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Trying to build a high powered ebike

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Trying to build a high powered ebike


Old 06-13-18, 03:38 AM
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Originally Posted by spectastic View Post
I've thought about building a electric motorcycle, thinking it'd be a nice project. However, they consume about 116 Wh/mile, while a ebike can get 20 Wh/mile.

So I want to build an ebike that can go fast (maybe 2000-4000W) which should get me to 35-50 mph without pedaling. I also want to put in there a 2.5+ kWh to get me a 100+ mile range.

does anyone have expertise in this realm? what would be the best option to get there in terms of quality, reliability, cost? I'm on a grad student budget, so i don't want to shell out $6k on one of those stock bikes. If I can rig up something for maybe $3000, I'll be happy.
Have you started working on this?
My friend is upto a similar project as I am speaking.
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Old 06-13-18, 11:10 AM
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i haven't built anything. right now, i'm kind of tied to a broken down motorcycle, and need to figure out what to do with it. instead of trying to get it up and running, i think i'm just going to part it out, and potentially try to make an electric motorcycle with some nissan leaf modules. I did some tape measurements yesterday, and I think the frame is big enough to accommodate a 20s4p 72V 136Ah setup, which should give me a pretty sweet highway worthy setup that has twice the low end torque as my other sv650. the main challenge is whether i'm confident i'd be able to pull it off. the frame i'm using doesn't have a whole lot of options as far as battery racks and motor mounts go, and I have ZERO experience with CAD and metal fabrication.. and it won't be cheap..
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Old 06-14-18, 03:39 PM
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Sanity check.

25mph, 10 miles uses 360WHr for me with my 36V, 500W hub motor -> ~36W-Hr/mile. At 25mph, aerodynamics dominates by a factor about 5, so about 6W-Hr/mile is going into friction (chain, bearings and tires), and 30W-Hr/mile is going into aero.

Doubling the speed, to 50mph takes 8 (=2^3) times the aerodynamic power requirements, the friction power requirement doubles with the doubling of the speed. This we are now consuming ~12W-Hr/mile (=2*6) for friction and aero goes to 240W-Hr/mile; for a total of 252W-Hr/mile at 50mph.

To get 20W-Hr/mile, my speed would have to drop 20mph. (15.4 W-Hr/Mi for aero, and 4.8W-Hr-mile for friction).

Get some data, and do the math.

See: https://www.slowtwitch.com/Tech/The_..._Bike_163.html

Last edited by nfmisso; 06-14-18 at 03:45 PM.
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