Posted by Bill Geyer on October 26, 2015 at 3:02pm
I want to offer a way to remove the instability of the helicopter to RATE_RLL_P. I believe that this is caused by the lead-lag of the blades coupling with the body dynamics which is a well known rotor instability for manned helicopters. Could someone send me data of a helicopter oscillating due to the RATE_RLL_P gain being too high? I would need the IMU data and RCOU data. I know the IMU data is at 50hz. Is it possible to get the RCOU data at 50hz? I will also need to know the distance from the center of the hub to the blade mounting bolt, the rotor radius and the rotor RPM.My idea to cure this problem is to put a 10hz low pass filter on the output of the p gain in the rate PID. This shouldn't affect the pilot inputs but will remove the chance of the p gain exciting this instability. This way the p gain can be set as high as needed to obtain necessary control like the multirotors. I will use the data to prove my theory and hope to engage the developers to implement the change so it can be tested.