angular control of stepper motor

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Sanduino
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angular control of stepper motor

Post by Sanduino » Tue Apr 19, 2016 7:08 pm

Hello to all the forum: I am working on a development with chipKIT Uno32, pololu A4988 driver and stepper motor. The idea is to control the position of stepper motor shaft position communicating with a terminal emulator.
The challenge is almost solved, but the problem of random motion of the shaft is shown for a few seconds in two different situations: 1) when I connect via Terminal Emulator COM port to chipKIT and 2) by pressing the RESET chipKIT.
It is obvious that in these two situations ports chipKIT trigger pulse arriving at Pololu A4988 driver having this effect. The question is whether there is a way to avoid such nuisance
Any advice or suggestion will be well received :)
best regards
Daniel

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majenko
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Re: angular control of stepper motor

Post by majenko » Tue Apr 19, 2016 10:17 pm

How is the driver wired to the Uno32?
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Sanduino
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Re: angular control of stepper motor

Post by Sanduino » Tue Apr 19, 2016 11:27 pm

the general scheme of connections is in attachment
regards
Daniel
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EmbeddedMan
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Re: angular control of stepper motor

Post by EmbeddedMan » Tue Apr 19, 2016 11:54 pm

Sanduino,

I would make sure that you have pull down resistors on the step and direction lines going from the micro to the stepper driver. That way, when the micro is not actively driving those signals (like when it is being reset and/or running the bootloader) you don't get noise triggering random steps. I have experienced this exact same thing in my own designs, which is why I added pull-downs on my Easy Driver and Big Easy Driver stepper driver designs.

*Brian

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majenko
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Re: angular control of stepper motor

Post by majenko » Wed Apr 20, 2016 12:28 am

Using pin 13 for Step is not a good idea. When the board reboots (as it does when you press reset or open the serial port) the LED that is attached to pin 13 (and of course anything else that is attached to that pin) blinks. That will be causing your stepper to step randomly.

By moving the Step signal to a different pin you should make your system more stable.
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Sanduino
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Re: angular control of stepper motor

Post by Sanduino » Wed Apr 20, 2016 3:26 pm

majenko and EmbeddedMan: Reposition the pin 13 to pin 11. Then I put pull down resistor to pin and direction steps and "voila", problem solved. Many thanks to both :D :D :D :D :D

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