Since we started making FED1.0 we found the hardest aspect of making a pellet dispensing to be.... dispensing pellets. 

There are several issues that need to be resolved, two of which are dust and pellets landing correctly in the well.  Dust is a serious issue that can jam the FED.  We have found that printing the front plate at a finer resolution (see 3D printing log) helps greatly with reducing dust.  Basically making the pellet path as smooth as possible for the pellets.  We have also noticed that pure sucrose pellets make much less dust than grain based pellets, which can be useful if you don't need to provide the whole diet to the mouse via FED.  Lastly, we included "drain holes" in the design to try to remove some dust.  That said, if you run FED for multiple days you should watch out for dust forming and try to clean it out.

The second issue was getting the pellet to land correctly between the arms of the photo-interrupter.  These little pellets are hard and they can tend to "bounce" when they drop out of FED.  To slow the pellets down and minimize bouncing, we use a curved pellet dispensing path, shown here (courtesy of the excellent visualization tools at 3D Hubs).  This seemed to solve the bouncing issue.