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help..How to calculate 6dof hexapod Frame

Discussion in 'Motor actuators and drivers' started by hannibal, Aug 3, 2019.

  1. hannibal

    hannibal Active Member

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    hey. im starting to move along with my project.

    i try to follow @wannabeaflyer2 sixdegreesofflight and @SilentChill 's builds

    i have noticed that dimensions for the hexapod are roughly the same..
    @wannabeaflyer2 your lovely pdf drawings (thank you) show a spacing of 1001 mm between actuators...
    @SilentChill , from the FLyPT diagrams you have kindly sent (thank you) i see your actuator spacing is 1034mm

    im trying to figure out how does some figure out the spacing...
    i know my actuators are about 960mm high from the bottom to the top of the linear bearing (not including the carbon tube potion)

    seems like everything is in triangles... but i just wanted to check in with my favorite 6dof folks @Pierre Lalancette @Flymen @pmvcda @wannabeaflyer2 for your thoughts... i dont want to just blindly follow someones design when everyone has some small differences.... plus, there seems to be a science to everything, and a best practice way..

    THANK YOU EVERYONE, love everyone here :) <3
  2. pmvcda

    pmvcda aka FlyPT

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    My thoughts on this when I made the rig:

    Smallest possible because of the wife (even so, my rig is now on the garage...)
    Being an hexapod, the principle is triangles.
    To have the perfect hexapod, top and bottom would be the same and joints should match defining those triangles.
    In practise this is not possible in most of the cases (type of actuator). That would be the ideal, giving you the best range distribution in all DOF's.
    So what I made is design the top and base hexagon.
    Then I pulled out the actuators until I had enough space for them to move (not collision between them).
    You can see it in the image bellow:

    Dimensions.png

    One of the limits I used is to have the side of the hexagon small enough to avoid the actuators being horizontal. On normal work, they don't reach those positions. Another particularity of this setup is that if you rotate the rig to the maximum (from the center position), one of the actuators is in the lowest position, while the next one is vertical.
    Of course those angles increase if you add more DOF's on the movement.
    Now this brings a problem and that's stability of the platform.
    Easy to solve by attaching it to the floor (my case). Or just increase the base structure to give more support.
    Those measures I show in the image, where made for a compact solution. It's the minimum for me and the chair I use. In the lowest position, the height is similar to jeep/suv, so easy to access the seat.
    Today I would increase the base hexagon to make access easier (space between seat a structure for legs to pass). Actuators could be enlarge also to compensate the hexagon side increase.

    Another note: That sunken design is made in such way, the structure doesn't touch the actuators. This is best for access to the rig, but also to make the center of rotation (center of the top platform) closer to your neck.

    Don't follow my measures without experimenting! You might need more space.
    My legs are almost horizontal. I tried to mimic my sports car measures. And that's a really small car.
    • Informative Informative x 1
    Last edited: Aug 3, 2019
  3. Pierre Lalancette

    Pierre Lalancette Lalancelot Gold Contributor

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    My design is quite simple.
    I have used three 100 mm carbon tubes to make the sides of my triangle.
    I have used three 30 cm tubes to attache them together.
    Every other decisions are based out of that.
  4. hannibal

    hannibal Active Member

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  5. Gadget999

    Gadget999 Active Member

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    lots of people use a hexagon shape for the base and a triangle shape for the platform

    the base can be a triangle also
    • Like Like x 1
  6. hannibal

    hannibal Active Member

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    after seeing @Psionic001 video on the new simtools release..
    i see the hex shape at the base..


    i hope i can follow @pmvcda 's calculations but have it end up like @Psionic001 frame based off my own build specs...
    there is a formula to the triangle!

    i would great appreciate your sunken frame dimensions @Psionic001 !!!!!!! please!!! :) :) :)
  7. Psionic001

    Psionic001 Active Member Gold Contributor

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    If I could do it again, I'd make the top platform a little larger by say 10% at the expense of less roll and pitch for which I already have plenty.
    Seat base is sunken 450mm which keeps the platform CoG nice and low so I don't need to bolt it to the ground

    Get the @hexpod plugin and it makes it easy to adjust the dimensions and test the design.

    Or wait for FlyPT Mover.....
    FlyPT Mover is currently not working as it's being rewritten I think. @pmvcda?? Looking forward to the next version which hopefully we can move forward with long term!

    Attached is a screen cap for you too.

    HexPod platform size.JPG


    • Informative Informative x 1
  8. hannibal

    hannibal Active Member

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    hmmm.. i didnt think of that to plug in values virtual with the FlyPT mover!
    wow.. i got homework to do. soo much.
    thank you for all the great info @Psionic001 @pmvcda
  9. hannibal

    hannibal Active Member

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    @pmvcda may i ask, how or why did you pick your values 125mm, 525mm and 1050mm in your hexapod dimensions?
  10. pmvcda

    pmvcda aka FlyPT

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    It's the smallest possible dimension for my chair an to fit me inside in the position I wanted.
  11. hannibal

    hannibal Active Member

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    @pmvcda
    so ideal is to base dimensions on chair... interesting.. i thought ppl fit chair around actuators/base, instead of fitting actuator/base around chair....

    so first thing to design is the sunken chair frame structure?

    wow.. totally different perspective of design and thinking!