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Where to put the u-joint?

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by Doon1, Jan 14, 2018.

  1. Doon1

    Doon1 Member

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    I've been drawing this up with the u-joint in the center point of the seat. I can design it so there is some fore/aft adjustment but is the center of the seat the best place for the u-joint?
    Doon1, Jan 14, 2018
    #1
  2. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    • Useful Useful x 1
    noorbeast, Jan 14, 2018
    #2
  3. Doon1

    Doon1 Member

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    Thank you.
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    Doon1, Jan 14, 2018
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  4. getti

    getti Currently building my first 2dof seat mover...

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    For a full frame rig you need to find the balance point with all peripherals attached and you sitting in the seat. For a seat mover design you need to put the u-joint as close to the rear of the seat as you can get it.
    getti, Jan 14, 2018
    #4
  5. Doon1

    Doon1 Member

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    Is 3 1/2 inches from the center of the joint to the seat bottom too much? I can flip over the joint as I made it bolt on both top and bottom. It would require a small plate welded on it for the seat to attach but one of the welding students did the top that you see in the picture so it's a non issue.

    Attached Files:

    Last edited: Jan 19, 2018
    Doon1, Jan 19, 2018
    #5
  6. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    It is preferable to have the u joint bolt directly to the seat without any sort of riser, as otherwise it introduces some of geometry and like adds a greater strain on the motors.
    noorbeast, Jan 19, 2018
    #6
  7. Doon1

    Doon1 Member

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    Just a little redesign then. I hope to mount it to the seat tomorrow. The motor bracket is done and I have the links. Still have to cut out the actuator arms. Why are everyone's arms so short? I was hoping for about 50 degree pitch and 50 degrees roll. Is that unrealistic?
    Doon1, Jan 19, 2018
    #7
  8. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    It takes far less degrees of moment than you may think to trick your brain and high movement angles mean a lot of power and speed are needed for anything other than gentle flight simulation.
    • Agree Agree x 1
    noorbeast, Jan 19, 2018
    #8
  9. Doon1

    Doon1 Member

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    That's the great unknown. I can't find the datasheet on my motors. I know the ratio is about 28:1, the unloaded power draw is 3 amps @ 24 volts, and the unloaded speed is about 120 rpm.

    Do the points where the connecting rods connect to the seat form a isosceles triangle with the u-joint to create roll and pitch symmetry?
    Doon1, Jan 19, 2018
    #9
  10. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    noorbeast, Jan 19, 2018
    #10
  11. Gadget999

    Gadget999 Well-Known Member

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    i put my rig on a metal bar and rolled it forwards and back till i got balance - easy to find the cog this way :)
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    Gadget999, Jan 20, 2018
    #11
  12. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    noorbeast, Jan 20, 2018
    #12
  13. Doon1

    Doon1 Member

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    Thank you. I now have the center of balance located. I hade to use a 4" diameter PVC pipe to roll it on but it worked.
    I've been using Simcalc but I'm getting some confusing results. Here's a pic of Simcalc and a CAD of the motor and u-joint as seen from the side. I'm fairly certain there shouldn't be 100% of roll and pitch.
    I also moved the seat closer to the u-joint and will be securing it on Monday.

    Attached Files:

    Doon1, Jan 21, 2018
    #13
  14. Doon1

    Doon1 Member

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    What a Maroon! I was inputting (mm) instead of (m) in the rod and motor location fields. This makes more sense.
    I'm using zero for the rest angle. is the rest point the location in the middle of the full range of travel?

    Attached Files:

    Last edited: Jan 21, 2018
    Doon1, Jan 21, 2018
    #14