5 Replies Latest reply on Aug 31, 2017 8:29 AM by Dan Pihlaja

    Over defined Assembly?

    Frances Martínez
    Frances Martínez Aug 23, 2017 7:56 PM

      I am creating an assembly that requires 4 linear bearing w/ spring like a shock absorber. Each subassembly will be mated to a ground and top plate. When engaged, the subassemblies will move and up and down w/ spring compressing as well. Out of the 4, 2 of the subassemblies work. However, when I attempt to mate the other 2, same mates and edges, an error pops up saying it is over defining the assembly and causes everything to go out of whack. Any suggestions?  

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        • Re: Over defined Assembly?
          Iain McEwen
          Iain McEwen Employee Aug 24, 2017 6:29 AM (in response to Frances Martínez)

          Hi Frances,

           

          Have you made the subassemblies flexible? Otherwise they'll be treated rigidly, similar to as though it were part.

          2017-08-24_11-29-07.png

           

          Alternatively, right click the subassembly and go into the properties

           

          2017-08-24_11-30-22.png

          • Re: Over defined Assembly?
            Dan Pihlaja
            Dan Pihlaja Aug 24, 2017 1:25 PM (in response to Frances Martínez)

            Can you share the assembly?

             

            If not, then can you at least share a screen shot of your mates folder with your assembly tree?

             

            I am thinking that the issue is that maybe it is over defining it because the position of the top plate is fully defined by the 2 concentric mates that are attached to the first 2 sub assemblies.  Then when you try to add a third, it over defines it.   Try to limit the mates between the (edit) 3rd and 4th linear bearings and the top plate to only point contacts or parallel constraints (if you can).  Let the bottom plate locate the bearings.

             

            There are some things that can happen in real life, but because of the mathematics behind the software, they are not possible (edit) in the software.

             

            An example:

            A stool with 4 legs sitting on the floor (assume point contact with the floor, lets say it has feet with rounded bottoms).

            Once you mate bottom of the 3rd leg to the floor, this now fully defines your z location of the stool (assuming that z is perpendicular to the floor).  Try to mate the 4th leg and it fails and says that it is over defining.   This is because 3 points in geometry makes a plane.

              • Re: Over defined Assembly?
                Frances Martínez
                Frances Martínez Aug 30, 2017 9:53 PM (in response to Dan Pihlaja)

                I tried playing around w/ the mates but same problem. This is what I have so far. If I add another mate, it throws off the whole assembly. Is it possible to make another subassembly w/ only the linear shaft? But how would I make them compress together at the same time? Sorry for the late reply.

                  • Re: Over defined Assembly?
                    Dan Pihlaja
                    Dan Pihlaja Aug 31, 2017 8:29 AM (in response to Frances Martínez)

                    Frances Martínez wrote:

                     

                    I tried playing around w/ the mates but same problem. This is what I have so far. If I add another mate, it throws off the whole assembly. Is it possible to make another subassembly w/ only the linear shaft? But how would I make them compress together at the same time? Sorry for the late reply.

                     

                     

                    Its all good.

                     

                    Question:

                    1) do you want to show a view of them compressed and then a view of them uncompressed?

                    or

                    2) do you want to basically be able to animate the compression?

                     

                    If the answer is 1, then do this:

                    1) Create 4 configurations of the spring: (at the part level)

                         a) Free length (this is optional, I like to add it for completion sake)

                         b) Solid length (fully compressed) (again, this is optional, I like to add it for completion sake)

                         c) Working Compressed length (the compressed state in the assembly)

                         d) Working extended length (the uncompressed state in the assembly)

                     

                    2) Then, in your assembly, you can create 2 configurations (1 compressed and 1 extended) and then toggle the correct configurations for the spring that would apply to your configuration of the assembly.

                     

                    If the answer is 2, then you might want to read this:

                    http://www.javelin-tech.com/blog/2016/10/solidworks-configured-assembly-dimensions/

                     

                     

                    Besides that, you will want to constrain your assembly like this (if I am understanding this correctly):

                    Constrain your springs to your pins using 1 concentric mate and 1 coincident mate (maybe a parallel mater for rotation control)

                    Constrain each of your pins to the bottom plate using 1 concentric mate and 1 coincident mate and 1 parallel mate.

                    This will fully constrain your bottom plate (assuming it is fixed), your pins and your springs.

                    Then add the top plate.

                    Create 1 concentric mate with 1 pin.  Then, 1 more concentric mate with the pin in the opposite corner.  Then 1 coincident mate.

                     

                    Anything more than this will over define the assembly.

                    Basically, you top plate will only be constrained to 2 of the pins via concentric mates and 1 pin via a coincident mate.

                    Let configurations drive the length of the springs and such.