Hub motors vs mid-drives: is unbiased comparison possible?

[parajared]

A quick note on off-roading; some of us own gasoline dirt bikes and chose to build dirt e-bikes too because of all those skinny, mondo hairpin, single track trails in the mountains that only a bicycle can reasonably ride on. If you try to ride your 40 plus killogram e-monsterbike down trails like that you are going to have a bad time.

 

[dogman dan]

I agree. There are trails and there are trails. Nobody, even on real motorcycles, can ride some of my local trails at 40-50 mph. The really rocky ones are just too nasty. Hard enough to stay on the bike at 15 mph on those trails. Same nasty rocky desert as Parajed has.

I'd love to try out the bafang 750w bb drive on some of them, but I'm broke. I can definitely point to some roads though, that I rode at 50 mph for many years. It just depends on the trail or road whether you need a bike, or some form of motorcycle type speeds. That may be where any bias exists, in the kind of trail in your backyard. I look at video's Hyena has made, and I'd definitely want a 40 mph hubmotor for those.

The only mid drive I've tried, is a weak brushed 250w. The ford think ebike. It does pull great, but 250w is not enough to get up the real trails. Shifting it under even a 250w load is pretty alarming. I'd like to try that bafang, put it in a low gear, and just leave it there all day though.



Same way I rode my slow rpm hubmotors. Up the steep hills, about 15 mph, and if it slowed more I'd just pump a few pedal strokes.

 

[snellemin]

Many great points here. I ride mid drive and dd all the time. Going to use my Raptor and old Fuji mtb as reference.

At 25mph mid drive use:
Mid drive is just too loud.
Off the line both pull the same.
Mid drive throttling is a bit different. Zombies throttle tamer works really well for a mid drive.
I run mine sensorless with zero issues.
Uses less current of the line.
Lighter setup for single track use.
Shifting under power sucks

At 25mph direct drive use:
Quiet.
Pulls the same of the line.
Smoother throttle.
Sensorless is harder for some people.
Uses more current of the line.
Heavier setup for single track use.
Shifting gears is easy.

I had also posted a comparison before the difference between the gng kit and ebay dd on the same fuji bike. I can't find right now though.

The cromotor climbs the same steep hills as my gng kit does.

But if you are limited to a sorry 250W setup, I suggest you just pedal your bike and carry some extra carbs and protein with you when riding trails. 250W is a decent assist for onroad biking.

For quiet 45mph high speed running, nothing will beat a direct drive in a bike setup.

 

[dogman dan]

I'm curios how noisy the new bafangs are, especially the 750w. My old ford think has metal worm drive gears. So It sounds a hell of a lot like a worm drive saw in use. Very noisy.

 

[teslanv]

I'm curios how noisy the new bafangs are, especially the 750w. My old ford think has metal worm drive gears. So It sounds a hell of a lot like a worm drive saw in use. Very noisy.

Remarkably quiet, actually.
Even alone on a quiet asphalt road, I have to listen hard to hear the drive over the other noises on my creaky bike.

 

[wineboyrider]

Can someone give me a reason why anything could be possibly be more efficient than a direct drive hub?

Easy, in hilly terrain it will amost always being running at an inefficient rpm.

It can have excellent stall rotor torque performance, all the way up to full speed. All drivetrains start at 0% efficiency at 0rpm, but a properly designed hub would be making that torque directly with greatest efficiency due to no additional power transfer stages.

For easy evidence, you can look at solar cars. Most efficient electric drive-trains on earth, and they use direct drive hubmotors almost exclusively.


I look at it like this, if you want 100ft-lbs of torque on the rear wheel, you can make 10ft-lbs at the motor and use 10:1 gearing, but this requires a gearing loss stage due to no power transfer being perfectly efficient. The alternative is to simply generate 100ft-lbs directly. As torque grows at the square of motor radius, you can grow radius until you've achieved the desired torque.

Think of growing radius on a motor like adding gearing. The magnet passes by faster even at low speeds which enables it to reach decent efficiency quickly.

Ok I am going to stick my puny neck out and say then why did Brammo empulse use gears on their motorcycle.?

 

[hydro-one]

haha with a topic like this , you have to expect comments all over the place- so here ya go.

