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Thread: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

  1. #21

    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    My Motors are CPM-SDSK-3421P-ELN. The motor can be energized, i.e. power applied, but there is an enable signal that determines if the output shaft is "free" or locked to the step commands .powered off or disabled, there is little difference in the freewheeling properties.



  2. #22
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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    I want to understand a few things please:

    1 are these servos a close loop for step / position?
    2 what happens when you hit the E-stop button when you realize there is a problem. Does everything stop in place in the same way my steppers do?
    3 what happens when the machine crashes and hits a fixture - does it stop or does it continue to want to push through

    Why did you choose servos vs a hybrid / encoded stepper.
    Thank you



  3. #23

    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    I can only speak for my setup - I'm not a pro by any stretch.
    1. The motor models I chose are specifically designed to replace a stepper. they are a servo inside but externally they don't provide the same level of feedback and control as a "real" server and driver combination. Step, Direction, Enable and a multi function output are all there is.
    2. I use Mach4 and a PMDX-126 so I can code the machine to do any extra things I want e-stop to do. I originally had it set to configured to clear the "enable" signal whenever the machine faulted for any reason - I was building it so I had lots of faults in the process. Clearing the "enable" lets the motor freewheel. Estop by itself on a PMDX stops the pulse train, but any pulses the motor itself has buffered will continue to run. I can't imagine that buffer equates to a lot of distance, but its there. Clearing "enable" will stop its logic immediately leaving only inertia of the drive part , not clearing it allows it to finish processing the pulse train it has already received.
    3. The motor itself will fault and stop if it exceeds its torque setting which is configurable, but again, it will freewheel. If the Z axis is on its way down, that would not be helpful



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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Quote Originally Posted by Old_Phart View Post
    I can only speak for my setup - I'm not a pro by any stretch.
    1. The motor models I chose are specifically designed to replace a stepper. they are a servo inside but externally they don't provide the same level of feedback and control as a "real" server and driver combination. Step, Direction, Enable and a multi function output are all there is.
    2. I use Mach4 and a PMDX-126 so I can code the machine to do any extra things I want e-stop to do. I originally had it set to configured to clear the "enable" signal whenever the machine faulted for any reason - I was building it so I had lots of faults in the process. Clearing the "enable" lets the motor freewheel. Estop by itself on a PMDX stops the pulse train, but any pulses the motor itself has buffered will continue to run. I can't imagine that buffer equates to a lot of distance, but its there. Clearing "enable" will stop its logic immediately leaving only inertia of the drive part , not clearing it allows it to finish processing the pulse train it has already received.
    3. The motor itself will fault and stop if it exceeds its torque setting which is configurable, but again, it will freewheel. If the Z axis is on its way down, that would not be helpful
    So then, going back to your other posts, there is no hard "brake" like there is in a standard stepper setup ? I recall my nema34 would stop colt turkey whenever I hit the E-stop. However, in the event of crash it would keep destroying anything until I pressed the E-stop. I guess that last past is not important because the bit/cutter will break if the machines crashed it on a fixture etc. At the point of any crash you have already lost something. =(

    How you looked at hybrid steppers? I wonder if they are any different when it comes to stopping the machine either manually or via a fault.
    The one reason for me to want to have encoded steps is to mitigate loosing work it I have to E-stop, or power goes. In my mind the machine should know where it stopped.



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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Hi,
    when you Estop the contents of the motion buffer, could be several hundred ms worth of motion, is aborted and therefore Mach loses reference.
    It doesn't matter if you have encoders or not....Mach has lost its place. If you wish to stop the machine WITHOUT losing reference then use <FeedHold>.

    Craig



  6. #26

    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    the hard brake occurs when there are no more step instructions to process. Joe is of course right about mach losing its place at estop, but these CP steppers have their own buffer, albeit much smaller that what you can enable in Mach and they will play out unless enable is cleared. I can't recall how big the buffer is and at 3200 or 6400 steps per revolution the actual travel is not very much.
    If the power goes or estop is hit, there is no way on earth that the machine will know where it is upon restart, they just don't work like that. Mach needs to be referenced at every startup. I suppose you could build a machine using absolute encoders which could do that, - but I don't think Mach can use them so you need different software and hardware that could somehow remember where it was, read where it is, and continue from there.... I'm no expert but that doesn't sound like a good idea from a precision point of view.



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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Hi,
    I suppose you could build a machine using absolute encoders which could do that, - but I don't think Mach can use them so you need different software and hardware that could somehow remember where it was, read where it is, and continue from there.... I'm no expert but that doesn't sound like a good idea from a precision point of view.
    Using absolute multiturn encoders IS the modern way to go. When you turn such a machine on it knows exactly where it is, no homing required.
    Mach4 can certainly take advantage of that, it would require a little extra code in the startup script, effectively an automatic homing routine where
    the machine does not actually move but rather read its current position by reading the encoders.

    The servos (Clearpaths, Deltas or closed loop steppers) which are mentioned in this thread are not absolute encoders and neither are they multiturn
    and cannot therefore be used in that manner.

    If you require such servos the Delta A3 series has 24 bit absolute multiturn encoders with battery backup ( and brake if required).

    Craig



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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Hi,

    The one reason for me to want to have encoded steps is to mitigate loosing work it I have to E-stop, or power goes. In my mind the machine should know where it stopped.
    Then you can have it....but it requires absolute muliturn encoders, all the top tier servo manufacturers have them but they are not cheap.

