16 Replies Latest reply on Oct 18, 2009 8:29 PM by Mauricio Martinez-Saez

    Rotary motor on sub-sub-assembly parts

    Benjamin Margolis

      Hello,

       

      I am designing a 3 degree of freedom parallel delta robot. To ease the drawing process, I made a series of sub-assemblies, so that the actual motor is nested 3 layers into the overall robot assembly. I have been having trouble putting a rotary motor on the arm joints to simulate the platform motion. Is there anyway to actuate parts within sub-sub-assemblies? Or am I missing something else altogether?

       

      Thanks for your help,

       

      -- Benjamin Margolis

      HMC Engineering '10

        • Re: Rotary motor on sub-sub-assembly parts
          Deepak Gupta

          Are you able to apply the motor but not getting the required motion, If this is your issue then, RMB on the sub assembly, select component properties and in the pop up window select flexible under solve as so that your sub assy has the freedom required for the motion.

          • Re: Rotary motor on sub-sub-assembly parts
            John Sutherland

            If all else fails, rebuild your assembly on one level and try again.  Dissolving your assembly is not an alternative.

              • Re: Rotary motor on sub-sub-assembly parts
                Benjamin Margolis

                John,

                 

                Why is dissolving the sub assemblies not an option? Will it just break all of the mates?

                 

                Would it work to change the way my sub-assemblies are structured, so that most of the arms are still in sub assemblies, but the "motor" parts that I want to apply the motion analysis motor to is on the highest level of the assembly? This robot has three symetric arms, and it would be a real pain to define every mate three times.

                 

                Thanks for replying. Based on what I read, I think that this is the best option. I was just hoping there was some way to avoid re-structuring my assemblies. I structured it like it would be useful for manufacturing, not in the way to get the most out of SolidWorks.

                 

                 

                Best,

                  • Re: Rotary motor on sub-sub-assembly parts
                    John Sutherland

                    Ian Hogg suggested, and I have not been able to disprove, that forces are not propagated through sub assemblies.

                     

                    I think the issue is that IDs of individual parts below the top level are not visible to the add-in Motion Analysis software, which pre-dates SW.   This might be an undocumented downside to using SW modelling short cuts which is what sub assemblies are.  It may also apply to multi-body parts and patterns but I have not been able to elicit an authoritative opinion of this.

                     

                    My models for analysis are huge simplifications of models for manufacturing.  Why would I detail something for manufacturing then enquire whether it would work?

                      • Re: Rotary motor on sub-sub-assembly parts
                        Ian Hogg

                        Hi John & Benjamin,

                         

                        If I said forces are not propagated through a sub assembly (which I don't recall, but then I forget what I said 10 minutes ago), it would have been in the context of a rigid sub assembly and not having insight into forces within the sub assembly structure. There are some limitations on what interaction your can have with flexible subassemblies in motion, more from the standpoint that mates in the sub assembly are not visible at the top level (at least it used to be that way in 2008/9) so you could not really work with mate management as easily.

                         

                        If you can move the parts at the top level assembly, then you should be able to move the parts with motion. One aspects to be wary of is what you are trying to enforce movement on. You may have a motor in the model, but is it hooked up to a gearbox, or a belt or is it direct to the pivot shaft? How is movement from the motor driving the system? It may be that while you can drag the arms of the robot, the motor is not coupled to the arm in the flexible subassembly. Without seeing the model, it's a bit of educated guess work.

                         

                        A simple test is to see with motion motors suppressed, is if under gravity the robot falls down like a pendulum. If it doesn't then there are some mates locking the rotation. In 2009 or later, you can have user defined mates in motion studies that you would not see in the regular assembly. You may want to check that.

                         

                        With regard to subassemblies and the like, care does have to be taken with dissolve or form new subassembly as there is the potential for mates to be destroyed depending on how they are defined. My personal preference with any motion model is to always structure it into the least number of moving bodies (rigid subassemblies) as possible to minimize complexity that is not necessary. This doesn't always align itself with the model structure for production, so I usually have to define a motion specific assembly and sub assemblies (yet still reference the same underlying parts to preserve change propagation).

                         

                        If there's not issue in posting the files, it makes it easier for people on the forum to review and provide feedback. Also provide information on which version you are using as they will help in determining the best approach.

                         

                        Cheers,

                         

                        Ian

                          • Re: Rotary motor on sub-sub-assembly parts
                            John Sutherland

                            Ian,

                             

                            "There are some limitations on what interaction your can have with flexible subassemblies in motion, more from the standpoint that mates in the sub assembly are not visible at the top level"

                             

                            If a sub assembly comprises two jointed parts, and the joint is invisible, then the joint cannot participate in the articulation?

                              • Re: Rotary motor on sub-sub-assembly parts
                                Ian Hogg

                                Hi John,

                                 

                                It's more an issue of in the motion tree, you just cannot see them or interact with them (The tree will only show top level mates from the assembly). They still participate in the simulation, but you cannot adjust them at the top level.

                                 

                                There is a work around for still taking advantage of them, for example if you want to plot forces on a mates that is from a flexible subassembly, use the regular feature tree (just not the motion tree) to select the mate and then plot the result component you want.

                                 

                                You need to make change changes to the mates in the subassembly file directly, but remember, it's just the mates that are inherited. No motion data propagates up to the top level of the assembly.

                                 

                                Cheers,

                                 

                                Ian

                            • Re: Rotary motor on sub-sub-assembly parts
                              Benjamin Margolis

                              Ian, thank you for your reply!

                               

                              Luckily, this is a school project, so there are no issues with posting the files. Although I have regularly used SolidWorks in school for drawing one-off parts for various projects, I am by no means getting the most out of the SolidWorks featureset. I am sure that the assembly is not as efficient as it should be, and I would love advice on how to use this tool more effectively.

                               

                              I do not know how to simulate the effect of gravity on the robot model. Is there a tutorial that explains this?

                               

                              The motor (hobby servo technically) is represented by the frame and pivot axis. I think I should just let the files do the explaining, but I can move the model in the top level assembly.

                               

                              Let me know if if there's anything wrong with opening files. I appreciate your help and feedback,