Motor recommendations for 16% climbs?

blufires

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Dec 26, 2023
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Brisbane, Australia
Hi there.
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I've got this 2005 Kona Stinky downhill/freeride bike with BMX handlebars fitted (for a comfy upright posture) that's an absolute riot to ride down the 5 acres of steep hillside that my house is on. I just don't want to pedal back up the 16% (9.2°) grade every time I go to get the mail, check on the garden etc. So I'm planning an electric conversion for the specific purpose of riding around my yard. I might also tow empty wheelie bins up the hill. The bike is about 20kg and I'm about 100kg.

* I've thought about a Bafang mid drive, but it seems like power is pretty limited and it kinda messes with ground clearance.
* I've also thought about building my own mid drive using a 2,000W RC helicopter motor mounted to the seat tube on front of the rear wheel and a custom belt drive using HTD-5M belts. I've already done this with some success on a 16" children's bike, so this would reuse the parts. I'd need to gear it very low, so a two stage reduction belt drive would be necessary. This could drive the rear wheel either through a Nuvinci hub I scored for $30 or a ~170mm belt pulley mounted behind the 200mm brake rotor (the caliper is at the back).
*I also thought about the time the custom mid drive would take to build and thought maybe it's better to just earn money with that time and buy a huge hub motor instead, but it seems like they're all geared for flat ground speed, and what I need is 10-30km/h with huge torque.
*Maybe I should just buy a Surron, but I like the idea of this being lighter (due to lipo battery for short range needs) and using better quality suspension parts (fork is a Boxer).

Anybody got experience with stupidly powerful builds on very steep terrain? Bonus photo: the 2,000W 16" children's bike drivetrain.
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Thanks I appreciate you posting link.
As far as steep hills I have a 10% grade hill where I live and my 1k watt bike makes it up but may require pedaling. On my 8k watt (qs205 50h 3.5T)running 72v @ 150amp I can accelerate on the hill from 35 to 49mph but had room.
I was surprised that on the higher power one didn't feel the hill.
2k watts might do it I originally specd out running about 5k watts at first but (80amp) controller, but wanted the ability to go up if it wasnt enough.
I didn't want a mid-drive for maintenance purpose. They also make a good mid motor like QS138, IYou would need to get a good programmable controller with a good battery pack that has continous discharge, depending on funds ...I went with a 200amp one so could drive my motor about 15k watts if needed to.
The bike you showed may not have enough room for a big hub motor (dropout). If it's a steel frame you can widen it, You can also overdrive some motors.Motors, I use a good economical fardriver controller as they are tunable and prices are good. If you look at endless sphere there is a lot of emotorcycle build where they take like an old dirtbike and convert to electric. Have fun.
 
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