Options to drive 24vdc motor - Page 2


Page 2 of 2 FirstFirst 12
Results 13 to 20 of 20

Thread: Options to drive 24vdc motor

  1. #13
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Location
    Canada
    Posts
    23053
    Downloads
    0
    Uploads
    0

    Default Re: Options to drive 24vdc motor

    Quote Originally Posted by Greg9504 View Post
    Hi Al,


    One thing I'm a little confused on with the DC drives is what mode to set them up in for use with Kflop.

    I think after reading a few dc drive manuals I'm best to set the drive up in torque mode with no encoder feedback to the drive. Then in this case since the included encoder is very low resolution, plus single ended, it's probably better to have an encoder measuring the table rotation. Then feed that to kflop. Sound right?

    Thanks
    Greg.
    They are not only single ended, they use 24vdc instead of the customary 5v, I have always used the torque mode for the drives with encoder back to the control.
    If you end up using them, there IC's out there you could convert to RS485 5v.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

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


  2. #14
    Member
    Join Date
    Apr 2007
    Location
    Canada
    Posts
    39
    Downloads
    0
    Uploads
    0

    Default Re: Options to drive 24vdc motor

    Hi Tom,

    overall reduction is 18252:1
    - motor planetary reducer: 234:1 - gear reducer output 7.7 rpm
    - slew drive worm gear: 78:1 - slew gear output ~ 0.1 rpm

    Accuracy? Hard for me to answer that intelligently wrt CNC world. If I cut a stone, told the table to turn 90 degrees, made another cut, then put a carpenter's square on it, I'm hoping that the cut looks square.

    Thanks for the info about the feedback, I hadn't thought that would be a problem. Looking at this table for ring encoders:
    https://www.rls.si/eng/mr100f-radial...able-160-poles
    If I'm reading it correctly, if I used the ring with the most counts, I'd end up with 3640.89 counts/degree (1310720/360). I believe the max RPM columns are for the various minimum edge separation configurations you can spec the encoder for (0.05MHz to 15MHz). Out of curiosity what is the minimum edge separation for KAnalog encoder inputs? There didn't seem to be much cost difference between the lower count and higher count configurations. Of course not as cheap as a simple rotary encoder on the motor itself. The reason I though going with the encoder on the table is that having the linear encoders on my other axis seemed to work well, even though they were fairly low resolution (~1100 counts/inch).


    Perhaps my first try should be:
    - pick up an older analog DC servo drive
    - adapter a better encoder on the motor and feedback to kflop

    Thanks
    Greg.



  3. #15
    Member TomKerekes's Avatar
    Join Date
    May 2006
    Location
    USA
    Posts
    3058
    Downloads
    0
    Uploads
    0

    Default Re: Options to drive 24vdc motor

    Hi Greg,

    Accuracy? Hard for me to answer that intelligently wrt CNC world. If I cut a stone, told the table to turn 90 degrees, made another cut, then put a carpenter's square on it, I'm hoping that the cut looks square.
    Well the stated accuracy of 0.17 degrees (which I suspect is basically gear backlash) would come out to about 1/32 inch of error (over 10 inch sides). Do you think that would look good enough on your carpenter's square?

    If so, that would work out to 0.17 / 360 * 18252 = 8.6 full motor revolutions. So precise motor positioning is not likely to buy you much. I'm thinking the 8 ppr encoder might work well enough for crude motor positioning. I'd try it. It isn't clear to me if that 8ppr is actually 32 quadrature transitions/rev.

    I think the spec says the encoders can work with 5-24V so they should operate at 5V.

    Thanks for the info about the feedback, I hadn't thought that would be a problem. Looking at this table for ring encoders:
    https://www.rls.si/eng/mr100f-radial...able-160-poles
    If I'm reading it correctly, if I used the ring with the most counts, I'd end up with 3640.89 counts/degree (1310720/360). I believe the max RPM columns are for the various minimum edge separation configurations you can spec the encoder for (0.05MHz to 15MHz). Out of curiosity what is the minimum edge separation for KAnalog encoder inputs? There didn't seem to be much cost difference between the lower count and higher count configurations. Of course not as cheap as a simple rotary encoder on the motor itself. The reason I though going with the encoder on the table is that having the linear encoders on my other axis seemed to work well, even though they were fairly low resolution (~1100 counts/inch).
    Well it is always great to have measurement directly on the table, if for nothing else but to know what is happening, but in this case I'm not sure how much it will help. If there is a relatively large amount of backlash and the motor must move a lot to take it out then correcting errors may be too slow to be effective. Software backlash correction might work as well or even better. Is there a way to preload the table to take out backlash?

    KFLOP Encoder inputs work up to 1 million quadrature transition counts/sec. Which is 1us per transition on average. KFLOP's encoder inputs have a programmable digital filter to reject glitches that defaults to 7 samples at 16.67MHz which is 0.42us. You might just conservatively use the 1us number. I doubt if any of this would be an issue for you.

    BTW I saw your backlash video. Very cool. Of course it is always best to remove backlash/slop where possible as you did, but I would have loved to have seen how well KFLOP's backlash correction would have worked in that case.






