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Showroom Grigory’s 6DOF 24V DC

Discussion in 'DIY Motion Simulator Projects' started by Grigory, Aug 9, 2016.

  1. SilentChill

    SilentChill Problem Maker

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    I watched the video again and it looks steady/firm enough. When mine felt a bit loose I had to rotate the arms 180 degrees to get a smaller angle which stiffened the whole rig up.

    I think the ideal angle of the arms is 45 degrees at centre if I'm not mistaken, however my math and anything technical is normally wrong lol
  2. Grigory

    Grigory Active Member Gold Contributor

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    I think I'll try replacing the threaded rods with square tubes and connecting gas struts to cockpit. That should make the structure more stable, I hope
  3. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Excluding people who are naturally over sensitive the most common cause in VR is that your axis movements are too large and slow, so you end up with a mismatch between your visual and vestibule systems.

    Try using less axis allocation and smaller Tuning Center values. What you are after is motion that is fast and precise for VR, even at the expense of large axis movement.
    • Informative Informative x 2
  4. SeatTime

    SeatTime Well-Known Member

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    Know were your coming from @noorbeast , but my 2cents worth is that you don't go to the trouble of building a 6DOF to use small axis allocations :) . The extra 'headroom' that is available on a bigger axis sim is to me a bonus - although your rig must be able to keep up. From the video the rig seems to be tracking what is on the screen quite well. Also with the Center of rotation being in pretty much the correct position it removes that 'steering your car from on top of your roof' feeling that you would get with big movements on a balance 2DOF rig, which can also make you ill.
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  5. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    I think we are saying the same thing, that the rig must be fast enough in motion to match the visual cues, else there is a mismatch with the vestibule system, discounting those who have a high sensitivity to VR and movement of any kind.

    Where that is depends on the person and their particular sensitivity to movement in VR, irrespective of a motion sim being part of the equation.
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  6. Archie

    Archie Eternal tinkerer

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    My Motion Simulator:
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    If everyone could stop making 6DOF's that'd be great! Making me very envious! :p

    I have three motors (two on the sim) so I'm halfway there I guess.....
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  7. bruce stephen

    bruce stephen Hammer doesnt fix it, must be electrical

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    sweet rig @Grigory i'm anxious to see it with the hardware.
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  8. Grigory

    Grigory Active Member Gold Contributor

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    Decided to replace the threaded rods with rectangular tubes for more rigidity:

    IMG_3982.JPG

    Unfortunately there's still quite a bit of wobble due to huge backlash in my gearboxes:



    I tried the rig with No limits again today and the movements are not smooth at all. Not yet sure if that is because of poor tunings or that backlash.

    Here's how it looks with my wife riding:
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    Last edited: Oct 8, 2016
  9. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    All wormdrive boxes will have some backlash, and while I have no experience with the gearboxes you are using it does seem excessive, exacerbated by long levers.

    This is what I consider normal backlash:

    • Agree Agree x 1
  10. Grigory

    Grigory Active Member Gold Contributor

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    I had to fight yet another problem when testing the rig yesterday.

    The issue was that when two motors controlled by a single Arduino were positioned so that one pot returned something close to 0V and the other one returned something close to 5v, Arduino's analog input connected to the lower voltage pot started to show terrible noise.

    I checked the wiring, tried adding capacitors -- nothing helped.

    Eventually the problem was solved by modifying the SMC3 Arduino code to make three consecutive analog reads instead of just one. I do not have an academically formulated explanation of the cause, but it appears that with the frequency at which SMC3 operates, the input of Arduino does not have enough time to make a proper reading when there is a large voltage difference between analog inputs. Issuing several analogread commands in a row takes care of this.
    • Informative Informative x 1
  11. Grigory

    Grigory Active Member Gold Contributor

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    Instead of learning to live with the gearbox backlash I decided to treat it in a radical way and to move the whole thing to linear actuators.

    Big thanks to @wannabeaflyer2 and @SilentChill for very detailed info on how to do it!


    Here's what i have now. The screws and some other stuff should be delivered this week, so I hope to have first prototype ready during the weekend.


    01.png 02.png 03.png
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    Last edited: Oct 31, 2016
  12. SilentChill

    SilentChill Problem Maker

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    Looks lovely and neat, did you use a CNC to cut it all out ?

    Don't thank me I just jumped on the band wagon :D its all @SeatTime and @wannabeaflyer2 hard work
  13. Grigory

    Grigory Active Member Gold Contributor

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    Yes, I have a small tabletop CNC router, which cuts PA6 plastic just fine. With PA6's relatively low friction, I may be able to do without linear bearing on top.

    Well, it was your build that inspired me for the whole process, so thank you for that anyway :)
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  14. Grigory

    Grigory Active Member Gold Contributor

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    The parts from aliexpress finally arrived and I managed to assemble the first actuator this weekend.

    The parts list is the same as in @SilentChill 's build, however I am using Sabertooth+kangaroo combination and quadrature encoder for feedback instead of potentiometer.

    Everything seems to work quite well after completing Kangaroo's autotune routine, however I have a problem with noise and vibration. I suspect that the cause could be that I had to invert the ball-screw nut to simplify fixing the carbon tube: I need the flat flange to face upwards, away from the motor. The ballscrews came from China with the flange on the motor side of the screw.

    I am right assuming that the nut is symmetrical and should work absolutely the same in both orientations?

    Here's how it sounds now:
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  15. SilentChill

    SilentChill Problem Maker

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    Sounds ok to me they are quite loud going at full speed.

    I don't think inverting the screw will make any difference though it's the same either way, just as long as you got all the bearings back in correctly :)
  16. Grigory

    Grigory Active Member Gold Contributor

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    Did some maths and I'm now wondering if my actuators will eventually be too slow.

    upload_2016-11-10_17-16-54.png

    @SilentChill, your motors are a bit faster with 4000 rpm vs my 3000 rpm, correct? Does it feel slow compared to your older setup?
  17. SilentChill

    SilentChill Problem Maker

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    I honestly can't tell you as I have not been able to run it at full speed yet :( I think it is similar TBH but with the extra range in movement it makes it look slower because there is so much more travel.
  18. wannabeaflyer2

    wannabeaflyer2 Well-Known Member

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    Hi @Grigory Welcome to the @SeatTime club , very nicely done ,great to see another DIY Actuator up and running, 6dof on the way very soon :) wow you managed to get the Kangeroo working now im impressed . personally i could not get the tuning right on my wheel chair motor 6 DOF attempts so its good to know someone has cracked it , Congratulation on a job well done @SeatTime sir you have started a revolution :) Grigory i would not worry about the speed just yet , Keep on with the good work and you wont be disappointed :) every time i ride my sim i have the biggest smile
  19. Grigory

    Grigory Active Member Gold Contributor

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    It should be slower on paper, but I do hope that this speed would be enough and also that the difference may be compensated a little bit with much higher pushing power of linear actuator -- it may be more responsive.
  20. Grigory

    Grigory Active Member Gold Contributor

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    Thanks! I used your plans linked from FAQ as a guidance :)

    Thanks, however there was not so much of a job here :) I've read that the problems occur when using Kangaroo with potenitometers, so I just took quadrature encoders. And I also have not yet connected it to Simtools. With DEScribe software it indeed works fine, but it is yet to be seen how all six will work together.