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Design considerations for realism

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by SeatTime, Jun 6, 2018.

  1. SeatTime

    SeatTime Well-Known Member

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    Just a observation..I hope the OP doesn't mind. Your setup is not too bad, but the roll centre height of some of these 'D Box' setups is nowhere close to optimal. For some of these, it must feel like your driving your car siting near the roof. Food for thought for anyone thinking about building something similar. Keep that seat low. Here is not what to do



    I often think that some of these 'Engineers' found their degree in a Kellogg's (cereal) packet :).
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    Last edited: Jun 7, 2018
  2. Ads Master

    Ads Master

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  3. Jerry Atrick

    Jerry Atrick this is my sim Gold Contributor

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    I often think that some of these 'Engineers' found their degree in a Kellogg's (cereal) packet :).[/QUOTE]

    Hi SeatTime, so is there an example showing how the engineering should be performed?

    Just so I know how I should be building it!:)

    Jerry.
  4. SeatTime

    SeatTime Well-Known Member

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    Hi SeatTime, so is there an example showing how the engineering should be performed?

    Just so I know how I should be building it!:)

    Jerry.[/QUOTE]What's funny is that it is not that hard :rolleyes: - just mimic the real world. Ie keep the roll center as close as is possible to what it would be in a real car. In the video example that I showed further back the roll center is way too low below the seat and would feel like he was driving the car with the seat close to the roof and his head through it. It could even make some people sick. Picture tells a thousand words. In the real world for a F1 car the driver actually sits below the roll axis in the N1 Dbox setup that are way above it - just so wrong. Even your standard real car seat is not that far above the roll center/axis. Maybe good for simulating a truck ...

    Car Roll Center_Axis.jpg

    The OPS design is sooo much better.
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  5. Jerry Atrick

    Jerry Atrick this is my sim Gold Contributor

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    HI SeatTime, thanks for the reply:)

    I think I understand:think
    So what this describes to me is; if I build this style of rig,

    The actuators have to be using a longer stroke therefore producing a higher lift, to compensate the lowering of the seat to equal the roll axis.

    If I use the D-Box image you supplied as the example: Say from the floor to base of the rig is 200mm, then the seated bum "if you will" should be about the same height.
    In the image above; the chair would have to be on the floor.
    Now this might not quite work for me, as at my age 200mm is a long way from standing up:grin

    So I might have to use this as a part of the rig upload_2018-7-2_21-16-7.jpeg

    Thanks again
    Jerry

    PS: how is the STM32 going?
  6. Brett Loxton

    Brett Loxton New Member

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    @Jerry Atrick if you moved the actuator up higher by moving the mounting point higher, both in green, and then make some sort of box/foot, in yellow, you'll get a better roll centre. Hope the pic helps.

    Attached Files:

  7. SeatTime

    SeatTime Well-Known Member

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    The more the rig can move the more a incorrect roll center becomes an issue. Its likely why they keep the movement of these DBox setups small. FI, with a 6DOF and the right math you can actually change the roll centre (this is not possible on a Dbox setup), which is what I use to do with the BFF software. But, so I could also use Simtools - I built my rigs so that the seat base is slightly below the natural roll centre, as a 6DOF can move allot. This ensures the roll center does not become unnatural and have more of a chance of upsetting a riders middle ear. Have a look at mine and others similar setups in the project folders.
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  8. Jerry Atrick

    Jerry Atrick this is my sim Gold Contributor

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    Thanks Brett, I think I can manage the changes needed:)

    Jerry
  9. Jerry Atrick

    Jerry Atrick this is my sim Gold Contributor

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    Thanks SeatTime, maybe I can invert the actuators to push up and not down like D-Box, changing the frames design, I'll have a scribble.

    Jerry.
  10. F22raptom

    F22raptom Member

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    I have to go high because sitting in the seat with my legs fully stretched is 130cm. Thats how long my frame is. 3DOF with a target of 45 deg tilt (total of 90 deg range).

    Yeah, keep it low if it doesnt move much.. but I dont want my frame to bend (and it will bend) if it's too low to the ground when I get dumped forward during a carrier landing with a tailhook

    If you have any design suggestions speak now because I fab it tomorrow.
  11. SeatTime

    SeatTime Well-Known Member

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    Were not talking about flight sims here ;).
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  12. F22raptom

    F22raptom Member

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    I dont want to bend my frame when I hit a wall driving a Ferarri at 150 miles/hr (and I will crash it into a wall)
  13. Jerry Atrick

    Jerry Atrick this is my sim Gold Contributor

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    Hi F22raptom, is it possible to do a full video coverage of the crash, don't care if its flight or track,
    I think all here would like to see it either way:)

    PS: with voice over please:grin

    Jerry
  14. MarkusB

    MarkusB Active Member Gold Contributor

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    The high/low discussion here is not about the overall height of the moving part of a simulator above the ground, but the height of the seat (and your body) above the roll axis. You can even have a 360 degrees simulator with a roll axis straight through your body or where ever you want it.
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  15. PaulB

    PaulB Titanium2dof

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  16. SeatTime

    SeatTime Well-Known Member

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    Looks like you have a nice ride there and a nicely setup washout :thumbs. In regard to realism, many people find large rolls and pitches to simulate surge and sway forces just never feel as realistic as a real surge and sway, either by a 6DOF, surge/sway table, or a G pressure system and can often mess with their inner ear. It also makes it difficult to then apply realistic roll and pitch. But if your having fun on your sim - what does it matter :).
  17. PaulB

    PaulB Titanium2dof

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    I'd agree, can never get G simulated properly. unless I get a larger room. : ) Role and pitch are just added to the surge and sway. That seems to work without a problem. I like this higher pivot setup, because you don't have the moment of surge while braking as with the lower pivot. I was surprised how much the proper FOV helped.
  18. Terje Helle

    Terje Helle New Member Gold Contributor

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    Can you show a picture or a movie of how it should be done?
    And maybe some “articles” of the science behind it? Or just send me in a right direction.
  19. SeatTime

    SeatTime Well-Known Member

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    It's all discussed in the thread above :).
  20. SeatTime

    SeatTime Well-Known Member

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    To be fair that thread was 2018, the physics are still relevant, but I have moved on from my old stewart platform - found new ways to fool the brain :).
  21. Terje Helle

    Terje Helle New Member Gold Contributor

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    I noticed, was about to delete the reply... I found your quote in another thread, and didn’t find any explanation there.. Sorry..