Multi Body Dynamics with FreeCAD + MBDyn

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josegegas
Posts: 39
Joined: Sat Feb 11, 2017 12:54 am
Location: New Zealand

Re: Multi Body Dynamics with FreeCAD + MBDyn

Postby josegegas » Sun Nov 17, 2019 9:25 am

vocx wrote:
Sat Nov 16, 2019 7:10 pm
josegegas wrote:
Sat Nov 16, 2019 8:28 am
Sorry, what do you mean by construction?
I think herbk means if you were to physically build this machine, it would probably not work as this ideal model. Did you add collision detection yet, or not?
Oh, I see what you mean. The parts that "collide" are not actually part of the model. The thing is that I'm using rigid bodies to define constraints, so for instance the cylinder that you see in the middle of the gear is not part of the model, but it rather represents the axial rotation joint that imposes the rotation to the gear. This is the way I'm interfacing the CAD model with the multi body dynamics software. A simpler example is a joint for a rigid pendulum. To define the position and orientation of the rotation axis, you place a cylinder, and the pendulum will rotate around the main axis of the cylinder. Spherical joints can be defined by a sphere, but the sphere won't be part of the physical model, and will only define the joint. Does this make sense? You can see this better in this video:

https://www.youtube.com/watch?v=mlvztzqhdGo&t=242s

This is also the way other MBD pre-post processors work.
josegegas
Posts: 39
Joined: Sat Feb 11, 2017 12:54 am
Location: New Zealand

Re: Multi Body Dynamics with FreeCAD + MBDyn

Postby josegegas » Sun Nov 17, 2019 12:22 pm

See how to define joints and constraints in ANSYS:

https://www.youtube.com/watch?v=8HixzW8eFGs

They also use those cylinders to represent the joints, and it also seems the bodies "crash", but the cylinders are only the joints for the MBD simulation, not part of the assembly. The same for the workbench I'm programming, those are the cylinders that seem to be crashing. What I should probably do is hide all the bodies that are not part of the assembly and only define joints and constraints once the user hits the "start animation button"? This could be a solution...

Have a look at other MBD animations using ANSYS and ADAMS:

https://www.ansys.com/products/structures/ansys-motion

https://www.mscsoftware.com/product/adams

In the end I'd like to achieve animations as that little truck in ANSYS or as that engine in ADAMS. I'm getting close to this:

https://www.youtube.com/watch?v=hCpwAwY_Xkk
josegegas
Posts: 39
Joined: Sat Feb 11, 2017 12:54 am
Location: New Zealand

Re: Multi Body Dynamics with FreeCAD + MBDyn

Postby josegegas » Sun Nov 17, 2019 12:32 pm

Here's another one with ANSYS:

https://www.youtube.com/watch?v=Ph11T82hbc4
vocx
Posts: 1915
Joined: Thu Oct 18, 2018 9:18 pm

Re: Multi Body Dynamics with FreeCAD + MBDyn

Postby vocx » Sun Nov 17, 2019 6:52 pm

josegegas wrote:
Sun Nov 17, 2019 9:25 am
... so for instance the cylinder that you see in the middle of the gear is not part of the model, but it rather represents the axial rotation joint that imposes the rotation to the gear. ...
Okay, I think that makes sense. I'm sure you will make this clear once you start writing the documentation for the workbench.

It is progressing nicely.