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DIY Motion Platform questions (Stewart in particular)

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by mciccarone, Jul 29, 2015.

  1. mciccarone

    mciccarone Principle Software Engineer

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    Hi All,
    I thought I knew a lot about what I was doing... that is; until I started reading all of the forums at xsimulator.

    A bit about myself; I am a Software Engineer and have no formal experience as an ME or EE outside of hobby. For my SIM I was planning on building a 3 DOF Continuous motion Ring based motion platform. After spending over $600 on a prototype I've come to realize that a full size variant would cost well above $15000 USD and from what I was reading on the forums here it won't give me the sensations of realistic movements. After reading the posts and looking at the other types of motion platform solutions out there I feel that I might want to change my approach and go for something a bit more practical.

    So here are some of my questions I hope can be answered:

    1. What is a JRK? I see it references in many posts, but I wasn't able to find out what it is.

    2. Are there any limits in Yaw/Pitch/Roll and Sway/Surge/Heave for Stewart platforms? I know that this depends on motors and actuator lengths, but are there any maximum travel distances that are inherent with the stewart design itself? (outside of +/- 90 degrees)
    I've seen many that have yaw limits of +/- 10 and pitch/roll of +/- 15, but I can't imagine those are the limits of the design itself.

    3. For those who have used a 6-DOF system, is there a point at which the rotation along yaw, pitch, and roll are no longer perceptible or don't add to the immersion?

    4. Again for those with a 6DOF: Is the sway, surge, and heave a noticeable effect worth the additional cost over a 3DOF system?

    5. Has anyone used Telescoping Actuators on DIY motion sims ? I don't know of any Screw or Worm gear telescoping actuators, but I have seen large professional motion sims that use telescoping Hydraulic actuators.

    6. What is a realistic estimate on how much money it would cost to build a 6-DOF stewart platform that can support a payload of 250kg with as much travel as possible? (Not including PC. Display, VR, Seat) [I need to know how much to save so that my wife doesn't divorce me for spending too much]

    7. Why is the Adruino the go-to choice for motor controllers? I've seen lots of the DIY projects on the forums here that use multiple Adruino boards and I don't know why one would opt to control each motor individually instead of all of them at a single control board. Why doesn't anyone use the Raspberry Pi to control the motors? It is a much more powerful platform and has a bunch of HATS that can be purchased that enable control of up to 32 motors.

    Regards,
    Mike C.
  2. hooshang

    hooshang Active Member

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    very welcome Mike ,for JRK you can ask wellexperienced jrk guy @bsft and also study for sure
    about 6dof ,yes everythings has its own limitation but you would better start with less DOF to realize concepts
    regards
    Hooshang
    • Like Like x 1
  3. tombo

    tombo Active Member

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    • Informative Informative x 1
  4. mciccarone

    mciccarone Principle Software Engineer

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    Hi Hooshang,
    I've been consuming as much information as I can find regarding the Stewart Platforms and it seems that 35 degrees is the maximum rotation. As for systems with less DOF I realize that they are easier to create, which is why I was asking questions 3 and 4. I've seen plenty of designs for Stewarts, what I haven't seen is feedback from people who have used one or more motion systems so that I can figure out if a 6 DOF system is overkill.

    I really want to get the feeling of rapid acceleration surge/sway/heave and I simply don't know if those feelings can be achieved without a 6 DOF sim.
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  5. bsft

    bsft

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    Yes it can be replicated as its a mind trick. Ive had professional drivers on my 2DOF seat mover and have said they can get the immersion idea of those forces.
  6. bsft

    bsft

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  7. mciccarone

    mciccarone Principle Software Engineer

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    My Motion Simulator:
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    Thats good to hear.

    I think I've decided to go with a 4 DOF (Yaw, Pitch, Roll, Heave) system using four line actuators.

    I'll start reading up on the 4 DOF systems and see if I can find an instruct-able or tutorial on building a scaled version so that I can play with the design a bit
    • Like Like x 1
  8. Gabriel Vuelma Romanzini

    Gabriel Vuelma Romanzini Member

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    Dear Mike C.
    I'm also a fan of Heave, I think the easiest way to get heave is with a 3DOF,

    SO MUCH stroke it's not good, as i heard from almost everybody here... For me, 30CM would be max, but with a speed of >>>>400/500mm/s <<<< Yes, speed is very important.

    3 Linear Actuators with 1 behind you, and 2 in the line of the steering wheel...

    [​IMG]

    VIDEO:
    ()


    And if you want traction loss, a 4DOF



    (Easier because have 2 actuators that take the load????? (Cheaper because have more components???)


    If you need some drawings, i work with solidworks, i do and send for you, free, obvious!

    Gabriel Vuelma Romanzini
  9. bsft

    bsft

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    If you people are so INSISTENT and it looks like have too much money and time to spend, then at least set a proper profile for racing on such a simulator, as seen in this video
  10. bsft

    bsft

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    pardon? I said 2 DOF, not 4 or 6 DOF. Am I not typing my numbers correctly?
  11. bsft

    bsft

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  12. mciccarone

    mciccarone Principle Software Engineer

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    Hi Gabriel,

    I want a decent stroke so that I can get good pitch and roll values. The yaw isn't as important, however the heave really is important as I want to really feel the simulated suspension. (My Target Simulation Software is for modeling high speed boats, aircraft, and of course rally cars!)

    After getting talked to my senses by bsft about going away from a 6 DOF stewart platform I thought I had settled on a design similar to the bottom link you sent (the one with 4 actuators in a square pattern).

    I'm now looking at the 3 Linear Actuator design you posted and it appears to me that the linear actuators are in fixed vertical alignment. This would eliminate the tangential torque forces on the motors, and would be great as it would let the motors focus all forces on the single vertical axis. I could probably do the same thing with 4 vertical actuators to help offload some of the weight from the single rear piston.

