GOBAO ECVT EMTB Mid-Drive Motor

[Astro66]

Once I rode an electric offroad motorbike with regen and was surprised how much range it was generating when riding down a fire road from about 1000m back to the valley.

This is the thing with an EMTB. If you use your legs mostly to accelerate, and only a little bit of assist, then regen for braking. You can capture quite a significant amount of energy, compared to what you are drawing from the battery.

 

[Astro66]

thanks - so the chain ring (ring gear?) would be driven via chain or belt from the rear wheel's inertia (whilst the pedals are disengaged) direct to the output gear - which in turn would force the motor to act as a dynamo
but at the same time the motor creates a braking force that is transmitted back to the rear wheel via the output gear via the belt.
I'm partly there... but maybe I need some diagrams

No, the output gear is where your chain connects. But effectively it is the same, just connected through a gear. Basically where the toy wheel is, is where your chainring goes.

Also. The wheel that says ICE, is where your pedal cranks connect.

Also. Those red planetary gears can spin freely on the ends of those shafts. So if your feet are stationary on the cranks, and the bike is coasting. Those red planetary gears will spin freely, driven by the ring gear, and not drive the pedals.

 

[emtbeast]

There are some limitations on regen can't be implemented in a way that the rear wheel via the chain and rear wheel inertia would enable regen. I think that this not a viable solution for regeneration on an emtb.

1. It would need a fixed rear hub, that adds problems for full suspension.

2. A fast spinning chain that now has tension on the underside not on the top as usually. That would mean slop on the top adding a serious possibility of chain derailment.

I think the only possible way of regen in an parallel ecvt mtb drive(what the versions of Gobao an Avinox due to the shape design most probably are) is only possible with active pedaling. The regen capability being different according to the riding situation.

 

[jeanjean]

Points 1 and 2 exist and are already solved on motorbikes, so it is likely that they can be solved on e-mtb as well.

 

[jeanjean]

Anyway I don't need regen.
I'm never living my house on e-mtb without the solar panels on my backpack

 

[Astro66]

Someone was suggesting a concentric pivot to alleviate suspension issues. Gets rid of the need for a tensioner, as there is no chain or belt growth and obviously, no derailleur. So the chainstay attaches around the output shaft\chainring, on the MGU.

 

[jeanjean]

US20200407016A1 - Power train - Google Patents

A power train for a pedal vehicle includes a main output chainring and a secondary output chainring coupled to the crankset shaft by a first freewheel. The crankset shaft is coupled to the main output chainring via a deformable transmission element and an epicyclic gear.

patents.google.com

See paragraphs 154 and 155

Even small things can cause regeneration...

 

[Ride 2d@y]

You can run a smaller battery. Drop some weight.

Also run lighter brakes too I would think

 

[Ndanger]

Adding regen to a e CVT , which is already complex and likely at a weight disadvantage would compound both challenges . Sadly, hub motors were born to regenerate, simply and at lower weight.

 

[jeanjean]

Adding regen to a e CVT , which is already complex and likely at a weight disadvantage would compound both challenges . Sadly, hub motors were born to regenerate, simply and at lower weight.

And since they are particularly suited for suspensionless bikes, you will save even more weight

Joke by side, wasn't recently a post with a link to the website of a guy having built an e-cvt hub motor with everything concentric?

 

[Ndanger]

And since they are particularly suited for suspensionless bikes, you will save even more weight

Joke by side, wasn't recently a post with a link to the website of a guy having built an e-cvt hub motor with everything concentric?

Haha, you get to have a choice, suspension and e CVT, or regen.

As if life wasn't a challenge, there you go, bringing up concentric.

 

[jeanjean]

Anyway, regen is by far not the raison why I want an e-cvt e-mtb...

From the technical structure, the Owuru is the one I like most.

From the software, I still have to wait until those drive units can be ridden in real condition.

 

[jeanjean]

Haha, you get to have a choice, suspension and e CVT, or regen.

On e-mtb, easy choice. Suspension and e-cvt.
Downhill the goal is anyway to brake as few as surviving allows...

I'm pretty sure Owuru will bring regen on the e-cvt city bikes in a close future.

 

[slickrock]

Regarding the "Dead battery" dilemma, on the OWURU drive unit, there is a freewheel between the pedal axle and the chainring to allow a direct transmission of power when the motor(s) are off.

