Electric clutch and pulley math

[Jbird5986]

Hello all im getting close to ready for a test run problem is i have a electric clutch and I dont think it can handle the stresss of car tires so I need to change pulleys and the math is killing me.I have 13 horse motor maxes out 3500 rpm and my tires have a diameter of 30 inches I tried using calculator with 3 inch engine pulley and 10 inch driven and im getting crazy numbers can anyone point me in right direction Thanks

[Woodside Kai]

3500 x 3 ÷ 10 = 1050 rpm     
30 × pi ÷ 12 = 8247 fpm

Might be a little too fast 

[Southside]

FWIW my Super 70 band speed is 5100 FPM if that gives you a gauge to go by. 

[GAB]

Hello all im getting close to ready for a test run problem is i have a electric clutch and I dont think it can handle the stresss of car tires so I need to change pulleys and the math is killing me.I have 13 horse motor maxes out 3500 rpm and my tires have a diameter of 30 inches I tried using calculator with 3 inch engine pulley and 10 inch driven and im getting crazy numbers can anyone point me in right direction Thanks

If you reduce the 3 to a 2 OR increase the 10 to a 16 you'll be closer to Southside's RPM.
GAB

[Jbird5986]

Ok thanks i kept getting really high speeds and thought i was doing something wrong i got a 2 inch in stock Thanks Ill upload some pics tommorow it will give everyone a good laugh

[beenthere]

Look forward to pics. We don't laugh, but we are interested and many do like to help.. even if it sounds like spending your money. 

[Joe Hillmann]

Ok thanks i kept getting really high speeds and thought i was doing something wrong i got a 2 inch in stock Thanks Ill upload some pics tommorow it will give everyone a good laugh

Were you dividing by 12? to go from inches per minute down to feet per minute?

[Hilltop366]

There is a band speed calculator in the tool box (red toolbox, bottom left of this page) under the machinery calculator.

A 2" pulley won't give you much traction with so little belt to pulley contact area. I would suggest as big of pulley for your driven as you can get so you could put a much larger drive pulley or jack shaft with a large and small pulley to step it down.

Another option might be to cut a bit of a grove in the car tire and run the belt on that?
That would let you run a 5" pulley on the engine and get you 4580 fpm band speed which is probably more like what you would want with 13 hp.

[RetiredTech]

Ok thanks i kept getting really high speeds and thought i was doing something wrong i got a 2 inch in stock Thanks Ill upload some pics tommorow it will give everyone a good laugh

Nobody laughed at my build, so I think you'll be OK.
I agree with increasing the driven pulley size instead of decreasing the engine pulley size. You'll need enough wrap around the pulley to supply the hp to the wheels. Too small of a drive pulley and you'll end up burning up belts due to slippage. From what I've read here on the FF, too much speed at the band can lead to very short blade life as it takes the set out of the teeth and overheats the band. I'd try to get that band speed down somewhere between 4000 to 5000 rpm. Mine is a little over that right now and I plan to slow it down when I can get back to work on it. Looking forward to some photos.