seeking 20" front fat tire hub motor

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kylerlaird   100 µW

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seeking 20" front fat tire hub motor

Post by kylerlaird » Nov 20 2020 11:14am

I'm building several electric bikes for my family to enjoy on our trails. My first project is a Mongoose Kong. I want AWD, so I need a hub motor for the front wheel. It has a 20"x4" 36-spoke rim. The current axle is 3/8"-24. A 10mm bolt fits much better in the dropout, though. It has a disc brake. The frame and fork are steel.

I want low speed and high torque for tackling steep hills/creekside. (It needs to be waterproof.) Originally I was hoping for a clutchless helical geared reduction but finding that has been daunting. I think the 20" wheels are likely to provide enough reduction to make a high-power direct-drive a more likely choice.

I strongly prefer a side-exit cable with a 10mm axle and torque arm - not slotted - in order to maintain the disc brake alignment.

Finally, I want something that I can order and receive quickly in the USA.

Does such a motor exist?

Thanks!
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john61ct   100 GW

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Re: seeking 20" front fat tire hub motor

Post by john61ct » Nov 20 2020 1:22pm

Grin All-axle ?

Balmorhea   1 MW

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Re: seeking 20

Post by Balmorhea » Nov 20 2020 3:23pm

john61ct wrote:
Nov 20 2020 1:22pm
Grin All-axle ?
Grin All-axle is a 100mm front hub.

OP is going to have to relent and get a flatted axle motor. It might hurt his feelings to have the rotor riding 2mm lower on the pads, but it won't make any difference in braking.

For a junky kid bike, I'd get a cheap 48V geared hub (with overrunning clutch) in the 200-250 RPM range, then run it on 36V. That should give a top speed in the 10mph range, which is fine for a kid riding off-road. He/she will be less likely to bog down the motor and burn it.

Ability to coast means the kid will have the ability to dash with pedal power, or zoom down a hill, without getting locked down by the motor's RPM.

Note that because the hole stagger in the rim is wider than hub motor flange spacing, the spokes will have to be laced to the far side of the rim.
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docw009   100 kW

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Re: seeking 20" front fat tire hub motor

Post by docw009 » Nov 20 2020 3:43pm

Generic 500W 36V motor. 280rpm, which is 20 mph with a 23" diameter tire (20x4"). Fits 135 dropouts,
Cheap and ships from US.

https://www.ebay.com/itm/E-Bike-Rear-Br ... SwUi5efraH

john61ct   100 GW

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Re: seeking 20

Post by john61ct » Nov 20 2020 3:45pm


Balmorhea wrote:Grin All-axle is a 100mm front hub.
As opposed to?

Are you saying you know the width OP needs?

How?

Balmorhea   1 MW

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Re: seeking 20

Post by Balmorhea » Nov 20 2020 5:00pm

john61ct wrote:
Nov 20 2020 3:45pm
Balmorhea wrote:Grin All-axle is a 100mm front hub.
As opposed to?

Are you saying you know the width OP needs?

How?
In the photo above, the caliper reads 134mm. 135mm is typical for fatty bike front forks.
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john61ct   100 GW

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Re: seeking 20" front fat tire hub motor

Post by john61ct » Nov 20 2020 5:35pm

Aha (blush)

markz   100 GW

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Re: seeking 20

Post by markz » Nov 20 2020 6:29pm

I see theres a little bump out on the inside of the fork, would that be the missing 1mm or what is the little bump, whys it there. Do most forks have that.


Balmorhea wrote:
Nov 20 2020 5:00pm
In the photo above, the caliper reads 134mm. 135mm is typical for fatty bike front forks.

Balmorhea   1 MW

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Re: seeking 20

Post by Balmorhea » Nov 21 2020 12:24am

markz wrote:
Nov 20 2020 6:29pm
I see theres a little bump out on the inside of the fork, would that be the missing 1mm or what is the little bump, whys it there. Do most forks have that.
That's the "positive front wheel retention device" required by the US Consumer Products Safety Commission since the early '80s or so. Also known as "lawyer lips", that feature keeps the front wheel from falling out if an idiot owner fails to tighten the axle nuts or quick release skewer.

In this case, it takes the form of a depression stamped into the fork tip, which results in a raised area on the inside of the fork tip. Not all forks have that feature, but almost all of them have some feature that keeps the front wheel from falling out when used by idiots.
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