Hello,
I do know how to find a DC motor's transfer function, but I wonder how could I find it for a stepper motor, permanent magnet, instead.
anyone knows??

thank you!

 

Thats a fairly difficult controls problem. A lot of times they can be estimated by a 2nd order polynomial. You might try hitting it with a step function and looking at the output and trying to apply some common 2nd order formulas. Or you might try computing the frequency response. Its a start at least.

 

Why would you want to know anyway? - is there some use for it?, and wouldn't it be easier (and more accurate) to simply connect it and run tests?.

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You would want to know it for the design of a controller. You can't simply run tests and design a controller, you need the specific transfer function (or at least a good estimate) to make it stable...etc

 

For a stepper motor?.

I presume you're talking about PID on a DC motor?.

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not really, the PID is the control and has an easily discovered trasfer function (A + sB + C/s)

FOr a DC-motor it is just the transform of an R-L load


Other motors...
I have a motor book here at home, give me a bit i will see if it has the S-trasform of some of them

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I needed to know the transfer funtion for some exercises I need to do for university.
I was thinking on frequency response function. Keep on making it ir turn faster and faster and measuring its speed. But it does not seem very easy neither very exact...

 

And you are using a stepper motor?, they don't turn very fast anyway, and basically produce less power the faster they go.

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Yes, I'm using a stepper because I need acurate positioning..
But when I started, I didn't think it would be hard to get a transfer function, as I already did with a DC motor

 

I don't really see how it applies to a stepper?.

What EXACTLY are you trying to do?, and why do you think a 'transfer function' might help?.

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Really,
I think it just won't help, but my teacher wanted up to get a transfer function ofr the control system we choose. I choose stepper, but I don't think transfer function would help. appart, which would be the input state for the transfer function??
Speed versus voltage ?? No, voltage applies to several windings.
Torque versus voltage?? Very hard to measure, and not very usefull

I think I will just make a control circuit, which I'm just finishing, and document all the stuff, as I really don't know how to find and use a transfer function for steppers..

 

u gotto replace the motor with a dashpot, spring of stiffness 'k' and as far as i remmber, mass.
now write ur transfer func as second order differential eq.

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