Hi Bill @bnsgeyer,
In order to solve the yow hunting problem, I have carefully inspected the rear rotor mechanism and discovered excessive backlash in the tail pitch control due to a plastic control link having excessive wear. In addition, by removing this part, I also discovered that one of the tail rotor grips had axial play. This was due to an unscrewed set screw on the tail pitch axis. Obviously, in the presence of oil and vibrations the blue Loctite was inefficient. Moreover, this mechanism which is known as fragile and prone to problems has been upgraded on the Raptor 30 v2, but unfortunately this machine is still a v1. Therefore, I changed the tail pitch control link, cleaned and degreased all the parts and sealed the tail rotor grips set screws with a much stronger green Loctite. I finally avoided any drop of oil. At the end, the mechanism was very accurate.
After setting the Attitude_Fast flag as recommended by you, I performed three armings with ATC_ANG_YAW_P set to 4.5, 4.0 and 3.5. I was very surprised: despite some small noise on the yaw, the helicopter was much stable! By gradually decreasing ATC_ANG_YAW_P, things seem to improve.
During the last arming (with ATC_ANG_YAW_P 3.5) I was quite happy with the helicopter controllability. I decided to land and take off again, just to burn the remaining fuel. However, during the last flight, I had a bad surprise: while hovering at about 1.5 meters above ground, the helicopter started to descend a bit. I reacted by increasing the collective pitch stick and once the hover height reached again, the helicopter still continued to climb.
I lowered the collective pitch, but without having any effect. I lowered the collective fully down this time, but despite this, the machine continued to climb! I thought about the risk of the machine going very high and then falling in a place where it could endanger people…
Therefore, I warned my friends to go away and disabled the motor interlock at approximately 10 meter height. The engine was put on idle immediately and the machine fell. When the machine approached the ground, I enabled back the interlock and gradually increased the collective pitch to maximum to cushion the fall. It seems that my cushioning technique was partially effective, as the rotor was not damaged: only the landing skids and the bottom of the frame were broken.
I think, the essential is that there are no physical injuries! Obviously, despite this mishap, we made some progress! I tried to analyse the last arming (which has two consecutive flights). Below is my analysis:
According to my observations, around 16:18:42.023, the PWM value of channel 3 of RCIN temporarily fell below the FS_THR_VALUE (set here to 975 us):
The reason of this “glitch” is unknown at the moment, but it might be:
- A temporary radio failure due to a poor battery contact
- A temporary radio failure due to a software problem
- A radio transmission jam
- A receiver failure
- A poor contact on the wire transporting the PWM signal from the receiver to the IBUS converter
- A PWM to IBUS converter module failure
- A flight controller’s processor overload
As a consequence, shortly before 16:18:42.223, the flight controller detected a throttle failsafe condition and immediately entered in RTL flight mode, according to the setup shown below:
Because the RTL is configured to return 15 meters above the take-off position, it would explain why, despite lowering the collective stick (channel 3 of RCIN in red) the signal sent to the collective pitch servo command (channel 3 of RCOUT in green) did not drop. One can also see the abrupt drop in throttle on RCOUT.C5 when I disabled the motor interlock:
I think that the following curative measure should be taken:
Check again and secure the electrical contact on the wire transporting the PWM signal from the receiver to the IBUS converter
As the throttle failsafe condition is likely to happen again and because the helicopter can’t fly yet autonomously, I think that the throttle failsafe function should be temporarily disabled.
At the moment, there is no flight mode setup other than “stabilize”: if the RTL flight mode is accidentally entered, there is no way to exit from this mode using the radio rotary button.
In the event you might have some time, please find on the following link the parameters and log file of the three armings: https://1drv.ms/u/s!AgF38cSpviIRgaxnPwDQl8XQrAZUWw?e=vaVzuA