Help with stepper motor position

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Zarakk
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Joined: Thu Dec 06, 2018 5:30 am

Help with stepper motor position

Post by Zarakk » Thu Dec 06, 2018 5:46 am

Hi everyone, I'm new here.

I don't have much experience with Electronics but I'm an engineer and programmer and have wanted to start playing about with some projects using a Raspberry Pi and/or Arduino.

One project I want to start involves very precise angular movements on motors. I'm looking at stepper motors but know very little (I'm an aerodynamic engineer so my skills don't translate lol). What I need is 3 motors, that can turn in increments of about 1 degree so I am looking at 1.8deg stepper motors with some micro stepping but the more steps the better. Two of the motors will turn very slowly, with the other having a max speed of about 1-2 revolutions per second.

The project isn't big and I have been looking at motors as small as possible (sub 45mm3 ideally)

My biggest issue is that ideally I need to know the angular position of the motors at any time even when turned of and on. I have looked at Absolute Radial Encoders and Potentiometers but wondered if anyone had any thoughts? Am I trying to do the impossible?

I would appreciate any help,

Thanks
Nick

lyndon
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Re: Help with stepper motor position

Post by lyndon » Fri Dec 07, 2018 9:22 am

The main benefit of microstepping is smoother motion, not more precise control. I wouldn't trust the accuracy below half step or so, depending on the particular motor you are using. If you need more precise motion, gear it down. For knowing startup position, yes you will need some sort of absolute position measurement.

jremington
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Re: Help with stepper motor position

Post by jremington » Fri Dec 07, 2018 12:09 pm

I agree with the above.

To determine the shaft position of a stepper after power down, you have only two options. One is to use an absolute rotary shaft encoder, the other is to "home" the stepper upon power up, using a limit switch (and rotate back to original position).

Zarakk
Posts: 2
Joined: Thu Dec 06, 2018 5:30 am

Re: Help with stepper motor position

Post by Zarakk » Sat Dec 08, 2018 4:46 am

Thank you for the replies.

I hadn't thought about the accuracy of the microstepping so thank you. I will go on the prowl for as cheap absolute encoders as I can find. Thanks a bunch

Nick

lyndon
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Re: Help with stepper motor position

Post by lyndon » Sat Dec 08, 2018 9:13 am

One important thing to bear in mind is do you need to know the position of the motor shaft, or the position of what it's driving?

BigPilot
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Re: Help with stepper motor position

Post by BigPilot » Sun Dec 09, 2018 8:36 am

Do you need the position instantly when you turn it on or can you move the stepper motor until you find an indication of its position? A hall sensor would do in that case, but it will be difficult to get 1 degree precision.

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