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.Adam

 

[Rafa]

1988 ajk give you the answer and for "Sadly, until the platform is built and set up I won't know how heavy it will be ". You can estimate it if you know what materials are been used and the size (dimensions) of platform

 

[1988ajk]

If you don't know the force your lifting you can't choose a motor, and you definitely cannot machine a rack and pinion as you have no idea of the stress the components will be under, which will help you choose the correct module etc.

the weight of the platform is the most important starting point of your design calculations, so that you can design all components around this force. this will ensure your system is SAFE

Note; if you have designed it with 3d CAD the weight is calculated for you...