I hooked up my prototype driver to the pan/tilt stage and valve to test the complete system, and it's working! Driver code for the Raspberry Pi has been started and is available in GitHub. Here's a little video of the functionality thus far:

Although this doesn't have wheels or wings, and doesn't walk, the description of this Hackaday Prize round says: "Build something that moves." Well, this moves! :) So I entered it. It may not be your typical robot, but the goal is to create an automatic robotic sprinkler after all. And if you don't agree, be careful or you might get sprinkled! :)