# Helping out with pulley diameter calculation

1. Jul 25, 2016

### Giannakoulis

Hey guys.. Sorry for my english, i'am only 16 and it's not my parent language. I need help about a problem on mechanical engineering, and i really appreciated if you can help me out. I assume that i've got a moter currents which gives me out 220-230 Volt trend, and has 1800 bends per minute. Now i want to know how much diameter should have a pulley to put it on another machine. I want this machine to give 80 bends per minute. And what pulley should i put in the original current moter to suit them. The starting transmission from the moter will be done with a belt.. For more details or clarifications, just ask me..

2. Jul 25, 2016

### BvU

Hello Giannakoulis,

Basically you have $n_1 d_1 = n_2 d_2$ (because the belt speed is the same on both pulleys). In this expression
$n_1 =$ motor rpm (revolutions per minute)
$d_1 =$ pulley diameter on motor axis
$d_2 =$ pulley diameter on driven axis
$n_2 =$ driven axis rpm ​

In your case you have $n_1/n_2 = 22.5$ so you want $\ \ \ \ \$ pulley diameter on driven axis = 22.5 times pulley diameter on motor axis

3. Jul 25, 2016

### Giannakoulis

thanks a lot!!

4. Jul 26, 2016

### CWatters

That is a large ratio. It is possible that the belt will slip on the small pulley. The maximum power you can transmit is limited by friction and the "contact angle" (how far around the pulley the belt wraps). You might need to use a toothed belt?

5. Jul 26, 2016

### Bandit127

Or a series of pulleys with a smaller reduction in each. If my maths is right three pairs with a reduction of 3, 3 and 2.5 gets you 22.5:1.

6. Aug 9, 2016

### Rx7man

I would probably look at a 10:1 or 25:1 gear reduction.. with the 10:1 reduction you'd need a 2.25:1 belt drive (2" to 4.5" or so), and with the 25:1 the driven pulley would have to be just a bit smaller than the motor pulley.. If you use a chain drive from the gear to the machine, you can adjust the ratio there as well (may be easier and more accurate than changing pulley sizes)