Ever since I saw videos on the rctestflight YouTube channel where he made some boats, I wanted to make one. The best way I could think to do it would be to put paddle wheels on the side of a piece of foam. However, I first needed to make a motor controller since RC controllers for DC motors don't exist on eBay. So I programmed an ATmega328 to control an L298N H-bridge which is connected to two 24-volt motors, and now I have this:

It gets around pretty well despite only having two wheels.

I still need to put some thought into the paddle wheels for the boat. In rctestflights videos, it seemed like getting stuck on things in the water was kind of likely, so I'll need to make something that isn't prone to anything getting tangled on it, because if it gets stuck in the middle of a lake then that might be harder to retrieve than an airplane stuck in a tree.