Inspired by Ikeda Yosuke's open/close sign design which relies on gravity and relatively frictionless joints, I decided to design one using planetary gears to drive the movement of the letters. An animation of the transition can be seen here: https://youtu.be/TmrUlpgojlY The model has now been updated to include the "d" in closed but the video is of an older version.

The gears are made to snap fit onto their respective axles, tolerances for rotational and press fit parts have been confirmed and should work well with a properly calibrated printer.

Updated 24/3/17:

• D in "closed" has finally been added to the design. Using the joiner.stl piece, the letter d should lay perfectly over the top of the c and the l. First glue the joiner to your gear_right in the correct position and then glue it to your letter d to allow proper alignment.
• Type has been refined a little bit, particularly on the letters e, d, c, and l.

Updated 11/2/17:

• Registration points added for letters to attach to gears
• Split base plate for smaller build platforms (minimum build size required 160 x 160 mm)
• Refined font to remove sharp edges
• E and S/N has been chamfered on the bottom edge to avoid catching
• Planet gears and gear_left have been heightened by 1mm in order avoid contact with the axle
• gear_left has modified gears to only allow rotation in the direction such that letters don't touch each other (idea by frankvdh)