Source: US20200198727A1 - Power train - Google Patents

The current E2 motor that's on the Decathlon city bike is not the same animal as the with the MG and X1P motors. Namely because the external drive gear is in series with the crank chainring, perhaps allowing a freewheel to be employed, which I'm not exactly sure is a good thing:

The E2 motor showcased last year (still not released) looks to be quite similar the newer motors:

Cant remember if I already added to this thread, but according to Gobao


"We stop giving power when the battery reaches 10%. The system then only shift. Without power the ratio goes to the lowest and you can theoretically pedal."

That's just to conservative to take out such a huge chunk of battery capacity and moreover doesn't adequately deal with further degraded mode issues, like actual battery failure. There's more than one way to address this and we need Gabao to state how various degraded modes will work

Yes you did (or maybe in another thread).
I've posted something similar about the city bike Owuru drive unit which is since 2023 on the market and lacking the freewheel.
I guess future Owuru drive units like the announced Owuru Ride for e-mtb and cargo bikes will have it.

Contrary to the Gobao solution, the purely mechanical solution provided by the freewheel still allows to pedal when the battery is fully drained. However without shifting.

And obviously it's still possible to combine the software and the mechanical solutions.

Can I add to this, that whilst pedalling with no power in an E-CVT, the pedals will drive the smaller motor, MG2. This will generate some power so that you could technically vary the gear ratio, by slowing MG2.

Whether the MGU manufacturer allows you to use power generated by MG2 to vary the gear ratio, when the battery is flat, will be in the software design.

Remember. When MG2 is stationary. The gear ratio is about in the middle.

How would the secondary motor remain stationary during battery failure (not just discharge)? There would need to be some kind of secondary motor lock up mechanism (i.e. some kind of solenoid that locks the motor when power is lost) to hold the counter torque to allow power transfer of pedal torque to either to the output drive or generator to recharge the battery, or both. If the battery is damaged, there would be counter torque from the generator, so more power is transferred to the output drive. I see this as worst-case degrade mode support (say, Level 3).

In a higher-level degrade mode (say, Level 2), In a complete discharge scenario (but functional battery), After enough power in the battery is replenished through regen, the solenoid could activate, opening up the secondary motor for gear shifting as needed divert more pedal power to the output drive . This could be electronically regulated until you get safely home (would be a slog).

In the highest degraded mode (say, Level 1), basically a lower-battery mode, divert all pedal power to the output drive until such time that battery levels drop to level that requires rider input to divert torque to the generator (back to Level2)

 

[jeanjean]

The current E2 motor that's on the Decathlon city bike is not the same animal as the with the MG and X1P motors. Namely because the external drive gear is in series with the crank chainring, perhaps allowing a freewheel to be employed, which I'm not exactly sure is a good thing.

Look to the Owuru and Gobao patent applications.
Freewheel everywhere, also with concentric pedal axle/ chainring combo.

 

[jeanjean]

Freewheel 71

Source: US20200198727A1 - Power train - Google Patents

 

[slickrock]

...
I see regen as a net positive. We get some additional charging. Speed is controlled on descents (grandma could set it to come on as low as 20 kph). No freehub in the rear wheel will allow for reverse gear for cargo bikes. No tensioner. But the bike won't coast as well.

There would be no motor counter torque, so it's still coasting, but added loss from fixed rear wheel constantly spinning the belt/chain for a mid-drive setup like the X1P.

Why would anyone want that on a performance emtb? I don't get it. I don't want a motor to control my braking. All I want my motor to do is give me assistance.

Mentioned this before, but I an incredible experience with regen braking and ABS on the TM-B. It was far more better than expected. Note also, that regen doesn't have to be integrated with the brakes. I would be OK if regen kicks in once you get to certain set speed, so it doesn't kick in during corning or being forced to pedal over technical sections (where you are at slower speeds and don't want to forced to pedal). Maybe a handlebar button control that allows you to lower the regen threshold when coasting back to home or to the car.

There are some limitations on regen can't be implemented in a way that the rear wheel via the chain and rear wheel inertia would enable regen. I think that this not a viable solution for regeneration on an emtb.

1. It would need a fixed rear hub, that adds problems for full suspension.

2. A fast spinning chain that now has tension on the underside not on the top as usually. That would mean slop on the top adding a serious possibility of chain derailment.

I think the only possible way of regen in an parallel ecvt mtb drive(what the versions of Gobao an Avinox due to the shape design most probably are) is only possible with active pedaling. The regen capability being different according to the riding situation.

Yes, you have to work the bike design to allow battery regen in the first place, as discussed in the battery regen thread. There can't be chain slop for regen to work - belts and chains must be taut, no spring tensioner, and concentric wheel path (i.e. single pivot).

