Friction error in MSC Adams

[Ingenierio]

Good afternoon, I am trying to model a crank and piston mechanism in MSC Adams. When I mold it, I see some default friction coefficients in the revolute joints. Right now, I want to study the model without friction, so I replace the values of the static and dynamic friction coefficients with 0.0. However, when I try to calculate, I get an error message saying that the static friction coefficient must be greater than or equal to 0 and that the dynamic one must be greater than or equal to the static one. I don’t understand this, since I specified a value of 0.0 for both, which meets both conditions. Why could this be happening? Is there any way to eliminate friction from the entire model?

Greetings and thank you in advance.

 

[GregLocock]

Try setting the friction very low, but not zero. I assume you are using View, have you completed the Latch tutorial? Oh, and can you post the exact error message?

 

[Ingenierio]

Try setting the friction very low, but not zero. I assume you are using View, have you completed the Latch tutorial? Oh, and can you post the exact error message?

Thank you very much for your response, I was using view,I tried these options:

First, I did the model using the older interface, beacuse my professor is using that one so it makes it easier to follow the class, I did the model, put all the joints, and in the rotation pair of the connecting rod, i put an angular velocity of 600 rad/s, as you can see in the following image:


Then, I simulated the mechanism during 2 seconds and with 200 steps, and the results I got in the post proccesor were these:


The speed and acceleration of the piston was falling down overtime, so I thought there has to be friction somewhere, I checked all the joints, and they had a mu static=0.5 and a mu dynamic=0.3, so I changed it to mu static=1e-08 and mu dynamic=1e-09, I simulated again but I got the same results.






After this, I tried to model the mechanism using the new interface, i put the exact same parts and joints, and I simulated the same time with the same steps, but this time the results were different, the speed and acceleration was not falling down during the simulation, maybe the joints work different in the new interface?



When I try to put mu coefficients of 0 in the old interface simulation, this is the error message:


So what I was keep the my static to zero and the mu dynamic I put 1e-09, but the simulation failed and I got this message:


I guess that there has to be an error on the way I put the joints or the intial speed in the old interface? I did not do the latch tutorial I was following what we were doing in class, so I guess I should start using the new interface for now onwards? It's strange because the joints in the new interface also have a mu static and mu dynamic of 0,5 and 0,3 by default.



Again, thank you very much for your response. Sorry for my english btw I have it a bit rusty.

 

[GregLocock]

At an angular velocity of 600 rad /s and 100 time steps per second you are simulating the mechanism at just over once per revolution. That will not work.

 

[chicopee]

In your original post, it is written ".....static friction coefficient must be greater than or equal to 0 and that the dynamic one must be greater than or equal to the static one..." It is odd to have a dynamic coefficient of friction greater than a static coefficient of friction, normally it should be less.

 

[GregLocock]

Good point. The example in the solver manual has it the right way round



FRICTION/102, JOINT=102, I_YOKE
, Mu_Static=0.03, Mu_Dynamic=0.024, Stiction_Transition_Velocity=0.1, Max_Stiction_Deformation=0.15
, Pin_Radius=12.25
, Friction_Arm=8.2
, Effect=All
, Inputs=Reaction_Force



The reason this must be so is that in the limiting case, a force just greater than static friction would start to move, and then hit the dynamic friction, and stop.

Also it might be an idea to read the ERROR message, it does not say what you said it siad.