- OS: Ubuntu 18.04/KDE
- FreeCAD Version: 0.19.2+dfsg1~202107140647~ubuntu18.04.1
Each part has a red orientation mark. On the main rods, this is an "L". These are visible in the images, along with the local (within the part) LCS of the main rods.
Not shown are the main rod caps, which are attached to the same LCS objects on the Model scaffold sketches (one for each crank journal).
These images show the second main rod flipping. The front rod (shown with pistons attached) flips at 180.00002 and 359.99998. The only thing changing is the Crank_angle value. This occurs when changing the variable manually and during assembly animation.
Crank_Angle: 0.0:
Crank_Angle: 0.00003:
Crank_Angle: 179.99997
Crank_Angle: 180.0
Notice how the red "L" on the second dark green main rod appears and disappears throughout the rotation as its LCS orientation changes.
Finally, the combo view showing the main rod local LCS properties:
I suspect this is related to the LCS being mapped with InertialCS, but I don't see how to map it otherwise as there is little physical geometry aligned with the origin point. The edges I used are the result of a fillet (but not created by it), which is not ideal.
All the corresponding Model LCS are mapped to a vertex and line in the scaffold sketch using OXY. This is the only mapping for them that is correct and remains stable.
In previous attempts to fix this, the parts turned 90 degrees on their local Z, or only flipped near Crank_Angle 180 and immediately flipped back. Unfortunately, I have no idea how I stumbled into those partial solutions and didn't save the file to preserve them.
How do I map the part local LCS in a way that remains stable?