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Thread: Stepper Options

  1. #25
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    Default Re: Stepper Options

    Quote Originally Posted by RCaffin View Post
    And to think, encoders used to cost hundreds of dollars - once.
    Hum ... capacitive rather than optical? Interesting.

    Cheers
    Roger
    But one still gets what they pay for to a certain extent. Those CUI encoders, although suitable, have jitter causing slop between shaft adapter teeth and hub grooves which not only varies from sample to sample but increases with each mount/removal cycle (to change resolution for example). It should come as no surprise that they cite the following;

    We recommend no more than three cycles of mounting and
    removal of the AMT top cover base. Multiple cycles of mounting
    and removing the top cover can cause base fatigue over time
    and affect encoder performance.


    Optical encoders, using screws instead of snaps and with the disc fixed to the shaft similar to a pulley, have no such slop/jitter issues.



  2. #26
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    Default Re: Stepper Options

    Hi eldata

    Yessss - I can imagine. Thanks for the warning.

    I originally used HP optical encoders on servo motors, but that was 20 - 30 years ago. They still work just fine. Alignment is still good.
    And the HEDS 5540 optical encoders I am using now are also just fine.
    Hum ... differential line drivers would have been nice of course, but they can be added 1" away. It works.

    Cheers
    Roger



  3. #27
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    Default Re: Stepper Options

    Yeah, HEDS or US Digital equivalents would be best for a more refined servo experience but for validating OLS integrity, like what 109jb has in mind, the CUI encoders should be more than suitable. I use them for R&D work in a similar manner.



  4. #28
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    Default Re: Stepper Options

    Nobody said anything about using the encoder for a PID servo type loop.
    Actually the original Post was about that and the basis for the comments , and it was your post that changed it to stop-on-loss rather than correction.

    And "theoretical" was not ignored....the whole thing is theoretical and the proper numbers need to be argued (even in a theory) not some meaningless resolution that is not there.



  5. #29
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    Default Re: Stepper Options

    In my limited experience (I have built one CNC and am building a second), I haven't had many opportunities to try out different systems.

    On my first build I used Gecko G201X drivers, never lost any steps, I believe that adding encoders to the steppers would have added no value. It would have been a waste of $$$.

    I'll be using the same G201X on my current build, but for my forth axis I will go with either a Leadshine (because of the $$, and because I have read good reviews on here) or perhaps an MDrive, which has the driver built in, because I know where I can get some N34 MDrives at a good price local to me in Canada.

    I'm guessing the automation technologies drivers are good quality too, I just don't have any personal experience and haven't read any specific reviews on them. I was under the impression that they are made by leadshine, and I think that you and Ger believe this as well, so from what I've read, they would be a good choice.

    As far as the motors go:

    I'm not very familiar with this conversion you are doing, I googled it, so I have a little bit of an idea. From what I found, looks like a mini mill with 0.2" lead ball screws, so about 5mm. Is that correct? And what kind of speeds and acceleration do you want to achieve? Do you want to do some high speed machining with this? In my view, these are the appropriate questions to ask, more relevant than using encoders or not.

    This conversion uses two nema 23 size and one nema 34, is that correct? So with 0.2" lead you'd want something with good performance at higher speeds (sufficient torque), low inductance. Have a look at the torque vs speed graphs and inductance value. Also the higher the power supply voltage, the better the performance at higher speeds, while you may never use the max amp draw at lower speeds and at higher speeds, your motors can't draw max amps. It depends on how fast you want to drive this machine.

    As this is a common conversion, the easiest thing to do is to find someone who has achieved good results and copy what they did for motor selection.

    In your shoes, on this project, I would be tempted to look on EBay, and see if I could find two Nema 23 MDrives, and one Nema 34 MDrive at a good price. Those are "smart" motors with good drivers built in.

    Schneider Electric MDO1PSD23A7 MDrive23 Plus +12-75VDC Stepper Motor + Driver | eBay

    I'm guessing the specs for those are found here:

    https://motion.schneider-electric.co...-control-ip20/

    At 75V, the single stack torque vs speed is almost flat at goes to 2000 RPM, looking at the numbers, I'm guessing that would work for you on X and Y. How heavy is the table on this mill? Anyhow, that's what I'd do. The higher torque at lower RPMs doesn't help if you never use it and don't have the torque at higher RPMs. I'm guessing you could get 300 to 400 IPM max speed with 0.15 to 0.2G accel using these on X and Y with a table that is less than 150 lbs all up weight, and a lead of approx 5mm, but that is just an initial guess.

    If you want a sense of how other motors might perform, then find a torque vs speed graph for them and post it.

    And here is a Nema 34

    New IMS MDrive34 MDOF3424 Nema34 Stepper Motor w/ Built-in Driver - CNC Rep Rap | eBay



  6. #30
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    Default Re: Stepper Options

    Hi NIC 77

    As far as I can see (because the data sheets are seriously lacking in explanations), those MDrives use a serial RS488 interface. IF (IF) that is correct, they would be totally incompatible with any modern CNC controller such as Mach3, Mach4, UCCNC, LinuxCNC, etc. They would belong to a generation from 50 years ago. But I may be wrong: perhaps they do accept the modern Step/Dir signals. Do you know?