Think of all the trails in all the parts of the world that we come from! how wonderfully variable, what bike would work best for all of them? well there is a perfect bike for every person, and every trail. thats how diverse things are, we need to find a "one fits all solution"? how smart we are, amazing really......a few copper bits, slap some paint on there and see! now it goes without peddeling,,,,,,,haha you guys who invent this stuff amaze me....im just a smart copycat....

so , i and friends had great luck with riding trails around my city winnipeg,mb, with my ht35 motors on downhillbikes and high voltage lipo....what kills your ride is weight, but you cant be breaking stuff, so its always been a compromise.....and i think hub/direct will always be. and i think the only way to go is DIRECT MID DRIVE all the way John, and others have noted, left side belt drive and keeping a bicycle drivetrain as well are the cats ass in my books. for high power drives on bicycles this seems fairly obvious

 

[kriskros]

I have both,recumbent trike with DD and two wheeler with 1600wCyclone motor running through a Nuvinci 360,, battery is 44v,20amp lipo driving a 20"wheel.. great climbing torque..excellent control of power usage under all conditions. 17mph in high gear and 29mph in low.Cyclone is ok in low gear ..I use very heavy MDS grease

 

[dogman dan]

My POV is that it can be like selecting the correct tool for the job at hand. A homeowner can have one hammer, and it will pound every nail he ever needs to drive. But as a pro carpenter, I owned about 10 different hammers, each one doing a particular task better than the others. I also had hammers that did more than the others good enough.

So if you ride one route over and over, you might want the specialized hammer. But if you will ride both street and trail, it might be better to choose the mid drive. I mostly just have hubmotors, but each one does either street or trail best.

But all the mid drives I have seen or ridden make some noise. Some a LOT of noise like my ford. I'm dying to find out what the bafang is like. I don't mind some noise, but I know a few kinds that are way too loud for me. Curries, Heinzmanns, and my ford think. The heinzmann is the worst, all metal gears that sound like a trip to the dentist.

My hubmotors do make some noise, but never so much I don't hear a car coming from behind. On a single track trail ride that won't matter, but I still don't want to have to wear hearing protection to ride it.

 

[teslanv]

I have no doubt that you will be impressed with the Bafangs lack of noise, Dogman.

 

[dogman dan]

Well, that makes the very first comment on it one way or the other I have seen. EDIT, I'm such a moron, I just read that it's silent in post one in the non hub section of the forum. I should read over there, but never was interested in fabrication of gears and sprockets. But of course, that's where the bafang bb drive discussion would be.

I wasn't finding a review of this motor in the review section, that I had looked in. How about you write one T?

I was really hoping the new generation of bb drive motors would be much quieter. The noisy kind I was referring to has the motor at a 90 degree angle, and worm gears to change that to turn the crank. And of course, many other kits had a second chain, and some chain whine with that. The chain whine is not that bad, but those metal worm gears are loud.

I don't require a silent ride down the trail, but I do prefer it to not require earmuffs. On the street, I really like as silent a motor as possible, so cars don't sneak up on me. No car ever passes me I don't eyeball. But it's easier if you know you will hear them in time to check the mirror.

 

[teslanv]

I wasn't finding a review of this motor in the review section, that I had looked in. How about you write one T?

Ron beat me to it. Actually where I first discovered the kit...
http://www.electricbike.com/bafang-bbso2-750w-mid-drive/

 

[Ypedal]

I'm testing a BBS01 Bafang Mid Drive now and can totally confirm , it's very quiet, right up there with the old trusty crystalyte 400 series on the DB scale.... i have various gripes with it but nothing bad to say about the sound level. 8)

 

[dogman dan]

I just read that review on Electric Bikes. Duh, I shoulda known they'd have the poop on it.

Love the stator heat sinked to the outer cover. That's going to be ideal for cooling a motor that tripped it's overheat protection. The trip will be in the controller I suppose, but cool that stator and the rest will cool.

Potted controller, looks very water proof to me.

Quiet. Fantastic.

This looks perfect for those that have a normal ride, but their home street has a 15% grade. Perfect also, for those that have found a heavy hubmotor too cumbersome, or too fast.

But I keep thinking about the long haul, which this motor is apparently not so good for if the load is 20 amps. But how about two motors? A rear hubmotor on a cargo bike, plus the bb drive to get up the steeper hills?

Very happy to hear you have your hands on one Ypedal. How long before you can start really riding it? Can you see asphalt on the street yet? This winter must have been extra long for you.

 

[liveforphysics]

Can someone give me a reason why anything could be possibly be more efficient than a direct drive hub?

It can have excellent stall rotor torque performance, all the way up to full speed. All drivetrains start at 0% efficiency at 0rpm, but a properly designed hub would be making that torque directly with greatest efficiency due to no additional power transfer stages.

For easy evidence, you can look at solar cars. Most efficient electric drive-trains on earth, and they use direct drive hubmotors almost exclusively.


I look at it like this, if you want 100ft-lbs of torque on the rear wheel, you can make 10ft-lbs at the motor and use 10:1 gearing, but this requires a gearing loss stage due to no power transfer being perfectly efficient. The alternative is to simply generate 100ft-lbs directly. As torque grows at the square of motor radius, you can grow radius until you've achieved the desired torque.

Think of growing radius on a motor like adding gearing. The magnet passes by faster even at low speeds which enables it to reach decent efficiency quickly.

Ok I am going to stick my puny neck out and say then why did Brammo empulse use gears on their motorcycle.?

