Simmechanics Weird behaviour when simulating a four bar linkage with an initial condition

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Rodrigo Hernandez
Rodrigo Hernandez on 28 Jul 2016
Answered: Steve Miller on 17 Nov 2021
Hello,
Could anyone please take a look to the example attached? It is a four bar linkage made in Simmechanics (Simscape Multibody). It is behaving really weird and I do not know exactly the reason.
I have been doing lately some matlab programming and the weirdest thingy is that this very mechanism, running under my code behaves exactly in the same way!!
It is a four bar mechanism sample slightly modified . One of the joints (Crank-Connector revolute joint) has a State Target Priority to define a specific initial position.
When simulated, the mechanism seems to find an attractor in one of the sides, and keeps oscillating around the position, which is actually supposed to be a repeller. There are not external forces applied (except the ones due to the gravitational field).
See this video .
Can anyone please give me some insight about this issue? I think I am going bananas...
PS: The example is attached as a .zip file. Just need to click on the play button.
Many thanks,
Rodrigo
  6 Comments
Rodrigo Hernandez
Rodrigo Hernandez on 1 Aug 2016
Sorry, my bad explanation again.
I meant, if I keep 20 cm in Simscape Multibody, should I guess that the simulation in Simscape is behaving realisticly?
Well...
As you have suggested, I have simulated the Simscape configuration right now in Autodesk Inventor and they are the same. It matches with my simulation in Matlab as well.
So yes, my intuition was wrong, and the simulation is ok.
Swarooph, a few words to you. Thank you for being in the front line, dealing with people like me and solving our questions.
Sometimes we come across problems that could be sooo frustrating... It is good to know there are people like you helping us to find ourselves into the dark and complex Maze.
So, thank you very much and wish you the best.
Rodrigo

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Answers (1)

Steve Miller
Steve Miller on 17 Nov 2021
As answered by Swarooph above, setting the initial conditions properly and ensuring the linkages are the right length resolved this issue. See the discussion in the comments.
--Steve

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