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(Yet another) 3DOF motion rig with g-seat for DCS

Discussion in 'DIY Motion Simulator Projects' started by hcee2022, Mar 10, 2022.

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  1. hcee2022

    hcee2022 Member

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    My Motion Simulator:
    3DOF, DC motor, Arduino
    Hello community,

    I was originally interested in building the actuator-based SFX-100, but then found out about Bergison's motion integrated G-seat and instantly knew that that would be much more suitable for my gaming (mostly DCS + VR).

    So, after reading tons of threads and admiring the great setups done here, I went ahead and gathered a bunch of stuff in January-February 2022 to build my own 3DOF + G-seat sim setup.

    Building the base took a long time, since I don't have access to sophisticated machining tools or welding kit, and can mostly work on it during the late evenings. I've also had to improvise quite much, for the better or the worse.

    This project owes a lot to Bergison's motion integrated G-seat, Sielu's awesome take on it, and, of course, momolic's thorough and excellent tutorial. On the software side I've been enjoying SMC3 by RufusDufus.

    Main parts:
    - 1x Arduino Uno R3
    - 2x Pololu G2 24v18 shield dual-channel motor drivers
    - 3x Alibaba Chinese 24V 300 W worm gear motors
    - industrial Siemens power supply 24V / 40A
    - 3x rotary hall sensors
    - 40x40 and 30x30 aluminium profiles
    - various 3D printed plastic parts

    Current status:
    - motion system has been built
    - seat part and G-flaps missing
    - first iterations with SMC3 PID tuning done
    - having issues with over-current protection shutting the system down in axis testings.. don't know if it's Pololu or the power source that's doing it

    Attached Files:

    • Like Like x 6
    Last edited: Aug 29, 2023
  2. Jumping Coin

    Jumping Coin Member Gold Contributor

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    Always great to see another gseat! Looking forward to your project!
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  3. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
    3DOF, DC motor, JRK
    With respect to PSU shutdowns there can be a range of possible issues, inadequate PSU capacity or settings refinement. Perhaps consider posting pictures of all of your settings and PSU specs, along with the trigger circumstance (often fast reversals or crash).
  4. hcee2022

    hcee2022 Member

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    My Motion Simulator:
    3DOF, DC motor, Arduino
    Many thanks for taking the time to look at this noorbeast;

    Please see attached screenshots with SMC3 settings and results with "motion" and "manual" (same settings used for all motors) as well as my Simtools settings. The SMC3 screenshots have been taken without weight on the platform. SMC is running in mode 1, no pot scaling etc.

    - In SMC3 everything works well (only one motor runs at a time). My current settings are using only Kp and (I think) quite conservative values for PWM.

    - In Simtools I haven't run any game plugins yet, as I'm still waiting for my DIY license. I've just played around with axis testing. When I'm sitting on the platform, a downward movement in heave (from top position to bottom position) shuts the system down. Otherwise it seems to stay within current limits with these settings.

    - The motor drivers are not running hot at all.

    - The PSU is Siemens SITOP modular 24 V / 40 A 6EP1337-3BA00 (sourced second hand from ebay, but appears to be in mint condition). According to the manual, it should light up overload LED before shutting down, but I haven't noticed that. Motor drivers and PSU power LED just turn off.

    - After the shutdown, the PSU doesn't come back online unless I unplug it for a minute. Detaching the motor drivers doesn't affect this.

    - Specs of the PSU's output attached as a pdf. The used input is 240V single phase.

    - The whole PSU manual is available online: https : // cache. industry. siemens. com/dl/files/578/81287578/att_21914/v1/modular_1-2ph_Handbuch_englisch_en-US.pdf

    Attached Files:

  5. hcee2022

    hcee2022 Member

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    My Motion Simulator:
    3DOF, DC motor, Arduino
    Few further images:

    1) Control boards.

    2) Siemens power supply.

    3) New hall sensor setup with 50/20 gears. Still using 3d printed plastic parts so precision isn't great, but now I have proper resolution and can limit the turn angle with SMC3.

    4) Old hall sensor setup. The SMC3 max limit of 255 wasn't enough for limiting the physical movement to ~120 degrees. It was also difficult to center the axles of the sensor and the motor. The sensor would move a bit when motor turned, causing unwanted jitters.

    (The lighting in my basement/mancave is poor; I'll take better pictures or video when I have the seat part done)

    Attached Files:

  6. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    First try refining your SMC3 settings further, as it is not tracking well.
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  7. hcee2022

    hcee2022 Member

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    I haven't yet adjusted the motor profiles with SCM3, but have been building the seat part. It's starting to look like a seat already.

    Now there's an issue with one of the motors.

    The motor is making a clicking sound when moving a weight down (turning counter-clockwise). When lifting the weight up it sounds normal. Also when running the motor freely (pusharms detached from motor axle) it sounds normal in both directions.

    In the video it's the one closest to the camera, on the left.

    Is that a busted gearbox or a bearing ? Next thing to do will probably be to detach the gearbox and look inside, but if someone already has ideas about what to look for, I'd appreciate any advise, thanks !
  8. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    I do think there is damage to the motor and the only sure way to know is to strip it down and check.

    I once had gearbox problem with a brass gear, I think that was just bad luck as its replacement and the one on the other side are still going strong, many years later.
    • Like Like x 1
  9. Sielu

    Sielu Member Gold Contributor

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    My Motion Simulator:
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    Awesome build so far @hcee2022 ! I'm glad mine could inspire yours!

    I'd agree that your issue definitely sounds like it's in the gearbox, but it is odd that it's only in one direction....it could just be something loose in the gearbox that is tightening itself when it's under load? Don't be afraid to tear it down and take a look, I've fixed a few of my issues by just taking this stuff apart.
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  10. hcee2022

    hcee2022 Member

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    Thanks for the comments noorbeast and Sielu !

