Most powerful hub motor below 5lbs

nowholeself

nowholeself

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Joined
Sep 28, 2019
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Location
Los Angeles
I'm considering a few new builds. One of them is a 20" wheel hub motor build. The top speed should be somewhere between 28 and 32mph, with lots of torque. I'd be using an aftermarket controller, most likely one of the ASI BAC's. And I'd likely use a high-C 21700 battery pack capable of 45amps continuous, with at least 48v, more than likely 52v if the motor can handle it. So I should be able to squeeze every last bit of performance out of any motor I use. The problem is that I also need the motor itself to be less than 5lbs. What's the best option out there? Is there a hub motor that can give me that kind of performance at such a light weight? I've been searching the forums here and have yet to find an answer to this question. But if it's already been answered here, please drop me some links. Thanks y'all!
 
A related question: why are all of these hub motors composed entirely of solid steel components? Where are the strategically drilled-out components? Where's the aluminum?
 
With a weight that low you can totally forget about getting any kind of power in any hub motor commercially available. It would have to be geared with a really badass high RPM RC motor inside.

As for where the high performance motors are this is a general problem in the ebike industry. All the highest power density drives are mid drives and they all tend to have fairly significant compromises with respect to noise, wear on the bike driveline and availability of suitable controllers. Those things can be addressed, but it's complicated.

Also ASI is a great choice for relatively low RPM hub motors, but doesn't do well with low inductance high RPM RC style motors which are what have the highest power density.
 
flat tire said:
With a weight that low you can totally forget about getting any kind of power in any hub motor commercially available. It would have to be geared with a really badass high RPM RC motor inside.
Click to expand...

That's what I'm realizing. Bummer dude.
 
ah yes, you clearly did say lbs. right in the title even.
that's how ingrained it's become when reading specs.
don't bother to read past the number as specs are always metric by default.

the d-motor itself is actually something just under 4kg without the internal controller.
only 75% more than what your looking for but not close enough i guess, oh well.
5.6 lbs. geared hub something you can live with?

nowholeself said:
flat tire said:
With a weight that low you can totally forget about getting any kind of power in any hub motor commercially available. It would have to be geared with a really badass high RPM RC motor inside.
Click to expand...

That's what I'm realizing. Bummer dude.
Click to expand...
falco Dx is the only one i've ever heard of that would qualify but turned out to be total vapourware & abandoned so wouldn't put much faith in the specs.
but rakesh is still plugging away so if enough money-bags were thrown his way he might be persuaded to revive the project.
 
nowholeself said:
The problem is that I also need the motor itself to be less than 5lbs.
Click to expand...

Why specifically does it have to be less than 5lbs?

KNowing the reasons might help to figure out an alternative (because I don't think you're going to find exactly what you want).
 
If you want a lightweight kickass offroad bike that grips and surmounts obstacles like an extension of your body with reasonably well engineered moderate power the cyc x1 mid drive is possibly a solid choice if you have a backup plan for the stock controller (I've never used it but hear it sucks. RC controller for the win.)

If you want high power go ahead and take the disadvantages of all that unsprung mass and get the QS205 or QS273. These motors easily take over 10kw burst and will see you to power wheelies at over 40 mph with a smile on your face. You won't care that it handles like shit offroad because it will be fast.

If you want both you're sort of SOL unless you pick a highly efficient axial flux motor and pair it with a sevcon that you pay beaucoup bucks for some expert to program. Emrax is a great option there.
 
The problem with 500W per pound of motor is that the waste heat has to go somewhere, which is first into the mass of the motor and then into the air. Even if the motor is phenomenally efficient, it's going to get hot if it's that light and powerful. And if its weight has been pared down to the minimum, that not only reduces mass to absorb heat, but surface area through which the heat may be dissipated.

RC airplane motors make it work through the use of powerful active air cooling. Bicycle hub motors don't have that going for them.
 
nowholeself said:
My bikes are solely for city riding. I make them all rigid. No shocks. So it's all unsprung mass. 🙃
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If you ride instead of carry, then weight is of little significance. If carrying is a big enough deal for a few pounds to really matter, then you should be building electric skateboards instead of ebikes.
 
If you ride instead of carry, then weight is of little significance. If carrying is a big enough deal for a few pounds to really matter, then you should be building electric skateboards instead of ebikes.
[/quote]

Weight affects performance. So it's obviously of significance. My current setup is incredibly lightweight relative to other ebikes. And its performance is excellent. That would matter even if I weren't carrying the bike often. But yes, in the city we often need to carry bikes up and down flights of stairs and on/off trains. So weight matters for that reason as well. You're welcome to make some super fast skateboards if you like. I'm sure there's a market. But so far I've yet to receive "why not a skateboard" in response to my small, fast, and lightweight bike. Rather, the primary response I've had so far is, "where can I get one?" Perhaps those who inquire such things aren't as attuned to your insights into the subject. Feel free to school us if you like.
 
