Slaving two axis with two drives anxiety!


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    Default Slaving two axis with two drives anxiety!

    I'm building another machine that will utilize two Rexroth CKK ballscrew stages powered by two steppers and Gecko Drives. Nice neat package. A lot of the work comes pre-packaged.

    I cringe and lose steep at the thought of what might happen if one side of the gantry quits or loses steps. The machine would literally tear itself apart.

    What recommendations might you all have for putting my worries at rest?

    Thanks in advance!

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    Default Re: Slaving two axis with two drives anxiety!

    Do your drivers have an output if they alarm? You could rig up a system to E Stop if one does?

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    Default Re: Slaving two axis with two drives anxiety!

    Not sure. Using Gecko 201 drives.

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    Default Re: Slaving two axis with two drives anxiety!

    I just took a look it doesn't appear they have an alarm output instead they have a disable input.

    Hey so I had a twin motor gantry that I would bite my lip if one motor stalled. But it's happened quite a bit in the past. Bit of gantry flex. Need to re home it to square it. Some of the other drivers have an output that you can e stop your machine if they fail.

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    Default Re: Slaving two axis with two drives anxiety!

    I cringe and lose steep at the thought of what might happen if one side of the gantry quits or loses steps. The machine would literally tear itself apart.
    1) Don't try to run it at the upper limit of your steppers.
    2) If one stepper stalls, it's usually because it ran out of power. Once one stalls, the second will likely stall almost immediately, as the load will be much higher.
    Not sure how one stepper doesn't wouldn't have enough power to move the machine, but the one slaved to it has enough power to tear it apart.

    I've had this happen a couple times when testing, and the second stepper always stalls right after the first one.

    Gerry

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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Slaving two axis with two drives anxiety!

    I'm considering running the proving runs using Nylon fasteners where the gantry meets the X axis just in case I miss something and things go south.

    The Gecko drives do have an enable pin, so maybe I can use that to trigger and E stop?

    Is a sentance fragment?


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    Default Re: Slaving two axis with two drives anxiety!

    Agree with Ger. When mine stall, the other side almost immediately stalls as well. And you might be surprised how much a very rigid gantry can actually twist before you get damage? I guess I used to think the same until mine stalled a few times. My only reason for hooking up an estop was to avoid ruining my workpiece (if it saved quickly enough)

    Not sure if the enable will be of use? You need an alarm or similar. If you REALLY wanted to do something you could..... gee, not sure how but use a strain guage system. But we are talking some clever design work there. Something to sense a signal, not sense movement, boom - signal estop. Arduino plus umm what's it called...... wheatstone bridge with a series of strain blocks????? Yes? No?

    Someone tell me I am wrong before I offer a completely wrong idea..... ha

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    Default Re: Slaving two axis with two drives anxiety!

    Since I'm only planning on cutting EPP foam I could limit the current to the drives to they would stall easily if something's afoot?

    Is a sentance fragment?


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    Community Moderator ger21's Avatar
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    Default Re: Slaving two axis with two drives anxiety!

    Which would only lead to stalling.

    You are worrying about nothing.

    A properly setup machine should never stall.


    If one side does stall, it only takes a small amount of binding to cause the other side to stall. If one side stalled, then the other one is not far behind it.

    You're "solutions" to a non existent problem are only likely to lead to more stalling.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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