Hub drive vs Chain drive

General Discussion about large electric scooters and motorcycles and other things with no pedals.

Hub drive vs Chain drive

Postby Bruno2hb » Fri May 05, 2017 3:19 am

Hello everybody!

Currently in a project for making a light electric motorcycle, I was wondering what were the Pros&Cons of Hub Drive vs Chain Drive.

I did find similar topics in the e-bicycles section, but I don't thing the same applies for motorcycles (there's no human power coupled with gear, only the motor!).

- Which system is more efficient?
- Does any of them have a more constant torque?
- Speed ranges?

I noticed that "low cost" motorcycle often have Hub drives and more "expensive ones" have Chain drives... :roll:

Thank you in advance for your answers!
Really looking forward for this new projet :mrgreen:
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Re: Hub drive vs Chain drive

Postby spinningmagnets » Fri May 05, 2017 6:09 am

Its not hard to fit a 4:1 sprocket set onto an electric motorcycle, so in that case, you can spec a higher Kv in the motor, and you will get the same wheel RPMs, using the same battery pack volts, but....the chain-drive motor will be spinning 4 times faster than a direct drive hubmotor.

I believe that would provide a major benefit towards efficiency and wheel-torque.
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Re: Hub drive vs Chain drive

Postby skeetab5780 » Fri May 05, 2017 7:46 am

depends if you have a lift gate vehicle or a fork truck to lift the ridiculously heavy hub motors or not. (haha)

I would go chain drive after having experience with both, I want to build a electric commuter soon
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Re: Hub drive vs Chain drive

Postby John in CR » Fri May 05, 2017 10:43 pm

The biggest advantages of hubbies is the same as for ebikes, they're easier and it saves space (the biggest premium on ebikes since batteries use so much space.

Power is equal to rpm X torque. That means for a given power a motor can be smaller by running higher rpm, which means a gear reduction.

You said "lightweight motorcycle", but that's a bit vague. For the accurate advice about the choice, you really need to specifically define how it will be used, ie speed, range, terrain, etc. Continuous speed and range are the killer for an electric anything, because what you give up to wind in the form of aero drag eats battery capacity so they increase pack size, weight and cost. In terms of terrain, hubbies are best suited for street use with flat terrain. While little guys get away with slapping a hubbie on a mountain bike and taking it off road, as you get more like a motorcycle in terms of weight, load, and performance expectations a hubbie will be an overheating anchor of unsprung weight in the wheel if you head off road on all but the simplest trail riding. 2 wheel drive with dual hubbies might be an exception, but I've yet to build one to confirm their capability.

Last there's the biggest factor that amazingly people still don't get, and it ties in with power = rpm X torque. The smaller the wheel diameter, the more performance you can get out of ANY good DD hubmotor. It's straight forward physics. The primary limitation of all hubmotors is heat, which comes from 2 sources, iron losses and copper losses. Iron losses increase mostly linear with rpm, but copper losses increase with the square of current while torque only increases linearly with current. While this is a bit oversimplified, I can't stress enough the importance of understanding this general concept. It's what enables me, a fat guy, to enjoy the highest performance from hubmotors on this forum for the past decade.

While the out-of-production high efficiency hubbies I've used since 2012 are part of the story, the real reason enabling my higher performance is that I run as small a wheel as possible. eg On the tiny scooter I use for my current 40 mile roundtrip commute, I fit the smallest 10" scooter tire I could find, which has a 16.5" OD inflated. The mid size motor I use has a Kv of 14.3rpm/volt (torque constant .68Nm/A) powered with a 111V nominal pack, and it comes in at about 14kg with the tire and built on rim. It sucks a peak of 150A from the battery through the 2 controllers (75A/ea) required to run it, for almost 18kw input with a fresh charge even after voltage sag. Gear that kind of torque and power with a small tire for a top speed just above 70mph and I slaughter everything I run across at every stoplight every day. My almost 3kwh pack gives me 40-50 miles of fun performance riding (probably double that range on flat land going slow) with the only real compromises being that it's a bit small and uncomfortable and it's only nice on smoother roads.

