How to use a 250W front hub motor with an aluminium for and survive?

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hrc   100 µW

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How to use a 250W front hub motor with an aluminium for and survive?

Post by hrc » Jan 22 2020 4:09pm

Yes, the common advise is NEVER to use an aluminum fork when using a front hub motor.
But on the other hand there are hundred of thousands of ebikes with aluminum forks and front hub motors (Vanmoof and many others).
So my question is, what would be the the key concepts to consider if you want to use and aluminum for with a 250W front hub motor?
  • Special torque torque arms?
  • Custom made aluminium forks for front hub motors?
  • Use special washers?
  • Limit the max power of the motor?
  • Combination of above?
Has anyone been able to use a small 250W motor with a aluminium fork with no problems? Any tips?
Thanks for your help!

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amberwolf   100 GW

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Re: How to use a 250W front hub motor with an aluminium for and survive?

Post by amberwolf » Jan 22 2020 4:31pm

if youre up for some reading, threads in these lists have answers to your questions. should be obvious by title which are relevant:

search.php?keywords=alloy*+fork*+motor* ... mit=Search

search.php?keywords=alu*+fork*+motor*&t ... mit=Search

there's also info in these but most aren't completely relevant and/or dont' have all the info within them that you want:
search.php?keywords=front+hub+motor*&te ... mit=Search

docw009   100 kW

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Re: How to use a 250W front hub motor with an aluminium for and survive?

Post by docw009 » Jan 22 2020 8:25pm

Ive had a 250W Q100H motor on my 20' minivello for two years. Alloy fork. I have torque arms on both sides, one home made and the other store bought. I'm running it off 36V and a 20A controller, so it can peak at 600-700 watts briefly.

I marked the nuts with a red pen, and they haven't moved. Nonetheless, it worries me. In one picture, you can see there was just enough thread to engage all the the hub nut.

This winter, it comes off and I will drive the rear wheel instead with a mid drive.
torqu1.jpg
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torque2.jpg
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markz   100 GW

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Re: How to use a 250W front hub motor with an aluminium for and survive?

Post by markz » Jan 22 2020 8:42pm

I am using a yescomusa direct drive 9c clone on the front, its 36V26A using ONE torque arm! T.A. is 1.5"x4"x1/4" steel flat stock, using an angle grinder I cut out the axle notch, then a small notch where the hose clamp fits in nicely and secures it tot he frame fork.
I recently inspected the front alum fork dropouts, they are fine.
btw I am fat at 375lbs, its stretched out fat so dont make no fat jokes.

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dogman dan   100 GW

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Re: How to use a 250W front hub motor with an aluminium for and survive?

Post by dogman dan » Jan 25 2020 8:21am

The first key thing for an alloy fork front motor, is you need the C washers. You must have an inner washer so the nut does not bear on the shoulder of the fork ( lawyer lips). Without this, just tightening the nut will crack the fork.

Then two decent torque arms. If its a shock fork, then you need the larger, more adjustable ones from Grin Technologies.

Weak motors do help, even steel forks can be wrecked by enough power. But 1000w setups, 500w rated motors running 20 amps, can be done if the washers and TA's are ok.

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motomech   1 GW

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Re: How to use a 250W front hub motor with an aluminium for and survive?

Post by motomech » Jan 25 2020 5:37pm

Yes, above exactly.
Here's a tip;
The C-washer has to sit flat against the fork ear.
If any part of the special washer contacts the ridge of the "Lawyer's Lips", one can go straight in with the flat side of a standard Dremel abrasive disc. It's exactly the same size of the C-washer and will clean-up the surface nicely.
Motomech


'07 GT Idive 4 4.0, Q100H 201 frt. mounted, 14S Multistar LiPoly, elifebike 9-FET 20A controller. Mean Well HLG-320H-54A, Crazy Bobs on Alex DM32's 21 to 22 MPH. viewtopic.php?f=3&t=28151&p=1373714&hilit=Idrive#p13737

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Hwy89   1 kW

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Re: How to use a 250W front hub motor with an aluminium for and survive?

Post by Hwy89 » Jan 25 2020 10:31pm

Where do you find the "C" washers for sale?
Installed a motor today on a fork with the most pronounced "lawyers lips I've ever seen. This evening reading this thread decided I'd better get C washers.

markz   100 GW

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Re: How to use a 250W front hub motor with an aluminium for and survive?

Post by markz » Jan 25 2020 10:33pm

Only one custom steel t.a.

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amberwolf   100 GW

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Re: How to use a 250W front hub motor with an aluminium for and survive?

Post by amberwolf » Jan 25 2020 10:42pm

Hwy89 wrote:
Jan 25 2020 10:31pm
Where do you find the "C" washers for sale?
https://www.google.com/search?newwindow ... +C+washers

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