Calculating Pulley Ratios for Scissors Lift

[R4de0n]

Homework Statement

Hi, I am having a problem with calculating the proper sizes for a pulley.The pulleys are turning threaded bars and I want them to turn at different speeds. They are connected via a Belt. There are three pulleys arranged in a triangle. One is the driver pulley(Ø31mm) which I don't have a problem with... the one on the bottom right(Ø31mm) is the same size as the driver pulley, my problem is that I want to size the pulley on the left(Ø46mm) to turn about half as much as the the other driven pulley.
Originally I thought that a ratio of roughly 1:1.5 (31:46) would be ok, but I made the pulley and the difference in rotations did not appear to be 1:1.5.

I was hoping someone would be able to point out if I am missing something glaring. Any insight into how to calculate the proper size so that my threaded bars will turn at the above ratio would be much appreciated

Homework Equations

The Attempt at a Solution

 

[nvn]

R4de0n: The left-hand pulley would need to have a diameter of 62 mm, if the diameter of the right-hand pulley is 31 mm. This would cause the left-hand pulley to rotate at one half the speed of the right-hand pulley.

 

[R4de0n]

Thanks very much nvn.