Weld-free electric bicycle conversion

[TheVictim]

I'm interested into converting a bicycle into an electric assist with the aid of a 24v 250w motor. Living in an apartment I have no welding capability and was wondering if this was practical and the best way to achieve it.

If one of the books or plans on this site could help I'd like to know which.

Thanks!

[AtomicZombie]

I would recommend a hubmotor kit. No welding, no fussing with gear ratios, no messing around matching controllers to motor, and you will be up and running in 2 hours.

How far and how fast?

Brad

I'm interested into converting a bicycle into an electric assist with the aid of a 24v 250w motor. Living in an apartment I have no welding capability and was wondering if this was practical and the best way to achieve it.

If one of the books or plans on this site could help I'd like to know which.

Thanks!

[TheVictim]

The prices on some of those hubmotor kits are a little much, I was thinking I could connect a chain from the motor to one of the rear sprockets. I don't want to go with a wheel that engages the actual tire, it seems you would waste a lot of power from tire friction.

I'd like to be able to get 15-20m off one charge, but as much of the trip as possible would be human powered. Speed isn't really a big concern, but I'd like to be able to navigate a hill at a speed at least as good as a brisk walk. If 250W isn't enough I could go with a 500W motor.

This http://www.scootercatalog.com/electircmotor-e7.html is my candidate for the 250W motor, they also have a 500W. I can get 12v 7Ah SLA batteries for $10 each locally, so if I need more than just 2 I can get more. 6v 12Ah batteries are also available if I need more range.

[TheKid]

That motor spins at 2500 rpm, so the rear sprocket will have to be quite large, or you'll need a gear reduction system of some sort. If you hook it up to one of the rear sprockets, the front chainwheel will spin as well. Without a gear reduction system, even if you use a 34 tooth rear sprocket, you'd have to keep the motor speed at a minimum.
I like that link. Here's a handy item for those hot days:

http://www.scootercatalog.com/x-50-300-cooler-scooter.html

[TheVictim]

If I need that much reduction, perhaps a wheel engaging the tire itself might not be such a bad idea after all. Just how much power would I be losing to friction though?

[Doc Hollywood]

I think you have the wrong idea about a hub motor. The motor is built inside the actual hub and there is little resistance. If there is some from a brushed motor but there are also brushless as well. Here is an example.

http://www.electricrider.com/crystalyte/index.htm

[TheKid]

I believe vic is referring to the motors that mount on top of a wheel and spin the tire, like a ZAP motor. They work on friction, and are known to wear out tires and are almost useless if the tire gets wet. The best solution for a bolt-on motor is a hub motor. I don't know how good those cheap scooter motors are, but Brad might. if I'm not mistaken, Brad warned against using those cheap controllers. You may want to search the old forum for Gil's DW's. He hooked a motor to the front wheel. and I think he was pretty clear on how he did it.

[TheVictim]

I'm not sweating the controller, I can build one no problem. I should probably DL some of his electric bike plans and see what I can glean from those.