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6dof motion platform ‘lite’

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by Tino, May 9, 2014.

  1. prilad

    prilad Well-Known Member SimAxe Beta Tester SimTools Developer

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    Hi, @Tino
    "Two words" about your 6-dof project.

    You should know that the levers can only change the relationship between force, speed and distance traveled end of the lever.

    If you have increase in force at the end of the arm twice - you just twice reduce speed and distance. Whatever the original lever you have invented.

    This I allude to the fact that it is much easier to simply reduce the length of the gear lever and get a greater force (but a smaller length and speed of displacement). IMHO

    Regards,
    Ale
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  2. telfel

    telfel Active Member

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    Hi @prilad

    A couple of members on this forum were working on it awhile ago @Planmix and @Robin. I believe Thanos 6dof plugin is based on Robins work, Would it be possible to have a 6dof sim tools plugin that way it can be used with more controllers, and be a bit more future proof.

    regards Terry
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  3. Historiker

    Historiker Dramamine Adict Staff Member Moderator Gold Contributor

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    I admit to being very confused...why would the current Simtools not work for your 6DoF? Mine seems to work fine.....
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  4. telfel

    telfel Active Member

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    Hi @Historiker

    I believe your 6dof platform has one point of the top platform at the front, if you take roll as an example the arms at the front motor pair move say left 1 up, right 1 down. The rear motor pairs on each side left up, right down have to move further because they are further from the roll center. Pitch is similar to roll but not the same, Heave is ok they all go up and down together, and yaw is ok one motor up, one down, sway and surge are the most complicated.
    Its a bit difficult to explain, have a look at the FMD video in slow motion.

    regards Terry

    ps sorry @Tino for going a bit off topic
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  5. Tino

    Tino Member

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    Hi prilad
    Would you agree that having a pivot point works good in 2dof simulators?

    In 2dof setup, two motors share the same pivot point for movement in 2 directions, for 6dof I plan each motor to have it's own pivot point, which should take on some of platform weight.
    Also 1/3 lever should help motors as they will always feel just one third of the platform weight.

    (In theory you could make 2dof by mounting seat directly to a motor shaft and 2 motors would do the job, but pivot point makes it possible to use much smaller engines)

    I plan to get around the speed and movement reduction problem by using 180rpm motors. if the speed is reduced to only one third, that leaves me with 60rpm.
    With lever there is less weight on the motors and you can use longer motor arm.
    You can say that this is the same thing as reducing the arm length in the first place (and not use any levers),
    but the motors which I plan to use can back drive, and 1 to 3 lever will give me confidence that this will not happen, also it should help gearbox and motor last longer.

    Regards,
    Tino
  6. Historiker

    Historiker Dramamine Adict Staff Member Moderator Gold Contributor

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    Hi Tino, have you worked out how to handle sheer force? There is a huge amount of pressure put on the levers from sideways motion, I have seen this on my 6DoF platform.
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  7. Tino

    Tino Member

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    Hi Historiker,
    Yes, I plan to use strong levers :)
    Also I'm thinking of having motors and lever at an angle so they would follow as closely as possible isosceles triangle movement for 6dof.
    [​IMG]
    [​IMG]
    However, sideways force will be the same as on your 6dof platform without lever, and hopefully another lever benefit would be reduced sideways forces on the motor.
    When using levers resulting motion is exactly the same as motion of motors with just motor 'arm', except you loose more motion as you use longer lever and lever motion has opposite direction.

    [​IMG]
    Here I have highlighted with a pen resulting lever motion on (left half circle) and ordinary motor motion with just motor 'arm' (right half circle)
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  8. NjMotion

    NjMotion Active Member Gold Contributor

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  9. Tino

    Tino Member

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    Hi merchan-e,
    Thanks!
    I think these 200W 180 rpm drive motors have quite powerful gearbox so as long as I don't put more than 20 Nm they should work fine, and that's why lever should help.
    I can play with lever length, lever ratio and motor rod length to find optimal configuration.

    Wow, these engines are really cheap, I am very interested how will they work in 6dof!
    Looking forward to your updates.

