Assuming the arm that is moving has a fixed radius, this will help you with plotting out the coordinates.
Starting from the horizontal of your triangle, the x,y coords (looking at it in 2d plane) are
x = radius*COS(angle)
y = radius*SIN(angle)
so if you want to stretch Y, you need to make a stretchy hotspot that changes the angle.
Just a quick thought process thrown in a comment, hope it helps a bit.
Remember if you are doing any rotation from certain points to 'move' your origin in the 3D script there.
Erwin Edel, Project Lead, Leloup Architecten
www.leloup.nlArchiCAD 9-26NED FULL
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