I have been working for a while on building RC quad copters. First I built a medium sized one following the Aeroquad hardware and software. But I was not very happy with the performance. Then I decided to build a small one which can be safely flown inside home for debugging and flight practice.  I tried aeroquad software on it first, but didn't get good result. Then, I was follwing the MultiWii threads and found they are expanding their code to support more hardware and that included Aeroquad hardwares as well. So I downloaded the latest MultiWii code and modified it to work with Aeroquad hardware (ITG3200 gyro, BMA180 accelerometer etc.). Here is how my mini quad prototype looks:

And here is short video of it in action:

I found this very nicely written article by Starlino on IMU AKA Intertial Measurement Unit which is the heart of any autopilot system for hobby RC aircrafts:

Link: http://www.starlino.com/imu_guide.html

Surfing around the web I found the latest trend on remote controlled, semi-autonomous and full autonomous model airplanes, quadcopters etc. There are several open source projects available out there with available hardware for purchase and software, as well as firmware downloads for free. Most of the projects have excellent manuals on how to assemble the hardware, upload the firmware and configuring it. If you are struggling to learn how to fly a RC helicopter or a plane, one of these project might help you learn how to fly, using the on board auto stabilization option. I will be listing a couple of interesting links here.

DiyDrones.com - It has the list of almost all the open/commercial projects out there in this area.

Some of the autopilot frameworks are based on the popular Arduino platform, which makes it very simple for arduino fans to modify and contribute to the code if needed. Here are the a few of those:

1. Ardupilot: They have excellent hardware and software that produces very stable RC aircrafts.
2. Aeroquad: Aeroquad has a large developer community contributing to the development of this project which is making the platform better everyday.
3: KKMulticopter: They developed a very easy to build solution for a very fun to fly quad/tri copter.
4. MultiWii: Another arduino based platform using the popular and easy to find Wii Motion Plus and Nunchuck sensors. They are currently expanding their hardware support for wide variety of sensors.

More to come soon..