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Electric Bike - now with chain-snapping power!

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Last weekend I decided to put a big electric motor I have onto my bike. I had all the parts already from various projects. The only parts I needed to buy were the U-bolts. The motor is a 36V PMDC motor, rated at 3.0HP ~= 2.2kW. No, I don't know where to get another one, or even who the manufacturer is- the name is scratched off on the nameplate. Control is simple on/off control with a White-Rodgers contactor. In the first beta build, I ran it at 12v because I didn't want to die. That proved to be boring enough that I stepped it up to 24v immediately, which worked okay on half-dead batteries but threw and snapped chains incessantly on a full charge, making it unridable. Some of the pictures show a LiPo on the bike- when the batteries were wired for 12v, I needed some extra voltage to throw the 24v control coil. It is plenty quick at 24v, but with this design the pedals spin just as fast as you're going. Imagine pedalling fast enough to go 25MPH in the lowest gear on your bike. That's how fast the pedals are spinning- keep your legs out the the way. This weekend, I will take the ubermotor off and see about putting on a more reasonable 400W Kollmorgen brushless. That should be less suicidal. However, I want to drive the rear wheel directly, so it will be more complex. Probably won't get completed immediately, as I know I don't have the right rear sprocket. Please, feel free to ask questions in the comments.

18 comments

Jan 16, 2012. 9:10 PM

triumphman says:

I have a razor punk bike and need to put a bigger motor on it. The one it has is so weak. I tried a sears drill but it spins too fast on the wheel and wears out the rubber tire edge. Any ideas to upgrade this little bike? I want to keep it electric and simple as possible! Thanks for your help!

Sep 7, 2010. 11:27 AMtwighahn says:

(removed by author or community request)

May 9, 2011. 9:57 PMCropJ says:

Hai-yah!...
Whats up.

Aug 2, 2010. 7:33 PMiloveairsoftstuff says:

you could just take off or cut off the pedals so they don't spin and you just have a shaft.

Mar 31, 2010. 7:27 PMlane29 says:

i made a bike over the weekend and i actuoly had a similar problem were i was going up a hill and one of my links broke in half do you hve any ideas on how to stop this from happening

Jul 11, 2009. 2:57 AM

uglymike says:

An option to keep from spinning you pedals is to replace the rear wheel with a one with a disk brake. Then replace the brake disk with a sprocket (you'll have to fabricate one) and drive the other side of the wheel. The rear sprocket will free-spin and keep your pedals from spinning. Of course this only works if you can run the motor in reverse.

Jul 11, 2009. 6:49 AMnedfunnell (author) says:

That is my ideal solution. However, I haven't found any reasonably priced disk brake hubs. Got any ideas? Right now, my plan is to emulate the cheap import motor kits by clamping onto the spokes with two steel rings with rubber. Simple, but not very good.

Feb 19, 2010. 4:39 PMpyrosloth says:

Kingsmotorbikes sells gas and electric motors for bikes. Their setup uses a sprocket bolted directly to the spokes. A quick google will get you there and I believe they sell the sprocket setup on its own.

Jul 26, 2009. 12:02 PM

uglymike says:

2 other options are to find on of the old "AutoBikes" from the infomercials of a couple years ago. The ones with the automatic shifting derailleur. The crank is a freewheeling crank allowing the derailleur to downshift without pedaling. I just picked one up from Craigslist so keep an eye out for one. Also, Cyclone Motors, who make intermediate drive bicycle motors that drive the chain, also use freewheeling cranks. You can but just the freewheeling crankset from them for $63 + S&H at www.cyclone-tw.com Hope this helps Mike

Jul 11, 2009. 12:44 PM

uglymike says:

You can get a good quality hub from these guys ( http://www.totalcycling.com), Of course you'll have to rebuild your wheel if you just get the hub. A complete wheel set up for disk brakes gets pretty expensive.
Another alternative is to buy a complete bike from here ( http://www.bikeberry.com ). There's a model called the 26" Micargi SX4 that comes with front and rear disk brakes. It's $150 and shipping to me was another $50. So for about $200 you can get the rear disk brake hub and front disk brakes, mind you not great quality disk brakes, but inexpensive.

Feb 1, 2010. 10:37 AMdataphool says:

I see you have 2 X 12 Volt batteries; series or parallel? Do you have a transmission? what kind of motor? How much power does it develop? What power does it deliver? What is the bike's speed? Do you have control of the power, or is it running one size fits all?

Dec 26, 2009. 12:04 AMcuica says:

How about driving the front wheel with the motor?

Jul 19, 2009. 2:13 PMrlnbkseeberger says:

You could always try to have a sprocket on the pedal cranks that has no teeth/grind all the bits, and shift to that sprocket when using the motor, so the chain spins but it can't grab onto anything.

Jul 11, 2009. 10:34 AMhg341 says:

have you tryed takeing off the peadles yet?

Jul 11, 2009. 11:12 AMnedfunnell (author) says:

No, one of my main criteria for the e-bike is to remain pedalable. It draws less ire from authority that way.

Jul 10, 2009. 10:08 PM

CameronSS says:

Wow, that looks horrifically dangerous. Yeah, making the pedals not spin and having the fast-moving chain not directly next to your leg would be a good thing.

There was a guy near here who sold electric scooters and bicycles--he mounted large hub motors on an old bike, front and rear, and called it his Insane-O-Cycle. He said that it cruised just fine at 55, and would easily have gone faster, but he didn't have the brakes to stop it.

Jul 11, 2009. 6:53 AMnedfunnell (author) says:

Dangerous, yes. I'm not sure I'd say 'horrifically'. It's easy enough to keep ones legs out of the the way, albeit uncomfortable without pegs. I wonder where Mr. Insane-o-cycle got hubmotors that would do 55- he must have replaced the controllers.

Jul 11, 2009. 10:34 AM

CameronSS says:

I'm sure I saw an actual page specifically about that bike somewhere, but I can't find it now. I do have evidence that it exists, though, so feel free to research it more yourself.

I wasn't terribly clear...I think this is an awesome project, I just don't think that I would be comfortable with the chain right there. On the other hand, I'd be riding an electric bike with an insane 2.2kW motor, so there's an inherent risk there no matter what. :-)