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cballantoni1-Visitor
1-Visitor
April 12, 2012
Question

Mechanism Dynamic Motion Failing, Kinematic works fine

  • April 12, 2012
  • 4 replies
  • 2682 views

Anyone had an issue where you have a kinematic mechanism model run perfectly fine but the dynamic run fails almost instantly.
I have a farely large chain model that uses 156 cam connections and a sprocket to move the chain around a fix body. It works great kinematically but fails within a .02seconds into the dynamic run.


Does anyone have any previous experience with models that use a lot cam connections? I'm assuming that's what is biting me with this model. Or any experience with large mechanism models run ina dynamic analysis that failed for any particular reason.

I've tried increasing and decreasing the accuracy of the mechanism assembly settings, but still it fails aroundthe same time.


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4 replies

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ChrisKaswer16-Pearl
16-Pearl
April 12, 2012
Corey,

Double-check your mass densities - it just takes one part with the default of "1" to make the weight of that part equal to that of the moon (depending on what units you're using) - MDO doesn't like trying to move something that massive - it will fail all the time right at/near the beginning.

Chris
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cballantoni1-VisitorAuthor
1-Visitor
April 12, 2012

I went back and ran a detailed list of component mass props and found one component with a density of 1. I corrected that, and re-ran the analysis. Thanks for the suggestion. Unfortunately it still failed to run at about the same time. I was really hoping that was the cause but unfortuantely it's still failing in the first tenth of a second.

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cballantoni1-VisitorAuthor
1-Visitor
April 13, 2012

Just another data point. When I remove the sprocket from the model that drives the chain and just allow the chain to sag and sit there it runs to completion but when the sprocket trys to move it fails. But in kinematic mode it moves fine.


The only connection between the sprocket and chain is the cam connections from the pins on the chain to the teeth of the sprocket.

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cballantoni1-VisitorAuthor
1-Visitor
April 13, 2012

And a couple more data points. I turned off friction and gravity with the same result. I then tried removing the chain and leaving the sprocket to run and the sprocket spun as driven by the motor. Whenever the chain and sprocket try to work together in dynamic mode it just won't run. But in Kinematic mode it works great.

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