneration which can be quite high. The rear wheel of my stromer St1x overall has about 8,5kg, so only the motor about 6kg. So the highest Stromer model motors 6,5-7kg I guess. Stromer batteries are usually 814 or 983 Wh and about 5kg. Total weight of a Stromer 28-30kg.
So for example a Specialized SL drive is definitely not suited for reg. braking. Also the small rear hub motors which have become common (at least in Europe) in city&trekking ebikes the last years never have reg. braking. No matter if it's a one for $1000 from the disounter or a $8000 high end ebike. When I was looking for the first time for assist drives, I was quite disappointed about this. Together with the really bad uphill capability of a small hub motor these assist drives aren't for sportive usage, more for cruising at 20km/h through the (flat) city. Geared middle motors are the choice for small assist drives for sportive bikes/usage.

More than a decade ago I lived near Darmstadt/Germany and had good contact to Riese&Müller, when they started with BionX (rear hub) ebikes. These bikes had similiar power like the actual Stromers and they already had reg. braking. And the motors died like mayflies exactly because of this. I guess this was one of the reasons for the fall of BionX and also Riese&Müller had great losses because of the unreliable BionX motors. I think this “BionX trauma” was the main reason for Riese&Müller to switch to Bosch and to stay so strictly to Bosch, now more than 10 years I think. I’m still waiting for the return of at least a few 45km/h models with hub motor and wrote two times to R&M, pointing out that it reliable rear hub motors are possible today, even with reg. braking. But never an answer, the trauma still seems to be big at R&M…

The main problem was afaik that the motor controller was inside the motor and overheated very easily. Also the first Stromers like (the old) ST1 had this problem and was far from the reliability of the later models starting with the ST2 (I think in 2014). But at least the ST1 motors did not die completely, just stopped motor support and needed a long time to cool down and recover or a short visit at the LBS.
With the ST2 the motor controller went outside the motor/e.g. in the frame and problems were gone. Actual Stromer models since ST2 have no problem with reg. braking or overheating, even if you ride the longest alpine passes up or down. If motor or battery overheats, power is reduced, but smoothly and it comes back soon and also smoothly. And it needs quite a lot of height meters, low speed/rpm and a hot day before this happens (due to the quite big motors).
Stromer also has combined the reg. braking nicely in the brake levers. Pulling them softly only activates the reg. braking, if you pull harder, the real brakes join. You can also activate the reg. braking via button in several levels, the higher ones quite strong. If the battery is full, simply almost nothing happens/no braking by the motor, but no damage to battery, controller or motor.

Ok, enough ads for Stromer... I know only one more ebike brand which is capable of reliable reg. braking, that is "Klever" which has similar ebikes like Stromer (not sure if they're sold in other countries or continents). There maybe a few more, but I'm not sure and if they work reliably.

But after all these fantastic details, the effect/the gained range on my Stromer is quite small. It’s difficult to measure, but I guess for me in my area (quite flat, but not like the Netherlands...) it’s maybe 2%. With some more hills maybe 4%. So it’s nice to have for me and it’s great to see that it works without any worries, but it’s not really necessary. It may be more for someone mostly cycling in a really really hilly area and of course it will be much more if you go only up and down mountains. But for average use it’s maybe 2-3% on a Stromer.

We also have a (fully) electric car since 2019 and even if it’s one of the lightest on the market (a BMW i3 with carbon frame) the effect is much much higher. In the same area where I gain maybe 2% of range with the Stromer, I gain about 10% with the car. In hilly areas it’s easily 15%, if it’s very hilly maybe 20%.

But I agree with mschwett, that the effect/the gained range in % should be similar on an ebike and I’m not sure why the difference to the car is so big...

btw, the necessity of motor and battery big enough for reg. braking is one (of several) fails of (most) hybrid electrical cars. The small motors can’t produce much reg. braking energy, but the small batteries already struggle with these currents. The high load during driving or reg. braking and the much higher number of full charging cycles (maybe 1-2 per day compared to 1-2 per week in a full electric car) kill the hybrid batteries about 10 times faster (in mileage). But as most hybrid cars here are with 2-3 years leasing (and a lot of grants), nobody cares... :-(
 
Bottom line, there is only a very very small gain as opposed to the benefits of mid-motor with so much better riding characteristics. If your experience is only with a Creo, Vado SL or even a Vado/Como you are really missing out on how much drag the older Turbo S have without power. Try tying a rope to a sheet of plywood and drag it behind your Creo with the power off. Maybe even have somebody stand on it.
 
