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

Automated Chicken Feeder

My roommates and I started keeping six chickens in our backyard last May.  We've raised four Buff Orpingtons, and two Easter Eggers that are likely Ameraucana cross-breeds.  I'd like to think that our chickens can be an economically and environmentally sensible thing for us to do, which means no overpriced commercial coop, very limited use of new materials, extending their feed with kitchen scraps, and generally taking every opportunity to minimize the amount of attention they need.