    I use a G203V driver on one stepper - very happy. For the rest I use G320 servo drivers on Baldor DC motors. Unstoppable.

    Cheers
    Roger



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    Default Re: Stepper Options

    Nic77

    Need to be careful when choosing Schneider/IMS motor drives. Not all of them support standard step and direction inputs. Need to look at the datasheet.

    I just picked up a pair of applied Motion TSM motors to test. Stepper servo with high resolution encoders.



  8. #32
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    Default Re: Stepper Options

    Quote Originally Posted by RCaffin View Post
    Hi NIC 77

    As far as I can see (because the data sheets are seriously lacking in explanations), those MDrives use a serial RS488 interface. IF (IF) that is correct, they would be totally incompatible with any modern CNC controller such as Mach3, Mach4, UCCNC, LinuxCNC, etc. They would belong to a generation from 50 years ago. But I may be wrong: perhaps they do accept the modern Step/Dir signals. Do you know?

    I use a G203V driver on one stepper - very happy. For the rest I use G320 servo drivers on Baldor DC motors. Unstoppable.

    Cheers
    Roger
    Quote Originally Posted by jfong View Post
    Nic77

    Need to be careful when choosing Schneider/IMS motor drives. Not all of them support standard step and direction inputs. Need to look at the datasheet.

    I just picked up a pair of applied Motion TSM motors to test. Stepper servo with high resolution encoders.
    I haven't heard this before. I honestly don't know the answers. I haven't used them. It was my understanding that you provide the same inputs you do to any stepper driver. Now that some doubt has been indicated, I would like to know the answer! Perhaps you gentlemen or someone else can educate us before I display too much of my ignorance on the internet?

    Here is a video I found on Youtube



    To me, it looks just like the one in the first add.

    I posted a link to the datasheet. With the drivers built in, if it works with a regular board, these would be a good choice, IMO.



  9. #33
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    Default Re: Stepper Options

    All I ever said is that I don't regard encoders on steppers as totally useless as was stated by another user.

    A rotary encoder can be bought for about $15, and LinuxCNC can read them through a $6, or surplus parallel port card. If you are like me and play around with 3D printers you can print up some simple mounts and for about $50 you can have a system that can detect lost steps and stop the machine. If a step is never lost then the machine never faults. In my opinion the peace of mind, and the education of doing it is worth the $50. It is also a lot cheaper to do this than to change to a closed loop stepper or servo system. If you disagree then fine, don't add encoders to your steppers



  10. #34
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    Default Re: Stepper Options

    Using an encoder on a stepper to AUTOMATICALY pick up faulting seems fine to me. After all, you may not always be right beside the machine if it is on a 6 hour run.
    But I would suggest that one should keep the fault-detection stuff outside the main computer - mostly because I don't know of any (modern) CNC programs which can handle that. But they can all handle an eStop signal.
    -----------------
    The MDrives - an interesting thing. Way back in the dark ages CNC machines had lots of dedicated electronics (huge boards of chips) but no 'PC controller'. One compromise to handle this was to drive the CNC in a completely different way: you sent a message to the X motor controller to tell it to go to point X at speed S with accel and decell as specified. Then you sent a similar message to the Y axis controller, and then to the Z axis controller. Then you broadcast a Start signal. All this communication was done over SERIAL lines. That was fine for a straight line move, but it could not handle arcs and spirals. In effect, that was back in the days of crank-starting your motor car. Today we have starter motors ... and tomorrow electric cars ...

    But some older companies had thriving product lines for ancient machines, and they are unwilling (or too short-sighted) to replace that older technology with more modern concepts. They are scared of abandoning a dying product line. The result is that they are being replaced by more modern companies with more modern concepts and hardware (at a lower cost). It is what happens in any technology.

    What will replace a PC controller and the Step/Dir interface in the future? Dunno. Could be a long while though.

    Cheers
    Roger



  11. #35
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    Default Re: Stepper Options

    But I would suggest that one should keep the fault-detection stuff outside the main computer - mostly because I don't know of any (modern) CNC programs which can handle that. But they can all handle an eStop signal.
    On quick thought, what you suggest should be able to be done outside the main computer using a microcontroller such as an Arduino by having the microcontroller count steps commanded as well as encoder position.

    I don't know if you regard LinuxCNC as a modern controller, but LinuxCNC can do what I propose. For a hobby machine it works great, and even for non-hobby it works well and has tons of user definable functionality, although not user friendly if you deviate from what the setup wizards can handle. It can do the fault on missed steps through parallel port with the only reason for needing a second parallel port being the need for additional input pins.



  12. #36
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    Default Re: Stepper Options

    Arduino - yes.

    LinuxCNC - yes. (Probably anything fully based on the NIST Standard.)

    Cheers
    Roger



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