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SimCalc related questions

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by Babylon_Jim, May 16, 2020.

  1. Babylon_Jim

    Babylon_Jim New Member

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    Hi @czgui,
    I have some questions:
    • Do you feel that moving the motors back under the seat and therefore reducing the leverage between the motor attachment and the main pivot has made your motors have to work a lot harder?
    • Does it make the feeling smoother, if not what was the reason to move them?
    • With the pivot Universal Joint positioned at the bottom of the post and not up near the seat do you feel like the seat is moving to the sides more than it is rolling in that direction?
    It would be interesting to know as I am planning a 2DoF build, my plan is more like your original drawings.

    cheers James
    Last edited by a moderator: May 18, 2020
  2. Ads Master

    Ads Master

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  3. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
    3DOF, DC motor, JRK
    You can have a play with SimCalc to get you head around the trade offs in design Vs physics, motor requirements and result performance and movement geometry output: https://www.xsimulator.net/communit...e-linear-speed-and-forces-of-your-design.270/
  4. Babylon_Jim

    Babylon_Jim New Member

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    Hi Noorbeast,
    It was a good starting point, but maybe I am missing something because although it gives the efficiency of a motor placement it doesn’t actually seem to take mass into account and whilst it references motor attachment points in relation to pivot point, it doesn’t take into account that Roll centres relationship to the CoG of the rig.
    I am probably missing something in the software. But it appeared that it could give me 100% efficiency (or close to) as long as you ensured that the motors Arm plane of rotation was planar with the pivot point, the arm to push rod was perpendicular and the rod to the imaginary pivot Lever was also perpendicular i.e you weren’t pushing off at any angle other than the direction you wanted the movement.

    so in theory as long as you met these rules you could put the motor anywhere, but in truth the further you put the motor mount from the pivot the more leverage you have and it would feel different or at least I think it would :)

    hence my question to the OP about the difference between the two mountings, i fully agree that the tool helped me confirm and solidify my thoughts.

    cheers,
    James
  5. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    SimCalc presumes a balanced rig with respect to mass and you can check out the mathematical assumptions behind SimCalc here: https://www.xsimulator.net/community/threads/simcalc-by-tim-mcguire.11277/page-2#post-140469
  6. Babylon_Jim

    Babylon_Jim New Member

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    Hi Noorbeast,

    I guess that is my point about responsiveness (and my question to the original poster of the thread this was in before ;) ). The motors have to overcome the inertia of the mass, even if the rig was perfectly balanced in its static rest point. So I was wondering if the moving of the motors under the seat as opposed to being down by the feet had made a significant change in the ‘feel’ of the motion.

    Something that I was thinking about; because the seat mover/ low pivot based rig type mostly hast it’s mass above the pivot point, surely it goes out of balance the moment it moves in any direction? Is SimCalc showing more than the ideal position of the motors for a given attachment point?

    cheers,
    James
  7. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
    3DOF, DC motor, JRK
    The biggest change in 'feel' with respect to motor position is that the geometry of movement will be a bit different.

    SimCalc is an informative tool, not comprehensive simulator design software, it gives basic information about basic design decisions.