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IndustryArena Forum > CNC Electronics > Servo Motors / Drives > Encoder/servo selection for a Robotool centroid retrofit
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  1. #1
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    Encoder/servo selection for a Robotool centroid retrofit

    Hi All,
    I was recently given a RoboTool CVM-1 mill. At this point I am in the information gathering stage on a possible either partial or full retrofit.

    My first thought is to see if I can just put some new encoders on the current servos, get rid of the old controller and swap it out for the Centroid acorn control. That would be the cheapest option by a long shot and I really like the Centroid interface and use it regularly at work, so having it at home would be great. On that thought, does anyone know if the old servo drivers that came with the robotool interface with the centroid?

    On the question of encoders, do you guys have any recommendations on encoders for a Centroid retrofit? Centroid has some for about $180 each, but thats almost half the cost of a full AC servo/encoder/driver replacement from DMM technology. The current servos on the Robotool are shown in a pic below. Any opinions on a full replacement vs trying to make them work?

    I also like what I am seeing from DMM, most people seem to recommend the 750w servos on the xyz axis for this size machine, so I would probably lean in that direction. I am open to any other good options though if people think I should look elsewhere.

    currently the Robo is setup for 220v 3 phase I think. Would a VFD be the best way to get that working on a single phase 220v I have at my home? also what kind of amperage circuit do people normally have this kind of machine on? Any recommendations on VFD brands? I see Hitachi seems to be pretty popular as well as the GS line from automation direct.

    Anyhow sorry to unload, thats a lot of questions for one post. I love this forum though, been a long time lurker and look forward to participating a bit more

  2. #2
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    Quote Originally Posted by WesM View Post
    Hi All,
    I was recently given a RoboTool CVM-1 mill. At this point I am in the information gathering stage on a possible either partial or full retrofit.

    My first thought is to see if I can just put some new encoders on the current servos, get rid of the old controller and swap it out for the Centroid acorn control. That would be the cheapest option by a long shot and I really like the Centroid interface and use it regularly at work, so having it at home would be great. On that thought, does anyone know if the old servo drivers that came with the robotool interface with the centroid?

    On the question of encoders, do you guys have any recommendations on encoders for a Centroid retrofit? Centroid has some for about $180 each, but thats almost half the cost of a full AC servo/encoder/driver replacement from DMM technology. The current servos on the Robotool are shown in a pic below. Any opinions on a full replacement vs trying to make them work?

    I also like what I am seeing from DMM, most people seem to recommend the 750w servos on the xyz axis for this size machine, so I would probably lean in that direction. I am open to any other good options though if people think I should look elsewhere.

    currently the Robo is setup for 220v 3 phase I think. Would a VFD be the best way to get that working on a single phase 220v I have at my home? also what kind of amperage circuit do people normally have this kind of machine on? Any recommendations on VFD brands? I see Hitachi seems to be pretty popular as well as the GS line from automation direct.

    Anyhow sorry to unload, thats a lot of questions for one post. I love this forum though, been a long time lurker and look forward to participating a bit more
    Centroid Acorn, with Acorn's new board should work well for this machine

    Dmm is a very good choice for a machine like what you have, encoder resolution is important, 16 bit is already standard with Dmm, so you won't find any other's with this resolution without a large price tag

    A VFD to drive the AC spindle motor is the normal way to get that part going, when you don't have 3 ph power, 240v single phase is all you need, you can only run the spindle motor with the VFD, not the rest of the machine, 25 amp mains breaker is what I normally use for machines like this, check your Ac spindle motor Hp as your VFD wants to be around 2Hp larger than the motor Hp, this may change the main breaker amp size
    Mactec54

  3. #3

    Re: Encoder/servo selection for a Robotool centroid retrofit

    I'm a real fan of the GS units. I had a GS2 on my mill for years, and later installed a GS3 when I went to direct drive and eliminated the vari-drive.

    I am also a real fan of linear encoders, glass or magnetic. I have 1 micron magnetic linear encoders on all of my machines. About $120 / axis. Putting the encoder on the axis rather than the lead screw automatically compensates for backlash and leadscrew errors.

