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Pathmate Animation Issue

Question asked by Dale Elde on May 16, 2012
Latest reply on May 22, 2012 by Dale Elde

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Hello,

First of all, I am new to the SW forums, so please let me know if I am posting in the incorrect area. Anyway, I want to animate a metal tab traveling around a slot-like pathmate, but I am having issues when it comes to the rounded portions. I tried setting the path constraint to "distance along path," but the tab does not travel the way I want. This seems like a relatively simple task - maybe I am missing something?

I tried to work-around by using a linear motor to push the tab along the path, but the linear motor direction does not change with the associated face. Lastly, I do not have motion studies.

Jim Boland May 18, 2012 9:57 PM

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The way I would approach this is to make it a chain. In the attached video, you can see three triangle looking parts. These are just links to connect the two tabs together. Why three links? One problem with this assembly is that the curves are very tight. If you use a distance mate or a single link, what happens when you get to the bend? You want the distance to be measured around the circumferance of the arc, but if you use a distance mate or a single link, you get a striaght line distance between the two tab which is geometrically a problem. Think what happens is the distance between the tabs is more than the diameter of the arcs. I chose three links just as an example as it shows that the distance between the two tabs is now segmented. The more accuracy you need the more links you would use.

You can also see that the links are hidden around the first index point. They are only shown in the first part of the animation so you can see what is happening. In the final animation, they would be hidden throughout the animation as they are not real components in the assembly, only dummy parts used for spacing and can be any shape or size you need to make the geometry work.

You can make the starting point of the path mate any value you want, it does not have to be zero. Just edit the value at the key points. If you have to go around more than once, you have to understand the "100/360 Rule". It is explained in the book "Creating Animations with SolidWorks" available from SW or Amazon, or you can view the presentation "Move It-Move It-Move It" from the SW World 2012 presentations.

Hope that helps.

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CHS - Test Assembly 01.zip49.6 KB

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Deepak Gupta May 17, 2012 12:43 AM
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Welcome to SolidWorks forums Joe.

There are no part files in the zip file. Please use Pack and Go option in the assembly and then attach the zip file or new files created via Pack and Go here.

Also check this thread which suggest lot of interesting stuff on Animate along a path

Please use "advanced editor" in case you want to attach any files.

You might also find this post helpful for your future reference.
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- Dale Elde @ Deepak Gupta on May 17, 2012 2:51 PM
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  Ok, I used pack and go on the file. I am fairly new to SW and most of the technical jargon, so that is why I was hesitant to post on an existing discussion. I understand the concept behind using a path mate for an object to follow rigidly in a single orientation, but I want the object to move like an object that is attached to the belt.
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  - CHS - Test Assembly 01.zip186.4 KB
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  - Jim Boland @ Dale Elde on May 18, 2012 11:37 AM
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    The attached files show the completed video and source files.
    
    The Guidance Rod Tab is driven around a path using a Path mate that has key points for 0% and 100%. If you want smooth motion, it is better in my experience to use a single curve for the path rather than using the Selection Manager to pick segments of a path. You also have to be careful as to how the parts are mated as the mates have to solve at every frame, so mates can flip if you do not have a good scheme. In this case, I used a path mate to control the motion along the belt, a coincident mate to hold its postion across the belt and a cam mate to hold it to the surface of the belt. I also increased the framerate to 24 frames per second as this is the movie standard. It also gives a smoother animation and it solves better on the curves as they are relatively tight, so the distance between solution points is smaller and there is less fear of a mate flipping.
    
    The original model had several issues with underdefined sketches and a Path part that was floating free. Animations work better when they are done with models that follow the basic modeling conventions.
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    CHS - Test Assembly 01.zip188.2 KB
    CHS - Test Assembly 02.avi2.9 MB
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    - Dale Elde @ Jim Boland on May 18, 2012 2:22 PM
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      Thanks, Jim. Ultimately, I will want the tab to index along the path. I figured that I could just move it manually to create an indexing animation, so is there a way that keeps the tab free to move but prevents flipping? I can probably make the 'percent along path' mate work; it would just take more time syncing up the associated parts.
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      - Jim Boland @ Dale Elde on May 18, 2012 5:26 PM
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        Two parts to the answer. First is the question of flipping mates. There are many mating schemes that work just fine when you are in the model tab but give bad results (usually flipping) when you animate them. The mathematics behind solving mates in not trivial, if it were the developers would have solved the problem long ago. For you as a user, the problem is coming up with a scheme that gives good results. If you notice, I removed all your mates and remated the tab component with a scheme that didn't flip. Usually, if you have a component moving around a path, the cam mate works well. Adding multiple path mates, usually works OK in the model tab but not so well in an animation. The key is knowing the choices and when one doesn't work, try something else. If at first you don't succeed..........
        
        As for indexing the tab, the easiest way is to just continue with what I gave you. If you don't like Percent along path, use Distance along path as I assume you know how far you want the tab to go in each step. The it is just a matter of moving the timebar to the time you want the tab to arrive at an index point and setting percent or distance to the correct value. To hold the tab for a time before having it move again, just copy and paste the last keypoint you just created down the timeline the appropriate amount. As both keypoints are for the same position, the tab does not move for the length of time between them.
        
