Third Field Test, Ongoing (Success)

The feeder's robustness is markedly improved.  I made several changes before putting it out for its latest field test, and it's run for several days without trouble.

Trophy for a Successful Field Test

I added a piece of thick cardboard inside the bucket to direct the feed towards the hopper.  This was a fun reminder that process often trumps planning.

Second Field Test

I made several improvements to address the most pressing failures in the first field test.  I used a piece of PETE from a water bottle to form a cover for the gear train.  Because this plastic can be deformed when hot, I warmed it in hot water and then molded it to match the motor mount before hot gluing it in place.  I also changed the mounting of the limit switch to better align it with the drive wheel.

Clear plastic shield over the gear train and motor

Leaky Bottles

Someday I hope to tell a skeptical child that cold bottles sweat because the bottles leak.  The fun part would be explaining away objections and attempts to prove this assertion false.

Leaky bottle of delicious ginger beer

If you lick the bottle, the stuff on the outside doesn't taste like the stuff on the inside.  Of course not, the bottle acts like a filter, letting the little water molecules through, while filtering out the big sugar, alcohol, and flavor molecules.  Sugars are long chains of hydrocarbons, while water is much smaller.

Assembly

Cut out the slot in the feed bucket, attached the blue box to it using three strips of the bucket material and wood screws.  Tested operation and verified everything works, then mounted the electronics in their enclosure.  Placed it out with the chickens, who incapacitated it within twenty four hours, I suspect by jamming the drive train with dirt.

Electronics

The electronic portion of the feeder consists of the motor controller and the solar charger.  The motor controller needs to power the gearmotor when the door position (DOOR) and the ambient light (LIGHT) are in opposite logical states.  We use a 7486 quad XOR to get this behavior.  A 2n2222 NPN transistor amplifies the logic output to drive the motor current.

Circuit Schematic

Printing the crank wheel

I'm never sure what to call this part.  It's the crank arm for the crank-slider assembly, but owes most of its shape to the need to trigger the roller switch during half the crank's rotation.  'Crank wheel' will work for now.  
 
There are several options for fabricating the crank wheel.  The simplest might be to cut the shape from 1/4" plywood using a jigsaw.  In this case, I thought I'd take the opportunity to explore some of the different free toolchains that are available for solid modeling of 3D printed parts.  I designed the part first in Autodesk's 123D, then in Trimble's Sketchup, and finally in OpenSCAD.

First (upper) and second (lower) version of crank wheel

Initial Design

I'm thinking about how to use an electric motor to simply and reliably open and shut the feeder.  I found a nice five gallon plastic bucket that's going to hold the feed.  I figure that will drain into a smaller hopper which will open and close automatically.

The first design that came to mind was to avoid having any linkages at all and simply place a disk with a hole in it on a drive shaft.  To open, it would rotate until the hole lined up with the opening to the feeder, and rotate again to close the feeder.  This is simple, but for a relatively large opening the size of the disk becomes a big unwieldy.  If the disk isn't flush against a support surface any overhang could catch and place a large axial load on the drive shaft, potentially jamming or damaging it.

First design idea for access control mechanism