12 Replies Latest reply on Jun 3, 2008 4:01 PM by Matt Graves

    Trebuchet simulation

    Sheldon Roberts
    Sheldon Roberts Jan 7, 2008 4:05 PM
      Not sure where to put this topic, here or Assemblies so I'll try both.

      I read about a trebuchet simulation to teach CosmosMotion that flings a ball on a rope. The arm of the trebuchet pulls the rope that has a loop on one end that attaches to a hook. The ball is pulled through a trough untill it begins to become airborne. At a point of the arm's arc, the ball/rope disconnects from the hook and flies off into never/never land.

      What I'm trying to figure out is how to set up the asembly mates, both how to keep the ball in the trough until it can fall out and the loop/hook that comes loose.

      Any ideas?
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        • Trebuchet simulation
          Ben Paprocki
          Ben Paprocki Jan 10, 2008 12:12 PM (in response to Sheldon Roberts)
          Although we have already discussed the solution to this Sheldon, I figured I would post the answer to your questions for others to try it out.

          No mate are required to achieve what you are attempting. While setting up the motion study you need to turn on both gravity and contact. When you place your parts in the model, place them so they are in their initial states without using any mates. You also need to make sure they are not interfering with other components in the assembly. Another way to approach it would be to use mates to locate your parts, but then suppress them right away in the motion study.

          You should post a video of the Trebuchet in action. It is quite amazing what one can do with the new tools built into Solidworks.
          • Trebuchet simulation
            Shachar li
            Shachar li Jan 16, 2008 11:15 AM (in response to Sheldon Roberts)
            http://www.youtube.com/watch?v=JTKM_fuWTrk
            I didn't made it, I just found it on youtube
            It looks like the thing should use some dampening at the end
              • Trebuchet simulation
                Dan Eldred
                Dan Eldred Feb 13, 2008 8:50 PM (in response to Shachar li)
                took your advice ben, but now all i get is my trebuchet exploding. all the parts fly apart. i have no idea why. i've been trying to get this damn trebuchet working for over a month and even talked to someone at SWW world about it to no avail. stinks 8(
                  • Trebuchet simulation
                    Ian Hogg
                    Ian Hogg Employee Feb 13, 2008 10:33 PM (in response to Dan Eldred)
                    Hi Dan,

                    I can take a look at it and get it running for you if you like.
                    Just let me know if you're on 2007 or 2008.

                    Cheers,

                    Ian
                      • Trebuchet simulation
                        Dan Eldred
                        Dan Eldred Feb 14, 2008 10:58 AM (in response to Ian Hogg)
                        ian i am on both, but i don't have cosmos motion. only the built in motion study that comes with 2k8.
                          • Trebuchet simulation
                            Ian Hogg
                            Ian Hogg Employee Feb 14, 2008 11:55 AM (in response to Dan Eldred)
                            Hi Dan,

                            Your best best is to do this in 2008 then. Physical Simulation has some representation of inertia, so you will gets a resonable action. It won't work in 2007 or earlier as is only does what I call quasi-static motion. It has no real concept of accleration or inertia (ie once something stops pushing an object, it stops moving immediately also).

                            I can still take a look at it for you if you'd like.

                            Cheers,

                            Ian
                              • Trebuchet simulation
                                Dan Eldred
                                Dan Eldred Feb 14, 2008 12:47 PM (in response to Ian Hogg)
                                i apologize ian. i am doing this in 2008 utilizing the Physical Simulation with gravity and contact between all components.

                                here is the assembly and components. i'm thinking of making the cup and arm one piece as it seems to work better with less parts. any help is much appreciated.
                                  • Trebuchet simulation
                                    Dan Eldred
                                    Dan Eldred Feb 14, 2008 5:14 PM (in response to Dan Eldred)
                                    ok after much tinkering i have succeded. what i found out was that i needed to tighten my clearences up to less than .125" as well as cut down on the moving parts. i combined the counterweight and the bar that connects it to the arm. before it was causing too much wobbling. it seems that when the turbulent movement is too great and causes the parts to interfere with eachother it self-destructs. so i made a guide for the counterweight to make it's movement more smooth. now it seems to work just fine. check it out.
                                      • Trebuchet simulation
                                        Ian Hogg
                                        Ian Hogg Employee Feb 14, 2008 5:23 PM (in response to Dan Eldred)
                                        Hi Dan,

                                        That's awesome!

                                        I'm glad you got it sorted out as when I tried to download the model it failed (not sure why and was going to let you know).

                                        Did you ever see the mousetrap (the game) demo done with SW2008?

                                        Cheers,

                                        Ian
                                          • Trebuchet simulation
                                            Dan Eldred
                                            Dan Eldred Feb 14, 2008 6:15 PM (in response to Ian Hogg)
                                            ok i fixed the download, but it's not the latest version as seen in the latest video. but feel free to mess around with it if you so desire.

                                            i have seen only a picture of the mousetrap game. i'd love to see it in action. that was one of the 1st things i thought about modeling when i learned that SW2K8 would give me access to motion studies.

                                            when i was at SWW2k8 last month i got to see a working trebuchet as well as a mouse trap(not the game), which was pretty cool.

                                            i may post a later version of my trebuchet when i've added some more goodies.
                            • Trebuchet simulation
                              Matt Graves
                              Matt Graves Jun 3, 2008 4:01 PM (in response to Sheldon Roberts)
                              I tried this myself using Physical simulation when 2008 first came out, and I could almost never get the same results twice. I started off by trying to simluate the rope "sling" of a true trebuchet, but even after reducing it to two stiff arms, it still had a hard time recognizing contacts- the loop on the sling would slip thru the hook on the arm a lot. The eventual goal was to have the ball hit a wall with a target area of some stacked blocks, but I never got it to work.

                              I'm trying to attach some avi's I made, but keep getting errors. I couldn't find anything on attachmetns in the FAQ's or Forum Help - is there a restriction on file types/sizes?

                              Thanks