Step Pulleys for Multi Speed Drive

[powdersummit]

I've been thinking about using step pulleys to be able to offer different gear ratios for a motored bike. It would be the same as changin speeds on a drill press. It would be like being able to change your sproket but being able to do it in 10 seconds. The only issue would be having to stop, kill the engine (You don't want to loose any fingers changing the belt position) release the tension on the belt and change to a differnt pulley ratio. There a quite a few people out that are running a single ratio, this would just offer a quick change ratio.

I know most people and me would like a quick on the fly gear change solution but this wouldn't be all that bad. If you were off road riding and wanted more torque than speed you would put in in a lower gear and if you were riding mostly flat ground you would put it in a higher gear for a higher top end. You could have a couple of ratios in between for different situations.

Let me know what everyone thinks.

 

[4950cycle]

This is exactly what I am building Powdersummit.

 

[powdersummit]

What ratios are you running or plan on running? I was thinking about using a standard V-belt but the minimum pulley diameter for the 3vx belts is 1.63 inches which isn't bad but if you go to a Poly V (serpentine belt) the minimum pulley dia is .8 inches. That would allow me to run a more compact system with a larger ratio range. I've got a full machine shop at my disposal, just need to run through the numbers and grind myself a 40 degree cutter for the groove ribs.

Carl

 

[4950cycle]

I have a slieghtly different version of your idea. I have a Maxtorque cen. clutch with a 3.2 pulley/sheave on it. Going to a roughly 8 inch pulley jack shaft. Go to my thread for some pics. its called "Rear rack mount Greyhound" . Anyway, I am going for a 2 speed to start with. My ratios will be low gear approx. 21.5 to 1, High gear approx. 9.45 to 1 . I know that kinda sounds wacky but I figured one low gear for work (trailer) or hard pulling (hills), And a high gear for low resistance running. I will use and or attempt to use a front derailer to switch the belt back and forth from low gear to high gear pulleys. I will use a slieghtly longer than usual armed sprung belt tensioner to keep adequate belt tension. My low gear uses a 1 3/4 inch (2 inch OD), my high gear uses a 4 inch pulley going to a 15 inch Whizzer wheel sheave (rear wheel). What do ya think ?

 

[powdersummit]

Those numbers seem ok if that engine isn't a higher RPM engine such as the honda or the subaru-robin which turns 7k. I'm not familiar with the grayhound motor but I'm assuming it's set up to turn 3600, and those numbers should work just fine.

I'm still in the process of figuring out what speeds I want and how many steps in the pulleys with a given reduction (I love spreadsheets for playing with numbers). From there I can draw up the individual parts and virtually assemble them so that I can figure out which belts I need and if I can get short enough belts. The shortest I've been able to find in a poly v is 18.5 inches and I may want shorter, so that means going to timing belts which are more expensive and take more to machine.

Carl

 

[4950cycle]

What speeds you wanna go and what speeds you can actually go can be a different story when you are dealing with only 1 1/2 to 2 1/2 hp. Especially when you weigh 228 lbs like I do. And if you can come up with a multi ratio setup using a flat type toothed timeing belt you are out of my league. I am going to try to run regular 1/2 back type A V-belt from clutch to my 8 inch pulley on my jackshaft. , then run 3/8 (I think ?) back V-belt from my two pulley setup (on the other side of the jackshaft) to the Whizzer rear wheel pulley/sheave. I know I might have some slippage in high torque instances, But that might not be a bad thing when you are talking about the pulsey type power larger 4 stroke motors put motor bikes through. " I know " I have used lawn mower/edger 4 stroke motors before on MBs. they can be kind of hard on them (the bike and gear). You asked about the RPM / powerband of the 2 1/2 Greyhound, On this site the experts say around 1800-clear to as much as 4500-5000 rpm for a broke in removed governer Greyhound. What do you think ? Will my ratios be in the right ball park ?

 

[4950cycle]

Powersummit, Have you tried CW Grainger for belts ? I was over there in person and saw some mighty short belts on the rack. They (Grainger) are on line. I'm just lucky and have an outlet locally. I'm about ready to throw the MB in the back of the S 10 and take it to Ace hardwhare and then Grainger if I can't find the belts to make her go at the Ace lawn mower dept. . Have to make a tensioner first though. Thats about it !

 

[spad4me]

Post number one on this thread will get you a nifty gear ratio calculator It works on Windows , And GNU/LIinux under the wine emulator.

Best of all it is free of charge.

http://www.motoredbikes.com/showthread.php?p=87814

 

[powdersummit]

Ok I get low range engagement of 6.4 mph up to 16 mph. On high range I get engagement of 14.6 mph and a top of 36 mph. These numbers are based off of 1800 rpm engagement and 4500 rpm max speed. You can start out slower but you will be slipping the clutch a bit. Slipping the clutch is fine I just wouldn't do it all the time. I think your numbers should work just fine. That gray hound should be putting out good torque. Based off of the numbers on a bike calculator I found online you should be able to hit top speed in high gear and be able to pull a bit of a grade.

I'm looking forward to see how your setup does. Having a larger engine with more torque does make things easier for gearing. When you deal with the high rpm gx35 or the eho35 you have to play with numbers quite a bit more not to mention high rpms could use some balancing to keep things smooth. I can't imagine how a gp460 would be for balancing pulleys spinning at close to 14,000 rpm.

Good luck and I can't wait to hear your results. Nice thing about pulleys is they aren't too expensive and you can swap them out for different gearing.

Carl

 

[4950cycle]

That sounds pretty good Carl. You mean at 6.4 mph the cen. clutch is fully engauged and is no longer slipping from getting me moving from dead stop ?