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  1. #1
    Long story, short - I blew my spindle controller on the Sieg SX2.7 a second time (the first was under warranty and within 30 minutes of powering on my machine from delivery)... this time, the machine is most certainly not under warranty. I've tried repairing the spindle controller board but I think I've a dodgy hall position sensor and that blew the board up quite spectacularly a second time. Enough is enough, and it's cheaper to replace the motor and controller card with a Chinese servo and controller. So, that's this weeks step into the unknown. And servos are pretty much an unknown to me. So, help!

    I've got a Chinese servo (this one: https://www.ebay.co.uk/itm/112227829185) that's slightly larger than the original BLDC motor. Finally managed to nibble a 10mm Ali plate to mount the motor and get it belt-coupled with the spindle. There's a knocking noise I need to bottom out but that's a different story (I think that's the spindle). I've managed to operate the spindle in a commissioning mode with the servo in speed mode and that looks to be the kind of set-up that's appropriate for a spindle. I'll have to check my pulley calls as well - looks to be somewhat faster than the old BLDC spindle though I thought I'd calculated the pulleys to get the same tool rpm. Low RPM is torquey as a very torquey thing - certainly I could hold the BLDC stalled at 40rpm, the servo is having none of that.

    Tomorrow I plan to start stripping down my controller box to support the servo signalling. I've got a 400 page Chinglish manual... looks comprehensive, but it's a right bugger to read, and certainly not something you can casually browse.

    I believe (99% confident) that it supports Step/Dir control and I'm using UCCNC - which also supports this. So, plan 1 is to remove the analogue drive and M3/M4 relay wires, and instead wire a couple of TTL->RS485 adapters off the back of the UC300ETH controller to generate differential step/dir signals into the servo controller. If used in step/dir mode is this a positional control mode in servo-speak?, or should the servo be configured for speed mode still? Is there a practical difference?

    But, what to do with an Alarm signal from the servo? I expect that if I'm spinning this quickly that there's going to be a good rate of step pulses, and if the cutter engages with a block of steel I could expect the servo to momentarily loose speed/position (but I guess the nature of a servo is that the position will be recovered?) There's an alarm output from the controller, need this be feed back into UCCNC in someway, or into the E-stop circuit? Can I expect sporadic alarms when the spindle cutter engages the workpiece? Should I simply ignore the wiring to the Alarm output?

    The servo came supplied with a 3m power and control cable. The power cable is crimped fork terminals to wire to the controller, so I'm fairly relaxed about shortening this according to the final installation on (in?) the mill. The encoder cable, however, is a multiway plug on one end and a 15-w sub-d type on the other. Is there merit in shortening this cable or is it simply not necessary (I might be able to stow this inside the column of the mill).

    I guess I'm hoping that someone can spell out any gotchas before I make a pigs ear of the integration into UCCNC. Like I say, servos are a whole new game for me.

  2. #2
    Quote Originally Posted by Doddy View Post
    I believe (99% confident) that it supports Step/Dir control and I'm using UCCNC - which also supports this. So, plan 1 is to remove the analogue drive and M3/M4 relay wires, and instead wire a couple of TTL->RS485 adapters off the back of the UC300ETH controller to generate differential step/dir signals into the servo controller. If used in step/dir mode is this a positional control mode in servo-speak?, or should the servo be configured for speed mode still? Is there a practical difference?
    I believe you can only use Position mode with Step/Dir signals. You need Analog to use Speed or Torque Modes.