ZeroEm said:
He needs that motor on the outrider trikes, what is the name of it?
Astro motor they are lite and powerful!
Click to expand...

Thanks for this suggestion! I've been looking at Astro Motors, as well as Neumotors. One of the designs I've got floating around in my head is a middrive based around these sorts of lightweight and impressive engines. If I work something up I think can compete with other middrive designs I've seen, I'll be sure to post here for some feedback. But I'd also like to put together something super simple but comparatively lightweight for city riding. Hence the hub motor request. From what I've gathered so far, there's nothing on the market matching my description. So I'll likely have to lower my expectations if I make such a build. Thanks for all this feedback y'all. :)
 
nowholeself said:
Thanks for this suggestion! I've been looking at Astro Motors, as well as Neumotors. One of the designs I've got floating around in my head is a middrive based around these sorts of lightweight and impressive engines. I
Click to expand...
The catch is that these types of motors run at high RPM to get the power they are "rated" at. So to drive the bike wheel in other than friction drive applications, they require high reduction ratios, sometimes two stages of reduction. (and they're often loud, or at least "whiney", because of the high RPM).

If you're willing to use them in a friction drive, driving the tire with them, then they dont' need a reduction (if you get the right kV version for your battery voltage and road speed), becuase they are essentially driving the road "directly", not the wheel,
 
I started the same way, had an idea but reality with what is on the market changes all of that. I found out that you don't need as much power to cruse unless you want to drag race. I used to want an astro motor but the gear reduction put me off and sure they make a lot of noise.
 
I also need high power, in my case for pushing heavy loads up long steep hills.

Setting weight-to-power ratio aside for now.

They say DD hub motors are not suitable since they don't develop enough power until they've reached a certain speed.

Internally geared hub motors are bad at dissipating the heat, and either noisy ot prone to stripping the nylon gears.

Hub motors just don't have enough power, full stop.

So my conclusion is, multiple motors are required for my use case.

Maybe the hub motor, geared way down to assist most with standing starts (human legs too AMAP).

DD hub(s) for helping get the heavy load up the hills, after the rig is rolling at a minimum speed.

Considering using a tandem as my base, so could maybe get multiple hub motors working together.

So, maybe this line of thinking is helpful for your use case?

 
Nothing wrong with dreaming. I keep dreaming of a larger geared hub motor, able to take 2000w continuous.

Meanwhile, your only real option is a 7 pound geared hub motor, and running at most about 25 mph.

And, look into friction drives, which can be quite light. But either way, less power, and 20-25 mph cruise is reasonable, while keeping it very light.
 
RE hub motors and heavy cargo, the solution can be two motors, but one larger one can be lighter, and do the job fine.

Depends on the load, and the hill. But I had no problems riding in the rocky mountains using a 25 pound hub motor ( just the 4motor) on this bike, loaded up to about 450 pounds total. 2000w, 48v 40 amps, and brisk pedaling got me up some very steep grades at 15 mph. 7-8% for miles. P2130006.JPG

Two DD motors would have been 30 pounds of motor. Could be worth trying an idea I never did test. a front geared motor, and a rear DD. That would come in also, at about 25 pounds.
 
Smaller wheels help with hub motors. This allows the motors to spin faster.

The lightest decent DD hub motors I know of are going be Goldenmotor's smart pie and Grin's All axle. Still a lot more then 5 lbs. Both would benefit from statorade.



A alternative would be left-hand drive. Use a adapter to take the disk brake and add a sprocket to it or a adapter that ties sprockets into the wheel spokes. I guess the disk brake adapter would be preferable. This is what they do sometimes for gasoline bike kits.

This way you could use a much lighter motor but still get most of the same sort of benefits of a DD hub motor. It'll be much more rugged then tying it into derailleur and you could have features like regenerative braking.
 
Setting weight aside, and low top speed is fine.

dogman dan said:
I keep dreaming of a larger geared hub motor, able to take 2000w continuous.
Click to expand...
So what is the highest-torque IGH motor you would recommend for reliability?

> look into friction drives

Can these be used for high power as well?

dogman dan said:
RE hub motors and heavy cargo, the solution can be two motors, but one larger one can be lighter, and do the job fine.
Click to expand...
My reason for multiple motors is to get gearing for one of them to help with standing starts heavily loaded middle of a steep hill, from 0 to say 10kph. At which point the DD motor can start helping without burning.

What is a "4motor"?

> a front geared motor, and a rear DD

Why is that better than the other way round?

I figured ebraking better on the front?

And IGH on the rear leaves open upgrading to other gearing options like outrunner + belt drive, or something like sleepy's idea above. . .
 
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