# How to determine linear force from rotational force?

mikegrundvig
Hi all; I'm building a mechanism that will raise and lower a small platform but I need to determine how much force is needed. Sadly, until the platform is built and set up I won't know how heavy it will be so I'm trying to just determine how to calculate the force various motors can put out so I can pick them correctly when I'm ready.

Basically, I'd like to use a rack-and-pinion combined with a stepper motor to handle the movement. I THINK this is a simple question, I have the strength of the stepper motors available in either ounce/inches or gram/centimeters and conversion between them is simple enough. The problem is that I have no idea how to convert that motor rating to linear "strength" or "holding point" based on a rack-and-pinion design. I'll be machining both the rack and the pinion so I'm completely flexible on the tooth size and count. BTW - here is a sample of the type of motors I'd like to use:
http://www.jameco.com/Jameco/catalogs/c111/P113.pdf

Any help or guidance here would be greatly appreciated. Thanks!

-Mike

1988ajk
Mike,

you could use;

motor power (W) = Linear Force from platform (Newtons) x Linear Velocity of platform (metres per second) = ....(Watts)

There are other ways of calculating it i'm sure, but this is quite simple.