Going from hub motor to 3000 watt belt drive. A good idea or not?

marka-ee

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My Nazca Pioneer recumbent bike currently has a 1000 watt gearless hub motor. While I do like the silence of it, and since I don't have any hills near me, it works fine except for one thing:The unsprung weight is a problem for my smoothness of ride if I'm not mistaken. I am toying with the idea of a fairly unorthodox drive that would use one of the fairly common 3000 watt BLDC motors from Amazon which sell for about $250 with a controller. The drive would be a belt drive and instead of doing reductions I would basically have the belt arranged on a extremely large sprocket arrangement that would be actually attached to the 26 inch rim thereby reducing the need for any multiple level drive reduction. The drive sprocket on the motor would be roughly two inches, which would still result in a fairly silent motor setup, I believe. Does anybody have any experience with these 3000 watt motors that are sold on Amazon? The price seems a little too cheap, and I don't know if they really live up to their specifications. Cooling might be another concern, as I expect the motor will be dissipating about 350 watts inside because of the 87% efficiency that motors are supposed to have. Anyhow, this would then make my rear wheel be almost as light as if it had no special motor at all, and perhaps get me more efficiency because the motor would be spinning a lot faster and I think would be able to transfer more power this way. Let me know if you guys think that it's a little bit too kooky to try this. I don't know if anybody's ever attempted a custom rim configuration that has a sprocket essentially attached to the side of it. So basically the sprocket would be roughly 25 inches in diameter.
 
If it’s the silver colored motor with the tiny sprocket, I see quite a few builds using them on the forum, although I can’t recall seeing the results of those builds.

EDIT: although they are rebranded under a bunch of names, search the forum on “Vevor kit” and you may find some similar builds or get some ideas.
 
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The closest thing I've seen to what you're talking about is the Golden Eagle belt drive kit for stinking smog bike conversions. That one uses a toothed belt and a fairly humongous belt sprocket that attaches to the bike's left rear spokes.

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In your situation, I'd go for a front hub motor 17 times out of ten rather than cobble together some noisy draggy hub-bearing-eating belt drive contrivance. If I'm not mistaken, your bike has no front suspension, therefore no unsprung weight issues there. Also SWB bents carry lots of weight on their front wheels.
 
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Not advocating, just shedding a few ideas ...


 
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Not advocating, just shedding a few ideas ...


Yes, I did see Tom's various videos on his e-bike adventures. I believe his last iteration of that bike actually used a dual belt system with the jackshaft reduction, which I am totally against because I believe it's even more inefficient and potentially noisier. It was educational to see his 3D printed large sprocket solutions.
 
In your situation, I'd go for a front hub motor 17 times out of ten rather than cobble together some noisy draggy hub-bearing-eating belt drive contrivance. If I'm not mistaken, your bike has no front suspension, therefore no unsprung weight issues there. Also SWB bents carry lots of weight on their front wheels.
Wouldn't moving to a front hub motor just move the problem to somewhere else? I'm thinking the extra large, even larger sprocket than the one you mentioned may not be very noisy because then the motor side pulley could be actually rather big compared to most of these types of solutions. If I'm not mistaken, that motor I'm considering likes to run at about 4,000 or 5,000 RPM, which also isn't really that fast. I'd estimate the front wheel of my bike only takes about 30% of the weight. Currently I have a fairly big Moto X tire on it which helps dampen it a little bit, but eventually I would like to work out a suspension fork for the front, but not a telescopic suspension fork because those are not as smooth as what I'd like to have.
 
Wouldn't moving to a front hub motor just move the problem to somewhere else? I'm thinking the extra large, even larger sprocket than the one you mentioned may not be very noisy because then the motor side pulley could be actually rather big compared to most of these types of solutions. If I'm not mistaken, that motor I'm considering likes to run at about 4,000 or 5,000 RPM, which also isn't really that fast. I'd estimate the front wheel of my bike only takes about 30% of the weight. Currently I have a fairly big Moto X tire on it which helps dampen it a little bit, but eventually I would like to work out a suspension fork for the front, but not a telescopic suspension fork because those are not as smooth as what I'd like to have.
Toothed belt drives get noisy at a certain teeth/min rate once the air is getting pushed to move out of the valleys in the belt and sprocket. Larger sprockets make the meshing more gradual, but they increase the belt speed.

Unsprung weight would be an issue for a front hub motor if you had a suspension fork, but until you do, the tire is your front suspension and the hub is on the "sprung" side.

30% is probably more front weight than my upright bikes have, and they do fine with front hubs running at up to 1000W input power. I weigh in the 270# range so you can scale accordingly.
 
If I'm not mistaken, that motor I'm considering likes to run at about 4,000 or 5,000 RPM....
You'd need 12to1 ratio to achieve 30MPH @ 4.6K RPM... assuming a 26" MTB. Not an ideal ratio for single reduction. Can it be done?... sure, but best approach is to find a motor with a much lower Kv rating.
 
You'd need 12to1 ratio to achieve 30MPH @ 4.6K RPM... assuming a 26" MTB. Not an ideal ratio for single reduction. Can it be done?... sure, but best approach is to find a motor with a much lower Kv rating.
Do you have any suggestions besides converting a hub motor to be remote mounted? I don't have the diameter room for that solution.
 
Unsprung weight would be an issue for a front hub motor if you had a suspension fork, but until you do, the tire is your front suspension and the hub is on the "sprung" side.
If you're going to craft a front suspension, use an Earles fork, and put the motor hub at the joint of the Earles fork. The weight of the motor will be 'above' the suspension. This is your original idea using a tiny motor with a belt drive.
 
If you're going to craft a front suspension, use an Earles fork, and put the motor hub at the joint of the Earles fork. The weight of the motor will be 'above' the suspension. This is your original idea using a tiny motor with a belt drive.
Interesting idea. Yes, if I do a suspension fork for the front, it will definitely be a linkage suspension of some type. The motor that I'm looking at isn't really all that tiny, so I'm not sure I could make it work on the front, however.
 
Changing the motor and/or the motor location is not going to significantly change the ride quality. You need fat tires and/or suspension.
 
Changing the motor and/or the motor location is not going to significantly change the ride quality. You need fat tires and/or suspension.
I have rear suspension and my rear tire is 2.12 wide which is the widest I can fit.
 
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