Hi Frederick,
The NodeEditor is not designed to do kinematics, but you can track the arm's rotation points via the "Select Filtered" node inside the Select menu. (Select/Select Filtered)

Pass the "Arm v01 Part 2 Shaft" (after rotation) into this node and set the mode to "Select Circle Edges", then use a "Bbox" node to determine its center point. (Objects/Bounding Box)

Here is the latest NodeEditor Plus version:
https://moi3d.com/forum/messages.php?webtag=MOI&msg=11614.1

Hi MO,

Thanks for the feedback.

I'm going to have to study what you have done - it looks a bit complicated but it works a treat.

While waiting for feedback I asked Google AI about the issue and it came back with a solution using vector math that works, at least for simple lines, which is what I tested it with.

I don't know if that approach will work for the 3DM file I posted here, with the arms representing real world objects, as opposed to simple lines.

See attached.

Frederick

Hi,
Yes, I think the better solution would be to calculate the angles; my method was more of a workaround. You can still add points as rotation center points and use those instead of the cylinder objects.

Please check out the attached nod file.
I just found this node in my archives! I created it a while ago using points and vectors for three arms. It behaves more like a mechanism! You can add or remove arms easily by copying and pasting nodes and setting your desired pin joint points. Let me know if this is close to what you want.

Here is a tutorial that shows how to use the point picker node:
https://moi3d.com/forum/messages.php?webtag=MOI&msg=11887.1