Re: FreeCAD as pre-post processor for MBDyn
Posted: Thu Jan 06, 2022 6:18 am
Hey josegegas, would you please make a tutorial on cycloidal gearbox simulation? It is helpful to understand force interactions between disks and pins.
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Hi. Sorry but what you see in the video is just an animation, not a MBD simulation. I basically just programmed a script to move the parts as they would in a real cycloidal gearbox.
OK, understood. Do you think the latest MBDyn WB is ready for this simulation? I want to try it myself as part of learning process.
Hi. Sorry but what you see in the video is just an animation, not a MBD simulation. I basically just programmed a script to move the parts as they would in a real cycloidal gearbox.
It depends on what exactly you would like to model. It is for sure ready to model all the mechanism but not the contact between parts. Contact is not a very mature part yet. To model the motion you only need the motion equations of the gearbox, which can be found easily on Internet or derived from the gearbox design, and then use the existing joints... It would be interesting to model it as in this example:JamesLiu wrote: ↑Sat Jan 08, 2022 1:18 amOK, understood. Do you think the latest MBDyn WB is ready for this simulation? I want to try it myself as part of learning process.
Hi. Sorry but what you see in the video is just an animation, not a MBD simulation. I basically just programmed a script to move the parts as they would in a real cycloidal gearbox.
It depends on what exactly you would like to model. It is for sure ready to model all the mechanism but not the contact between parts. Contact is not a very mature part yet. To model the motion you only need the motion equations of the gearbox, which can be found easily on Internet or derived from the gearbox design, and then use the existing joints... It would be interesting to model it as in this example:
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<class 'AttributeError'>: 'Part.Solid' object has no attribute 'CenterOfGravity'
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Running the Python command 'MBdyn_AddStaticBody' failed:
Traceback (most recent call last):
File "C:\Program Files\FreeCAD 0.20\Mod\freecad-mbdyn-dynamics-workbench-master\MBdynGui.py", line 1856, in Activated
dyn.AddStaticBody(b[0])
File "C:\Program Files\FreeCAD 0.20\Mod\freecad-mbdyn-dynamics-workbench-master\dynamics.py", line 504, in AddStaticBody
Dummybody(a, baseBody, baseBody.Label)
File "C:\Program Files\FreeCAD 0.20\Mod\freecad-mbdyn-dynamics-workbench-master\dummybody.py", line 56, in __init__
obj.addProperty("App::PropertyDistance","absolute center of mass X","Absolute center of mass","absolute center of mass X",1).absolute_center_of_mass_X = cmx
Invalid property name 'absolute center of mass X'
Did you somehow select the node and the surface and then wrote an expression for the vertical force equal to the penetration multiplied by a stiffness, and zero when the penetration is negative, or is there a GUI button that I failed to find?josegegas wrote: ↑Wed Dec 22, 2021 4:32 pm The elastic contact example was set exactly as you described it. There is a structural force determined by the distance between the two nodes. It is basically an adaptation of this example:
https://www.sky-engin.jp/en/MBDynExampl ... /ex09.html
The "bouncing brick" is also the same, although there is one node at each corner of the brick, to which a structural force is applied. All the nodes are rigidly attached together.