    I shared the video also with the supplier (Alibaba seller) and they instructed to first test switching left and right side motors to check if there's a mechanical issue in the seat base itself. Result was that clicking just changed to the other side so the motor is the culprit. They will send a replacement gearbox for free, which is great.

    Other than the clicking sound, the motor seems to run fine for now; power consumption is the same as others and it doesn't struggle with the weight when I'm sitting on the seat.

    I also detached the gearbox and looked inside, but visually everything was good and spinning it by hand didn't show anything special. I also tried reseating and switching left and right side axle bearings, but that did nothing.

    Building the seat itself has moved forward -- the G-flaps are now done and moving. I also did some cable management and tuned my DCS profile. Surge effect are great; shaking on the runway is a bit too much. I'll have to test with smoothing and deadzone.

    Btw, there has been no shut down issues in actual sim use so I guess the power source / motor drivers can handle actual use without issues.

    Next up is the headrest, some foam cushioning, some kind of cover for the base's moving parts to prevent kids putting their fingers there, ejection handle, paintwork and seatbelt (still in the mail).

    Attached Files:

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  11. hcee2022

    hcee2022 Member

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    Another photo from a better another angle.

    Attached Files:

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  12. Sielu

    Sielu Member Gold Contributor

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    Awesome work friend! I really like the recumbent angle on the seatback pylon support. You'll have to let me know how well that translates to flap-movement!
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  13. NickD

    NickD New Member

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    Somehow in the time I have looked at these projects, I have missed a "G Seat." This looks great! Compact and less parts than a 6DOF. I like the idea too of the seat providing some force from the flaps against you as the rig moves around. I am currently waiting on 6 worm gear motors to start my project but now I may have to rethink things after seeing this.
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  14. hcee2022

    hcee2022 Member

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    Thanks mate ! The pylon wasn't planned, but I had that alu profile piece as a spare and it seemed like the perfect solution :) The nice thing is that I can slide the wooden piece up and down to adjust the neutral flap position.

    The flaps themselves do give a decent push to the back -- I'll make a video later.
  15. hcee2022

    hcee2022 Member

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    Hi NickD, thanks for the comments !

    I've never tried a 6DOF myself, so I don't know how those feel like. The advantage of a g-seat to me is that it's able to simulate sustained forces, not just movement, which adds a lot to VR flying. Bergison's introduction video (below) has a great explanation about the concept.

    I think people have also built g-seats with separate motors, so that the g-flaps can be operated separately from the seat's movement. That way it would be possible to have 6DOF + g-seat combination as well (but that's a lot more moving parts, like you said !)

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  16. Sielu

    Sielu Member Gold Contributor

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    The other two big advantages to the MGS (Motion G-Seat) design are (also covered by Bergison's video above) are

    1. Negative Gs: as long as you have a harness set up attached to solid points on your rig, you can get a really nice 'negative' g feeling when going over curves in flight. Even though you technically have panels pushing you from the bottom, having the side panels 'release' you while suddenly feeling pressure from the harness really makes you feel like you're being 'lifted up' out of your seat. I wasn't expecting this to be such a satisfying feeling but on my rig I find it much more impactful than the 'positive' Gs.

    2. No need to worry about motion cancellation for VR: having read a lot of people struggling with motion cancellation I've become very thankful I don't have to worry about it. Because the range of motion on the MGS is so limited you really don't need to cancel the movement, and if anything the slight lateral shifts add to the immersion because your eye position is moving "with" the Gs in the cockpit.

    The last major advantage I've discovered through use--which Bergison does not mention--is the vibrational component that the full motion seat can provide. I'm sure this is the same on a 6DOF setup, but I can't imagine it's as pronounced on a 'pure' G-Seat with only pressure flaps. Going over a rough runway on takeoff/landing, or the past few days flying the AH-64D and feeling the whole aircraft vibrate roughly with the rotor movement, not to mention the 'kick' that the guns produce... has all been just immensely immersive. I also have a bass-shaker but it just can't compare.

    **EDIT** Turns out what I thought was vibration coming through the motors WAS actually just bass shaker... When I first felt it I reached down to feel the bass shaker and it wasn't doing anything so I presumed all the nice vibes I was feeling was coming from my motors. Turns out THAT bass shaker just had a loose wire, and the other one was shaking the whole rig to bits! So, disregard that last paragraph... and get a bass shaker if you don't have one!

    Granted, I'm biased having invested in the MGS vs. a 6DOF platform, but I truly feel that this route offers a best-of-most worlds while offering its own unique advantages AND having a much smaller footprint and less technical design. For a primary racing setup, I can see an argument that a full 6DOF is superior to a 3DOF, but if you're primarily flying I think a 3DOF MGS actually edges out a 6DOF on many fronts.
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    Last edited: Mar 27, 2022
  17. hcee2022

    hcee2022 Member

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    Crafting 6 identical cranks for the motors of furniture tube was hard, but I have to say doing the seat cushioning and textile finish looks even more challenging now (the wife may have to do this part eventually...)

    Attached Files:

  18. Sielu

    Sielu Member Gold Contributor

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    I was very intimidated by that part as well! I just ended up hot-gluing the fabric on to the back of the foam. Doesn't look great from the back, but as soon as the cushion's down on the seat it's fine!
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  19. NickD

    NickD New Member

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    I'm super green in the simulation world and didn't even think about the negative G's this could also provide! This type of rig has really piqued my interest. I will be extending my research to this type of rig now while I am waiting for my worm gear motors to arrive from China.
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  20. Sielu

    Sielu Member Gold Contributor

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    The only other way I know how to do it would be to either have a full 360 rig, or attach small motors to your harness to apply pressure.