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Winging a 3DOF (pitch, roll, yaw) build.

Discussion in 'DIY Motion Simulator Projects' started by Buj818, Feb 6, 2024.

  1. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    I am not sure if anyone has done a direct comparison between the two, but the mathematical assumptions behind SimCalc are available here: https://www.xsimulator.net/community/threads/simcalc-by-tim-mcguire.11277/page-2#post-140469

    Both should be taken as a guide, as other factors can come into play, such as mass and inertia, depending on design.

    Leverage effectiveness is related to mounting distance and angle, the likes of SimCalc helps give an idea about the impact of design choices.
  2. Buj818

    Buj818 Member

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    I decided I'm going to cut my rods down to 19". After 45°'ing all angles (rest angle, rod angle, and pivot angles), I found the intersecting point right at 14" on seat back frame. It still gives me plenty of pitch (17°) while maintaining 99% efficiency, and roll at 71% efficiency. I'm going to keep a long CTC lever (5.3") unless someone tells me directly it's an absolute horrible idea. I'm still having issues wrapping my head around why a 2.5" CTC is the golden rule.
  3. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    I am not trying to sway you one way or the other, so just some things to take into account:

    The longer the CTC of a lever the greater the linear speed but the less the effective torque, which itself is somewhat dependent on design, so the less distance the motors are from the pivot and the greater the mass the greater the torque required.

    Another factor is gearbox backlash, which varies depending on type and manufacturing, but where present, like with wormdrives, the longer the lever CTC the more pronounced the backlash.
    • Like Like x 1
  4. Buj818

    Buj818 Member

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    Thanks! Today I mounted yaw motor, made lever for that (2.5 CTC) and also made holes at 3 and 4 inches CTC on my pitch and roll motors. After cutting rods down and manually pitching the seat base, I'm still only getting 11.2 degrees max (so much for simcalc telling me I'd get 17°, lol). It's alright, I just want to get this thing wired up and into simtools testing stage. That'll hopefully be this Wednesday. Only thing holding me up is I gotta make the yaw rod. Maybe I'll knock that out tomorrow evening.
  5. Buj818

    Buj818 Member

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    Mounted the 3 pots last night and made the last control rod. I cannot find a 3 motor diagram for Arduino and IBT2s. Can anyone helpe out with that please? Would the green from the third IBT2 go to 6, and the blue go to 7 of the Uno R3? This is the last thing holding me up from testing.
    Last edited: Feb 28, 2024
  6. Buj818

    Buj818 Member

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    Sorry, forgot to add the diagram I'm working with. Would the correct config be green 6 (PWM) and blue 7? Wiring-2-Motors.jpg
  7. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    I am presuming you are using SMC3 from the picture, in which case you are better off using a second Arduino for the third motor, because of the Arduino processing.
  8. Buj818

    Buj818 Member

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    Ah man. Yes I am planning on using smc3. I haven't seen any tutorials on using a second Arduino. Are they wired in series or do I need to get a separate USB cable for it? This is gonna set me back quite a ways timewise. Gotta do what I gotta do I guess.
  9. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    Yes you need a separate USB, and the computer will assign the second Arduino a different com port.
    • Agree Agree x 1
  10. Buj818

    Buj818 Member

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    So the 2nd Arduino arrives tomorrow, but I have yet to find how to wire the IBT2 for motor 3 to it. Would I wire the IBT2 into PWM pins 2, 3, and 9 of the second Arduino? Or to PWM 6, 7, and 11?

    Also, did power on testing on Saturday. One of the IBT2s was bad. 3 more of those arriving tomorrow as well. But for the controllers that worked, they dialed in pretty quickly. As of right now, rig is stripped down for clean up and paint. I'ma post a lot more pictures after work today.
  11. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    In SMC3 you basically replicate what you did with the first Arduino, just using a different com port and only wiring one IBT2.

    In SimTools Interface settings you can add the second Arduino specifying its com port and the additional interface setting.
  12. Buj818

    Buj818 Member

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    Just to be clear, the wiring position for motor 3 on the 2nd Arduino does not matter? I can wire it in same position as motor 1 on the first Arduino?
  13. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    Yes you can, it is differentiated by comport.
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  14. Buj818

    Buj818 Member

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    20240306_175818.jpg 20240306_175832.jpg 20240306_175850.jpg 20240306_175907.jpg 20240306_175924.jpg 20240306_175942.jpg 20240306_180038.jpg
    • Like Like x 1
  15. Buj818

    Buj818 Member

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    So the structure itself is 95%'ish finished. Gotta make TV mount and possibly a dual caster wheel drop for the rear. The electronics are half way finished, hopefully done by Friday night, with full motion in seat testing Saturday.
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  16. Buj818

    Buj818 Member

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    Quick question on setting the motor rest position. When power is applied to the motors, which software and where is the rest position set? I'm running SMC3, but when power is applied, they randomly set themselves. They are not running away or spinning, I'm just trying to get them to find their initial "set here" spot when turned on.
  17. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    Centering and range is set in SMC3.
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  18. Buj818

    Buj818 Member

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    After searching "centering", a few threads popped up that I'm going to dive into. Centering was the term I needed. Thanks again for that.
  19. Buj818

    Buj818 Member

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    Having a ridiculously hard time testing in SMC3. Pots are accurate, all centered, but when it comes time to motion test, it will only do 3 revolutions and then the motor cuts and the arm of the motor being tested just drops to max bottom. The sine wave is nowhere near close to clip or max. Only powering 1 motor at a time. This happens with all 3 motors. Watched multiple tuts, and no matter what I try, it keeps dropping out on me. Manually, I can move it with cursor without any issues. Any suggestions or should I just move into simtools? Screenshot_20240309_171603_Gallery.jpg
  20. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    My guess is if it is cutting out without reaching the limits, and particularly if unloaded, it would most likely be faulty hardware, so PSU or control boards.