    Regards, Tino.
    Last edited: May 11, 2014
  10. SeatTime

    SeatTime Well-Known Member

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    I will also be interested in the results as in my opinion 48rpm and 16nm may be a bit on the small size torque wise to reliably lift a person + rig at a reasonable speed. I'm load testing 60RPM approx 45NM motors for a 6DOF and think I'm pushing it. Don't forget that the motors rated torque is at the shaft so once you add a lever it will reduce the longer it gets. Tino, you have so many variables in play, a model will help but in the end you will just have to try it and see full size. Good luck, I look forward to further news of your journey.
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    Last edited: May 11, 2014
  11. Tino

    Tino Member

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    I just can't believe how cheap these motors are :)
    6 of them cost 199.5 euro, that's mad!

    What would you say a good speed and movement distance would be for a 6dof seat?
  12. bsft

    bsft

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    if you run them on 24v, its ok 48 rpm is slow for race, ok for flight. If you run these motors on 12v, forget it, waste of time. thats going down to 24rpm, 8 nm torque, basically half the 24v figures.
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  13. Tino

    Tino Member

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    Then 24V it is.
    To power the motors I'm thinking of using 2 cheap server psu.
    Converting them to work on 24V is fairly easy.
    http://www.tjinguytech.com/my-projects/diy-24v-47a

    How does electronics (controllers) handle 24V?
    do I need to get different boards than for 12V?
  14. bsft

    bsft

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    ard with run any hbridge with the right code, so yes, you would need 24v hbridges.
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  15. NjMotion

    NjMotion Active Member Gold Contributor

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  16. ferslash

    ferslash Active Member

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    sorry i did'nt wanted to start a fight :D (my comment could be rude, so i am sorry about it) :D

    best regards :D

    and i insist, i really like your dev... i hope to see it working :D
    fer
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  17. Tino

    Tino Member

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    Hi fer,
    No offence taken.
    Hopefully it wont bee to long before I start building this. (It's not going to build itself :)
    What are you working on?
  18. Tino

    Tino Member

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    As an alternative solution (if the lever thing falls through because of the reduced motion) I was thinking of using simple bicycle style gears and chains (sprocket solution):



    With 3 to 1 gear ratio I would still loose 2/3 of the speed (which is fine for 180RPM engine) but I would get 3 times the torque.
    Because wipers in a normal simulator design cannot do more that 180 degree movement (half circle), I could get back all the motion by moving the vipers 3x 180 degree in both directions.

    What are the general experiences of using gears and chains on wiper or worm drive motors?

    So far these are pros and cons of both solutions
    Seesaw (lever) 3 to 1 ratio:
    Torque: increased 3X
    Speed: decreased 3X
    Movement: decreased 3X

    Gears (sprocket) 3 to 1 ratio:
    Torque: increased 3X
    Speed:
    decreased 3X
    Movement: Should not be affected (provided motors move 3 x 180 degree in both directions)

    Basically at the end I should get 60Nm torque, 60RPM and same movement (as if there was no sprocket) out of these motors:
    http://www.motiondynamics.com.au/worm-drive-motor-12v-24v-200w-180-rpm-20nm-torque.html

    Also, two sprockets and chain bolted onto the simulator frame should help with all the forces motors usually have to face without any lever or gears to reduce the workload.
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  19. ferslash

    ferslash Active Member

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    @Tino, man thanks for asking.. i am working in my second 2dof, the first was crap and it worked 2 hours, so i beggined with the scond... but i have almost no time to build :(

    by the way... if you can aford "morally speaking" to construct your lever solution, and resist that it dont work fine... then...

    i guess you shold try to use in the first place the levers and just if it does not works... then try the sprockets.... because using sprockets will complicate you a lot.

    best regards from mexico

    fer
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  20. Tino

    Tino Member

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    Hi ferslash,
    Thanks, hope the second simulator works better.
    Did wipers gears get chewed out, or you had some other problems?


    I think sprocket solution actually might be simpler :)
    There are loads of cheap used bicycle sprockets available and new bicycle chain is about £4-5 and can lift 1000Kg


    The idea is to connect the motor to the smaller sprocket (and allow it to move more that 180 deg.) and attach the pushrod (which will connect to the seat) to the bigger sprocket.
    But this is just research and design phase, so suggestions or criticism are welcome :)
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