V-Belt Setup Problems

[Gokussj5okazu]

Hey guys, awesome forum!

I'm having some trouble with a custom belt setup I'm running. See, I'm using a B&S 12.5HP vertical motor, connected to a Spicer transaxle, with an idler pulley setup as the clutch. I press the brake/clutch, the idler loosens and applies the transaxle's brake.

Well anyhow, the transaxle is a 6 speed, with a 12:1 ratio in 6th. On the motor I have a 3.75" pulley, and a 1.75" on the transaxle, they're all I had and I wanted some speed. Well with the tranny in 1st or 2nd, it pulls great, gobs of power, just slow. However, with the tranny in 3rd there's a lot of slippage in the belt going up hills, and 4th, 5th, and 6th gears are useless as they slip constantly unless someone pushes to get it started.

So, I'm racking my brain trying to figure out a way of correcting this. There's about 25lbs of tension on the belt right now, and I have no way of adding more. So, I've come up with two possible solutions and would like some input.

A; Get a cogged V-belt to better cope with the smaller pulley and add more grip.

B; Eliminate the clutch and use a chain drive with a cent. clutch. I hate cent. clutches though and I don't think one would hold up well in this situation.

So, any ideas?

 

[EagleTalons]

Add a larger pulley on the transaxle and a larger on onto the engine. That small of one on the transaxle is a bad idea.

Believe it or not a chain drive is a really good idea. It eliminates alot of belt nonsense.

 

[Kaptain Krunch]

add a stronger spring for the tensioner, and get a slightly larger pulley in the back so the belt grips more, i'd say atleast 3" in the back, you can get a larger front pulley if you'd like more speed.

So I'm guessing this is a racing mower? check out my mower build.
http://www.diygokarts.com/vb/showthread.php?t=3731

 

[dpaxson]

did you make sure the tensioner pulley is on the side of the belt opposite the one taking the torque of the engine?

 

[EagleTalons]

http://www.diygokarts.com/vb/showthread.php?t=3595

Here is my nonsensical build... it needs...things...

 

[Gokussj5okazu]

Actually, no it's not a racing mower, it's a completely hand built cart. I'll get some pics up tomorrow.

Alright, here's a crudely drawn pic of my setup. lol

As you can see, the tensioner pulls opposite of the pull from the tans to the engine. The engine is also litterally sitting atop the trans, so that belt's only 24" long.

I figured that trans pulley was too small, but the next size I have is a 4" one, which will trash any speed.

For a chain though, is there a good cent. clutch that would hold up to constant on/off conditions?

 

[EagleTalons]

Just get an 8 inch pulley for the engine.

 

[modelengineer]

You may be tensioning the belt on the wrong side, but this only matters if its a spring loaded tensioner.

 

[Gokussj5okazu]

Alright, well I can't increase the motor's pulley size any, it's already about 1/2" from the frame, so that's out of the question.

I think what I'm going to try, is welding a bar out, under the clutch/tensioner arm and put the tensioner pivot point closer to the pulley, there by multiplying the spring's pulling force.

Does that sound reasonable?

 

[dpaxson]

is there any way you could make the tensioner push on the belt instead of pull? that would give you more contact area on both pulleys

 

[anderkart]

Just a thought:
With your drawings tension-er pulley location, your belt is only contacting about 1/3 of your tranny pulley. I think that might be your problem here. (the further a belt wraps around a pulley, the better its gripping ability will be)

If you could relocate that tension-er pulley (like over the axle/with a shorter belt) so you got a good 2/3rds wrap around both the engine and tranny pulleys, you'd have more belt/pulley contact area and a much better chance for the belt to actualy grip the pulleys.

 

[Gokussj5okazu]

Alright, thanks for the tips. The way my setup is, I can't change the tensioner to push on the belt. ALso, I cannot move the arm back any, as my left tire is only about 1.5" from the left frame rail, so no room for an arm. However, anderkart's suggestion seems feasible.

Here's what I've come up with. On the left, I'll weld out a piece of tube, and put the tension arm's new pivot point there. Then, with that new arm, the belt will have more surface area on the trans pulley, and the lengthened arm will give the spring more leverage over the belt side of the arm.

The only problem I forsee is getting a short enough belt. My current setup only uses a 24" circ. belt. This will probably need something like...18", maybe.

 

[modelengineer]

So it is spring loaded... in your diagram which way does the motor shaft spin? It is important that the tensioner is on the correct side or it will require MUCH more tension than if it was on the correct side.

 

[Gokussj5okazu]

The motor spins clockwise.

 

[mike75925]

my uncle did this. he filed a vert shaft's shaft till it fit the cent clutch took and welded a socket to the top of an outboard's drive shaft. socket was same size as the twelve teeth and placed the engine on risers. worked pretty well considering how it looked. the pulleys will allow you to tune your ratios but as you have a tranny you may not need it. cheerio!

 

[Kaptain Krunch]

The motor spins clockwise.

Theres your problem, tensioner is on the wrong side.