Bought a small, cheap RC heli a while ago. Didn't play with it much, decided it was time to see what was in it! Unfortunately I neglected to take a bunch of photos of the internals - I might do so later and will fix this article up if I do.

I got the heli from Hobbyking - it was only $10, an impulse buy on top of an existing order: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=11309

Cracking open the shell reveals a pair of DC motors (one for each main rotor), a battery and a control board. The control board is tiny, and only has one IC along with a few surface-mount passives and transistors. I'd guess the IC is just reading the IR in and demuxing/mixing it to 3 PWM channels (the two main rotors and the tail rotor). Combined with the remote, this could be pretty useful! One thing to note is that nothing is happening here to stabilise the heli - no gyros or accelerometers - the rotors are designed to remain stable using the angular momentum of the bar on top, with some interesting mechanical linkage.

There's also a big flashy LED sticking out of the board, it only has two leads, but flashes multiple colours when the copter is running. I think there are different flash patterns for "low battery", "no signal" and so on. Not sure how it works, maybe it's serial, maybe I'm just not seeing something.

The battery is itself an interesting piece of kit. 3.7V, 75mAh, about 2mm thick and the size of my thumbnail. No protection built in. You can recharge the copter by plugging it into the remote, so there is a suitable charging circuit either in the remote or on that PCB in the copter (it could be as small as a single 3-pin IC, so either is possible). Either way, there are plenty of neat things you can do with a tiny rechargable power source (it will probably run a 3.3v ATmega for a couple of hours, smart throwie?).

The motors are simple DC brushed motors, and are geared down to drive the rotors. They are wired such that they spin in opposite directions - yaw is controlled by varying the balance of torque between the rotors. They have gears attached and would be easy to repurpose. The tail rotor also has a tiny DC motor direct driving a small propeller for pitch control. This one seems to be about the right size for a phone vibrate motor.

So, heaps of interesting bits and potential in one of these. Not bad for $10! I ended up making a Nyancopter, but I have a few more ideas. Maybe you have some old toys lying around - crack them open! There are also a lot of toys in the MHV junk pile gathering dust (including some helis), why not see what you can do with them?

http://www.youtube.com/watch?v=u_678x0u39s