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Stewart 6DOF or 4DOF+TL+Surge

Discussion in 'New users start here - FAQ' started by Troymx576, May 14, 2020.

  1. Troymx576

    Troymx576 New Member

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    My Motion Simulator:
    4DOF
    I am in the planning and soon to be building process. This motion setup is for racing, mainly Iracing. I am debating building a full Stewart platform with the actuators top pivot point around chest level. The other option is to use 6 actuators on my current rig, 4 corners, traction loss and surge. I am not sure what would be better and why. I would think the second option would be easier to make and I could make it in two stages, the first is the 4 actuators and then add traction loss and surge later.

    Thoughts on pros and cons of each?

    Thanks
    Troy
  2. Thanos

    Thanos Building the Future one AC Servo at a time... or 6

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    My Motion Simulator:
    AC motor, Motion platform, 4DOF, 6DOF
    On 6DOF Stewart type platform, the load is shared between all actuators.

    On 4DOF (+TL +Surge) the load falls entirely on the 4 actuators, while the TL and Surge just displace the load momentarily when needed.
  3. Troymx576

    Troymx576 New Member

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    Thanos, I plan to use your controller for either build and amazing impressive work there buddy. In finding your controller for my planned SFX-100 build it got my mind pondering. This is your fault, haha, in a good way.

    I am just pondering if one is that much better than the other and why?

    Does one of the two choices give a much more realistic experience? I can see the servo and motor system on the Stewart being larger and therefore more tq needed, plus speed possibly since they will be longer. The 4DOF platform can take up less space compared to the 6dof.
  4. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    My Motion Simulator:
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    A 6dof gives more scope in terms of refining the tuning across all 6dof axis.
  5. Madonion

    Madonion New Member

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    My Motion Simulator:
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    Im in the same boat.
    i do alot of racing and it looks like 4 DOF with TL and surge is the way forward for me. Then i see Dirt 2 and the longer travel of the 6 DOF would make jumps more realistic. Just cant see the traction loss or surge be as impressive as i see on 4 DOF with TL and surge? Then again Flying in Ms 2020/DCS/ Elite dangerous would be epic in 6DOF.
    • Like Like x 1
  6. Historiker

    Historiker Dramamine Adict Gold Contributor

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    My Motion Simulator:
    3DOF, DC motor, Arduino, Motion platform, 6DOF
    I have both, my hexapod 6dof is great, my SFX100+100 +TL+Surge+Sway 6dof only has the TL, Surge and sway right now as I am waiting on the hollow shafts from China. However, the motion even with only those three is Fantastic.

    A buddy who also has a hexapod 6dof test drove my new rig the other day and wants it.

    Either way you go, you will be happy I bet
    • Informative Informative x 2
  7. Thanos

    Thanos Building the Future one AC Servo at a time... or 6

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    My Motion Simulator:
    AC motor, Motion platform, 4DOF, 6DOF
    Think of it from software support side...

    6DOF --> FlyPT mover, perhaps Ian's BFF 6DOF motion software too.

    4DOF+TL+Surge --> Simtools, FlyPT mover, SRS ...

    A bit more software options for 4DOF+TL+Surge...
  8. SeatTime

    SeatTime Well-Known Member

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    My Motion Simulator:
    AC motor, Motion platform
    Having built both, realise that your normal peg leg design has the centre of rotation quite low. In the end I built a bit of a hybrid 3 actuator design, which locked down the actuators from any unwanted movement and raise the centre of rotation. For the amount of movement I wanted, a Stewart platform would be too large and difficult for many of my family and friends to get into and out of. Will be adding some dedicated surge and sway systems later. So which is better? If you don't mind climbing in and have the room : Stewart Platform _ adjustable roll centre, stable and less inertia if you start adding surge and sway systems to a pegleg.
    Last edited: Apr 17, 2021
  9. Madonion

    Madonion New Member

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    Thankyou for the informative reply. im also leaning more towards 4dof with TL and surge and yea im sure i will be happy either way :p.
  10. Madonion

    Madonion New Member

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    Thankyou! heard alot about SRS. i will order 6 motors either way so if i really felt like it i could do either one with abit of labor and try it out with a test rig. Man im gona be stoke buying that thanos controller and motors! Cant believe it! so cool!
    • Like Like x 1
  11. Keith

    Keith Active Member

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    Did you decide what you are going to build? I currently have a 2dof with TL and am looking to build something new.
  12. Gadget999

    Gadget999 Well-Known Member

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    My Motion Simulator:
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    having 4 actuators does not give you 4DOF - it is only 3DOF pitch, roll, and heave

    a 3 peg leg sim is more stable than a 4 peg leg design
  13. Thanos

    Thanos Building the Future one AC Servo at a time... or 6

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    My Motion Simulator:
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    3 peg leg can be stable on all cases even if the actuators are not coordinated ( wrong motion cues ). But you will need to make sure the center of gravity is low, otherwise its easier to make it tip over from load displacement.

    Using 4 actuators one on each corner indeed is still 3DOF (PITCH,ROLL,HEAVE) but you can place load on the rig even right on the corners without fear of tipping. And proper motion software can ensure all 4 legs are always touching the floor during motion. The only time I have seen a 4 actuator rig lifting one leg was from early simfeedback development (could be fixed by now):



    :p
    Last edited: Jan 24, 2022
  14. cfischer

    cfischer Active Member Gold Contributor

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    Stable is an interesting choice of words. 3 pegs can tip = not stable. I've tipped over in vr(blind to the world) in a 3 peg leg design. Scary AF.
    • Agree Agree x 1
  15. Gadget999

    Gadget999 Well-Known Member

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    It needs to be designed correctly - unfortunately a lot of sims are an evolution of a static sim and were not designed for motion in the first place.

    We have all been to a restaurant where the table is wobbly, 3 legs on the table make it more stable.

    You need to ensure the legs are far enough apart to ensure the cog is well inside the tipping point
  16. C.Y

    C.Y New Member

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    Just to confirm my understanding … a Stewart design is the same as a Hex pod design right ?

    I did a google search and they look identical

    it’s just different terminology right ?
  17. Gadget999

    Gadget999 Well-Known Member

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    My Motion Simulator:
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    A stewart platform allows 6dof

    Heave
    Sway
    Yaw
    Surge
    Roll
    Pitch

    A hexapod usually means 6 actuators - if they are arranged correctly you will the the same motion as a stewart platform. I have seen rigs called hexapods but actually they are 3dof
    Last edited: Feb 28, 2022