Hi heron, Thank you for your explanation. I think I now see the difference between the way we've done things. FreeCAD has two ways of referring to angles: a) specifying the axis of rotation and the angle to rotate about that axis, and b) specifying the angle to rotate about each of the X, Y and Z ax...

Hi heron, Thank you for your very informative reply. I notice you are using a slightly newer FreeCAD version than I am. I've now updated mine to be the same, 0.19.24291. The strange Y axis behaviour I see is still the same. There is still the difference that you are running on Windows 10 and I'm run...

heron wrote: ↑Tue May 18, 2021 4:19 am That doesn't happen to me

Interesting. Could you post your Assembly4 Workbench version (from Addon Manager) and your FreeCAD version info (Help --> About FreeCAD, Copy to clipboard)?

Thank you.

If rotations about the local Y axis are avoided, everything works very well. As an example, here's a simulated walk cycle for a simple servo-driven robot leg. The inverse kinematics equations were implemented as FreeCAD expressions using Assembly4 variables. The simulation was generated using Assemb...

However with AngleY, the LCS reverses direction at 90 and 270 degrees and flips by 180 degrees:AngleY.gif This is clearly a guimbal lock I'm not familiar with the internals of FreeCAD or the Assembly4 workbench. Are Euler angles used to represent rotations? Is the issue a bug which is fixable or is...

Here's another even simpler example file which clearly shows the rotation reversals and flips on the Y axis. This just has a single LCS, LCS_XYZ, which is set up to rotate about the X, Y and Z axes, controlled by variables AngleX, AngleY and AngleZ respectively. When AngleX is varied from 0 to 360 d...

First I'd like to thank Zolko and the others who have worked to develop the Assembly4 workbench. It's a really great addition to FreeCAD. I've been trying to model a robot arm using LCSs, and found something unexpected. I have attached a small test file, and I'd be grateful if others could try this ...