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What mate can I use to create the correct movement in my linkages

connor_macmurrayconnor_macmurray Member Posts: 9 EDU
edited June 3 in Community Support
I am drawing up an automaton and the linkage required to move a component is as below:

The lower section only moves up and down which controls the upper one which makes a wing flap, but as the mechanism is moving back and forth the central section needs to allow for that movement at the connection points. 
The link to the project is:
https://cad.onshape.com/documents/31f30302463325747d2c2c3b/w/6ef69631a6a7bdcbe148e925/e/2a17ef97183a05e2a89b946b
The part studios for the lower section and upper two sections, and the assembly of all three parts can be found in the 'Control rods and connectors' folder with the names 'lower wing control rod', 'middle and upper wing control rod' for the part studios and 'wing control rods' for the assembly.
The complete automaton is in the creatively named 'completed automaton' folder and you can see what the whole thing looks like.
If you animate the first revolute mate you will see what it is supposed to do. 
Also the lower section of this control rod is supposed to engage with a crankshaft and it does, but not properly, I tried doing a tangent mate with the pin that drives it (as shown below) but I think I need to create some sort of offset path for it to get it to work properly. I just don't know how.
Any help with this would be greatly appreciated.
Connor

Answers

  • connor_macmurrayconnor_macmurray Member Posts: 9 EDU

  • john_mcclaryjohn_mcclary Member, Developers Posts: 2,033 PRO
    You will need to make your link public.
  • billy2billy2 Member, OS Professional, Mentor, Developers Posts: 1,300 PRO
    That's border line physical dynamics where the motion is determined by contacts. 

    Without that, I'd use spherical joints for the loops & tangent for the bar/cylinder contact.

    Also when an assembly is indeterminate, not enough constraints to determine one movement, I use the triad manipulator to move these components. 

    I believe once you get it defined, you might be better off using the manipulator to move it.

    It'll be smoother motion with the manipulator.



  • john_mcclaryjohn_mcclary Member, Developers Posts: 2,033 PRO
    edited June 3
    i started with a dummy cube (1mm) and used that as a intermediate mate feature. Essentually you need a ball mate with 2 axis and limits.

    I got it half working before i had to start my actual job, i'll try and finish the last mates up by the small joint at lunch.

    Maybe I'm just not familiar enough with this toy's linkages. I've seen them before. But to me with the 3 piece linkage you have, it is like pushing chain. It tends to collapse on itself like a wet noodle

    https://cad.onshape.com/documents/79661f41bc762ab11318f71c/w/353f776b245d01c0ca38427f/e/9fa1751d7a7ce7cced56ce36


  • john_mcclaryjohn_mcclary Member, Developers Posts: 2,033 PRO
    Ok, I see now, that short piece needs to just be fastened to the wing, instead of using the eye feature :)

    It's working now

    Pretty cool model by the way




  • owen_sparksowen_sparks Member, Developers Posts: 2,391 PRO
    Now that's cool :-)
    Owen S
    Production Engineer
    HWM-Water Ltd
  • larry_haweslarry_hawes Member Posts: 411 PRO
    Now that's cool :-)
    Owen S
    +1
  • john_mcclaryjohn_mcclary Member, Developers Posts: 2,033 PRO
    @connor_macmurray did a great job with it
  • connor_macmurrayconnor_macmurray Member Posts: 9 EDU
    Thanks all, especially John for solving it. I'm still having limp noodle issues with it! So did you end up using the ball mate? I was trying it with revolute, but it needs to flex sideways too and when I try to hook it up, the linkage collapses and tries to turn the wing over. When I use the ball mate it doesn't seem to offer me any constraints to guide the movement.
    The idea eventually is to 3D print it and use wire for the linkages but I may have to scale it up for that if the wire is too thin. If I can get it to work it will be a project for students doing graphics in Year 9 in Australia (aged about 15) so that they can learn how to use the different tools in a CAD package and then customize their dragon using the skills they've developed. If I can get the little sod to fly consistently I'll do some legs for him too 
  • owen_sparksowen_sparks Member, Developers Posts: 2,391 PRO
    Can we add a "not_a_flame_thrower" to it as well please Sir?
    Production Engineer
    HWM-Water Ltd
  • john_mcclaryjohn_mcclary Member, Developers Posts: 2,033 PRO
    edited June 3
    You want to "fix" the short pin to the wing, any degrees of freedom between 2 linkages like that will collapse in compression.
    In the end I never needed to add any limits to the mates, they are free to move.

    so the long middle arm should be the only "free" member.

    On each end of the eyelets I added a small cube, you can see that in the post above.
    The cube is a cheat, I don't rely on tangent mates in CAD most of the time, because they tend to do odd things (for example your cam on the lower linkage is crashing thru the follower on the wheel)

    From there I added two mate connectors using the center mate connectors of the cube as axis
    Here they are pulled apart.

    the blue cube is revolute to the center of the vertical eye,
    the other revolute is perpendicular, and uses the mate connector I added to the part in the studio

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