    EDIT: Your other question about the interface with the Acorn controller, no they won't. The Acorn system is step & direction, the drives you currently have appear to be analog control. And in that case, the encoders won't do you any good. The only encoder input on the Acorn is the spindle encoder. I like the ClearPath SD ''servos'', they seem to work well. There are a number of closed loop stepper options also.
    Jim Dawson
    Sandy, Oregon, USA

  4. #4
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    Quote Originally Posted by mactec54 View Post
    Centroid Acorn, with Acorn's new board should work well for this machine

    Dmm is a very good choice for a machine like what you have, encoder resolution is important, 16 bit is already standard with Dmm, so you won't find any other's with this resolution without a large price tag

    A VFD to drive the AC spindle motor is the normal way to get that part going, when you don't have 3 ph power, 240v single phase is all you need, you can only run the spindle motor with the VFD, not the rest of the machine, 25 amp mains breaker is what I normally use for machines like this, check your Ac spindle motor Hp as your VFD wants to be around 2Hp larger than the motor Hp, this may change the main breaker amp size
    The spindle motor on this machine is a 8.6 amp, 3HP, 220v, 3 phase, 1720 rpm motor. So you think I should try and get a 5HP VFD? Is there any particular type of VFD I should look at for compatibility with the acorn setup? or will any 5hp quality VFD work? Sorry for the newbie questions, I would rather ask dumb questions then make dumb mistakes!

    I was looking at this VFD, but if you think I should step it up, I will look at the 5hp version.

    https://www.automationdirect.com/adc..._VAC)/GS2-23P0

  5. #5
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    Quote Originally Posted by WesM View Post
    The spindle motor on this machine is a 8.6 amp, 3HP, 220v, 3 phase, 1720 rpm motor. So you think I should try and get a 5HP VFD? Is there any particular type of VFD I should look at for compatibility with the acorn setup? or will any 5hp quality VFD work? Sorry for the newbie questions, I would rather ask dumb questions then make dumb mistakes!

    I was looking at this VFD, but if you think I should step it up, I will look at the 5hp version.

    https://www.automationdirect.com/adc..._VAC)/GS2-23P0
    You always want bigger than the motor rating, 5Hp is fine and what you need when going to single phase, don't worry if the VFD drive says it is for 3ph input they work fine on single phase, any good quality VFD will work fine, just some are more confusing than other to set up, but out of the box for your motor, yours would run, as the default parameter settings would be at 60Hz, you can adjust some of the Parameters to suit after you get it running

    As Jim said, just the encoders won't help you, you want the complete Dmm package if you are to use there system
    Mactec54

  6. #6

    Re: Encoder/servo selection for a Robotool centroid retrofit

    The GS2-23P0 is rated at 3 HP on single phase. I had that exact unit on my 3 HP spindle motor running on single phase for years with no problems. You also want to buy the braking resistor.
    Jim Dawson
    Sandy, Oregon, USA

  7. #7
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    Quote Originally Posted by Jim Dawson View Post
    I'm a real fan of the GS units. I had a GS2 on my mill for years, and later installed a GS3 when I went to direct drive and eliminated the vari-drive.

    I am also a real fan of linear encoders, glass or magnetic. I have 1 micron magnetic linear encoders on all of my machines. About $120 / axis. Putting the encoder on the axis rather than the lead screw automatically compensates for backlash and leadscrew errors.

    EDIT: Your other question about the interface with the Acorn controller, no they won't. The Acorn system is step & direction, the drives you currently have appear to be analog control. And in that case, the encoders won't do you any good. The only encoder input on the Acorn is the spindle encoder. I like the ClearPath SD ''servos'', they seem to work well. There are a number of closed loop stepper options also.
    Ah ok, that answers that question, I should have figured they were analog. I don't know if there would be any point in just replacing the encoders and drives, but at this point I think I am looking at a full DMM servo/driver replacement. I do plan on pricing out a closed loop stepper system, but from my initial research it seemed like they were going to end up costing pretty much the same as, or close to the DMM AC servo system. The more I look the more it seems like the DMM setup is a great value.

    On the subject of closed loop system, from what I understand the DMM systems are closed loop at the encoder? Not sure I completely understand that, any pros/cons vs closing the loop via controller?

    Quote Originally Posted by mactec54 View Post
    You always want bigger than the motor rating, 5Hp is fine and what you need when going to single phase, don't worry if the VFD drive says it is for 3ph input they work fine on single phase, any good quality VFD will work fine, just some are more confusing than other to set up, but out of the box for your motor, yours would run, as the default parameter settings would be at 60Hz, you can adjust some of the Parameters to suit after you get it running

    As Jim said, just the encoders won't help you, you want the complete Dmm package if you are to use there system
    Sounds good, at this point I will plan on using a GS2 5HP VFD. For the DMM package do you have any recommendations on the DYN2 vs DYN4 drives? The main difference I can find seems to be the DYN2 are used on drives up to 750w while the DYN4 go up from there. Are there quality and or performance differences? Assuming I want to hit a max of 300 ipm rapids with normal probably being closer to 200 ipm on this machine.

