Just make a decent revvy, that reacts quickly and does what it is supposed to.
Revvys come with their eyes on a connector, so if you find the connector (its very common) you can use the stock eyes.
EDIT:
When I said it would be easy to demostrate, what I mean is its easy for the teacher to get his/her head around how an agitating hopper is very useful compared to a non agitating hopper.
At the moment you dont need to make a product that everyone will want, or even one that works better than the current system. You just need to demonstrate that you can follow a project through all its stages from start to finish.