1. #1
    I can't find where I downloaded it from now, so I'll put this in General.

    Here's what I found. Perhaps someone can check this over.

    I deconstructed the spreadsheet and simplified it, getting the same results.
    Then I looked at the equations.

    I think I have found these errors:

    1. rotor inertia conversion error. Should be 1e-7 conversion not 1e-8.

    2. torque to accelerate the gantry should include the ballscrew efficiency.

    3. <deleted> my error


    Net result is I get different values for 2 of the 4 torque components.
    Attached Files Attached Files
    Last edited by jimbo_cnc; 10-03-2015 at 03:17 PM. Reason: removed 1 non-error!

  2. #2
    Quote Originally Posted by jimbo_cnc View Post
    Net result is I get different values for 3 of the 4 torque components.
    Ye and then in real world use the Net result will be another complete different reality.!! . . . Why because of the stuff like build inacuurecy and friction etc not bearing any resemblence to what the limited data in those sheets work upon.! . . . . So IME treat it as a very rough guide only before wasting too much time on it.!
    Last edited by JAZZCNC; 10-03-2015 at 02:21 PM.

  3. #3
    Not completely different I would hope.

    The acceleration torques are not much influenced by alignment.

    Besides I would build accurately :)

  4. #4
    Quote Originally Posted by jimbo_cnc View Post
    Not completely different I would hope.

    The acceleration torques are not much influenced by alignment.

    Besides I would build accurately :)
    No I'm lying to you it will be exactly the same has the sheet says.!! . . . Crack On.

  5. #5
    I can't reply to that, because it makes no sense. 'Not completely different' does not equal 'exactly the same'.

  6. #6
    This is the thread:

    http://www.mycncuk.com/threads/1524-...2489#post42489

    You have correctly identified the errors.

    I made my own version, as a script posted here. I added calculations for efficiencies, friction in different parts and the pulley inertia's. The latter makes a big difference... after including those things I've found it to be a good match with reality.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  7. #7
    Thanks Jonathan. The second link is same as the first, but if it's the octave script then I've seen that. I preferred to use the spreadsheet, but now I will pick up some of the equations from your script.

    Any thoughts on nice values for acceleration for large wood panel cutting, or small plastic parts cutting?

  8. #8
    Sorry yes, I got the wrong link:
    http://www.mycncuk.com/threads/7355-...t=octave+servo
    By all means copy the equations or whatever you want...

    Acceleration will limit the minimum arc radius the machine can move round whilst maintaining the specified feeedrate, so you can work it out from that.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

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