  8. #8

    Re: Encoder/servo selection for a Robotool centroid retrofit

    Quote Originally Posted by WesM View Post
    Ah ok, that answers that question, I should have figured they were analog. I don't know if there would be any point in just replacing the encoders and drives, but at this point I think I am looking at a full DMM servo/driver replacement. I do plan on pricing out a closed loop stepper system, but from my initial research it seemed like they were going to end up costing pretty much the same as, or close to the DMM AC servo system. The more I look the more it seems like the DMM setup is a great value.

    On the subject of closed loop system, from what I understand the DMM systems are closed loop at the encoder? Not sure I completely understand that, any pros/cons vs closing the loop via controller?
    Another option is to use your original drives and motors and install a Kmotion or Galil controller. Nothing wrong with your DC servos if they are working OK, no need to replace them. Kmotion sells their Kflop/Kanalog system designed to run those type of drives. Kmotion also has CNC software for their system as well as compatibility with Mach3. Galil Motion Control products will also work great, and also compatible with Mach3. Galil products are my prefered system, all of my machines are running on them. There may be other options, but I have not researched any of them.

    Closing the loop at the controller is the most accurate method of machine control. With the encoders on the table, the controller will make sure the axis reaches it's commanded position, normally +/- 1 encoder count it everything is set up correctly.
    Jim Dawson
    Sandy, Oregon, USA

  9. #9
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    LinuxCNC is also an option for a retrofit that retains the original motors, drives, and encoders.

    LinuxCNC has full closed loop feedback to the controller so things like following error
    (distance between commanded and actual position) are always available at the controller.

  10. #10
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    Quote Originally Posted by WesM View Post
    Ah ok, that answers that question, I should have figured they were analog. I don't know if there would be any point in just replacing the encoders and drives, but at this point I think I am looking at a full DMM servo/driver replacement. I do plan on pricing out a closed loop stepper system, but from my initial research it seemed like they were going to end up costing pretty much the same as, or close to the DMM AC servo system. The more I look the more it seems like the DMM setup is a great value.

    On the subject of closed loop system, from what I understand the DMM systems are closed loop at the encoder? Not sure I completely understand that, any pros/cons vs closing the loop via controller?



    Sounds good, at this point I will plan on using a GS2 5HP VFD. For the DMM package do you have any recommendations on the DYN2 vs DYN4 drives? The main difference I can find seems to be the DYN2 are used on drives up to 750w while the DYN4 go up from there. Are there quality and or performance differences? Assuming I want to hit a max of 300 ipm rapids with normal probably being closer to 200 ipm
    on this machine.

    The loop is closed in the servo drives, no pros/cons, both ways work just as well, the loop closed in the servo drive means a lot less to setup for a system like this

    LinuxCNC with a mesa board would be the next choice, but a greater learning curve

    There are no difference with the quality, just a speed performance difference, it would be hard to reach the 300 IPM with the Dyna2 drives with your machine

    200 IPM to 250 IPM no problem with the low voltage Dmm drives 300IPM is possible using the DYN2 drives using the max voltage input up to 70v I have used them up to 72v, the speed will also depend on, your Ballscrew pitch, most are 5mm for this type of machine, and if you are using any type of gear ratio, my experimental machine below, is using the low voltage drives in this 3 axes test, the Dyna4 high voltage drives, is a better choice if you want to have more speed, and use a gear ratio of 2:1, In the video the gear ratio is 1:1

    https://www.youtube.com/watch?v=cAJaIowXwAY
    Mactec54

  11. #11
    Community Moderator Al_The_Man's Avatar
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    One of the principle advantages for me when using a system where the servo loop is closed back to the controller is the ability to use simple, (cheaper) transconductance amp type drives, A-M-C etc with virtually no set up.
    Less wiring etc.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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    Re: Encoder/servo selection for a Robotool centroid retrofit

    You could look into flashcut CNC if you are replacing the control system. fairly robust controller with a solid CNC user interface.

