7 Replies Latest reply on Jun 20, 2014 5:43 PM by Jared Conway

    Spring Force in a Drop Test

    Michael Cattafe

      I have a drop test where I'm essentially dropping an assembly of a spring loaded latch, it uses a compression coil spring. Is there anyway to accurately model the force of the spring acting on the latch during the drop?


      Thanks!

        • Re: Spring Force in a Drop Test
          Shaun Densberger

          Possible, but I'm having issues visualizing your system; can you post a diagram?

          • Re: Spring Force in a Drop Test
            Jared Conway

            is a spring connector supported in drop test? if so, you could use it

            other wise you're talking nonlinear dynamic

            or motion would work if you don't care as much abotu the deformation of parts but rather how the spring behaves in the system

              • Re: Spring Force in a Drop Test
                Michael Cattafe

                Spring elements are not supported in drop. I care about the force that ends up acting on the spring by the other parts in the assembly that are in contact with it during the drop. See the picture for more details. How can I model the drop in Motion? I haven't used Motion before?

                 

                Thanks

                2014_06_19_08_40_18_SolidWorks_Premium_2014_x64_Edition_Assem2.SLDASM_.png

                  • Re: Spring Force in a Drop Test
                    Jerry Steiger

                    Michael,

                     

                    Drop is not simulated in Motion, but in Simulation.

                     

                    If you are talking about a normal coil spring, then the ideal, but probably unrealistic, way to model it would be to actually model the coil. I say it is probably unrealistic because it would probably require a lot of elements to get a realistic response and the contacts are going to be very tricky. An easier approach would be to approximate the spring by using a solid or annular cylinder. Fake the material properties so that the cylinder has the same mass and stiffness as the calculated spring behavior of your real spring. This should work reasonable well, with a more reasonable number of elements and much easier contacts, although it won't capture the non-linearities at the beginning and end of the spring stroke. Those may not be that critical anyway. If the spring bottoms out before your latch does, then you may have to come up with some way to simulate how the spring becomes extremely stiff as it completely closes, say a very stiff cylinder that is the closed length of the spring..

                     

                    Jerry S.

                      • Re: Spring Force in a Drop Test
                        Jared Conway

                        this would require nonlinear dynamic and would be painfully slow to solve

                         

                        if evertthing could be treated as rigid except for the spring, the spring could be replaced and dropped in motion

                        the output would be the displacement of the spring

                        which would mean with the spring stiffness, what force the spring has exerted on it

                          • Re: Spring Force in a Drop Test
                            Michael Cattafe

                            Jared,

                             

                            The simulation seems to work alright in "Basic Motion" but I need information on force from the "advanced mode". The advanced mode seems to break down, parts go through each other and the spring does not seem to respond. Do you have any thoughts? The simulation is attached.

                             

                            Thanks,

                              • Re: Spring Force in a Drop Test
                                Jared Conway

                                basic motion uses a completely different solver than motion simulation

                                you need to pay a bit more attention to your mates and setting up appropriate conditions

                                 

                                looks like to me this model needs to be modeled with better use of subassemblies to reduce the mates at the top level

                                parts that move together should be in the same subassy for example

                                from there the assy should be drag able, if not, motion won't work

                                 

                                i'd suggest starting with tutorials and some really simple models to get the hang of motion and then move to your model. it is simple but not that simple.