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Motion Studies: 3d contact in motion analysis

Question asked by Siva Praneeth on Aug 25, 2012
Latest reply on Aug 27, 2012 by Jim Boland

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I am trying to simulate the motion of a ball through a hollow spiral,
but the ball doesn't touch spiral when released, it directly falls through the spiral instead of touching it. Please help me how to fix this problem

This is what I tried-

1) I used the 3d contact and applied gravity downwards, and positioned the ball at a certain distance above the cone, so that when simulation starts, the ball will fall into the cone and eventually roll down the helix.

2) The simulation ran peacefully (i.e., ball went down the spiral) when "Basic Motion" is turned on, in which I couldn't apply friction and co-efficient of restitution in between the bodies.

3) However, when I changed the mode to "Motion Analysis", using the same settings and gravity, the ball just fell straight down "through the spiral" as if it were not hindered by any thing.

4) When this didn't happen, I tried bouncing the ball on a rectangular sheet. Even then using motion analysis made the ball go through the sheet after bouncing few times.

Attached are the video and the solidworks file.

Thank you for your time.

Jim Boland Aug 25, 2012 9:37 AM

Correct Answer

You haven't told us what you did to try to solve the problem. After reading the Help topics, what changes did you make to the contact settings and what were the results? What solver(s) did you try and what setting adjustments did you try? Why wasn't the model attached?

When you post a question with no explaination of what you have done, with no model attached, it just makes it look like you have spent no time trying to learn the software and just want us to teach you. If you show that you have made an effort, you will tell us what problems to rule out and will usually allow us to go directly to the problem and get you a solution. If we have to guess what you have done, your post has a good chance of getting ignored.

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Jim Boland Aug 25, 2012 9:37 AM

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Siva Praneeth @ Jim Boland on Aug 25, 2012 10:08 AM

Hello Mr.Jim

Thank you very much for letting me know how to post a question. I am relatively new to this forum. I am sorry that I didn't attach the file.

I have editedthe discussion for attaching the file and explaining the problem clearly. Please check into my problem and let me know where I went wrong.

Thank you for your time.

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Jim Boland @ Siva Praneeth on Aug 26, 2012 3:05 PM

This problem was a little odd because Basic Motion solved and Motion Analysis did not. This is backwards from what I normally see as Basic Motion does not always handle high closure rates very well. It does rolling contact well, but something being dropped onto somethine else can be difficult.

Like so many other problems, the root cause of this problem was not Motion Analysis but the model itself. When I first ran the Motion Analysis study, using all default values, the solver worked for several minutes before the ball started to move, this is generally not a good sign. I tried all three solvers, and got the same result of the ball falling through the spiral. I changed the contact to "Precise Contact" and still got the same result. When there is fall through, one thing to look at is part thickness, so I tried increasing the wall thickness of the spiral to 5mm, but in doing so I ran into trouble because of the model construction. I took a closer look at the part "Spiral" and noticed that it was two bodies instead of one merged body because of the modeling techniques used. I tried just merging the bodies, but they would not merge because the top cone did not fit properly to the two sweep sections.

I remodeled the top cone so that it merged properly with the sweeps and then the motion analysis worked using all three of the solvers. I reduced the wall thickness back to 3mm and it still worked.

The bottom line here is that you have to start with a good model, rather than expecting the analysis software to overcome the bad geometry.

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Siva Praneeth @ Jim Boland on Aug 26, 2012 4:47 PM

Hello Mr Jim, thank you very much for your reply.

I have tried remodelling the top cone and merging it as you mentioned and increased the thickness too. Still, I am getting the same result. Could it be the problem with the software?

I changed the geometry of the cone from using a spline to using a simple straight line.. still the same problem.

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Jim Boland Aug 26, 2012 7:38 PM

While no software is perfect, don't blame the software until you know it well and what all the settings and options do.

You did not say what contact settings you are using, nor which solver(s) you tried. Also, after every change, make sure you take the timebar back to zero and do a forced rebuild (CTRL+Q) before pressing Calculate.

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Siva Praneeth @ Jim Boland on Aug 27, 2012 12:33 AM

I have used the default contact settings, and tried all the 3 solvers. Yes, I used forced rebuild everytime I made changes to the model.

Still, no difference.

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Jim Boland @ Siva Praneeth on Aug 27, 2012 4:45 PM

If your remodeling has resulted in the spiral being a single solid body, then it really doesn't matter if you used a straight line or a spline, so that is not your problem. If I assume that you now have a good model and I told you that this motion study will work (the attached video shows that it does), then the only conclusion can be that you just don't have the problem set up correctly.

If you want to solve it, you need to go back to the original problem of "contact". Acording to your post, all you have done is run the analysis with the default contact values, WHY???? If you perceive the problem as one of contact, and there are contact options, shouldn't you be reading the Help file to find out what each option does and then experiment with them? There are two adjustments and one option in the Motion Study Properties that control contact. It should only take a couple of minutes to run the analysis multiple times with settings at the different combinations of high and low limits, and Precise Contact on and off, to get an idea of what they do and what will work. The answer is right in front of you!

