Here is a video showing a fascinating motion built into a wooden automata piece by Dean O'Callaghan.
Mr. O'Callaghan is from Bath UK and there is more information about his work here, although no mention of this sculpture. The cam action just pulls you right in visually.
The theme of water droplets falling into a puddle is one that has caught David's attention as well. Although he seldom starts trying to portray a specific motion, we often see reminders of motion in the finished piece. Such is the case with Summer Rain from 2010.