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Motion simulator with the universal joint at the top?

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by francis72, Jul 28, 2015.

  1. francis72

    francis72 New Member

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    Hello
    First let me present myself. I have the idea of building a motion driving simulator for years, but I was thinking it was too complicated and almost impossible until I find this forum a few day ago. Wow!!

    Anyway, my idea was to built a motion simulator with the universal joint at the top, because of the sensation of acceleration (givin a wrong Gforce sensation) when the seat is moving. See the picture below, to explain what I mean.

    But since I never tried a motion simulator, do you have this sensation of acceleration in the wrong direction when you are driving your simulator. Is it worth it.?? gforce2.jpg
  2. Daguru

    Daguru Rally drivers do it in the mud

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    That looks like it would be more of a swinging motion don't look right to me but hey I'm no expert might be ok for flight sim good luck !
  3. Vef445

    Vef445 Active Member

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    @francis72 , it's not the acceleration of the seat that transfers the motion, but it's position. The gravitation does the rest ;)
  4. bob williams

    bob williams OSW

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    Yep u used the explenation from frex. As Vef445 explained it is gravitation that gives us the sensation of gforce. To me it feels natural. When I play a sim without motion its very dull.
  5. bob williams

    bob williams OSW

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    Also step 2 the yellow arrow is not correct. ther is never a force to the right.. you just drop to the left so the force is always correct. It just builds up until you are at the maximum angle.
  6. bberger

    bberger Member

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    Agreeing with what bob said.
  7. francis72

    francis72 New Member

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    Thanks for your response everyone.
    I will do it with the universal joint on the bottom. Its less complicated, and from what you are saying, its feeling natural this way.

    regards
  8. mrbeginner

    mrbeginner Active Member

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    Hi!
    I made myself too the joint on the bottom version just to see how it moves and feels. It's easier to do next version after you figured how differend forces feels. Good luck to your project and it's never too late to "thinking out the box."
  9. Pawks

    Pawks New Member

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    Hi @francis72 , i was wondering the very same thing since i started to think about building my own simulator...now i got my answer, thanks...:)
  10. noorbeast

    noorbeast VR - The Next Generation Staff Member Moderator

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  11. Pawks

    Pawks New Member

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    Thanks @noorbeast, seems logical way to go with. :)
    • Agree Agree x 1
  12. SeatTime

    SeatTime Well-Known Member

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    To answer Why 'as close as possible to the seat base'? To best simulate a race car, as can be seen below, ideally it would be even higher. IMO it may be why big movements on a pivot based Car Sim never feel realistic.

    Car movements.jpg
    • Informative Informative x 2
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    Last edited: Sep 4, 2015
  13. Pawks

    Pawks New Member

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    @SeatTime , you're right...limited with 2DOF it would be ideally to do something like OP mentioned but it leads to IMO much more complex design.
    So yes, for more realistic feeling it's probably best to add more degrees of freedom...
  14. SeatTime

    SeatTime Well-Known Member

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    Could it be one of the reasons why I am building a 6DOF capable sim :) ;).
    • Like Like x 1
  15. Ben V

    Ben V Member

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    I considered the same thing @francis72 when I was working on ideas for my simulator. Imagining a car accelerating, it made sense that you should feel the surge forward of the chair, then the chair would have moved to a leaned back position to sustain the g-force feeling.

    The factors that held me back from pursuing such a design further are:

    Space - A much larger frame would be needed to support the chair from a u-joint at the top.

    Power Requirements - Placing the u-joint as near as possible to your center of gravity (such as just under the chair) reduces the force necessary to pivot the chair and greatly reduces the motor power necessary to get the chair to move adequately.

    Sensation of Acceleration - If the chair pivots at the top, most of the acceleration would be in your lower body. When I tested braking and cornering in a real car, I noticed the acceleration mostly in my head and chest. For this reason, I felt it was better to maximize acceleration of the head and chest with the pivot below the seat.

    I'm quite curious how well such a design would work out, but as @SeatTime and @Pawks suggest, maybe it's best to leave that type of sensation for the 6DOF rigs.
  16. hooshang

    hooshang Active Member

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    good idea having universal joint at the top,but the concept @francis72 mentioned just works for sway not for surge.
  17. Pawks

    Pawks New Member

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    If universal joint is used, then it should work for both sway and surge. Why do you think it wouldn't?
  18. hooshang

    hooshang Active Member

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    @Pawks
    Hi,

    base on the picturs in the first post and the directions of the Gforces and comparing it with
    sway and surge separately. imo when the universal joint is at bottom the sway motion with the real gforce are opposite
    but in surge they are at same direction and vise versa when the universal joint is at the top
    regards
    Hooshang
  19. Pawks

    Pawks New Member

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    Hi, @hooshang

    I made a simple picture showing forces when accelerating in forward motion.

    1. Fwd acceleration would ideally be simulated by doing just that - accelerate seat in forward motion (red arrow), so you feel pushed back (green arrow) just like accelerating when in real car.
    But this would be very unpractical, since one would need an infinite available room to move seat in particular direction to achieve feeling of continuous acceleration...
    2. The problem of 1. can be solved by using gravitational force by leaning seat backwards - this way the body feels pushed back (green arrow) like it would when accelerating.
    Also note that by doing this, you lower the feeling of the gravitational force (blue arrow), cause the actual gravity is now also used to simulate acceleration - but this is not a big problem.
    3. When you try to simulate acceleration with joint at the bottom - you want to get to seat position like in 2., but by doing that you do the opposite of 1. and you feel pushed in the wrong way (green arrow) until you achieve final position.
    4. When doing the same with joint at the top, you want to achieve the same position 2., but here you do the same thing as in 1. and feel pushed to the back of the seat right away.

    The same thing applies to sway and left/right acceleration, this is the way i understand it... :)
    surge.jpg
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  20. hooshang

    hooshang Active Member

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    @Pawks
    Hi
    good ,base on your explanation yes the both ,sway and surge have the same behavior.but as you know .
    motions and the forces in simulators are somehow defferent from the real world,the best example for this is comparing sway with roll or
    surge with pitch in 6DOF stwart platform,you can never put or fix the forces you explained in your nice painting on a 6dof rig.
    regrads buddy
    Hooshang