Quadcopters are just plain cool.
Further, quadcopters require an onboard computer in order to remain stable. As such, microcontrollers are prefectly suited to this sort of project. The frame and motors are from a quadcopter kit made by 3D Robotics, but I designed and built and programmed the main flight controller board. The board consists of a R/C Reciever, an Inertial Meausurement Unit (IMU), and a Teensy 3.0 (an ARM powered Arduino variant) as the central controller. The Teensy takes gyroscope, accelerometer, and magnetometer readings in order to figure out the quadcopter's current orientation. It then adjusts the power of the motors accordingly in order to keep the quadcopter stable. The angle at which the quadcopter tries to stay at is based off of input from the remote control. In the future, I'd like to add a GPS, giving the quadcopter autonomous flight capability.