The presented build was intended for use in my undergraduate research project.
I wanted to explore the possibilities of Time-Of-Arrival(TOA) acoustical ranging in civilian quadrotor drones.
Typical TOA-based ranging schemes uses the time a ranging signal takes to get from A to B.
Once the time and the velocity of the ranging signal(typically a constant) is known, a simple equation for calculating the distance is used (d = v * t).
So an acoustical TOA-based ranging scheme multiplies the speed of sound with the amount of time the signal was in the air to estimate the distance.
Since the drone needed a way to produce the sound (preferably a loud one) and record it, I needed a speaker with a good enough amplifier, a recording and computing device (in this case, a smartphone), and ways to attach them unto the quadcopter.
I eventually finished the build and done some ranging experiments, but the results turned out a bit grim :( The noise of the drone was too great for outside sound to be heard! But I ended up with a drone with an amplified speaker attached, which was nice. I could attach a smartphone on the drone and connect it to the drone's speaker to turn on some music, and thankfully it can be heard despite the characteristic humming noise coming from the drone.
Anyway, the software and hardware are listed below.
The drone became darn heavy after all the attachments (I had to raise the throttle 70 percent just to keep it level!), but it still flies with stability.
If I get the chance, I'll post a video with the thing flying with music flowing out of it like some kind of a noisy, flying sound box!