Looks great (at least at this image size)!

The cylinder with yellow label looks misplaced: it can't move the
arm because it is pointing to its axis of rotation. The base point
of this cylinder should lie a bit backwards.

If you want the direction of the "fingertips" (not only the position),
you will either need a

  second sphere on the "finger", transform it the same way as the
  position-sphere, detect its final position with the min_extent/max_extent
  trick and find Direction = SphereMidpoint1 minus SphereMidpoint2,

or

  use additional parameters Position and Direction (possibly Rotation also)
  with the construction macros and transform them along with the components
  of the arm,

or

  use a parameter Transform to describe the position, direction and rotation
  of the robot's tool.

This would enable you to spray the sparks (or water, paint, laser beam, ...)
in a direction relative to the robot's tool. You also could attach a tool
*after* the arm is positioned.

You will show us two more robots holding the parts to be welded together,
won't you?!? And more of them in the background for preprocessing and
postprocessing, grabbing the material, stacking the final products?!?
Robots building a robot?!? Animated?!? I'll stay tuned ...

   Sputnik

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