People make mistakes. There high performance race bikes don't use gears fortunately, and I think we will hopefully see that added paracitic drag and weight and noise removed from there future products.

 

[Drunkskunk]

I'm testing a BBS01 Bafang Mid Drive now and can totally confirm , it's very quiet, right up there with the old trusty crystalyte 400 series on the DB scale.... i have various gripes with it but nothing bad to say about the sound level. 8)

That sells me on it. I think my next build will be with one of these. Now if they would just make a version for 100mm BB fatbikes.

My take on Hub motors vs mid-drives: A direct drive Hub motor is a 9 pound Sledgehammer. You can do anything with a Sledgehammer. When I was young and poor I couldn't afford a hammer, but I had a 9LBS I had found in a street once. I used it for everything, from putting together flatpack furnature, to tapping dents out of a car I was restoring. And occasionaly I had to break a few rocks with it. It worked well for me once I developed the skill to use it.

A mid drive is like a small tool bag of hammers. You need a claw hammer, its a claw hammer. You need a tack hammer, it's a tack hammer. You need a rubber mallet, it's a rubber mallet. All around, it's more versatile, fitting many of the jobs better.
But if you need a sledgehammer, you're SOL.

 

[Ypedal]

why did Brammo empulse use gears on their motorcycle.?

I watched an interview a while back and they talked about catering to the existing motorbike mindset of shifting gears.... it's not needed.. but it satisfies the habitual behavior and mentality.

 

[wineboyrider]

Kind of the answers I was thinking along the lines of...hehe. It makes total sense that the rpm and and turn of the motor can make up for any gearing within the range of the electric motor. I guess now that the control of the electric motor is a lot more precise than it used to be the transmission model used on ice engines makes little or no sense...........

 

[teslanv]

Dogman,
Video I took. All you can hear is the wind.
http://youtu.be/UMtmMTij2Mo

 

[Warren]

Luke,

"For easy evidence, you can look at solar cars. Most efficient electric drive-trains on earth, and they use direct drive hubmotors almost exclusively. "

They don't run solar races in the mountains. They are all on flat desert courses, or a track. Also, the hub motors they use have the magnets right out at the rim, not hidden behind the brake disc like most e-assist bicycles.

Clearly, the Zero SR is more efficient without a gearbox, than the Brammo Empulse is with one, over the EPA drive cycle. I don't think we have had the final word on this issue yet, however. I will be very interested to see what the Yamaha does, if it ever comes out.

If you ride an e-assist bicycle for maximum speed, a hub motor will win. If you ride for maximum efficiency*, on varied terrain, a drive through the gears will win. Try climbing double digit grades at 8 mph, and 350 watts on a hub motor bicycle. Sure, you could lace it up in a 16" wheel, and run 72 volts to get your top end back. But then it wouldn't be a normal bicycle either.

*I am referring to Wh/mile, not motor efficiency. A Crown hub motor will climb that hill at 89% efficiency, but at 20 mph, pulling huge watts.

 

[Eskimo]

I had chance to test new Bosch S-pedelec mid-drive today. Very impressive. Sensor worked flawlessly, very well. Power came on strong, considering that sticker says 350W. It really functioned well, he said it had torque sensor.
I said my bike is as fast as his. He said bike costs 3000 euros. I said mine costs 800 euros But yeah, very nice system to ride.

 

[Warren]

Eskimo,

"He said bike costs 3000 euros. I said mine costs 800 euros But yeah, very nice system to ride."

Yours is home built for that price. Bafang has now made DIY mid-drives simple and much more affordable.

 

[Emmett]

If the motor in today's Formula E race car can produce 8KW per Kg, then does that mean that for E bikes, it is inevitable that hub motors are going to make mid drives obsolete?

When you consider the serious disadvantages of mid drives, it sure seems inevitable to me.

Are today's production e-bike hub motors positively stone age?

With some kind of passive cooling solution (like oil in a sealed hub with good external heat dissipation), surely the technology exists today to get to say 2KW per Kg. I'd certainly enjoy a 4Kg hub that pumps out 8KW! Even 4KW sustained with 8KW peak would be awesome from a 4Kg hub.

See https://en.wikipedia.org/wiki/Spark-Renault_SRT_01E#Electric_Motor

 

[riba2233]

Formula E doesn't have hub motors, they even have gears lol.

 

[MadRhino]

Gears will always exist, and the technologies developped for ICE will have a strong tendency to persist in the development of EV. This doesn't mean they are best, or even appropriate. The quest for performance and efficiency will optimize EV power trains sooner or later, to the point that it will have little to do with today's conception of it. It will be simple, lightweight and compact, like we never could have dreamed building ICE racing machines. A new era is beginning, where power to weight ratio possibilities, opens a whole new vision of performance engineering.

We are not finished inventing the wheel, and our fight against gravity is still in its first round.