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Having trouble with Tangent Mate, sometimes it works after a reload, sometimes it doesn't

cogzoidcogzoid Member Posts: 3
I'm working on a gear driven linkage for creating a shaking movement.  The Tangent Mate in this Assembly seems to be kind of iffy.  Sometimes it works fine when I Animate one of the Revolute Mates, and other times I get an error or even worse, a bunch of broken Mates throughout the assembly.  Sometimes I can fix it by just reloading the entire document.


Is there a better way to do these Mates so that they're more stable?  I might also be doing the Tangent Mate wrong?  I extended the slot .004 longer than the travel of the crank pin and that seemed to help stability, but not entirely.  Any advice is welcome.

Best Answer


  • john_mcclaryjohn_mcclary Member, Developers Posts: 2,852 PRO
    edited January 7
    tangents will always be unstable. It is just in their nature.

    You are correct that extending the slot so you never bottom out is one solution.

    You basically trying to keep in the "red" part of the curve.. just before it snaps from positive value to a negative value. Which flips the mate alignment, which causes the error. 

    On second thought, try a pin/slot mate. You may need to add an additional part to act as an axis, seeings how the pin rotates while traveling the slot.

    It may actually be that compound rotation of the slot itself and the pin within it that is causing the jump from positive to negative..
  • cogzoidcogzoid Member Posts: 3
    I'm not sure how to implement a pin/slot mate that will solve this.  When I try it I get all sorts of bizarre behaviors because my pin is rotating.  I just tried adding a rotating hidden pin, but I'm doing something wrong because the pin doesn't stay in the slot.  Is there a better additional part that I should be adding?

    Part of this is just academic.  I'm able to design the assembly just fine, but I'm trying to learn more about Onshape and I'm surprised that this is a limitation.  Surely I'm not the only guy using a crank pin in a slot...
  • cogzoidcogzoid Member Posts: 3
    I finally figured out how to use Pin Slot Mate correctly.  The instructions were a little vague on Step 2 https://cad.onshape.com/help/Content/mate-pin_slot.htm.  But I realized that a new Mate Connector that was pointing the right way was the key.  Thanks for the help!
  • john_mcclaryjohn_mcclary Member, Developers Posts: 2,852 PRO
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