Belt Drives

[__Tango]

So, in reading the specs on the new Zeros (http://www.elmoto.net/showthread.php...4849#post24849), i was thinking about belt drives. With the small tooth pitch of the belt (8mm or close to 5/16") vs. a chain (example 520 chain is 5/8" or almost just under 16mm pitch), one might think it'd be easier to get drive ratios that are better suited vs. a chain.

Is this true?

Also, how feasible is a belt drive for DIY folks like (some of) us?

[podolefsky]

I looked into this a lot and there are a few problems. Main one is finding rear sprockets large enough for ratios greater than 3:1 or so. They're out there, but they're expensive and usually made of cast iron (heavy).

You can find aluminum Harley sprockets, but they're for a larger pitch, so still not big enough to get a good ratio.

I think Ripperton ran a belt drive, but it was custom made and a pretty low ratio for racing (IIRC).

I'm guessing Zero is making their own (or has a custom supplier). Would be nice if they sold them.

[__Tango]

I see. I looked at the specs of the Gates belt (the one that the zeros use), and i can't tell what the large sprocket is. I wonder how hard it'd be to CNC manufacture one out of Aluminum?

[TonyHelms]

I have done a lot of research on this too, and it is possible. But would end up costing a LOT more then doing say a number 40 pitch chain. I think the biggest advantage would be the noise reduction! i hate that all I hear is my chain, I wish it were more like a Tesla where all you hear is the motor and gears wind up (sounds like a jet engine)

[Richard230]

I see. I looked at the specs of the Gates belt (the one that the zeros use), and i can't tell what the large sprocket is. I wonder how hard it'd be to CNC manufacture one out of Aluminum?

From the specs, it appears that Zero is using a 28 tooth front cogwheel and a 132 tooth rear cogwheel on the S model and a 25 tooth front sprocket on the DS model (if that was your question). I also find it interesting that Zero offers a chain-drive version for the DS (according to the manual), presumably for those owners who want to ride the bike off-road.

[ZoomSmith]

one might think it'd be easier to get drive ratios that are better suited vs. a chain.

There are several design limitations for belt drives. The biggest factor is the minimum sprocket (bend radius) size. Small sprockets bend the belt too much and reduces the life-cycle of the belt. There are also torque and RPM limitations to work around.

The Gates Poly Chain GT Carbon Design Manual is a great reference: Polychain Design Guide

I like the Zero belt drive, but would have opted for the next size wider on the belt.

[__Tango]

Ripperton was interested for the weight savings as well.


Does Gates (or any other belt company) give out the specs of the tooth profile so you could cut your own sprockets? a sheet of 12"x12" aluminum (6061 or 7075) in say 5x8" is well under $20. Given some time on a CNC mill and with the proper profile, you could probably cut it to the proper shape.

As far as the minimum sprocket, that makes sense, though i thought that the smaller pitch would give you more of an ability to get a good drive ratio. For some reason, in my pea brain, i have this feeling that it'd be easier to cut a rear sprocket for a belt than for a chain. I have no emperical evidence nor experience to support that gut feeling though...

[podolefsky]

I think Gates has CAD models on their website. I'd love to see someone cut one of these on a CNC...seems like a really big job.

One idea I had was to get a cast iron gear (which you can sometimes find on e-bay cheap), cut most of it out and replace with an aluminum hub.

But if you don't have a frame set up for belt, you have to take the swingarm off to change it. I finally decided it was to big a PITA and just went with a chain, especially since I'm still messing with gear ratios. You pretty much have to have your gears nails down if you invest in a belt drive.

[ZoomSmith]

Given some time on a CNC mill and with the proper profile, you could probably cut it to the proper shape.

I don't think Gates publishes that profile geometry (still looking), but their authorized partners have access to it.

i have this feeling that it'd be easier to cut a rear sprocket for a belt than for a chain. I have no emperical evidence nor experience to support that gut feeling though...

Given the number of teeth required is higher for synchronous drives and the material you are cutting is thicker (2x-3x), I'd have a hard time backing that theory.

Really not trying to discourage you from attempting it. I'm sure it can be done, but the effort ($$) will be significant.

[podolefsky]

I think you can find the profiles here (but not positive).

but like ZoomSmith said, this would be a huge undertaking. Poly chain profile isn't a simple profile.

I'd LOVE to be wrong about this. If anyone can find someone that will do custom belt drive sprockets for similar prices (even 2-3X) that of chain, I'd be very interested.