        An alternate approach is to start with the full loop animation. Then to establish the index points, drag the timebar and watch the tab component. When it gets to the point you want it to be for an index point, select the tab component in the MotionManager design tree, then click Add/Update Key. Once you have all the keys, you can drag them on the timeline to the place in time you want each to be, then do as above to create the copied keys.
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        CHS - Test Assembly 03.avi3.7 MB
        CHS - Test Assembly 02.zip194.6 KB
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        Dale Elde @ Jim Boland on May 18, 2012 5:47 PM
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        That should get me through this project. I just have on last question; is there any way to mate an object behind the tab so that it will follow around the path? The final direction will be reversed, but I have used a distance mate to try and make another object move with the tab (this is probably doomed to fail because of the math involved). Like you said, it is about knowing your alternatives. I would rather not have to move each rod/tab separately, but I just can't seem to find a way to sync the travel of the tab with the rod for the entire loop. At a distance of 1 inch, both can almost make it, but at a distance of 3.75 inches (which is what I need), it falls apart before rounding the first curve. It would also be nice if you could choose the starting point for percent/distance along path...any thoughts on that? These tabs and rods will be in series around the belt.
        Attachments
        CHS - Test Assembly 01.zip258.5 KB
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        Jim Boland @ Dale Elde on May 18, 2012 9:57 PM
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        The way I would approach this is to make it a chain. In the attached video, you can see three triangle looking parts. These are just links to connect the two tabs together. Why three links? One problem with this assembly is that the curves are very tight. If you use a distance mate or a single link, what happens when you get to the bend? You want the distance to be measured around the circumferance of the arc, but if you use a distance mate or a single link, you get a striaght line distance between the two tab which is geometrically a problem. Think what happens is the distance between the tabs is more than the diameter of the arcs. I chose three links just as an example as it shows that the distance between the two tabs is now segmented. The more accuracy you need the more links you would use.
        
        You can also see that the links are hidden around the first index point. They are only shown in the first part of the animation so you can see what is happening. In the final animation, they would be hidden throughout the animation as they are not real components in the assembly, only dummy parts used for spacing and can be any shape or size you need to make the geometry work.
        
        You can make the starting point of the path mate any value you want, it does not have to be zero. Just edit the value at the key points. If you have to go around more than once, you have to understand the "100/360 Rule". It is explained in the book "Creating Animations with SolidWorks" available from SW or Amazon, or you can view the presentation "Move It-Move It-Move It" from the SW World 2012 presentations.
        
        Hope that helps.
        Attachments
        CHS - Test Assembly 04.avi3.1 MB
        CHS - Test Assembly 04.zip337.3 KB
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        Dale Elde @ Jim Boland on May 21, 2012 2:07 PM
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        That is exactly what I needed. Thanks for all of your help, and I will look into getting that book.
        
        I have started adding links to the chain, and I was wondering about processing issues. The animation is running fine, but the "calculate" command is quickly taking much longer to complete. I am thinking that animation calculations just bog down as you add more complicated mates, but I am curious as to how complicated you can make an assembly. Here are my computer specs:
        
        Intel Core i5 (3.3 GHz)
        8 Gb RAM
        Nvidia Quadro 4000
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        Jim Boland @ Dale Elde on May 21, 2012 2:21 PM
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        To not Calculate, is not an option. When you press Calculate, SW determines the positions by starting at time zero and recording the frame. It moves all the driving components ahead one frame, then rebuilds the model, solves all the mates and in-context features and then records the frame. This continues until the end of time. If you make changes and do not calculate, the motion you see when you hit Play is the last motion calculated and may not be correct for the changes you made.
        
        As for the time to calculate, a 3.3 GHz cpu should be fine. I did a chain and sprocket animation with 32 links and over 130 top level mates. For a 12 second animation at 24 fps, it took about 50 seconds on a 2.0 GHz cpu. Once it is calculated, it plays smoothly at real time.
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        Dale Elde @ Jim Boland on May 21, 2012 5:52 PM
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        I have been adding links without too much trouble - I have been able to work around the snags until now. When I try to add another spacer (whether I use one or more mates), the chain stops moving towards the end of its path. Any ideas?
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        Test 06.zip405.7 KB
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        Jim Boland @ Dale Elde on May 22, 2012 12:47 PM
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        I spent a bunch of time going over this assembly to see where the problem is. There is no easy way to solve this problem as there are no automated tools to find the problem, so you have to do it manually. Basically you suppress the components at the end of the assembly until the animation works, Then you unsuppess the components one at a time to see which componet/mate is stopping the motion. Once you locate the component/mate that is the problem, change it or try a different method to get it to work.
        
        When you have an assembly with as many components as you have, it is good to organize you components and mates into folders to make it easier to find things. Rather than the monolithic structure you started with, you could organize it like this:
        
        This also makes it easier when you want to hide the spacers as you just hide the Spacer folders and all the components in the folder become hidden.
        
        Back to the original problem. The animation will work until you get to Guidance Rod <10>. You have two choices with the Guidance Rods, one is to mate them to the path and have the spacers just pull them along, or mate all the spacers so that you have an animation that works and then add the Guidance Rods to the appropriate connection points between the spacers.
        
        As you can see, chains are difficult because of the very large number of components and mates which slows the solution. You said in the beginning that you didn't want to drive the tabs separately, but an alternative is to break the total chain into a couple of segments and drive each segment separately. This is the middle ground between the two solutions. It will eliminate a lot of the spacers and mates but you then have to syncronize the segments to move together. It is a tradeoff, so you have to figure which gets the results you are looking for with the least amount of work.
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        Dale Elde @ Jim Boland on May 22, 2012 3:42 PM
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        As time goes on, I may be willing to drive the tabs separately; staggering starting positions of the tabs/guide rods may be easier. I had no idea how involved chains could become! I tried adding two of my previous attachments together, but I ran into a different set of roadblocks. I started another thread before I realized that I should have just added it to this one...sorry!
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