Simulation setup question

[Liam Murray]

Good morning Chrono community!

I hope this message finds you well. I am currently trying to simulate a system with three drums that rotate. One drum is located at the center and rotates as expected around its local axis. However, I am encountering an issue with the other two drums, which are offset from the origin. Instead of rotating about their own local axes, they appear to be rotating around the global origin.
I have tried changing the mesh origin points in blender, which did not seem to help. Do you have any suggestions how to configure the system so that these drums rotate about their respective local axes?
I appreciate your time and assistance with this matter and am happy to provide additional details or share the relevant portions of my simulation setup if needed.

best, 

liam

[Liam Murray]

We tried a few more iterations of trying to modify the obj file and some work arounds, still nothing. Any help would be appreciated

[Ruochun Zhang]

Hi Liam,

First thing: Are you doing this in Chrono DEM-Engine, or are you using Chrono core for simulating a multi-body system (which could potentially be the co-simulation agent for another DEM simulation)?

Thank you,

Ruochun

[Liam Murray]

Chrono DEM-Engine

best,

Liam Murray
AeroFly LLC
D1 Swimmer
SDSU

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[Ruochun Zhang]

Hi Liam,

First I'd like to name a possible cause. I guess all three drums use the same mesh, so for the second and third one, you loaded the mesh file, then used Move to move them to their initial locations, then the rotating motion is realized in the script by using some family-based angular velocity specification. The problem with that is, that the Move method will change how the solver views the CoM of the mesh, and that will be the location you "moved" it to (you can check out the method's comments, it's in fact the inverse operation of InformCentroidPrincipal, therefore not for moving objects but for setting CoM). So what you should do is either use SetInitPos, you use a tracker to SetPos after system initialization.

If you did not do what I just guessed, then probably I'll need to know what you did first. I say because there are many ways to get it done. I'd suggest you have a look into this conversation. There, I tried to answer a question about assigning "composite motion" to an object, which appears to be similar to what you need. You can use a tracker to set the pos/vel of the drums step-by-step, if calculating this information yourself is easier than having the solver do it for you; or you can still use family-based prescribed motions, but remember the rotational motions you specify there are always wrt to the CoM of the mesh.

Thank you,

Ruochun