possible idea for variable speed belt drive

[SunkyWorks]

I am not sure of the shipping.

http://www.bmikarts.com/30-Series-Driver-Unit-with-34-Bore_p_993.html

30 Series Driver Unit with 3/4" Bore
$49.95

 

[keatonx]

$85 plus $12 for shipping is cheaper than my local dealer, but I had another idea. A stepped pulley might be able to be shifted without having to do it by hand. A front derailleur turned around backwards might work with the spring-loaded, lever operated belt idler. Anyone have any thoughts on that? I think it could work. I would set the tension in high gear, then the lever would pull the idler off the belt and I could shift, then release the lever and the idler goes back to its position. This would only work with two pulleys, so the larger pulley would have to match my current ratio, and the smaller pulley would give me just a little more torque. Any thoughts?

Should work, but the front derailleur's rectangular hole would have to be bent out considerably to fit the belt, then cut so the belt can be slipped into the loop (solder/weld closed after). Also your belt idler would need to loosen up quite a bit when the drive is disengaged (enough that the belt can easily be flopped over into the other groove). Cuz the return spring in the derailleur isn't super strong. And you can't just add a massive return spring or your shift lever might not be able to pull against it or the shifter might not stay in it's "clicks" (spring force pulls shifter and clicks it into the other gear).

So design the tensioner so it allows the belt to fall (or almost fall off) the largest engine pulley when disengaged!

 

[butterbean]

That's what I was thinking. As far as the derailleur goes, I was just going to cut the bottom part off the triangle and leave it like that. I will have to look at it and get a better idea. I'm having a little bit of trouble tracking down the size pulleys I want. I want one pulley to be about 3.25" and the other roughly 2.5 or so. I found a stepped pulley with these two sizes, but it's $50. That's not too terribly expensive, but if I can find two single pulleys in those sizes it might be cheaper.

 

[butterbean]

If I buy the $50 pulley, which I am seriously considering, my top speed in high gear will be the same as it now, about 31mph, and in low gear will be about 24mph, so that should give me enough torque, considering I don't have that much trouble on moderate hills as it is, but it should give it a nice boost and be able to handle most any hill around where I live. It should also provide much smoother takeoff and acceleration.

 

[butterbean]

I'm also considering getting a hilliard extreme duty clutch. They can be had for 60 bones at surplus center. I will have to bore mine out for metric.

 

[BigBlue]

Try not to shop by the diameter of the pulley, but by the Belt Pitch Diameter. The Belt Pitch Diameter will depend on the type of belt you use. The following is an example of a 3.75 inch diameter pulley. You can use the following belts: 4L, A, AX, 5L, B, or BX Type V-belts. If you used a 5L belt, the Belt Pitch Diameter is 3.4. If you use a 4L belt, the Belt Pitch diameter is 3.0.



Here's some information on pulleys and belts that might help: http://www.gizmology.net/pulleysbelts.htm

It maybe possible that you may be able to use two different types of belts to get close to what you want on your ratios.

Chris
AKA: BigBlue

 

[butterbean]

With the variable pitch pulley from grainger, I will get the ratios I want with a 5L, B, or BX type belt.

 

[butterbean]

I was thinking of using a BX belt, because I seem to remember hearing that they were a bit more durable. Seems like they must have the widest pitch, because they gave a larger diameter than any other belt type. That might also help with belt tension.

 

[butterbean]

A guy on the minibike forum (which I only visit because I'm using a minibike engine) seems to think that shifting the belt won't work. He says I won't get enough slack on the belt to shift it, that the derailleur return spring isn't strong enough to force the belt on and off the pulleys, and that the belt will wad up and destroy itself. He says there needs to be two sets of pulleys, two belts and two idlers (impossible on a bicycle) but I think it will work just fine.

 

[james65]

The two belt system has been done on a bike somewhere on this or the other forum. It takes a good amount of effort and design.

A guy on the minibike forum (which I only visit because I'm using a minibike engine) seems to think that shifting the belt won't work. He says I won't get enough slack on the belt to shift it, that the derailleur return spring isn't strong enough to force the belt on and off the pulleys, and that the belt will wad up and destroy itself. He says there needs to be two sets of pulleys, two belts and two idlers (impossible on a bicycle) but I think it will work just fine.