Any sources for 8mm bore 1/2" bicycle chain motor sprockets?

[fitek]

Working on bike #2 using standard bicycle chain (1/2" pitch), the No.25 chain was a pain in the butt on bike #1. I'd like to just attach the motor (which has an 8mm D shaft) to the rear wheel sprocket. This is a single speed children's bike and the rider's pedaling does not connect to the wheel. The rider connects to a 36v DC motor that will be used as a generator. For that, since the forces aren't too great, I just brazed a bicycle sprocket onto the no.35 sprocket that came attached to the motor.

I could switch the whole thing to #25 chain, but I'm rather tired of the stuff. I'm not sure what would happen if I disassemble the rear wheel. I imagine the rear sprocket on a single speed wheel with an internal brake is not as easily swapped out as on a wheel designed for multiple gears.

Haven't found anything so far, so I may just get one machined.

Edit: I seem to have made a confusing post, not using 8mm chain but 8mm d-shaft motors and standard bicycle chain

 

[iberkt]

MonsterScooterparts has just a few but there is not a lot of choices (they have a 20 tooth drive and a 44 tooth and 54 tooth driven sprocket).

http://www.monsterscooterparts.com/35chdrspgass.html

ElectricScooterParts has the same two driven sprockets but they have a few diffrent drive sprockets (they have a 10, 11, & 13 tooth).

http://www.electricscooterparts.com/sprockets.html

I'm not sure if this will give you enough gearing options but it is a start.

 

[safe]

Yuck... get out of the 8mm chain. Switch to the #35 chain instead, much more to choose from.

 

[vanilla ice]

He's asking for a bicycle chain sprocket. That uses like regular bicycle chain. I'm looking for the same thing, same bore size. Can't find anything at all. I think the easiest way to do it is bolt a #25 or whatever sprocket to the bicycle cluster and just use the odd pitch chains.

 

[fitek]

Vanilla, I haven't found anything still. My buddy has an old CNC machine for his business and we're going to take a shot at milling a regular bicycle chain sprocket with an 8mm bore in the next few weekends.

It's totally a time/cost thing, so if it takes too long I'll just have to go with #25. We're kind of thinking it won't work. If it somehow does works, I'll try to make a couple, maybe I can provide you with an extra, but no promises as its not my machine and shop time is limited.

As a note, I attempted to run the generator a few nights ago and it did not work out. The internal 9:1 reduction plus about another 4:3 due to the crank gearing was not enough. I pedaled as fast as I could and only made 13v tops. The Kollmorgen 300W only makes noises at that voltage. So I'll try using different sprockets, but not sure if I can get the gear reduction high enough.

I may need some buck boost converter to raise the voltage when it's too low; but I also need to protect against the voltage being too high.

 

[vanilla ice]

I would just machine an aluminum adapter that has an 8mm bore and can bolt/thread on a standard bicycle sprocket. Otherwise what will you do when it wears out.

You're using a geared motor right? If not, you won't be able gear down enough like with the small chain. With #25 you can do 11/90.

 

[fitek]

You're totally right Vanilla. Somehow in my rush to get going I never calculated out the sprocket sizes I would need. I'll never find the right sizes of bike chain sprockets.

So, I'm probably going with #25 chain. In this case, I will just need an adapter from the coaster brake wheel hub to the large sprocket.

I could use #35 chain, which is much cheaper, but then I'd need to make an adapter for a #35 motor sprocket to use the 8mm d-shaft, and another for the rear wheel.

I see the value now in starting with a bike that has a rear derailleur. I could use totally off the shelf parts.

One other option I have is to swap the rear and front wheel on the bike. I still have to make an adapter for the large sprocket to the wheel, but at least I can save time by not having to attach mountings for brakes on the front. Just figure out a way to use the coaster brake on the front.

I don't have specs on the Kollmorgen motor I am using, but I went with 11/90 on my other bike and, though I was using batteries on their last legs, it didn't feel like I was going to make it up to 25mph. I made it to about 15mph. So I was thinking of going for 11/60 or 11/66 on this bike.

 

[Dr. Shock]

I got a #41 sprocket from McMaster Carr and adapted it to bicycle chain. I think you can get them with no bore or a smaller bore than you need and drill them out to the size you need.

#41 is the right pitch for a bike chain, but the teeth are too wide, and if you get a cog with a small number of teeth, they are also too tall. Look at the shape of the guide sprockets in a rear derailleur and you'll have an idea of the shape you need. Small sprockets make each link rotate more than a larger sprocket, so to avoid unwanted contacts, you need shorter teeth.

It was surprisingly easy to adapt the #41 sprocket. First, I got it mounted on the motor shaft and set the motor spinning. As the gear was spinning I gently started grinding the sides of the teeth with my angle grinder. I had a bike cog to compare it to, so that I didn't go too thin. By spinning the sprocket with the motor, I made sure that the grinding was about the same for each tooth.

Next, I ground down the tops of the teeth. I did this in several stages, setting the chain up and taking the bike for a ride between each trial and seeing if it threw the chain. After a few trials, the chain stayed put and seemed "comfortable." When you spend a little time with the chain setup you get an intuitive feeling for whether the chain is seeing a lot of resistance or whether it is slipping easily on and off the sprocket.

You could do this better with a lathe, but my way is cheap, quick and works well.

Hope that helps.