    Have you found Linear Actuators that have a 300mm stroke yet can travel 400mm / 500mm per second? I want to have a total payload (rider + cockpit frame + cockpit components) of around 220-250 kg?

    I've seen magnetic linear actuators (example - IAI Intelligent Actuator) that have tremendous travel speeds, but I haven't seen them used anywhere on the forums here. I am assuming they are very expensive and that EMF may also interfere with the various electronic components.

    What kind of motor / actuators are used to control the platform Yaw?

    Regards,
    Mike C.
  13. mciccarone

    mciccarone Principle Software Engineer

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    Hi Bsft, You are indeed typing your numbers correctly. :) I always build scale prototypes prior to investing in the larger hardware.

    As for why I'm going for a 3/4 DOF is that the sim is intended to be used for Flight/Aquatic/and Automotive simulations and all rotations are a requirement, heave is also very desirable for simulating vertical impact/suspension forces.
    • Like Like x 1
  14. Gabriel Vuelma Romanzini

    Gabriel Vuelma Romanzini Member

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    And the sensation of the Heave is just awesome!!!

    @mciccarone :

    It don't have yaw, in reality it have a traction loss controled by the 2 behind actuators ( 4DOF)... I think there isn't linear actuators with that speed, as it's so specific and low demand... I think the only way is build your own actuators...

    @bsft :

    I don't have a lot of money... Here in Brasil, don't have worm motors and to import will cost me A LOT, yes a LOT, because we pay 2x tax on final price... ( Yes, Brasil is a shit)

    But i can say that i will do something really good, it will take time, but will be good....

    I can do all mechanics at home, as i have a Go Kart Mechanic and some equipment... I Think in few weeks i will be buying a lathe, so will help a lot more...
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    Last edited: Jul 31, 2015
  15. mciccarone

    mciccarone Principle Software Engineer

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    My Motion Simulator:
    3DOF, DC motor, Motion platform, 4DOF
    This is a basic idea behind the 4 DOF design (Parts are not accurate scale) -
    - I fully expect the Motion Control Hardware (motors, frame, actuators) to cost above $2000 USD, this does not include Chair, PC, HID, or Display
    - Yaw would be controlled by rotation of entire platform using AC or DC electric Wheel Motor
    - All linear actuators are vertical @ 90 degrees.
    - Four corners are intended to equally distribute weight of Rider and Components above center of rotation.

    4DOF_design_a.jpg
  16. Gabriel Vuelma Romanzini

    Gabriel Vuelma Romanzini Member

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    Remember that with this metod of link (Behind actuator in corners) you don't have traction loss...

    Yaw can be how you said... With this metod you will get Roll, Pitch and heave...

    With this drawing equally will not be, because the driver weight more than other components at front, but can be equally with some math or software like solidworks...
  17. bsft

    bsft

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    What games do you intend to play? If its racing, shorten the throw of the actuators. If its flight, leave it as is.
    Seriously man, start with a 2 DOF seat mover, get an idea on how profiles set work, then move on up from there. You will be surprised what information and learning about motion profiles you will get from a 2 DOF.
    Also, is there anywhere near you that has commercial simulator rides currently? If so, go spend money and play on them. Thats also a good idea of how things run
    I am guessing you have just been watching videos of big movement sims and thought "yes, thats what I need".
    Ages a go a mate of mine insisted on a full frame, screen static 2DOF with 18 deg total throw. Even though he played on my sims with substantially less throw, he was convinced he needed lots. So I built it, and now he sets the profiles so its shorter throw.
    • Agree Agree x 1
  18. bruce stephen

    bruce stephen Hammer doesnt fix it, must be electrical

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    i agree start simple. even a proto wont tell you about the feeling. youll be surprised how little movement it takes. the design above seems fine but the actuators used like that is overkill. save your money and use gearmotors. you can get the same effect without actuators.
  19. mciccarone

    mciccarone Principle Software Engineer

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    My Motion Simulator:
    3DOF, DC motor, Motion platform, 4DOF
    Long long ago I rode in a SEGA R360 and other than doing loops or rolls the huge range of motion was completely unnecessary.
    That said, I programmed several aspects of a SH-60 Seahawk motion simulator for the Navy and was able to fly in a very large 4-person stewart platform made by CAE. It was extremely realistic, but several million dollars outside of my budget. Unfortunately I don't know anyone who has a motion simulator of any kind in my area so i'm not sure how I could test the profiles.

    Everyone seems to think i'm over-stretching with a 4 DOF so I'll start with a 2-DOF seat mover .... provided I can find parts that can be reused with a 4-DOF system.

    As for what games I play the answer is 'all of the above'. My primary trade is programming for real time motion capture so I want to be able to come up with a realistic motion feedback based on various platforms (boats, cars, planes, helos, etc. That's the primary reason I want the 4 DOF. I think I could fake forward/lateral surge/sway motions with a combination of pitch/roll and surge motions)
    Last edited: Aug 4, 2015
  20. mciccarone

    mciccarone Principle Software Engineer

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    My Motion Simulator:
    3DOF, DC motor, Motion platform, 4DOF
    I had no idea linear actuators were that much more expensive until I started looking for some that could move at a decent pace while supporting a large payload. To be honest I don't know what formulas are used to choose a suitable motor and I simply used linear actuators in the designs because the SCN5 seems to be a rather popular option for DIY rigs. I'll post a question on another thread I saw regarding choosing the right motor as it seems like my plans are still to ambitious for a first full size rig.

    And you're right. the prototypes look cool, but they don't let me actually feel the forces, all they do is allow me verify the design and the controller signals.