Hub motor weight reduction

M

Mathurin

100 kW
Joined
May 24, 2006
Messages
1,166
Location
Quebec
Code: 
   --< Original >--

5.875Kg  Total

2.675kg Core & cables
784g    Face plates
88g     Bearings
2.22kg  Magnet ring 
110g    Nuts, washers, screws



   --< Current >--


2.64kg  Core & cables
I pruned ~2oz and used up ~1oz

Left in about as much material as I felt comfortable with.  I could have gone for perhaps 1/3 more without weakening it further if I followed up with dremel detailing, there's still a lot of essentially useless material there, but that's the thing: there's a lot of it, and I got pretty fed up of grinding.  Also, unless you really want to, it's not worth it; I only gained ~2oz.

The cables are quite a bit fatter then the originals because they were too thin to do the job as required, most of the weight I consumed went there, also a greater portion of that weight is actual conductor since there's no fat sheath that follows the entire cable.

~10g went to the female mini XLR connector, it's made of thick-ish metal when something in plastic would have done the job, in total the XLR represents about 20g of weight that I could have avoided with a bit of foresight, and that sucks.



Before, ~2.675 kg:
IMG_5278.jpg



After, 2.625Kg +-5g:

bc9e676f.jpg


9c2b15ab.jpg
 
Can you read chineese/asian?

84234a65.jpg




I figure the axle is still the weakest link anyways... Kinda disappointed at the weight gain compared to the amount of work though but, oh well. The heavy part seems to be at the circumference, it's needed for the motor to be efficient as I understand. Also, I regret not having weighed the thing more precisely before pruning it. BTW I've cleaned it up since the photo, metal dust everywhere.

Still to come: I plan to shave off the excess material between the spoke holes, that part's made of steel or something too, so there should be a bigger gain there.
 
Man, I hope you looked up the compression strength of aluminium before you did that. Although I think a spoke on a spoked rim would collapse before one of those members.
 
outer magnet ring thing: 2.220kg +-5g
 
Still to come: I plan to shave off the excess material between the spoke holes, that part's made of steel or something too, so there should be a bigger gain there.
Click to expand...

That's nuts! You're risking the physical integrity of your hubmotor for a miniscule gain almost certainly too small to provide real-world measurable, reliable performance improvement.

Replacing the entire covers with aluminum ones might be worth it, saving about a 1/3 kg on a 40x, and 2/3 kg on an x5.
 
xyster said:
That's nuts! You're risking the physical integrity of your hubmotor for a miniscule gain almost certainly too small to provide real-world measurable, reliable performance improvement.
Click to expand...
Click to expand...

But it's for the Emperor!


Actually, I think removing the spokes will be fine. There's no side loading.
 
fechter said:
Actually, I think removing the spokes will be fine. There's no side loading.
Click to expand...

Hmmm, for every action there's an equal and opposite reaction right, so does this mean that as much torque as the motor develops is also applied to the stator? Logic would seem to suggest so. So theoretically, if the motor developed enough torque, it could simply snap the remaining spokes and turn the stator into a rotor.

I'd be more worried about long term fatigue cracking the remaining spokes as you bump through potholes etc, then one day it just lets go and locks up the wheel. I figure manufacturers, especially Chinese manufacturers are all about making profits, so if they could leave some material out then they probably would... I guess it depends on how much the windings and laminations in the stator weigh. If it's not much then there won't be much load on the spokes and if it doesn't develop much torque it shouldn't be an issue. I guess. Just thinkin' out loud here.
 
I don't know if removing the steel from between the spoke holes will
decrease efficiency? I know steel is needed around the magnets to
concentrate the magnetic field or something, though there's plenty left.
Anyways this is it for now, I need a new grinding disk to continue. Pruning
the outer ring is definitely a more effective way to slash weight: I've only
touched the top side yet, and it's yielded 2.185Kg +-5g:

e529e477.jpg
 
From a magnetic field stanpoint, 1/4" thick steel behind the magnets should be enough to prevent saturation. Beside the magnet backing ring and the stator laminations, nothing else really needs to be steel (well I suppose the axle better be steel too).

I have no idea what quality of metal they used or how strong it is mechanically. This is usually determined by destructive testing.

Let us know the test results.
 
This is usually determined by destructive testing.
Click to expand...

What, in your world, isn't? :)
 
In my book there's two kinds of materials, plastic and metal. Plastic breaks and cannot really be repaired, metal bends and can be un-bent. The aluminium in this motor is the kind like kickstands are made of, the one that breaks when it's-40 and you hit them pretty hard like throwing your bike on a bike rack or something. Therefore, to me it is made of plastic. Still, in pruning it I applied Occam's razor, that is to say I don't see it breaking anytime soon. Same principal with the outer ring, the continuous metal between the spoke hole things is pretty obviously superfluous. Overall I expect to gain almost a kilo when I'll be done with this hub motor, then prime & paint it black for better heat dissipation, and have it mounted on a DX32 rim, saving yet more weight over the steel POS rim it came with. Should end up with a reasonably light front end.
 
When yer done with the motor, you can drill-out the fork too... :twisted:

If you want even more weight off the front, you might consider a set of ape-hanger handlebars to get you in a more upright position: more weight on the saddle, less on the bars.


8)
 
If I've done anything wrong or out of place let me know and I won't do it again... I promise.
Click to expand...

Not a worry on this forum!
The admins are nice, relatively normal, and very easy-going people.
Others of us have our quirks and peeves though .... :)
 
Eric G said:
I couldn't resist....a photoshopped version.

If I've done anything wrong or out of place let me know and I won't do it again... I promise.

Eric
Click to expand...

The only thing that made me pucker my sphincter (just a little) was seeing the web removed from the spokes. (That's the perpendicular ridge that runs the length of the spoke for anyone going 'Hunh?'). That's only because every time I've even cut into a reinforcement such as that, let alone remove it outright it didn't take take long for it to crack. You might be okay since it looks like you left some at the roots where it counts the most.
 
Right, I should whip out the dremel and round the curves that have jagged bits to prevent the formation of cracks.
 
As like Toorbough, I regret the loss of the web. Why?
Aluminium’s strength is it’s lightweight, so you can use enough of it to prevent excessive deflection; its weakness is fatigue.
http://www.industryoutsider.com/?p=22
Click to expand...

btw, Ellsworth's is to be the first firm to introduce the NuVinci CVP
transmission in this cruiser
 
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