    Quote Originally Posted by Doddy View Post
    But, what to do with an Alarm signal from the servo? I expect that if I'm spinning this quickly that there's going to be a good rate of step pulses, and if the cutter engages with a block of steel I could expect the servo to momentarily loose speed/position (but I guess the nature of a servo is that the position will be recovered?) There's an alarm output from the controller, need this be feed back into UCCNC in someway, or into the E-stop circuit? Can I expect sporadic alarms when the spindle cutter engages the workpiece? Should I simply ignore the wiring to the Alarm output?
    The fact UCCNC doesn't provide a Spindle or Servo Alarm input to connect upto means your only safe option is to tap into the E-stop.
    This will need to be done because when the Servo faults it doesn't just throw an alarm to say it's lost position, it cuts the outptuts and stops the Servo.
    You will also need some way to Reset the Fault as well. This can be by powering down the drive or pulsing one of the inputs and configuring it to Reset the drive.

    I doubt you'll have any problems because the default Peak torque is 200% and rated for 8s so you'll have 5Nm for 8's before it faults, it's also programable in the drive so you can increase to 300% and set the time current fault overload time to 80s if needed. But I can smell the smoke already if you did that...Lol

    This should give you planty of torque when entering the material, there are also over options in the drive you can play with to boost torque if required. Provided you can get past the Chinglish.


    Quote Originally Posted by Doddy View Post
    Is there merit in shortening this cable or is it simply not necessary (I might be able to stow this inside the column of the mill).
    They are easy enough to shorten but I would just leave it if it's not causing you any grief.
    -use common sense, if you lack it, there is no software to help that.

    Email: [email protected]

    Web site: www.jazzcnc.co.uk

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  4. #3
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 3 Days Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,908. Received thanks 360 times, giving thanks to others 8 times.
    I started writing a reply to this earlier, then got side tracked.

    Dean's answered all the questions, so I'll just add a couple comments for anybody else.

    Position mode officially requires a pulsed input (or some form of serial communication if the drive is fancy enough), which can usually take the form of Step/Dir, CW/CCW, or Quadrature input. Quadrature is the best option as it eliminates pulse timing issues, although as this is a spindle, that's not really an issue.

    Speed/Torque are analogue modes. The key difference between speed and torque mode, is torque mode bypasses some of the internal drive filtering. It can allow better drive tuning if you're running it closed loop, but is often harder to tune as it's inherently more unstable.
    If you wanted, you could just run speed mode, and interface in a similar way to old controller, it all depends on how accurately you want to control your spindle speed.


    As for excess cable, if they can't be shortened simply, just cable tie them out the way somewhere.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

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  6. #4
    m_c: Part of the problem with the old controller, and part of the reason for its demise was the lack of a controllable input - other than through push-button control. I intimated a 0-10/CW/CCW control, but that's a generic wiring for two mills controlled by the single controller - so I'm looking to break commonality and have different solutions for the Starmill (Ana/switched) and the Sieg (Step/Dir). Back of my mind I'm thinking that this might open up rigid tapping vs analogue control (although I think there's an encoder output on the servo controller, also. Either way, Jazz and m_c, thanks, you're giving me confidence in pursuing this (it's also an eye opener to the performance of servos vs steppers)

  7. #5
    Quote Originally Posted by Doddy View Post
    (it's also an eye opener to the performance of servos vs steppers)
    Servo's will always Rip a stepper to pieces in most ways except complexity, which you are just about to experience.!! This is why I always tell people who are new or don't require what servos offer to stay away.!

    Wait until the encoder throws a bitch fit then you'll truly appreciate the difference between Steppers and Servo's.....
    -use common sense, if you lack it, there is no software to help that.

    Email: [email protected]

    Web site: www.jazzcnc.co.uk

  8. #6
    Quote Originally Posted by JAZZCNC View Post
    Servo's will always Rip a stepper to pieces in most ways except complexity, which you are just about to experience.!! This is why I always tell people who are new or don't require what servos offer to stay away.!

    Wait until the encoder throws a bitch fit then you'll truly appreciate the difference between Steppers and Servo's.....
    Having to bore/ream the pulley to 16mm and broach the keyway kinda painted a picture that it isn’t going to mess about. Hoping that the use as a spindle motor will be a gentle introduction to servos. Was looking at the price and you can’t escape that they are more expensive than steppers but factor in psu etc and that gap is coming down.

