12 Replies Latest reply on Oct 20, 2017 12:09 PM by Rollo Jarvis

    Belt that can change shape

    Rollo Jarvis

      I would like to model a belt that changes shape as the components in an assembly move.

       

      In the attached diagram, when the spring moves down, the arm at the right should swing out accordingly. The built-in belt feature assumes that the center of rotation of all the rotating parts is fixed in space. (p.s. I am aware of the obvious mechanical issues of this model, but I'm only interested in answers to the question asked, thanks!).

       

       

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        • Re: Belt that can change shape
          Mark Kaiser

          You have to design the part while working inside the assembly, and make sketch relations to the parts the belt rides over.  You also may have to do a ctrl-q (used to be called force rebuild) to get the belt to change shape each time.  Look up in-context modeling.

          • Re: Belt that can change shape
            Solid Air

            Look up Belt/Chain Assembly Feature in SolidWorks help; I think this is what you want.  There is also a Belt/Chain using sketch blocks.

            • Re: Belt that can change shape
              Rollo Jarvis

              Thanks to the replies. Unfortunately, they don't work. I am already using the belt/chain assembly. Also when i force-rebuild, the total length of the belt changes. Is there a way I can force these the total length of the belt to remain constant when I change the position of one of the components so that the dependent components will move accordingly?

               

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                • Re: Belt that can change shape
                  Josh Brady

                  So you are really attempting to create a mating scheme in your assembly that willl simulate a belt, right?  I'm about 99% sure you won't be able to create a belt part such that when you push down the spring the bucket moves.  You'll need to figure out some type of mating scheme to achieve those kinematics.

                   

                  Also, I'm not sure what "mechanical issues" you're aware of... Pressing down the spring will definitely not swing the arm to the right.  It will allow the arm to swing left.

                  • Re: Belt that can change shape
                    Dan Pihlaja

                    Rollo Jarvis wrote:

                     

                    Thanks to the replies. Unfortunately, they don't work. I am already using the belt/chain assembly. Also when i force-rebuild, the total length of the belt changes. Is there a way I can force these the total length of the belt to remain constant when I change the position of one of the components so that the dependent components will move accordingly?

                     

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                    I think that you might have a problem there. 

                     

                    I assume that you are going to be pushing down on the left handle to depress the spring, and this will, in turn drag the top of the pivoter to the left.

                     

                    The problem that you are going to have is that the distance C and the distance B are BOTH going to get smaller during this.  Therefore, either your belt will start to sag during this process, or the weight of the bucket at the bottom will just pull it tight again and it won't actually move.  Distance A will just get greater.

                     

                    Maybe I am totally misunderstanding the process though.

                    • Re: Belt that can change shape
                      Scott Stuart

                      You need to use a path length dimension to hold the overall belt length constant.

                        • Re: Belt that can change shape
                          Rollo Jarvis

                          I think this is exactly what I need, but I'm having trouble drawing a path that links the three rotating pins in the assembly space. Should I be drawing a triangle whose vertices lie on the central axis of each pin over which the belt lies?

                           

                          Here's an updated diagram for Dan Pihlaja to show that hopefully as the pin is compressed and moves upwards, the arms should swing outwards.

                           

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                        • Re: Belt that can change shape
                          Solid Air

                          Not sure why the Belt/Chan Assmebly feature is not working for you.  Can you upload your assembly and parts?

                          • Re: Belt that can change shape
                            Solid Air

                            To further my post.  Below are screen shots of a pulley system using the belt/chain assembly feature.  I moved the yellow pulley on the left.  The white pulley is free to slide horizontally.  In the top shot, the white pulley is to the right center of the yellow pulley below it.  In the bottom shot the white pulley is now closer to being centered over the yellow pulley.  In order to the belt chain feature to move the takeup pulley you must set the belt length to be driving (see very bottom screen shot) and allow the take up pulley to move..