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  1. #31
    Turns out he's not offering a bigger motor, so I have to trade speed for acceleration.

    In what aspect is the drive just about cutting it? (for the 25mm design)

    Here's an updated calcsheet.
    I'm still workig on what an appropriate accelration is to plug in for my two requirements.
    Using Mach3, dialling back the acceleration made next to no difference on my plastic parts, but that might be because I cut so slowly in the first place.
    Attached Files Attached Files
    Last edited by jimbo_cnc; 10-03-2015 at 04:21 PM.

  2. #32
    Ger21's Avatar
    Lives in Detroit, United States. Last Activity: 11 Hours Ago Has been a member for 5-6 years. Has a total post count of 508. Received thanks 68 times, giving thanks to others 0 times. Referred 1 members to the community.
    If you can achieve .2G, I think you'd be doing very well.
    Calculating stepper motors for a target acceleration is very tricky.

    Most inexpensive controls use a linear acceleration, meaning you need the same amount of force from start until you're up to speed.
    The problem with that, is that steppers lose torque as rpm's increase.
    So you have to base your acceleration on the amount of torque your motor will have at your target speed. This may be only 1/4 of the motors rated torque.
    Gerry
    ______________________________________________
    UCCNC 2017 Screenset

    Mach3 2010 Screenset

    JointCAM - CAM for Woodworking Joints

  3. #33
    As I understand it, I'm below corner speed even at max feedrate, so I have full torque available.

    Advantage slow machine! :)

  4. #34
    Ger21's Avatar
    Lives in Detroit, United States. Last Activity: 11 Hours Ago Has been a member for 5-6 years. Has a total post count of 508. Received thanks 68 times, giving thanks to others 0 times. Referred 1 members to the community.
    The only time you have "full torque" available is when the motor is not spinning. That's why it's called holding torque. As soon as it starts spinning, the available torque starts decreasing.
    If you're spinning so slow that you don't lose much torque, then your resolution is probably poor.
    Gerry
    ______________________________________________
    UCCNC 2017 Screenset

    Mach3 2010 Screenset

    JointCAM - CAM for Woodworking Joints

  5. #35
    page 3
    https://www.geckodrive.com/gecko/ima...cs%20Guide.pdf

    Torque doesn't start reducing straight away, it's not until corner speed it falls off.


    Resolution is what it is. It's 10mm pitch direct drive and I don't have the option to gear the motor faster on this machine. Driver has serious micro-stepping capability, depending on how you think theoretical resolution translates into real-life accuracy.


    When I add power into the calcs, it may reveal some acceleration problems at lower speeds.

  6. #36
    Ger21's Avatar
    Lives in Detroit, United States. Last Activity: 11 Hours Ago Has been a member for 5-6 years. Has a total post count of 508. Received thanks 68 times, giving thanks to others 0 times. Referred 1 members to the community.
    Look at a chart from a motor manufacturer. They don't look like the one from Gecko.
    Torque starts dropping immediately.
    Gerry
    ______________________________________________
    UCCNC 2017 Screenset

    Mach3 2010 Screenset

    JointCAM - CAM for Woodworking Joints

  7. #37
    At very low speed the torque is approximately 2/3rds of the rated holding torque. The then gradually lowers from that value then quickly drops off at the corner speed.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  8. #38
    The first chart from the first hit on google looks a lot like the gecko chart :)
    http://www.orientalmotor.com/product...-only-1-8.html

    But I see many different characteristics, so yes, new torque model needed before I look at power and stall.

  9. #39
    Ger21's Avatar
    Lives in Detroit, United States. Last Activity: 11 Hours Ago Has been a member for 5-6 years. Has a total post count of 508. Received thanks 68 times, giving thanks to others 0 times. Referred 1 members to the community.
    Yes, 60oz motors have flatter torque curves. But we don't use those.
    Gerry
    ______________________________________________
    UCCNC 2017 Screenset

    Mach3 2010 Screenset

    JointCAM - CAM for Woodworking Joints

  10. #40
    Quote Originally Posted by Ger21 View Post
    Yes, 60oz motors have flatter torque curves. But we don't use those.
    And if you find a Chinese supplier that gives you an accurate Chart for that particular motor then Frame it because it will be a Rare thing.!!

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