possible idea for variable speed belt drive

[butterbean]

Your previous illustration shows that I'm right. But I'm now thinking of a two-speed, using a locking clutch lever. Pulling the clutch lever in would move the tensioner pulley away from the belt, thereby decreasing the tension obviously and putting the engine into a lower gear ratio and allowing for more torque i.e hill climbing and getting off the line. Leaving the clutch lever in the "engaged" position would leave the engine in top gear, or normal cruising speed.

 

[butterbean]

Got it all figured out, 9t gear on crankshaft, 22t on jackshaft input, clutch with belt pulley on jackshaft output, Whizzer sheave on rear wheel. Locking clutch lever with cable attached to tensioner pulley pivot arm to control belt tension. This will be a 2 speed, clutch lever in locked position puts bike in hill climbing/takeoff gear, clutch lever released puts bike in cruising gear. Locking the clutch lever will loosen the tension on the belt, releasing it will increase the tension. My cruising ratio will be 12:1, really not sure how to tell my hill climbing ratio, but the bike doesn't struggle up hills much as it is so it should be even better with this setup. It's also going on a 1955 Roadmaster frame (current setup is on a repop schwinn).

 

[Jax Rhapsody]

are you trying to build a variator?

 

[keatonx]

I'm not sure if you,re understanding my idea. The shifter cable would control tension on the tensioner spring. I would start with medium tension for a baseline ratio, basically close to the ratio I'm running now. Down-shifting would give the belt more slack, which would give the engine more torque for climbing hills and getting off the line (at least I am assuming). So perhaps this wouldn't be a true variable ratio, more like a clutch that loosens the belt. Now from what I understand about belts, less tension = torque while more tension = speed. I still haven't gotten a straight answer as to whether this is correct or not. This is the foundation of my idea, if it's wrong then I won't pursue this any further.

Slipping the belt doesn't give it more torque, but it will let the engine get into it's powerband on take off. Just a normal clutch. If you drop a car in 5th and feather the clutch out you still won't accelerate as fast as you would normally. Not to mention clutch wear (or in this case you would wear flat spots into the belt).

If you use a variator (like on a torque converter/CVT) as your drive pulley and had a spring loaded belt tensioner to pick up the slack, then you would have a variable ratio system

 

[SunkyWorks]

If you use a variator (like on a torque converter/CVT) as your drive pulley and had a spring loaded belt tensioner to pick up the slack, then you would have a variable ratio system

A number of mopeds use this system, except the the motor pivots to provide belt tension.

As cheap as CVT's have gotten on Ebay it would be interesting to try.

 

[keatonx]

I'm surprised somebody hasn't already replaced the engine pulley on a GEBE setup with a cheap pocketbike variator

 

[BigBlue]

I'm surprised somebody hasn't already replaced the engine pulley on a GEBE setup with a cheap pocketbike variator

There have been builds that use pocket bike CVT, but they just don't hold up without modification.

Chris
AKA: BigBlue

 

[HeadSmess]

Basically the most important part of my question is this. If I'm running a primary chain and secondary belt with the clutch on the crankshaft, will simply varying the tension on the belt vary the gear ratio? Or are my assumptions incorrect?

simply, with no jargon

NO.


you require a "variable pulley" which consists of two discs, held together by spring tension. belt rides on the outer diameter of discs for high gear (if this pulley is the DRIVER) and the discs spread apart on the shaft, against that spring, which then lets the belt ride near the shaft, or the inner diameter of the two discs, which will result in LOW GEAR.


the ideal setup is TWO such pulleys, as one gets larger, one gets smaller, and no belt tensioner is required! using only one variable pulley will require a belt tensioner, and also, the belt will experience some offset if only one disc moves. if both move an equal distance from the centreline, the belt will remain on the centreline.


you could use a single pulley, and vary the ratio by changing the belt tension, as long as the spring holding the two discs of the pulley together, is slightly weaker than the tensioner...


i used jargon, didnt i?


im sorry


simply reducing the tension on the belt alone will act like a clutch. and when it slips, you will burn your belt out. smoke, heat, squealing... think a car when the belts loose/worn out and its steering is turned to full lock. the belt will HOWL!

you NEED a variable pulley. be it the two discs that move together or apart (commercially available) or an expanding drum type (um....never seen one...)

 

[HeadSmess]

Slipping the belt doesn't give it more torque, but it will let the engine get into it's powerband on take off. Just a normal clutch. If you drop a car in 5th and feather the clutch out you still won't accelerate as fast as you would normally. Not to mention clutch wear (or in this case you would wear flat spots into the belt).

If you use a variator (like on a torque converter/CVT) as your drive pulley and had a spring loaded belt tensioner to pick up the slack, then you would have a variable ratio system

i was beaten to it. I agree.

 

[butterbean]

Ok, two more questions. One, if I use a variator pulley, can I manually control the speed by manually controlling the belt tension with a lever-actuated idler pulley (same idea as above, only in conjunction with variator pulley). Two, anyone know where to find a variator pulley that can fit a 5/8 keyed shaft?