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  1. #61
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 13 Hours Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    I think all it means is that you shouldn't connect the power supply 0V to it as the main connection to the board - that needs to go in to 8). The tracks from 3) to the rest of the circuits are probably very thin and come via the processor. May get damaged if you try to run the power supply connection in through them. But when you run the step/dir signals to the stepper / servo drive, you should take the associated 0V from 3) to give you the three wires you need. Better noise immunity.

    The digital / logic circuits on the board are powered from the 5V either directly from 4) or by an internal step-down regulator fed from 7). Which ever you choose, the associated 0V to the power supply should connect to 8), not 3).

    Hope that make sense....

  2. #62
    Ahh yes, that makes perfect sense now you've said it!

    I've got the one axis wired up and started to try and get it going, then it dawned on me I haven't got a clue what I'm doing!!

    When its powered up the motor is quiet until you try to move the axis (by hand or by jogging on control software) then I just get a humming noise from the motor and that is all...

    So I fired up the PID tuning software and its all nonsense to me, I cant even begin to understand how I would calculate the figures I need to enter...

    I've attached a photo of what the settings are and the default values that were there.

    The other thing is I'm not 100% on the wiring of the encoders, so it could also be that... or it could be the settings in UCCNC... could be any number of things with me involved!Click image for larger version. 

Name:	Servo Config 1.PNG 
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  3. #63
    Stroke of luck managed to get the one axis working, when I looked into what all the parameters actually were I was able to get them down to somewhere useable, probably no where near perfect but at least it's a starting point!

  4. #64
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 13 Hours Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    Did you see this? http://www.cncdrive.com/downloads/help.pdf

    Looks half sensible. I'll also see if I noted my own values somewhere for you to compare against.....

    EDIT - that's annoying. I seem to have logged almost everything else I ever did on this machine but there's no trace of the PID settings in the servo tuning. Sorry about that. I seem to recall that you could plot the response in the software as you played with the numbers.

    You start with I and D turned off (to zero) then turn up the P term until it gets unstable then back off. Then dial in some D term until it gets a bit nervous then back that off a bit. Play with turning P and D up together until it seems happy and the response is good. Finally dial up the I term until it starts hunting again. Then dial it back a bit and play with all 3 together until you are sick of it. Note down some of the settings that seem to be getting there because you will screw it up and forget what looked promising.

    The I term doesn't make a lot of difference to the speed of response but you need it to eliminate steady state error. It's a bit of a black art and there's loads of bollocks talked about it but the above is the guts of it. There are autotuners in some of these programs but in my experience they are usually pretty crap. I've done several courses on digital control systems over the years and I still end up doing a lot of it by trial and error.
    Last edited by Muzzer; 26-06-2020 at 04:22 PM.

  5. #65
    Nope didn't see that one, thank you! I'll give that a go today.

    I spent a couple of hours trying to look into understanding it and how it all works but it went straight over my head!

    Had another strange issues yesterday.. when I connect the 5V DC power to all three drive units none of them work, but when I unplug one of them the other two work. it doesn't matter which one I unplug the others will then fire up. power supply issues? I am only using one unit to feed the three drives and the controller board....

    I have got a 12V DC unit somewhere which I'm pretty sure can be used for the drive units, might give that a go see if that makes a difference.

  6. #66
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 13 Hours Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    Yes, sounds as if the 5V supply can't supply enough current to get more than 2 of them started up. There may be an inrush current surge at turn-on that is upsetting the PSU. As you say, feeding 12V into pin 7 is an alternative. It may also be safer if there's an internal regulator in each of the drives to drop it to 5V by the sounds of it. Pretty sure that's what I did for my 3 drives.

  7. #67
    Finishing up my degree has taken up the last couple of months, so progress has been pretty slow up to now.

    I had the machine roughly wired up to test everything before spending the time making it look tidy, the machine was working great and ran through some programs with no problems. It needed a few tweaks to the settings to get the dimensional positions a little closer but I didn't want to spend too much time on that until it was together for the final time.

    Since re wiring it I'm having a nightmare! I managed to get the transformer wiring wrong on the primary coil, so when I fired that up to check the DC voltage output the cabinet filled with some lovely black smoke from the braking circuit. luckily I had unplugged everything else at this point so I didn't cause too much damage (hopefully).
    I didn't stick around to check the actual voltage that was being output from it but could this have potential caused damage to the bridge rectifier and capacitor?

    I re wired the transformer and checked the voltage output and its back to what I was expecting, but since wiring the drivers and motors back up I'm having power issues with all three drivers when I try to tune them. They all seem to get an voltage error and go into error mode..
    I don't know at this point if it's power supply to the drives that's the issue or if its referring to the power to the motors.. need to do a bit of reading on the error codes.


    I also managed to snap the silly little pins the USB connection boards plugs into on one of the drives so that's going to need replacing/repairing!

    So all in all I've taken a few steps back at the moment!

  8. #68
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 13 Hours Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    If you have blown your braking module and the DC voltage is close to the max limit, you may be getting an overvoltage condition when you decelerate your axes. Slowing down / stopping movement will generate voltage on the bus. Perhaps you could try reducing the feed rates in the controller to start with and see if that helps.

    What DC voltage have you got? You need a good 30-40V below the overvoltage threshold. That threshold is probably shown in the manual.

    You may need to replace the braking module unless you want to see glacial feedrates. But first see if this is the issue by slowing things right down to reduce any overshoot. If you have a scope or DVM, you may be able to observe what is happening to the DC voltage when you decelerate.

  9. #69
    I think I'm on the low side on the DC voltage already at 130V, the drives are rated at 160V 36A. I haven't actually checked the Amps on mine though, cant imagine it being higher than that though?

    The braking circuit didn't actually get damaged in use, it started smoking the second I turned on the power when I had the wires mixed on the transformer... I will get a new module on the way, like you say it will probably cause me more issues leaving a potentially (definitely) damaged unit wired up.

    I'll try reducing the feed rates as well and see if that helps, it does seem that they initially start to move the axis a rotation or so then goes into error state.

    I also had a rather scary issue with one axis, when I hit the reset button the axis just went into rapid on its own! Managed to hit the E stop before it done any mechanical damage to the machine ( hadn't wired up the limit switches at this stage) So i may have some encoder issues as well on that motor.

  10. #70
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 13 Hours Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    You may have that motor connected up incorrectly, as you say. If your A and B encoder wires are swapped over, it will think the motor is going in the opposite direction. That causes the servo to run away. Or you might have 2 or 3 of the phase connections swapped around.

    130vdc doesn't sound bad. I don't recall precisely but I think the voltage clamp / braking module starts clipping at around 170V or so, so you shouldn't be seeing a problem.

    Shouldn't take a lot of current to jog the axes. 35A should be more than enough. You would be overcoming a large force to require that sort of power, possibly break something. I've jogged my table against a hard end stop a couple of times. Luckily on my system, the drive trips before anything snaps but that's down to the design of your machine. You could really f*ck something up, like a ballscrew / ballnut or its mount / yoke. Worth seeing what would take the load in that event and convincing yourself it would be OK come the crunch.

    Going into error when starting to move doesn't sound like overvoltage, which would only happen if you try to bring an axis to a rapid stop. I wonder if it's an encoder / motor issue?

    I'd disconnect 2 of the drives and remove the belt / coupling from the third. Then try to run the servo just using the tuning software. No point getting the controller involved yet. When that works, reconnect the ballscrew and try tuning the response with the software. Finally, connect up the controller and see how it plays together.

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