Despite my love of the silence, simplicity, and efficiency of my hubbies, when I do build an offroad bike, the motor will be out of the wheel.

John
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Re: Hub drive vs Chain drive

Postby Noq » Mon May 08, 2017 5:35 pm

I'm sad because I think I killed my 8kW QS hub motor yesterday. See pics on my build thread here. I need a replacement that's more able to handle high power levels, like 20-40kW bursts (maybe as high as 50-60kW). Torn between chain-driven and hub motors now. I wonder what the best chain-driven motor is like. The best hub I can find is a 17" 14kW (~30kW peak) watercooled by QS. They're taking pre-orders for it here. If you were going nuts with electric around 80-120V yet battery power draws as high as 620A, what would you put in that won't die after a year? I'm open to suggestions. I might have to go low-power for a while as I consider what to do.
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Re: Hub drive vs Chain drive

Postby Boulter EV » Sat May 13, 2017 1:14 am

Just to add my 10p in, hub motors aren't just heavier, they are also unsprung mass, affecting the ride and handling. With a separate motor you have more flexibility over you rear axle design, but by far the biggest advantage is what John says, higher motor speeds equals better efficiency and better energy density which can is much more easily achieved by having a separate motor.
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Re: Hub drive vs Chain drive

Postby bobc » Mon May 15, 2017 5:30 pm

A major hubbie advantage is reliability - just the one moving part & that's the wheel.
The unsprung weight thing is a real issue on my little emax scooter - hate to think what more power would be like.
I'd go for toothed belt rather than chain, less mess, less maintenance, much longer life. The smooth torque & "no bump starts" with electric surely make chain inappropriate?
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Re: Hub drive vs Chain drive

Postby John in CR » Mon May 15, 2017 10:26 pm

No way for noisy greasy chains unless you're using a high Kv hubbie as high voltage in a mid-drive, so the gear reduction is low, which allows a larger drive sprocket and greatly reducing chain noise. I've got several sizes of Gates PolyChain pulley stock, so I can't wait to experience the silence of a hubbie with little or no unsprung weight. I already have the 21" moto on/off road wheels ready for my first trailer riding ebike. 8kwh of advance design battery modules + a 14.5kg HubMonster at 118V nominal which will be geared down to effectively a 10-12" OD wheel should be just the ticket to eat MX motos' lunch just like I've been doing on a daily basis to their street bike cousins on a daily basis with my e-scoot running a MidMonster. 8)

PS- The secret to any performance setup is gearing so the motor sees a load much lighter than they're capable. Then you can push them with much higher power than they're rated, because the max current demands are extremely short in duration, and that leads to greater efficiency and reliability. Anything short of ABSOLUTE RELIABILITY is unacceptable AFAIC.
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Re: Hub drive vs Chain drive

Postby skeetab5780 » Tue May 16, 2017 7:41 am

I was recently watching some of those Motopeds youtube videos with the direct drive hubs mounted in the mid with a chain drive. They looked pretty weak from what they did in the videos. They were running up to 72v 40 or 50a and as low as 48v lithium but had to pedal up hills and didn't see fast acceleration.

Not saying its not viable but pound for pound it seemed like you'd get better performance from a standard motor (LR/BHT/LMX)

But once you get to power level stated above from John don't ask me, it might start becoming a better solution
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Re: Hub drive vs Chain drive

Postby John in CR » Tue May 16, 2017 11:33 pm

skeetab,

I agree that common ebike hubbies aren't up to the task, but then neither are the "standard motors" you mention, at least not at the performance levels I demand. Of course for lightweight people and lightweight bikes almost anything will work. My statements were geared more toward when a chain drive makes an acceptable level of noise to me, which is near silence since I stick to street riding and prefer the silence of hubbies where tire selection is the greatest influence on noise levels. I haven't seen the motoped videos you refer, but it sounds like they have either a controller setting or gearing issue.

