Even though the IMU stabilized quadcopter is not yet complete, there have been enough requests for the source code to justify releasing it as it is. Please let me know if you try it out on your design and especially if you make any improvements. As soon as the weather improves around here, I am planning to try the stabilizer on my EasyStar. I will likely have more improvements at this time.
Download the source code from here.
I was at last able to have the first successful indoor flight! Hover seems to be very stable, with only a slight drift. Small corrections are still needed to keep the quad in one spot, however much less input was needed to hover compared to a helicopter (I am flying a TRex 450).
Development took a bit more effort than I originally anticipated, due to the effect of vibration on the accelerometers. Having four (unbalanced) motors does produce quite a bit of vibration. I had to spend some time trying to understand the vibration and its effect on the accels. Given the constrains I have on the Propeller, I opted for a moving average filter on the accelerometer channels and I noticed a big improvement on the IMU response. The vibration would basically make the roll and pitch output of the Kalman filter drift by up to 15 degrees. With the filters I was able to keep any error below 3-4 degrees. Some more tuning on the filter length and Kalman parameters is possible, however I am quite satisfied with the performance of the IMU stabilizer so far. The results can be seen in the video above, during the flight some small corrections were needed but nothing major.
I would not declare victory just yet, there is still some room for improvement and more testing is needed on outdoor flights (for example the effect of centripetal force during a turn). However I am quite satisfied with the performance of the controller, considering that low cost gyros and accelerometers are used.
As soon as the weather improves I will also try it on my EasyStar. I will post the source code and design files on this blog soon, stay tuned!