    Craig



  9. #29
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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Quote Originally Posted by joeavaerage View Post
    Hi,

    Using absolute multiturn encoders IS the modern way to go. When you turn such a machine on it knows exactly where it is, no homing required.
    Mach4 can certainly take advantage of that, it would require a little extra code in the startup script, effectively an automatic homing routine where
    the machine does not actually move but rather read its current position by reading the encoders.

    The servos (Clearpaths, Deltas or closed loop steppers) which are mentioned in this thread are not absolute encoders and neither are they multiturn
    and cannot therefore be used in that manner.

    If you require such servos the Delta A3 series has 24 bit absolute multiturn encoders with battery backup ( and brake if required).

    Craig
    It does not matter what manufacturer's servos you use they all have absolute encoders options, that can remember where they are at, they don't have to be Delta or multiturn Dmm have had this with there system since day one,and even without a battery backup which gives you around 30 to 45min before the position is lost

    Mactec54


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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    have to ask then, what is the advantage of the clear path servos or hybrid steppers then?



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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Hi,

    have to ask then, what is the advantage of the clear path servos or hybrid steppers then?
    The main advantage is speed. Servos maintain their rated torque right up to their rated speed whereas steppers lose torque the faster they go.
    Servos also have a good overload tolerance. Commonly a servo will produce three-four times its rated torque,at any given speed, for short periods.
    Steppers when confronted with an overload situation, PARTICULARLY at speed, stall.

    A motor with an encoder, be it a DC servo motor, an AC servo motor, or a closed loop stepper, offers much higher resolution than a regular stepper.
    A regular stepper (200 step/rev) can increase its native resolution by half stepping (400 step/rev) and maybe at a squeak, quarter stepping (800 step/rev).
    Microstepping beyond that does not result in increased resolution despite the seductive hope that it should do so.

    A motor with an encoder can however hold a position at any given encoder count. For instance many closed loop steppers are fitted with 6000 count/rev
    encoders and therefore have a resolution of 6000 counts/rev. Most modern servos have very much greater resolutions again. For instance my (entry level)
    B2 series Delta servos have a 160,000 count/rev encoder. I might point out that is far greater than I could ever use, but its there. Later model servos
    have greater, often much greater resolution.

    Mactec is correct, all the top tier servo manufacturers have absolute multiturn encoder models, including Delta and DMM. You do need to look for it and be prepared to pay
    a premium for them. For example I recently paid (including three day DHL shipping to New Zealand) $620USD for a 750W B2 series Delta servo/drive/cables. The same size
    and power servo/drive with a multiturn encoder (A3 series) would cost about $900USD.

    There may be a resaonable way for you to achieve at least some of what you wish without fancy multiturn encoders. Some controllers, the CSMIO/A for instance
    monitor incremental encoders continuously and in realtime and so even if you Estop at least the machine does not lose reference, although it will not 'remember' where it is
    if the servo, or rather the encoder, is de-powered and so you would still have to home at the beginning of a session.

    LinuxCNC can do a similar thing, that is maintain position in realtime with incremental encoders.

    Craig



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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Teknic sells a brake for their servos now.



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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Hi,
    last time I looked they wanted eye watering money for their braked servos....has that changed? They wanted an extra $400USD....and that was on top of what is an overpriced servo.

    I bought a braked servo for my Z axis, it cost $650USD compared to the same size and power un-braked servo for $438USD...so you pay a premium, but not $400USD.

    Craig



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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Upgraded my 8” Z to the 12” and it comes w/a “drag holding brake” to prevent exactly the unpowered movement of the spindle you describe. Corey explained its use - you might ask if it can be retrofitted to your machine. From what I’ve experienced, the guys at AvidCNC can be enormously helpful. Good luck.



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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Here is a link to the Teknic brake.

    https://teknic.com/products/spring-a...er-off-brakes/

    en



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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    I have exactly the same servos and am having the same problem. Avid even sent me a brand new drag brake but it hasn't fixed it, about 50% of the time the drag brake will catch the Z axis, otherwise it drops.
    I'll likely get the Teknic brake as it's the cleanest option, but $USD300 hurts a bit... a nema34 DMM braked servo costs $460... maybe should have gone that way to start with



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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Hi,

    but $USD300 hurts a bit... a nema34 DMM braked servo costs $460... maybe should have gone that way to start with
    Yes, Teknics are perfectly OK servos but are expensive for what you get. Delta and DMM are easily as good quality, more IO, better encoders, more power, and optionally a brake, for less money.

    Craig

    Last edited by joeavaerage; 06-22-2022 at 05:17 PM.


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    Default Re: Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

    Just a heads up on the whole Teknic motors and AvidCNC Pro machines; that 0.002" repeatability and 0.005" accuracy are those rack and pinions. The Z axis is ball screw so the Teknics would shine there, no doubt. But it would be a waste to drive that pinion on those racks with a Teknic motor. I think the steppers are actually better because they will stall long before they get unrulily!

    Last thing about the Teknics on the rack and pinions; the pinion gear is aluminum and it is held against the rack by a tensioner spring. It is very easy to make those Teknic motors spin with enough acceleration and torque to chew through those teeth.

    I am a OEM for Teknics, btw. I do sell them in all of my products. The SDSK and the ClearCore are just wonderfully cool tools.



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Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.

Avid Z stage, Clearpath motor and a 22 pound Spindle. Z drops when powered off.