Back to hubbies vs chains. If you're going to the trouble and expense to build your own transportation, then why give up one of electric's prime advantages and listen to a bunch of noise? Use a toothed belt instead of a chain...however, with small gear reductions, relatively low rpm, and large sprockets, a chain drive can be nearly silent. I know because I've done it, and the reason I went that route with a hubmotor, is because I had a high Kv high efficiency small diameter hubbie that can spin up to high rpm with low iron core losses, so the only way to unleash its potential is a tiny wheel or a gear reduction. I did a chain drive with a 2:1 reduction, so it was the equivalent of putting the motor in an 11" outside diameter wheel. I was extremely surprised by how quiet the drive ended up, with tire noise being far greater than the chain once I dialed a properly aligned chain. My next one will have a Gates Polychain Carbon Drive belt. If Zero Motorcycles can run 54hp with a 12mm wide belt, then it will handle my needs, and my larger drive pulley will help ensure mine is event quieter than Zero's.
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Re: Hub drive vs Chain drive

Postby bobc » Wed May 17, 2017 2:11 am

re gates polychain: great product but... incredibly expensive. It's engineered for chain replacement on a roadie bike where the tight side can have over 2000N tension. If you're "gearing the other way" so you have the bigger pulley on the wheel, you don't need the carbon tension members & MUCH cheaper solutions exist. I would have thought a wider belt with 5mm tooth pitch might be nearer the mark.
There was a thread on here about making toothed sprockets for the back wheel - might be worth a re- look at.
Oh yeah - while I'm on.... later gates carbondrive had "centretrack" instead of flanges. I have flanges, a colleague at work has centretrack, mine is as new after 12000miles, his had to be replaced after 1200. I made my own pulleys the exact size I wanted, he had to buy expensive proprietary pulleys with limited choice at each end. Just saying, the nobbles on a centretrack are way less than half the size and they seem to therefore be fragile.
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Re: Hub drive vs Chain drive

Postby John in CR » Wed May 17, 2017 12:13 pm

"Incredibly expensive"...You're talking about bicycle ripoff priced stuff. In the size range I need the belts are under $40, which seems pretty reasonable to me. BTW wide means more friction losses, not to mention greater bike and pulley widths.
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Re: Hub drive vs Chain drive

Postby bobc » Wed May 17, 2017 1:12 pm

John in CR wrote:"Incredibly expensive"...You're talking about bicycle ripoff priced stuff. In the size range I need the belts are under $40, which seems pretty reasonable to me. BTW wide means more friction losses, not to mention greater bike and pulley widths.

yep :)
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Re: Hub drive vs Chain drive

Postby Chalo » Wed May 17, 2017 1:37 pm

John in CR wrote:"Incredibly expensive"...You're talking about bicycle ripoff priced stuff.


Part of the ripoff pricing goes to making reasonably sized belts that don't need excessive tension to work, and pulleys that can retain such belts without weighing a ton. Static belt tension is damaging to bicycle parts that aren't designed to tolerate it, and industrial belts need a lot of tension if they're to work correctly. Gates Carbon Drive belts are spec'ed for 40lbs static tension if I remember correctly, whereas industrial belts rated for similar torque require more. Even 40 lbs of tension while overrunning can destroy normal freewheels, but of course the less you can get away with, the better for the bearings and for friction losses.

Chains are the proven cost-to-benefit winner in this game. That's why almost everybody uses them, for puny little toy scooters, the most powerful motorcycles, and everything in between.

P.S. -
I've used toothed belts for machinery, and they aren't at all silent unless they run slowly. They don't sounds like chains, but they do make noise.
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Re: Hub drive vs Chain drive

Postby Boulter EV » Wed May 17, 2017 3:44 pm

As a plus point for hub motors you have none of this to worry about!
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Re: Hub drive vs Chain drive

Postby Chalo » Wed May 17, 2017 9:36 pm

Boulter EV wrote:As a plus point for hub motors you have none of this to worry about!


