Over the quarantine I've been working on tweaking a few things on the FED3 parts.  This log will go over the new tweaks, which are available in the Files area.

1.  The back cover latching mechanism has always been a bit hard to use.  I've now put notches in the part to make it easier to take on and off:

2. The motor mount used a clip, combined with small self-tapping screws.  The screws could cause problems by either stripping the 3D plastic, or tapping in with the motor misaligned.  Either one could run the print.  Now I use two 8mm M4 0.7 threaded bolts with M4 0.7 nuts to secure the motor. This is much more reliable than the self-tapping screws and does not risk destroying the print if the screws go in misaligned. Because the bolts work so well I also removed the clip, which makes this part easier to print.

3. Finally, researchers Zane Andrews and Claire Foldi at Monash University showed me that mice could steal an extra pellet by poking their nose in the pellet well and grabbing the pellet before it enters the photo-beam.  This would cause FED to not register a pellet was dropped, and therefore drop another one.  I updated the front piece to include a "canopy" over the pellet well to prohibit this behavior.

So those are the newest edits.  Editable TinkerCAD parts are here.