 # Calculate the force needed for a stepper motor

Hello all,

I made some calculation for force needed for a stepper motor. Can someone check if I am wright about it?

Thanks  Most of what you posted doesn't make sense.

See https://www.pololu.com/blog/10/force-and-torque and http://www.societyofrobots.com/mechanics_dynamics.shtml for some useful background.

I get this from http://www.leadshine.com/pdf/calculation.pdf, sorry that I didn't post this in the first place.

I'm not an engineer and I don't have any experience, so I don't know if they are wright or wrong.

I just try to validate if my linear drive will be the same like in the figure that they are presented, and if I put the right values in formulas.

Do you think that they are wrong in the calculation?

Thanks for support.

Can you set up some sort of test rig and measure the force needed to move your object?

There is a suggestion for a simple measuring method in Stepper Motor Basics

...R

The formulas in the .pdf file appear to be correct, however there are several things wrong with what you posted. It is very important to understand the units involved and if you are very careful to use those units, the numbers you get should be meaningful.

For example, the units of the moment of inertia (not “inertia”) are kg m2, not kg/m2.

Torque is measured in N m, not N/m. The acceleration due to gravity is in m/s2.

The formulas are only an approximation, as you will need to account for friction. Where did you get the value of the frictional coefficient mu = 3?

Your posting is almost impossible to follow - its a case of using a spreadsheet where a spreadsheet is not appropriate (all too common).

I think all you need to do is multiply the force presented by the load by the sprocket diameter, in compatible units, to give the torque. (and perhaps also angular acceleration x effective moment of inertia)

But the real issue you won't have considered is that dynamic stepper motor torque is not well-behaved, it depends on the speed, vibration/resonance, microstepping setting. If you are lucky you will find a dynamic torque/speed graph for a stepper motor, but even then I'd take that as a rough guide - miss-stepping due to vibration and resonance is really something that you will find by experiment, not by calculation. And those graphs are different for each value of supply voltage.