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XPro V5 and Lead 1515 stepping config

Discussion in 'Control Software' started by Allistar, Mar 14, 2021.

  1. Allistar

    Allistar New
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    Hi all,
    I'm nearing the end of my Lead 1515 build. I'm using the XPRO V5 controller. I have all motors working in the correct direction. I'm confused about the settings. The lead screws move 8mm per rev. I found that XPro defaults the microstepping to 8. When I lower this to 1 I expect the steps/mm to be 25. E.g. 200 steps per rev and 8mm per rev. But when setting it to that it moves extremely slowly. When I set microstepping to 4 I would expect a value of 100 to be correct for steps per mm. I.e. 200 * 4 / 8. What I find by using digital calipers is that this needs to be set to 108.

    Why isn't it exact? I can't imagine the lead screws are not 8mm per rev.
    Why doesn't setting the microstepping to 1 seem to work?

    The machine seems to move fast (I haven't tensioned the lead screws or squared the gantry yet so can't do a full test). Is there a problem setting the microsteps to 4?

    Thanks,
    Allistar.
     
  2. Alex Chambers

    Alex Chambers Master
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    Torque drops off as you increase microstepping, but not as much as some people think. 8 x microstepping is a good compromise between torque and smooth movement - is there any particular reason why you want to reduce it?
    The steps/mm settings don't match the arithmetical calculations because our leadscrews (on all this type of machine, not just the Openbuilds ones) are formed by "hot rolling" the thread, and the pitch of the thread, although very close, will not be absolutely precise.
    Alex.
     
  3. Allistar

    Allistar New
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    Hi Alex,
    Thanks for the reply. I mistakenly assumed that microstepping of 1 was the preferred way to go. I thought if power to the steppers are turned off then it will "forget" the microstep it's on. Though in reality that's probably a tiny fraction of a mm. I want this machine to be fast and I thought the way to do that is with microstepping being disabled.

    I'll change it back to 8 which was the default is and will see how that impacts performance. Hopefully I can just change the 108 steps/mm to 216 and have it still be accurate!

    Thanks again and regards,
    Allistar.
     
  4. Alex Chambers

    Alex Chambers Master
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    That does still feel like a large error on the steps/mm though - typical adjustment would be something like 199.? for 8 x microstepping. Check by jogging back and forth repeatedly that you aren't losing steps somewhere - if you jog between marks it should not deviate from the marks. If it does check that you haven't got any stiffness/binding and that the motor coupler isn't slipping on either the motor shaft or the leadscrew.
    Alex.
     
    sharmstr likes this.
  5. Allistar

    Allistar New
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    I've changed it to 8 x microstepping and the steps/mm axes is 201.25, which is pretty close to the nominal 8mm/rev. Thanks for your help.
     
    sharmstr and Alex Chambers like this.

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