Yes. On the minus side, they are heavy, they make weak wheels, and you can only change the motor's gearing range by changing the battery and controller voltage-- which itself is not particularly helpful when the hub motor doesn't drive a full diameter wheel efficiently at even 36V. (Many of them don't.) Screw up an installation and they'll screw up your bike's frame, plus maybe you too.

Hub motors are the right tool for some jobs, not so much for others. I think they get somewhat overused because they're cheap and conversion is simple. On the other hand, you could do worse than having a cheap, simple system that's a bit suboptimal for purpose.
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Re: Hub drive vs Chain drive

Postby skeetab5780 » Thu May 18, 2017 1:59 pm

Do you think 18s 120a is enough for a 200lb dirt bike? I don't think its enough factory engine says it puts out 11.5kw this will be a bit less
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Re: Hub drive vs Chain drive

Postby kingjamez » Thu May 18, 2017 3:13 pm

skeetab5780 wrote:Do you think 18s 120a is enough for a 200lb dirt bike? I don't think its enough factory engine says it puts out 11.5kw this will be a bit less


What do you mean? 18s 120a sounds like a battery. Is 120a the maximum discharge rate? Link to the battery?

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Re: Hub drive vs Chain drive

Postby skeetab5780 » Thu May 18, 2017 3:49 pm

AKA is 8kw enough for a 200lb bike
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Re: Hub drive vs Chain drive

Postby kingjamez » Thu May 18, 2017 4:11 pm

skeetab5780 wrote:AKA is 8kw enough for a 200lb bike


Not in my opinion. I run twice that on a 100lb bike and think it's just about right.

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Re: Hub drive vs Chain drive

Postby skeetab5780 » Thu May 18, 2017 4:51 pm

Thats what i thought
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Re: Hub drive vs Chain drive

Postby Noq » Fri May 19, 2017 1:40 am

What about hub motors at this level?

QS 17" 14-34kW 80H water-cooled
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Re: Hub drive vs Chain drive

Postby bobc » Fri May 19, 2017 3:53 am

Noq wrote:What about hub motors at this level?

QS 17" 14-34kW 80H water-cooled

Few thoughts (random sorry)
1) "application sport" - really? with all that unsprung weight? it's bad enough on my emax....
2) water cooling - seems a bit OTT if we guess at 95% efficient there's 700W to pass which should be doable to air in a 50mph wind...
BTW I had an interesting idea about cooling such a hub motor - are there any UK manufacturers of such things?
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Re: Hub drive vs Chain drive

Postby skeetab5780 » Fri May 19, 2017 7:29 am

Wow its already over 100 pounds before you put a tire or a bike or a battery or a person into the mix...

That's insane. Are there even stand alone BLDC or PM motors rated this high for EV applications? Id imagine they are sized for a full size motorcycle
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Re: Hub drive vs Chain drive

Postby Noq » Fri May 19, 2017 3:27 pm

Yeah, it's for full-sized motorcycles. It's the latest and strongest mass-produced QS motor. It would be nuts on a scoot. You'd want to use something like a 180/55 tire on it, even though the default rim width is 114m (4.5"), but they'll customise it for you. Otherwise, no traction because the contact patch is too small. I agree, the 50kg unsprung weight is not ideal, but hopefully manageable vis à vis 150kg+ sprung weight in the rest of a build (frame, batteries, controller, components, riders, cargo, etc.—a full-size bike). I assume that's why you'd want water-cooling, so you can maintain major torque despite the weight of such a beefy build, and not worry about heat. Hubs get hot when you're talking about 30-50kW bursts and 15kW continuous, although I only have first-hand experience running 8kW and 5kW 16" hubs way over current (got really hot). Surely this winding would fare better, but the cooler the better (means you can push it harder). There's an air-cooled version rated slightly less if you prefer (28kW vs. 34kW spec peak rating). These motors are purported to reach those powerlevels almost immediately. I like hubs. They're quiet, simple, and space-efficient. They are heavy and unsprung though, and carry other disadvantages. It's up to you to decide if in-runners' pros and cons give you a better deal.
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