  9. #7
    Okay, this is progressing slower than I'd like (having to work from home and it's planting season down the allotments with the wife), but today I managed to get the spindle under UCCNC control... of sorts.

    There's a few scaling issues that I have to resolve, but that I think is pretty straight-forward (I hope). I think I need to resolve the servo drive to a normalised rpm, and use UCCNC to provide Pulley scaling to give a spindle speed. But, trying to get the servo spinning at the rated 3000rpm (spindle 2000rpm), with a 3000 line encoder (3000 ppr?) UCCNC maxes out at 1980 rpm (out of 3000), with a kernel frequency of 100kHz (default). That sort of makes sense to me - 100kHz kernel = 100,000 / 3000 * 60 (sec-to-min) = 2000 rpm @ servo.

    I can increase the kernel frequency, but that feels like a sledgehammer solution (and I'm not keen on increasing the pulse frequency for all the problems that can come with that... but it is an option).

    The other figure that influences the pulse rate to attain the RPM is the resolution of the servo encoder. Now, given that I'm only using this for a spindle I'm pretty sure that I don't need the resolution that this offers. Is there a feature with servos that allows the resolution to be reduced (i.e. fewer pulses to get a single revolution)??

    The manual talks of "positional regulator gain", but I think that's a dabble-too-far, and there's reference to "electronic gearing" with some esoteric terms such as "pulse electron gear ratio of molecule 1", as well as a more understandable "demoninator of a pulsed electronic gear ratio".

    Given that I'm using pulse/dir signalling, is this electronic gearing a route to reducing the resolution of the stepper, and allowing me to present fewer pulses per revolution, and therefore increase the achievable RPM without fiddling with UCCNC kernel frequency?

    Or am I barking up the wrong tree?, is there another route here? Sorry, shed-time is limited at the moment and I'm trying not to jump into too many rabbit holes.

  10. #8
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 3 Days Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,908. Received thanks 360 times, giving thanks to others 8 times.
    You've got the right tree.

    There will be two main gearing ratios. One is for the input pulses, and one will be for the emulated encoder output.
    You want to change the input pulses.

    I've not got time to check the manual to see what they've translated the terms to, but try changing one setting at a time, reboot the servo drive, and try it.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  11. #9
    Ok well, your problem is a little worse than you think because 100Khz won't give you 2000Rpm at the Servo. The encoder on the servo is 2500ppr x 4 (quadrature) so 10,000ppr
    So 100Khz will only give 600Rpm (100,000/10,000*60).

    So to get Full RPM out of the servo you need to use electronic gearing so watch this video I did because I'm not explaining it all again.!!

    You could possibly use the E-gearing to give you what you want and then feed the Servo Encoder output back into UCCNC, thou I've got a feeling UCCNC will only allow a max 1000ppr Encoder to be used.?


    -use common sense, if you lack it, there is no software to help that.

    Email: [email protected]

    Web site: www.jazzcnc.co.uk

  12. #10
    Ah, an entertaining video (actually, I recall watching that fairly recently, maybe when you first posted, but before I got into this particular forced-upgrade cycle... and as it held no relevant context for me at the time I promptly forgot about it) - you sound as amused with the manual as I've felt frustrated - though I'm coming from a position of zero knowledge.

    I'm not going to argue the numbers - but, yes, from the last couple of hours of trying to work it out by first principles I've given up, set up PN098 to 10, PN102 to 1, and "tweaked" the PPR in UCCNC until my super-calibrated rev counter (finger on spindle, so I can count RPM against a stop-watch*) and 60 rpm, I'm pretty confident I've got back to a 0-2000rpm spindle speed, now programmable by UCCNC (previously only manual panel control). And I've use the spindle to machine a slot in the belt cover to allow me to get the servo cables out without fouling the Z-column. Life is good again.


    (* My real, laser-diode rev counter appears to have re-invented itself as a random number generator)
    I

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