This thing looks equally challenging and fun to build! There’s a video below showing it in action, and you can grab all the files and parts list here at Rob Ives’s project page. (Update: a ZIP of the files is available; add the free ‘product’ to your cart and proceed to checkout, and you will receive a download link.)
And a hat-tip is due to Just Add Sharks for sharing this wonderful gem of a project (and the animated GIF!).