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Thread: Testing stability of a model

  1. #1
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    Testing stability of a model

    Hello,

    I am working on designing a mobile base for the UR10 robotic arm from Universal Robots. Whilst I am confident to use CAD to find the centre of mass, and maths to work out the moments whilst it is stationary, I understand that as the robotic arm moves the inertia will also affect the stability.

    I have attached 2 images to demonstrate one of the movements which the robot would be doing with a very basic base (Final design will have a lot more to it than this).
    Robot Position 1:

    Robot Position 2:


    I was wondering if there is a suitable CAD program to simulate the inertia of the arm & its role on the stability of the base? If not what would be the suitable equation to factor in intertia to the moments?

    I keep coming across posts on various forums about working out moments whilst stationary, but nothing for moving objects....

    Thanks
    Adam W
    Attached Images Attached Images
    Last edited by administrator; 11-09-2017 at 01:36 PM. Reason: Removed Spammy Images

  2. #2
    Administrator Kelly Bramble's Avatar
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    Virtually ALL mainstream CAD programs provide Center of Mass location for a 3D model.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Lead Engineer Cake of Doom's Avatar
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    You could always work out the stationary 'worst case' moments and then apply a suitable dynamic factor to account for stop/start load increase. This should, at the very least, get you in the right ball park.

  4. #4
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    Quote Originally Posted by Kelly Bramble View Post
    Virtually ALL mainstream CAD programs provide Center of Mass location for a 3D model.
    ''Whilst I am confident to use CAD to find the centre of mass, and maths to work out the moments whilst it is stationary, I understand that as the robotic arm moves the inertia will also affect the stability.''
    As i said I understand this...

  5. #5
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    Thanks,
    For the dynamic factor, would looking to the torque from the acceleration/deceleration of the arm and simply adding it to the staitionary moment be suitable as a ballpark estimate? Im not sure if the physics works like that (I understand that the pivot of the arm's motion is different to the pivot of the base tipping)....

    Thanks!

  6. #6
    Administrator Kelly Bramble's Avatar
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    Mass moment of inertia can be calculated from the center of mass... Most mainstream CAD/CAE software can do this.. Some CAD packages have an addon that can be purchased..

    What CAD software do you run?

    Also, see:

    Mass Moment of Inertia Equations and Calculator

    Quote Originally Posted by adam_widdowson View Post
    Thanks,
    For the dynamic factor, would looking to the torque from the acceleration/deceleration of the arm and simply adding it to the staitionary moment be suitable as a ballpark estimate? Im not sure if the physics works like that (I understand that the pivot of the arm's motion is different to the pivot of the base tipping)....

    Thanks!
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  7. #7
    Lead Engineer Cake of Doom's Avatar
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    What sort of holding down system did you have in mind?

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