Someone was suggesting a concentric pivot to alleviate suspension issues. Gets rid of the need for a tensioner, as there is no chain or belt growth and obviously, no derailleur. So the chainstay attaches around the output shaft\chainring, on the MGU.

View attachment 188332

Yep, this bike would be an example, though there's no need for a rear hub motor. Also here, the output drive elevated above the pedal axle, giving you high-pivot concentric wheel path, which provides needed anti-squat. Unfortunately this is not how the X1P is designed (and for that matter the Avinox MG motor as well) as pedal axle and output drive via chainring is coaxial. Would need a second chain loop linking chainring to an HP idler and then another chain loop linking the idler to the hub.

Haha, you get to have a choice, suspension and e CVT, or regen.

As if life wasn't a challenge, there you go, bringing up concentric.

No choice, pal. Single pivot or faux-bar suspension is the only way to get mid-drive battery regen from MGU/ECVT.

 

[ArmyOfEvilRobots]

And since they are particularly suited for suspensionless bikes, you will save even more weight

Joke by side, wasn't recently a post with a link to the website of a guy having built an e-cvt hub motor with everything concentric?

You're probably thinking of Cedric's post here: eCVT e-bike hub motor

That's definitely a prototype though; he's not proposing that layout for a suspension MTB.

 

[mustclime]

Lack of ground clearance is a big issue with this motor, look how high up the cranks are on this motor.

 

[jeanjean]

Lack of ground clearance is a big issue with this motor, look how high up the cranks are on this motor.

...lower center of gravity...

 

[Suns_PSD]

How come no performance motorsports used eCVT? Not MotoGP, not MX racing, not auto racing in any form, etc.

I still suspect that this product and others like it are going to be most appropriate for cargo bikes and the like, but I hope I'm wrong.

 

[jeanjean]

Test it!

I did

 

[DylanJM]

How come no performance motorsports used eCVT? Not MotoGP, not MX racing, not auto racing in any form, etc.

I still suspect that this product and others like it are going to be most appropriate for cargo bikes and the like, but I hope I'm wrong.

What does it matter? Emtbs are completely different from motorbikes and cars. Just because eCVTs may not be the most useful thing for those applications doesn't mean it's it can't be a useful thing on an emtb.

 

[Suns_PSD]

What does it matter? Emtbs are completely different from motorbikes and cars. Just because eCVTs may not be the most useful thing for those applications doesn't mean it's it can't be a useful thing on an emtb.

Certainly, people operate them differently, just like road cars are treated differently than race cars. But for many, they are high-performance machines.

So, I do think power transfer, efficiency, etc. matters. We'll see. exciting times for sure.

 

[slickrock]

How come no performance motorsports used eCVT? Not MotoGP, not MX racing, not auto racing in any form, etc.

I still suspect that this product and others like it are going to be most appropriate for cargo bikes and the like, but I hope I'm wrong.

Wells there's the whole F1-CVT ban thing, but the glib answer is that you don't provide pedal power on these motorsports, nor are there hybrids in the bunch. As soon as you need multiple power sources to drive power delivery in an optimized way (you get to chose efficiency or power curves, power reclamation, etc. ), then ECVT starts to make more sense. Hybrid drives are usually biased to efficiency and high-mileage, but there's no reason to not have a greedy design tune if you want. You just need a sensors and control system that responds every millisecond or so to get a true instantaneous feel. First gen systems will probably more like 20-25 msec, but over time this will draw down.

 

[Suns_PSD]

Wells there's the whole F1-CVT ban thing, but the glib answer is that you don't provide pedal power on these motorsports, nor are there hybrids in the bunch. As soon as you need multiple power sources to drive power delivery in an optimized way (you get to chose efficiency or power curves, power reclamation, etc. ), then ECVT starts to make more sense. Hybrid drives are usually biased to efficiency and high-mileage, but there's no reason to not have a greedy design tune if you want. You just need a sensors and control system that responds every millisecond or so to get a true instantaneous feel. First gen systems will probably more like 20-25 msec, but over time this will draw down.

That's good legitimate reasoning. Thanks!

 

[Ndanger]

How come no performance motorsports used eCVT?

In one word... Weight - which lends credence to your prediction that it is ideal for cargo applications.

Speaking of performance, how is this for starters : 180 hp shoe-horned into a 430 pound vehicle and uses a pully / belt CVT as an example although it is not a great comparison, referring to Snow Machines like the Polaris Pro 9r.