If you'd like to study up on what CAN be done using regen, have a look at Grin Technologies GMAC geared rear hub. If you haven't seen anything on it yet, and have an interest in anything regen, you need to see this....

GMAC - Grin Kits - Product Info

The GMAC motor is Grin’s customization of the powerful rear MAC motor, modified to run without a clutch for regenerative braking, a huge plus for cargo hauling applications. A round axle and integrated torque arm allow for powerful regen without risk of axle spinout.
ebikes.ca ebikes.ca
 
AHicks said:
If you'd like to study up on what CAN be done using regen, have a look at Grin Technologies GMAC geared rear hub. If you haven't seen anything on it yet, and have an interest in anything regen, you need to see this....

GMAC - Grin Kits - Product Info

The GMAC motor is Grin’s customization of the powerful rear MAC motor, modified to run without a clutch for regenerative braking, a huge plus for cargo hauling applications. A round axle and integrated torque arm allow for powerful regen without risk of axle spinout.
ebikes.ca ebikes.ca
Click to expand...
Unlike the weird website posted in the OP's question, the ebikes.ca web page is a legitimate explanation of the system and why it has no application for a lightweight e-bike like a Creo. They do provide the numbers to show applications that work but not so much for the topic of this sub-forum.
 
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"the effect/the gained range in % should be similar on an ebike and I’m not sure why the difference to the car is so big..."

Bigger being the key factor......

"Vehicle size may be the largest factor in the effectiveness of regenerative braking for the simple reason that heavier vehicles have much more momentum and kinetic energy. Just like a big flywheel is more effective than a small flywheel, a four-wheel electric car has a lot more kinetic energy when in motion than an electric bicycle or scooter."

Quote taken from here:

electrek.co

Regenerative braking: how it works and is it worth it in small EVs?

Ever since the first Toyota Prius rolled off the line over 20 years ago, the concept of regenerative braking has...
electrek.co electrek.co
 
Hmm, you’re right. It’s no voodoo in the reg. braking system of electric cars or something bad reg. braking systems in ebikes. It’s just physics and maths. I played a little bit with a “bicycle power calculator” with weight and road gradient. A 2 ton system like an electric car already delivers reg. energy in soft downhill gradients, where a much lighter system like an ebike still needs energy to maintain the same speed. The small potential and kinetic energy in the lighter system is still small compared to rolling resistance and air drag. Also in higher downhill gradients where the ebike starts to recover energy, the percentage is quite low and several times with the electric car.
In my quite flat area here I wood have almost zero gain with my Stromer, but stopping at street crossing etc. delivers at least some reg. braking energy/some gained range.
Or vice versa, a (theroetical) very light electrical car with only 30kg would deliver the same small percentage of gained energy by reg. braking as an ebike…
The waste of energy (compared to an ebike) with an electric car due to weight is so big, that there is quite some energy to regenerate and the waste would be even bigger, not using this energy. Or vice versa, an ebike is such an efficient system (compared to electric cars), that it does not really benefit from reg. braking and doesn’t really need it. For a heavy cargo ebike this would be different, but I don’t know many models here with hub motor. One came out last year from Bullit with an Alber Z20 motor, so seems this is capable of reg. braking as well.

At the same (low) average speed already our small electric car needs about 10 times more energy just to carry me around than my Stromer ebike. If I use a lot of highways, about 20 times more (of course the Stromer would need here as wall much more energy if it could reach 100km/h or more...).
So even electric cars shouldn’t get any public grants, but ebikes! ;-)

p.s. very interesting article!
 
AHicks said:
Guys that have used regen in hilly areas can tell you it's WAY more about the braking power offered than it will ever be about charging the battery. Noteworthy is the fact that this regen works by charging the battery. If the battery is fully charged, as in encountering a big down hill section as you leave the house, there can be all sorts of problems in the electonics, as the battery is going to refuse any further charge....
Click to expand...
I love the regen feaure on the low cost Eahora bikes it saves the heck out the brakes on particular downgrades with a stop sign at the bottom and no sun shining( mid fall very chilly in the morn)
 
I’ve got about 550 miles on my Trek Verve+3 so far. We took them to Moab with us on vacation. I rode about 25 miles a couple days ago on a paved trail. It had a fairly steep climb and it was a back and forth trail. On the way down there was about a mile of long braking. The rest of the downhill part I was just coasting. So I’ve ridden 550 miles and 1 or 2 miles I would have used regenerative braking. I see why people say it just isn’t worth it.
 
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