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Question SimCalc sanity check

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by chadat23, Apr 21, 2021.

  1. chadat23

    chadat23 New Member

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    Has anyone double checked results from SimCalc?

    I read some of the associated PDF and a few things raised an eyebrow so I plugged in some numbers for geometry for which I could solve by hand, which I then solved using a few different strategies. I also wrote a program to solve for any such geometry which uses a 3rd set of equations. All my strategies matched each other and differed from SimCalc so either I'm making a dumb/systematic mistake, or SimCalc is wrong.

    I'd love to either understand where I'm going wrong or find out if SimCalc has an error in it.

    In case it's not clear from my drawing, everything's aligned along the X axis, the Motor Position is at the Pivot Point and the ctc - rod mount rod runs vertically. And I know I'm using geometry that doesn't actually make sense for a motion rig but it made pitch torque easy to calculate by hand.

    upload_2021-4-21_12-24-10.png

    upload_2021-4-21_12-19-36.png
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  3. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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  4. chadat23

    chadat23 New Member

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    Hmm, I reread it and while we employed different approaches, we make about the same assumptions. And while I've never used his matrix approach to transforming between frames while doing kinematics or dynamics (I've always used trig), his approach seams perfectly valid and I see no obvious reason why my above model system would break it. Past experience is simultaneously telling me that I haven't made a mistake (I used to be a Sr. mechanical engineer), and that being new to the community, I shouldn't assume that it's tool is wrong, which brings me back to my initial question. :)
  5. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    The SimCalc dev @Tim McGuire is an active member, so will likely chip in at some point.
  6. chadat23

    chadat23 New Member

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    Awesome, I hope he does!

    My programmatic solution is a little bit more generic so once I flush it out a bit more I'll be able to do things like calculate max acceleration or speed, and linearity for any combination of pitch and roll. I'm tentatively planning on making visualizations that cover those things over the full range of motion. And I'm happy to share such tools but I'd hate to do so if it makes mistakes!

    Edit: and maybe I'll add support for asymmetric shapes (I feel like I've seen that on seat movers)
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    Last edited: Apr 22, 2021
  7. Tim McGuire

    Tim McGuire "Forever a work in progress"

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    Hi Chadat, noorbeast!

    You've dragged me out of retirement! Haven't posted in ages! It's entirely possible that simcalc has errors, which is actually one of the reasons why I uploaded the math behind it. I'm an electrical engineer by vocation, so this is definitely not my area of expertise, I will go check my math, but defer to you if I can't find anything obvious. I was a little in over my head as a programmer at the time as well, so it's definitely possible there's just a coding error somewhere in there.

    Truth me told I've been pretty swamped with life/work the past couple of years (silicon valley engineering isn't as rosy as they paint it to be, eh?), so I really haven't had time to touch the sim or the program for a long time. If you're planning on making a tool of your own, I would recommend that @noorbeast supplant simcalc with your program, something tells me it'll be more well supported ;)

    Cheers!
    -Tim

    P.S. Where in california are you at? I moved to the bay area about a year ago
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  8. chadat23

    chadat23 New Member

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    Ha, I was wondering if you were a EE, the pdf read like it was written by an engineer but I can't imagine an ME ever using a matrix for anything ;)

    I know where you're coming from with the lack of time. I was in R&D for one of San Diego's more ambitious biotechs for some years until I ran away to the mountains, now I'm a Yosemite Wilderness Ranger :)

    The next 6 months are going to be "real busy" for me so my tentative plan's to, for as long as I don't hit any major roadblocks, work through coming up with a flushed out design, source parts, estimate costs, bla, bla, bla, and then if things make sense, start spending money and cutting metal in the fall.

    Now that you talk about supporting software maybe I don't want to share it ;) No, seems like people always have good ideas for feature requests up front and then things usually trail off so hopefully if there's a need for future support I'll be able to continue to supply it.
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