Need some geometry/gearing help please

[727737Nut]

This is one of my weak areas, lol.  I have a control cable that moves 7" total. The cable will be turning a pot via a grooved pulley.  How do i determine how many turns different size pulleys will make the pot move?  Hope that makes since?
Thanks,
Rob

[jackpilot]

Hi Rob

The formula is:  C=2 X Pi XR
C is the circomference of the circle
Pi (greec) is 3,1416
R is the radius.

Lets go to metric because the imperial medieval system is a nightmare.
7" is 178 mm

If you want one turn (360°)
C = 178mm

178= 2 X 3,1416 X R
or 178=6.283 R
then R= 178 / 6.283
R= 28,3 mm

For one turn your pulley must have a radius of 28,3.mm or a diameter of 56.6 mm
or , back to medieval 2"3/16 ...

2"¼ diameter will do .
You can use the formula at will.
JP

[Aerosim Solutions]

Hi,
Jack's formula is sound although I would like to add that rotary pots generally only travel through a maximum of 290 degrees. In all of my Aerosim solutions products that use potentiometers, I ensure that all the pots are driven 270 degrees, this gives a good wide signal range without the potentiometer's wiper arm coming into contact with the ends of it's travel within the housing.

Given that 7" = 178mm (I agree Jack, millimeters rock!) The diameter of a circle with a circumference of 178mm is determined by dividing 178 by Pii (3.142), this equals 56.6mm

To use 270 degrees of a circle we need a bigger circle and this is calculated like this - [(56.6 x 4) divided by 3] = 75.46mm which is close enough to three inches diameter.

I suggest you use a 3" pulley for your task, this will provide 270 degrees of rotation from seven inches of linear motion!

Cheers, Gwyn (Mech Eng.)
www.aerosimsolutions.com.au

[727737Nut]

Thanks guys!  What if i went to a 3 or 5 turn pot, wouldnt that allow a smaller pulley? Space may be tight for a 3" pulley

[Ricardo Carvalho]

For one turn your pulley must have a radius of 28,3.mm or a diameter of 56.6 mm
or , back to medieval 2"3/16 ...

2"¼ diameter will do .
You can use the formula at will.
JP
[/quote]

Metric rules!!!!!

[Aerosim Solutions]

For a 3 turn pot - 18mm diameter, 5 turn pot - 10mm diameter should do it!

Cheers Gwyn