A highly optimized, clean-sheet engineering target for a 180 hp eCVT system would be 85 to 120 pounds.

Compared to the 20-pound mechanical system it replaces, an eCVT adds a net penalty of 65 to 100 pounds to the sled,. In a 430 pound deep-powder sled, adding 85+ pounds to the chassis would completely alter its handling dynamics, dropping the power to weight ratio significantly and making it uncompetitive for extreme mountain riding despite the benefits of perfect, electronic ratio control and instant torque manipulation.

 

[DylanJM]

The total system weights of what Avinox and Gobao have shown are only marginally heavier than current middrive motors + standard drivetrain so the weight argument doesn't really apply to emtbs.

 

[Ndanger]

The total system weights of what Avinox and Gobao have shown are only marginally heavier than current middrive motors + standard drivetrain so the weight argument doesn't really apply to emtbs.

Good call, that appears to be the case with eCVT emtb…

When looking at the new eCVT designs and all those extra internal gears and components, I was in the mindset that there had to be a weight cost. So after running the numbers, I may have to eat some crow. Gasp.

Here's what I'm seeing for comparison, keeping in mind no cassette or derailleur needed:

Gobao eCVT: 3.85 kg for the motor-gearbox unit
Avinox M2S + SRAM GX Transmission (cassette, derailleur, shifter): ~3.5 kg

Net difference: roughly plus 345 g for the Gobao. But it's basically a wash, Gobao's 900 Wh battery comes in at 3.7 kg, which is actually lighter than Avinox's 800 Wh battery at 3.74 kg.

Gobao vs. Pinion MGU

Gobao's also lighter than the Pinion E1.12 MGU (4.14 kg), though Pinion does offer a wider 600% range vs. Gobao's 500%.

Avinox MG Concept

Avinox is cooking up their own eCVT prototype too, but no detailed weight specs yet. Their current M2S motor is 2.59–2.63 kg, and once you add a traditional cassette/derailleur you're at 3.5 kg.

What you get for that small weight penalty:
No derailleur to destroy in crashes
No cassette or chain , Gates Carbon belt drive, lasts 3x longer than a chain
Reduced unsprung mass at the rear wheel (better suspension feel)
Virtually maintenance-free
No shift interruptions under load, just seamless power delivery

So yeah, the small weight penalty is more than traded off for durability, less maintenance, and smoother power delivery. Color me surprised.

 

[slickrock]

Good call, that appears to be the case with eCVT emtb…

When looking at the new eCVT designs and all those extra internal gears and components, I was in the mindset that there had to be a weight cost. So after running the numbers, I may have to eat some crow. Gasp.

Here's what I'm seeing for comparison, keeping in mind no cassette or derailleur needed:

Gobao eCVT: 3.85 kg for the motor-gearbox unit
Avinox M2S + SRAM GX Transmission (cassette, derailleur, shifter): ~3.5 kg

Net difference: roughly plus 345 g for the Gobao. But it's basically a wash, Gobao's 900 Wh battery comes in at 3.7 kg, which is actually lighter than Avinox's 800 Wh battery at 3.74 kg.

Gobao vs. Pinion MGU

Gobao's also lighter than the Pinion E1.12 MGU (4.14 kg), though Pinion does offer a wider 600% range vs. Gobao's 500%.

Avinox MG Concept

Avinox is cooking up their own eCVT prototype too, but no detailed weight specs yet. Their current M2S motor is 2.59–2.63 kg, and once you add a traditional cassette/derailleur you're at 3.5 kg.

What you get for that small weight penalty:
No derailleur to destroy in crashes
No cassette or chain , Gates Carbon belt drive, lasts 3x longer than a chain
Reduced unsprung mass at the rear wheel (better suspension feel)
Virtually maintenance-free
No shift interruptions under load, just seamless power delivery

So yeah, the small weight penalty is more than traded off for durability, less maintenance, and smoother power delivery. Color me surprised.

While I'm a huge MGU/ECVT fan, what I hate to admit is a lots of folks, when counting weight differentials, fail to account for the added weight of the belt/chain tensioner and also the snubber if using a belt (but you can skip the snubber because belts are way lighter than chains). Some tensioners, if designed well can be quite light, but other are downright heavy, like this UT tensioner that Nicolai uses on their Saturn:

And I like this tensioner because it tucks nicely behind the motor instead of underneath it. Doesn't help that the swingarm is made of ferrous metal, but at that weight it rivals the weight of T-Type derailleur with a battery! Yet another reason why I prefer rear suspension designs that don't require them.