An Electric Bicycle

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An Electric Bicycle

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ivansgarage:
Here is a great place for dc motors. http://www.robotmarketplace.com/products/npc_ungeared_motors.html

I have been running the black maxx on my bike for the last 6 years.
http://ivanbennett.com/e-cycle.html

vtsteam:
The heat load if the above calculation is correct will be ~60 watts at full power. So think of a 60-75 watt light bulb.

On the plus side for cooling this is a relatively open frame motor made largely of aluminum with an outrunner spinning around, and the bike is traveling, so in early tests just put a hand on the motor perodically -- the best temperature gauge for this kind of thing. And if it feels hot, add a fan.

Steve you mentioned questions about motor torque. Given the RPM and assumed power, seems it should be possible to solve for torque. Looking it up on the internet I found the equation:

power = torque x 2pi x rotational speed

so

torque = power(watts)/ (revs per sec * 2pi)

so

torque = 500/ (5700/60 * 6.28)
torque = .84 Newton meters (or .62 foot pounds)

A 26" wheel at 30 mph is doing 388 rpm (if I also got that right --- better check that, too) so your final reduction is maybe 5700/388 or 14.7 to 1.

If you had a 3 to 1 sprocket ratio on the chain drive, your gearbox ratio would be 14.7 / 3 or about 5 to 1.

So torque out of the gear box would be about 5 x .84 = 4.2 Nm or 3.1 ft lbs at that speed.

Could be a lot of incorrect assumptions or outright units blunders here..... take with a grain of salt! :doh:

S. Heslop:

--- Quote from: ivansgarage on June 01, 2014, 08:45:20 AM ---Here is a great place for dc motors. http://www.robotmarketplace.com/products/npc_ungeared_motors.html

I have been running the black maxx on my bike for the last 6 years.
http://ivanbennett.com/e-cycle.html

--- End quote ---

Hey I remember finding that website when looking electric bike stuff up. It looks cool as heck but i'm not sure on the legality of a purely motor powered bike in the UK. In the UK Segways are illegal to ride on both paths and roads (not that i'd ever want a segway).

I was looking at youtube again last night and found this video. He doesn't show much but it looks awfully similar to what i'm planning. I did think about mounting the motor there originally, but I didn't like the look of the motor being so exposed.

Looking a bit further this website looks like it could have some good information on it: http://endless-sphere.com/forums/viewtopic.php?f=28&t=29531

Keeping the motor cool was something I was concerned about. Another thing that bothers me is maybe getting my parachute pants tangled around the spinning outer case, so maybe a shroud around the motor won't be a bad idea.

If I figured it out correctly the free wheel should work with it the right way round. It still shouldn't be too much of a problem to flip it though, i'd just need to cut grooves to help tighten it.

S. Heslop:

--- Quote from: vtsteam on June 01, 2014, 09:18:30 AM ---The heat load if the above calculation is correct will be ~60 watts at full power. So think of a 60-75 watt light bulb.

On the plus side for cooling this is a relatively open frame motor made largely of aluminum with an outrunner spinning around, and the bike is traveling, so in early tests just put a hand on the motor perodically -- the best temperature gauge for this kind of thing. And if it feels hot, add a fan.

Steve you mentioned questions about motor torque. Given the RPM and assumed power, seems it should be possible to solve for torque. Looking it up on the internet I found the equation:

power = torque x 2pi x rotational speed

so

torque = power(watts)/ (revs per sec * 2pi)

so

torque = 500/ (5700/60 * 6.28)
torque = .84 Newton meters (or .62 foot pounds)

A 26" wheel at 30 mph is doing 388 rpm (if I also got that right --- better check that, too) so your final reduction is maybe 5700/388 or 14.7 to 1.

If you had a 3 to 1 sprocket ratio on the chain drive, your gearbox ratio would be 14.7 / 3 or about 5 to 1.

So torque out of the gear box would be about 5 x .84 = 4.2 Nm or 3.1 ft lbs at that speed.

Could be a lot of incorrect assumptions or outright units blunders here..... take with a grain of salt! :doh:

--- End quote ---

Thanks for doing the calculations. To be honest though i've got no real frame of reference for those values, and Google isn't giving me any useful information. Yeah though with this gear reduction, and the motor running at 6000rpm, I got about 370 rpm on the 26 inch wheel.

S. Heslop:
I mocked up the placement of the motor today with a block of wood, and it turns out it was in the way of my legs. So i'll have to mount the whole thing elsewhere.

Eventually I came up with this over complicated monstrosity.

It has a v-belt that might serve as a clutch and reduces the rpm of the wheel down to 250, but it might not be so efficient.

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