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    Re: Encoder/servo selection for a Robotool centroid retrofit

    Quote Originally Posted by PCW_MESA View Post
    LinuxCNC is also an option for a retrofit that retains the original motors, drives, and encoders.

    LinuxCNC has full closed loop feedback to the controller so things like following error
    (distance between commanded and actual position) are always available at the controller.
    I have looked into this and it would definitely be the most affordable option. However, I am not confident in the reliability of the electronics on a 1980s machine, especially one that has had some problems in the past with some of the electronics components.

    Quote Originally Posted by Jim Dawson View Post
    Another option is to use your original drives and motors and install a Kmotion or Galil controller. Nothing wrong with your DC servos if they are working OK, no need to replace them. Kmotion sells their Kflop/Kanalog system designed to run those type of drives. Kmotion also has CNC software for their system as well as compatibility with Mach3. Galil Motion Control products will also work great, and also compatible with Mach3. Galil products are my prefered system, all of my machines are running on them. There may be other options, but I have not researched any of them.

    Closing the loop at the controller is the most accurate method of machine control. With the encoders on the table, the controller will make sure the axis reaches it's commanded position, normally +/- 1 encoder count it everything is set up correctly.
    Honestly I really shy away from mach3, the interface just throws me off. I have not looked into Kmotion, but will read up on it.

    Quote Originally Posted by Al_The_Man View Post
    One of the principle advantages for me when using a system where the servo loop is closed back to the controller is the ability to use simple, (cheaper) transconductance amp type drives, A-M-C etc with virtually no set up.
    Less wiring etc.
    Al.
    Can you show some examples of those drives? some of this terminology is new to me as I try to get up to speed

  14. #14

    Re: Encoder/servo selection for a Robotool centroid retrofit

    Quote Originally Posted by WesM View Post

    Honestly I really shy away from mach3, the interface just throws me off. I have not looked into Kmotion, but will read up on it.
    Me too, that's the reason I don't use it.
    Jim Dawson
    Sandy, Oregon, USA

  15. #15
    Community Moderator Al_The_Man's Avatar
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    Advanced motion has recently updated their line, I traditionally used the older versions now avail on Ebay etc e.g. 271838848572.
    Also Aerotech and Copley controls are similar.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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    Re: Encoder/servo selection for a Robotool centroid retrofit

    So I was thinking about this today I calculate it will end up costing about $2000-$2500 into a full servo/driver/VFD setup. So I was trying to think of a less expensive alternative that still included a driver/amp replacement but cut down on the cost a bit.

    What do you guys think of a setup where I replaced the drives and encoders, while using the existing servos? Would something like the Gecko 320X work with a compatible encoder and the Acorn?

    Existing servos:
    63 Volt DC
    3.75 Amp
    .25HP
    2000 RPM

    According to the machinist who ran this machine, he could get 200ipm with these servos.

    Did a little reading on the Kflop setup and it does look very interesting. Kflop software seems to be a little more involved though so I could see using that on a second machine.

  17. #17

    Re: Encoder/servo selection for a Robotool centroid retrofit

    A cursory look at the Gecko 320x indicates they would work. I did not review the manual. They are step & direction so that would be compatible with Acorn. They have encoder inputs, so they close the loop at the drive. Overall I think that would make an economical system.
    Jim Dawson
    Sandy, Oregon, USA

  18. #18
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    On the subject of encoders, are there any brands you guys recommend? Iv seen digikey CUI encoders thrown around a bit, and it seems to be what the people at Gecko recommend with their products, are these hobby grade encoders I should avoid?

  19. #19

    Re: Encoder/servo selection for a Robotool centroid retrofit

    Linear encoders would be my choice even with the Gecko drives. There is no downside to using them, and many advantages. You just have to match the resolution to what the Gecko drive is capable of reading.
    Jim Dawson
    Sandy, Oregon, USA

  20. #20
    Community Moderator Al_The_Man's Avatar
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    I initially purchased the CUI BLDC encoder development system for programming the simulated hall tracks for the BLDC motor encoder version, but got anything but satisfactory results, and the tech support was no help, so it left a bad taste.
    I traditionally used Renco, but then Heidenhain took them over and the line selection shrank quite a bit.
    Koyo are good as well as Hengstler.
    If possible I usually fit through hole type to avoid mounting and a coupler.
    Your original servo's may have had tach feedback which is not used now on DC motors, as Torque mode drives are used as opposed to the DC velocity type which had a tach back to the drive.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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