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Linear actuator with AC servomotor (beam design)

Discussion in 'Motor actuators and drivers' started by dureiken, Dec 21, 2019.

  1. dureiken

    dureiken Active Member

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    Waiting for the parts, need to design the link between actuator and base and top frames.

    I have 2 questions :

    1. what is the difference between
      [​IMG] [​IMG]

    2. How to link U-joint to frames ? FIX at the base and rotation free at the top ?
    Thanks a lot !
  2. pmvcda

    pmvcda aka FlyPT

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    My Motion Simulator:
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    In my build, I fixed at the bottom and allow rotation at the top.
    That way, the actuator is not rotating.

    I used ujoints similar to the top ones, but with an hole to fix them, take a look at my build https://www.xsimulator.net/community/threads/flypt-6dof-brushless-diy-actuators.10799/
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  3. Thanos

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

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  4. dureiken

    dureiken Active Member

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    Hi

    almost a first prototype is finished :

    [​IMG]

    but some people me doubt on discord : foldback design have a problem with the belt and wobble in some case ?

    could you confirm that or not ?

    thanks

    Edit : inline design :

    [​IMG]
    Last edited: Jan 20, 2020
  5. 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
    The Inline design is better recommended for 6DOF platforms, as you won't have to worry too much for collisions of the motor on the base during extreme angles positioning. This is important when using recessed 6DOF platform designs where the actuators angles are like this:



    If you use foldback you would have to make higher type platform like this:
  6. dureiken

    dureiken Active Member

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    @Thanos
    ok so the 200mm I loose with inline design is maybe good for the rest of the rig ?

    thanks
  7. Dirty

    Dirty Well-Known Member Gold Contributor

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    Hmmm,.... *scratching head*

    How do you come to this conclusion? Is this just a "concern" or are there logical arguments supporting this that I have overlooked?

    I have to admit, I've had similar concerns. But when I actually simulated different rig setups (Fusion360, forward kinematics) and checked for collisions, I found this: The angles I had to go to in order to make the foldback-motors collide with other parts were way outside anything that will ever be possible. More precisely: Every actuator has 5 brethren that will have hit their end stops long before the actuator itself can be in a position that will let the motor collide with other parts.
    Of course, if the lower joints are close together and you have the motors top-mounted, then they will collide. But if they are rotated outwards slightly having the motors off to the outside of the "lower circle", I found it virtually impossible to have them collide with anything.
    In that sense I agree: Using an inline-setup will keep you safe. Using a foldback-setup will require some considerations for the angle of the actuators.

    The bathtub setup (as I like to call it:) does bring it's set of problems, but I don't see any of them connected to foldback motors. As far as I can tell, the top part of the actuators are identical and that is the only part the bathtub will ever get to see.

    Cheers,... Dirty :)
  8. dureiken

    dureiken Active Member

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    @Dirty thanks :)

    and do you have any ideas with belt problem ? thanks
  9. pmvcda

    pmvcda aka FlyPT

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    My Motion Simulator:
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    Go with inline.
    Simpler, less expensive, maybe stronger.
    What you loose at the bottom is nothing.
    I doubt you roll the rig to those positions, because with heave and a recessed cockpit you would touch the ground going so low.

    Edit: Unless you want to change rotation speed between motor and ball screw.
  10. wannabeaflyer2

    wannabeaflyer2 Well-Known Member

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    Hi @dureiken looking at the last 2 pictures you posted i would say the Inline version is much simpler ,

    This could be done cheaply and would only need you to add one extra 5 -6mm plate at the base to mount either Universal Joint or other option ..

    i did a proof of concept mod on one of my 6 DOF actuator and found it very easy to convert from DC motor without encoder to all singing all dance AC servo setup .. So much so that im going to be selling off all my DC gear to re-invest in the AC servo route ( this is just my thoughts on the way i will do my 6 DOF upgrade...

    The 4 DOF sim i have built is absolutely brilliant for CAR simulation totally in awe of how its performing but think 6DOF is the way to go for Flight simming, im single so i can do both LOL China will be getting more business soon :)
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    Last edited: Jan 20, 2020
  11. MagicMunkyNuts

    MagicMunkyNuts Nothing ventured, nothing gained.

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    Couldn't the fold back issue be solved by rotating the motor mounting position on the actuator by 90 degrees so that they are facing outwards of the assembly? This makes sense in my head but please correct me if I'm wrong, thanks.
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  12. Dirty

    Dirty Well-Known Member Gold Contributor

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    That's my strategy as well and as far as I can tell this will allow you to keep the motors clear:thumbs . You can even have one motor rotated towards the outside and his neighbor rotated towards the inside. That will basically give you clearances like an inline configuration would.

    However, I totally agree with the proponents of the inline setup that the foldback configuration is...
    ...a little bit of a hassle,
    ...costs a little bit more money,
    ...requires a few more considerations,
    ...is pointless if the bottom of the (bathtub-)platform will hit the ground before the actuators reach their travel limit and
    ...is something that I would only do if your operating space is limited by ceiling height.

    But IF you are limited by ceiling height, then it is at least an option worth considering to squeeze another ~200mm of travel out of a system that is otherwise limited by hard constraints.

    Happy building :thumbs
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  13. dureiken

    dureiken Active Member

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  14. MagicMunkyNuts

    MagicMunkyNuts Nothing ventured, nothing gained.

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  15. Dirty

    Dirty Well-Known Member Gold Contributor

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    It sure does! Speaking of design,...

    Do you intend to have all of the load of the actuator on this 3d printed part? Or will the back of the motor carry some of it?
    Bildschirmfoto 2020-01-23 um 07.52.50.png

    I am using 8mm laser cut aluminium. These parts were under 10$ a piece.
    IMG_8920.jpg

    And you don't just get a piece of aluminium. You also get "peace" of mind :grin:grin:grin
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  16. dureiken

    dureiken Active Member

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    Yeah I discussed about that on discord and I will replace this part with 5mm steel because it sees all the load.

    I'm now waiting for the parts and I will focus on plateform design (I should have start by that :p)

    Specially I don't know dimensions of top frame and the link with u-joint.
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    Last edited: Jan 23, 2020
  17. PeterW

    PeterW alias Wickie

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    Hi dureiken!
    really nice actuator!! Like it.
    One thing came to my mind: Have you thought about to add some kind of damper? Keep in mind that in case you have an ermergency shutoff of your sim, the platform will go/fall down very fast and stop at the mechanical deadstop in the actuator. I have build in three dampers (Diameter 15mm, 20mm long), but think it would have been better to have bigger ones....
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  18. dureiken

    dureiken Active Member

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    Hi :) do you have pictures ? :) not sure to see what you mean

    thanks
  19. PeterW

    PeterW alias Wickie

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    Hi
    Here is a picture of my 3 dampers. They avoid that the moving upper part of the actuator hits the fixed parts without dampening. 20191031_134943-1.jpg
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  20. dureiken

    dureiken Active Member

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    yes thanks :)

    do you have a picture actuator mounted ?