Help with mate connectors and assemblies

michael_stalls

Hi im trying to design the pilot elevator control linkages for this aircraft project. i havent really done any mechanisms like this in onshape before and im not sure what mate connectors to use. If i link up the elevator pushrods (blue tubes) with revolute mates the whole mechanism comes out overdefined. If i use cylindrical mates the tubes move but go crazy. I have drawn up the paths of each tube ....the blue tubes in the screen grab represent the neutral position and the sketch lines indicate the max forward and aft travel of the elevator tubes. has anyone done anything similar to this 
thanks 
Michael 

konstantin_shiriazdanov

Try to use rotational constraint on one end of the rod and cylindirical on another one, thus you would have just right number of degrees of freedom for planar motion of a linkage. If your motion isn't planar you can try spherical constraints on both ends, but that would left you another unfixed degree of freedom.

michael_stalls

Hi 
here is what it looks like so far. when i link two members together the motion is correct. but when i go to link in a third memeber it becomes overdefined. ive tried revolve, cylindrical , planar and ball and each time it comes out over defined and fails. is it possible to do linkages like this ? i sketched out the paths of each link and they should be the correct lengths to solve. I tried putting limits on the vertical supports so that it can solve but it doesnt seem to help. 
thanks
michael 

konstantin_shiriazdanov

If I'm understanding your kinematic scheme correctly you purpose should be to have a pair of 4-bar linkage mechanisms with common linkage in the middle to synchronize motion. This linkage in the middle on my scheme marked by black arrow should have a cylindrical joint with the ground on one end and with a pair of maiting rods on another one to create the type of kinematics described above. But as I can see from screenshot you may not have a separate linkage there, but a joint part with one of the mating rods which creates a rigid triangle from the mated rods with zero degrees of freedom. And this may cause further issues.

matthew_stacy

@michael_stalls, if you could share a link to a public document (perhaps a simplified model of defining the essential linkage geometry, without revealing proprietary aspects of your product design) someone in the OS community can surely help you figure this out.  Mate connectors, mates, and degrees-of-freedom can be tricky.

Even better than a PUBLIC document, is sharing edit privileges with specific individuals to collaborate directly on the same document.  That seems to be a revolutionary capability of Onshape, that none of us utilize anywhere near often enough.