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by keithp
Thu May 20, 2021 11:01 am
Forum: Assembly
Topic: Assembly4: Strange behaviour when rotating LCS about Y axis
Replies: 13
Views: 2941

Re: Assembly4: Strange behaviour when rotating LCS about Y axis

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...
by keithp
Wed May 19, 2021 8:51 am
Forum: Assembly
Topic: Assembly4: Strange behaviour when rotating LCS about Y axis
Replies: 13
Views: 2941

Re: Assembly4: Strange behaviour when rotating LCS about Y axis

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...
by keithp
Tue May 18, 2021 6:54 am
Forum: Assembly
Topic: Assembly4: Strange behaviour when rotating LCS about Y axis
Replies: 13
Views: 2941

Re: Assembly4: Strange behaviour when rotating LCS about Y axis

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.
by keithp
Mon May 17, 2021 6:40 pm
Forum: Assembly
Topic: Assembly4: Strange behaviour when rotating LCS about Y axis
Replies: 13
Views: 2941

Re: Assembly4: Strange behaviour when rotating LCS about Y axis

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...
by keithp
Sun May 16, 2021 11:04 am
Forum: Assembly
Topic: Assembly4: Strange behaviour when rotating LCS about Y axis
Replies: 13
Views: 2941

Re: Assembly4: Strange behaviour when rotating LCS about Y axis

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...
by keithp
Sat May 15, 2021 2:21 pm
Forum: Assembly
Topic: Assembly4: Strange behaviour when rotating LCS about Y axis
Replies: 13
Views: 2941

Re: Assembly4: Strange behaviour when rotating LCS about Y axis

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...
by keithp
Fri May 14, 2021 1:51 pm
Forum: Assembly
Topic: Assembly4: Strange behaviour when rotating LCS about Y axis
Replies: 13
Views: 2941

Assembly4: Strange behaviour when rotating LCS about Y axis

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 ...

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