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Spiral_MA.avi2.6 MB

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Jim Boland Aug 25, 2012 9:37 AM
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Correct Answer
You haven't told us what you did to try to solve the problem. After reading the Help topics, what changes did you make to the contact settings and what were the results? What solver(s) did you try and what setting adjustments did you try? Why wasn't the model attached?

When you post a question with no explaination of what you have done, with no model attached, it just makes it look like you have spent no time trying to learn the software and just want us to teach you. If you show that you have made an effort, you will tell us what problems to rule out and will usually allow us to go directly to the problem and get you a solution. If we have to guess what you have done, your post has a good chance of getting ignored.
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- Siva Praneeth @ Jim Boland on Aug 25, 2012 10:08 AM
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  Correct Answer
  Hello Mr.Jim
  
  Thank you very much for letting me know how to post a question. I am relatively new to this forum. I am sorry that I didn't attach the file.
  
  I have editedthe discussion for attaching the file and explaining the problem clearly. Please check into my problem and let me know where I went wrong.
  
  Thank you for your time.
  Like • Show 0 Likes0
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  - Jim Boland @ Siva Praneeth on Aug 26, 2012 3:05 PM
    Mark Correct
    Correct Answer
    This problem was a little odd because Basic Motion solved and Motion Analysis did not. This is backwards from what I normally see as Basic Motion does not always handle high closure rates very well. It does rolling contact well, but something being dropped onto somethine else can be difficult.
    
    Like so many other problems, the root cause of this problem was not Motion Analysis but the model itself. When I first ran the Motion Analysis study, using all default values, the solver worked for several minutes before the ball started to move, this is generally not a good sign. I tried all three solvers, and got the same result of the ball falling through the spiral. I changed the contact to "Precise Contact" and still got the same result. When there is fall through, one thing to look at is part thickness, so I tried increasing the wall thickness of the spiral to 5mm, but in doing so I ran into trouble because of the model construction. I took a closer look at the part "Spiral" and noticed that it was two bodies instead of one merged body because of the modeling techniques used. I tried just merging the bodies, but they would not merge because the top cone did not fit properly to the two sweep sections.
    
    I remodeled the top cone so that it merged properly with the sweeps and then the motion analysis worked using all three of the solvers. I reduced the wall thickness back to 3mm and it still worked.
    
    The bottom line here is that you have to start with a good model, rather than expecting the analysis software to overcome the bad geometry.
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    - Siva Praneeth @ Jim Boland on Aug 26, 2012 4:47 PM
      Mark Correct
      Correct Answer
      Hello Mr Jim, thank you very much for your reply.
      
      I have tried remodelling the top cone and merging it as you mentioned and increased the thickness too. Still, I am getting the same result. Could it be the problem with the software?
      
      I changed the geometry of the cone from using a spline to using a simple straight line.. still the same problem.
      Like • Show 0 Likes0
      Actions
Jim Boland Aug 26, 2012 7:38 PM
Mark Correct
Correct Answer
While no software is perfect, don't blame the software until you know it well and what all the settings and options do.

You did not say what contact settings you are using, nor which solver(s) you tried. Also, after every change, make sure you take the timebar back to zero and do a forced rebuild (CTRL+Q) before pressing Calculate.
Like • Show 0 Likes0
Actions
- Siva Praneeth @ Jim Boland on Aug 27, 2012 12:33 AM
  Mark Correct
  Correct Answer
  I have used the default contact settings, and tried all the 3 solvers. Yes, I used forced rebuild everytime I made changes to the model.
  Still, no difference.
  Like • Show 0 Likes0
  Actions
  - Jim Boland @ Siva Praneeth on Aug 27, 2012 4:45 PM
    Mark Correct
    Correct Answer
    If your remodeling has resulted in the spiral being a single solid body, then it really doesn't matter if you used a straight line or a spline, so that is not your problem. If I assume that you now have a good model and I told you that this motion study will work (the attached video shows that it does), then the only conclusion can be that you just don't have the problem set up correctly.
    
    If you want to solve it, you need to go back to the original problem of "contact". Acording to your post, all you have done is run the analysis with the default contact values, WHY???? If you perceive the problem as one of contact, and there are contact options, shouldn't you be reading the Help file to find out what each option does and then experiment with them? There are two adjustments and one option in the Motion Study Properties that control contact. It should only take a couple of minutes to run the analysis multiple times with settings at the different combinations of high and low limits, and Precise Contact on and off, to get an idea of what they do and what will work. The answer is right in front of you!
    Attachments
    Spiral_MA.avi2.6 MB
    Like • Show 0 Likes0
    Actions

Motion Studies: 3d contact in motion analysis

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