    It would be simplest to obtain a +/-10V analog torque drive, but with a bit more work a KFLOP PWM output connected to something like this could possibly work.

    https://www.robotshop.com/en/pololu-...ontroller.html



    Regards
    TK http://dynomotion.com


  4. #16
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Location
    Canada
    Posts
    23053
    Downloads
    0
    Uploads
    0

    Default Re: Options to drive 24vdc motor

    Quote Originally Posted by Greg9504 View Post
    Thanks. Those will help point me in the right direction once I get my hands on the motor.
    Greg.
    What part of Canada are you in?
    I have a number of surplus AMC and Copley DC drives if interested, I have a 25A8D it is actually a Galil Motion but they re-label AMC drives, it is rated 12v to 80v to 12A.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

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


  5. #17
    Member
    Join Date
    Apr 2007
    Location
    Canada
    Posts
    39
    Downloads
    0
    Uploads
    0

    Default Re: Options to drive 24vdc motor

    Quote Originally Posted by TomKerekes View Post
    Hi Greg,

    Well the stated accuracy of 0.17 degrees (which I suspect is basically gear backlash) would come out to about 1/32 inch of error (over 10 inch sides). Do you think that would look good enough on your carpenter's square?
    Yes that should be good enough. Although hoping it works out a bit better. Once I get power to the motor I'll measure the backlash.

    Quote Originally Posted by TomKerekes View Post
    Software backlash correction might work as well or even better. Is there a way to preload the table to take out backlash?
    I'm not sure how. It's basically a worm gear, it looks like this inside:
    Options to drive 24vdc motor-hourglass-png
    But there's also the backlash in the planetary gearbox attached to the motor.

    Quote Originally Posted by TomKerekes View Post
    BTW I saw your backlash video. Very cool. Of course it is always best to remove backlash/slop where possible as you did, but I would have loved to have seen how well KFLOP's backlash correction would have worked in that case.
    Thanks. Yes it would have. I'll will try with the rotary axis. That board is so small, and cheap! I may have to try it. I read https://www.dynomotion.com/wiki/inde...WM_Output_Mode . The given OutputToPWM_sign_mag_single_axis.c would be good starting point. The docs for the board state:

    In this configuration, motor direction is determined by the states of the INA (clockwise) and INB (counter clockwise) pins and motor
    speed is controlled by the duty cycle of a PWM signal supplied to the driver’s PWM pin.
    ...
    Note that it is also possible to save a microcontroller I/O line by directly
    PWMing the INA and INB pins while holding the PWM pin high (e.g. by connecting it directly to
    VDD).
    So for the simplest connection I'd use two output pins for controlling direction. I'm not sure how to connect for the second scenario they describe. Wouldn't that only turn the motor in only one direction?

    Thanks for your help.
    Greg.



  6. #18
    Member
    Join Date
    Apr 2007
    Location
    Canada
    Posts
    39
    Downloads
    0
    Uploads
    0

    Default Re: Options to drive 24vdc motor

    Quote Originally Posted by Al_The_Man View Post
    What part of Canada are you in?
    I have a number of surplus AMC and Copley DC drives if interested, I have a 25A8D it is actually a Galil Motion but they re-label AMC drives, it is rated 12v to 80v to 12A.
    Al.
    Hi Al,

    I am in Ottawa. 12A is more than enough, motor is rated 2.8 A, 3.5 peak. Please PM me the details.
    Thanks!



  7. #19
    Member TomKerekes's Avatar
    Join Date
    May 2006
    Location
    USA
    Posts
    3058
    Downloads
    0
    Uploads
    0

    Default Re: Options to drive 24vdc motor

    Hi Greg,

    That board is so small, and cheap! I may have to try it. I read https://www.dynomotion.com/wiki/inde...WM_Output_Mode . The given OutputToPWM_sign_mag_single_axis.c would be good starting point. The docs for the board state:

    In this configuration, motor direction is determined by the states of the INA (clockwise) and INB (counter clockwise) pins and motor
    speed is controlled by the duty cycle of a PWM signal supplied to the driver’s PWM pin.
    ...
    Note that it is also possible to save a microcontroller I/O line by directly
    PWMing the INA and INB pins while holding the PWM pin high (e.g. by connecting it directly to
    VDD).
    So for the simplest connection I'd use two output pins for controlling direction. I'm not sure how to connect for the second scenario they describe. Wouldn't that only turn the motor in only one direction?
    Yes I think the 1st scenario modifying the program to use two Outputs to control the direction would be simplest.

    For their 2nd scenario they move both directions by either pulsing the INA or the INB pins. This would require a switch to move the PWM from one pin to the other. To avoid the necessity of a switch a workaround is to use two KFLOP PWM outputs and command either one or the other to pulse.

    Regards
    TK http://dynomotion.com


  8. #20
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Location
    Canada
    Posts
    23053
    Downloads
    0
    Uploads
    0

    Default Re: Options to drive 24vdc motor

    Greg, PM sent, here is the PDF.
    Includes the external connectors.
    Al.

    Attached Files Attached Files
    CNC, Mechatronics Integration and Custom Machine Design

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


Page 2 of 2 FirstFirst 12

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

Options to drive 24vdc motor

Options to drive 24vdc motor