WIP. So far there has not been a successful 3D printed engine but this is the idea: A 3D printed spring's energy is captured and released to a series of gears. The design so far is promising but needs work.

Update with upload of V1.2: http://joesmakerbot.blogspot.com/2013/01/fully-3d-printed-engine-update-2.html

Refer to the exploded diagram as you read these steps.

1. Print the spring in ABS with zero fill layers, zero infill, and 4 extra layers. (Not discounting PLA, but I don't know the settings.)
2. Cut the spring at the obtuse angles to make 2 springs. Flip one so that their curves compliment each other (like a flat DNA helix).
3. Print the rest of the pieces with your normal settings.
4. Place the springs inside the case, side by side.
5. Put the drive gear with the straight line of teeth on. Line up the groove beneath the teeth onto the ridge on the case, putting the arm through the hole into the case to cap off the end of the case to compress the springs. (Does anyone have better names for these parts?)
6. Put GearIn1 in the left most hole on the case so that the teeth mesh with the drive's straight teeth.
   7, Glue the pin in the GearFloater. Put it in the next leftmost long hole
7. Put the GearOut1 (with the shorter secondary gear) in the next leftmost hole.
8. Put the two GearOut2s in the last two holes in the case.
9. Put the HolderPlate into the slot in front of the GearIn and bend it to snap into the slot above it making sure the floating gear peg goes into the hole.
10. Take the holderArm and hook one side into the HolderPlate, wrap it around the output gears making sure the pegs hold the gears in place and hook it into the case, pushing the drive gear in slightly and locking it in the case.
11. Glue the key in the hexagonal hole in the GearIn1 gear (not shown in exploded illustration).

Wind up the engine to compress the springs. Then let it go. The output gears should not move when winding and when released they should each move at gradating rates.

As of this time the actual output speeds and whether they can be slowed down is unknown. Also I suspect that the spring will break frequently so I made easy access to replacing them. Kind of like batteries.

If this works it can be used to (briefly?) power an action.