Stepper Motor Sizing

[Saturn-V]

I am working on sizing a stepper motor, and I'm curious how resistive torques will affect motor selection. Let's say the system has an inertia ratio of 2, which is well within the recommended values of 1 to 10.

If the system has a lot of resistive torque caused by friction, less than but a substantial amount of the total motor torque, how will this affect the system? Will it not matter as long as the motor torque exceeds the friction, or will this resistive torque somehow make the motor think the 'effective load inertia' is higher than the actual load inertia and affect the inertia ratio?

 

[3DDave]

The motor doesn't think anything. The tuning from the motor controller may depending on how the loop, if there is one, is tuned.

Friction is usually on the plus side as it tends to damp motion - the motor slows when current/voltage drops.

Inertia id on the negative side - too much causes the motor to not slow when the current/voltage drops.

 

[drawoh]

Saturn-V,

How well do you understand your friction? Do you have an accurate and reliable measurement, or are you just guessing?

How important is it that your motor is small? Does it run continuously, making power consumption critical?

Is this going to be mass production, where...
[ol a]
[li]...the cost of each component in your system is critical.[/li]
[li]...you can spend NRE testing the heck out of everything, i.e., it is safe to take risks.[/li]
[/ol]

If this is a one-off test platform, you need it to work on the first try, without a lot of hacking around. The cost of an oversized stepper motor that easily manages your inertia and friction is trivial compared to the engineering costs of debugging.

--
JHG