I could have buy a hub motor instead, but I will not abandon this project, yet.
this might work.
I want to get this thing to about 40-50kmh
Did u calculate what speed it will be doing based on the gear ratio, wheel size, voltage, and kv?
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ok @Stallion-4x iāve used inrunners on an mtb 12s 135a each motor on 1:5 235mm wheels. and the torque is low on starting (gives a good kick around 20mph tho)
inrunners love amps and speed. single inrunner motor/drive imo needs atleast 240A-350A
dual motors 135A min prefer 150-200A
(again these amp suggestions are based on 1:5, 9 inch wheels)
Itās not because the driving surface of the bike wheel should be going the same speed as the surface of the longboard wheel. So itās the same gear ratio as setting the longboard wheel on the ground.
edit: ninjaād
This still isnāt making sense to me. A 100mm wheel spins 5 times to turn a 500mm wheel once. Surely thatās a 5:1 gear ratio? What am I missing?
Edit: I think I get it now. So the overall speed over ground wouldnāt change since 5 rotations of a 100mm wheel travels the same distance as 1 rotation of a 500mm wheel. That would also mean the acceleration would be the same - 100mm on ground vs driving a 500mm wheel.
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Axle speed is irrelevant, which is what youāre measuring.
The distance the tire rolls on the ground is the same as the distance the longboard wheel would roll on the ground, when they are set up in a friction drive, pressed together.
The axle speed would certainly slow down by a large factor, but the wheel circumference will increase by the exact same factor.
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Different motor designs can have the same total power output, but only under very different conditions that make them more or less suited for a specific job. Forgive the overly simplistic examples but; a tractor can put a lot of power, but only at low speeds with a big cargo load. A medium size family car can also deliver power, but only with moderate cargo at fairly high speeds. Both a Toyota Corolla and a medium sized John Deere tractor come in around 140hp, or 100kW.
The motor you have spins at very high speeds and with low inherent torque, so you need to convert that to a lower more useful speed and a higher torque, or choose a different motor. That motor also requires very high currents to make its max power (any motor needs either very high voltage or current to hit 5kW to be fair, itās a simple P = V x I equation). So if you want to use this motor you definitely need a big gear reduction, and you probably need to use an ESC from a drone or big RC vehicle, theyāre designed for this type of motor so they can survive the very high currents. That motor also isnāt really supposed to be run at this high of a voltage, I think they get hotter and less efficient from friction and magnetic losses when you spin them that fast
The biggest and smallest bicycle sprockets I could find on a quick Google are 9 and 112 teeth respectively, which would actually be pretty much the right reduction for your use case. Horrible to make it work though, youād need to adapt a big ass sprocket to a wheel thatās much smaller than itself, and retain the whole thing. Itād look something like this
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To give you some perspective, I had a scooter with an 800kv motor and it needed a 40:1 gear reduction to get any useful torque out of it on 12s and that is with only a 10 inch tire. With your setup, the motor has no leverage so it is going to struggle immensely under load. Youāre probably gonna need a large two or three stage gear reduction like the model @mr.shiteside showed above, which will add a lot of complexity and friction to your drive train.
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If I raise the ESC amps up to 120A, will I see better results?
Iām not planning to climb hills with it, itās mounted on a BMX