Need help stabalizing large tricopter in Pitch

[William_Walker]

Hi,
I am having trouble getting my tricopter vehicle to hover after changing firmware from Plane ver 4.0.9 to Beta 4.2. Here is a link to see the vehicle and details about it:

New full scale unmanned winged tiltrotor VTOL

Hi, I am developing a new type of winged tilt rotor vtol, similar in functionality to the Convergence RC model. It is a flying car with 4 large wheels, that uses the body as a wing, So there are no wings to unfold and the vehicle flies just as it is. The vehicle is capable of horizontal and vertical flight. In addition it is amphibious. The vehicle weighs a 150 pounds it is 15’ long 8’ wide and 4.5’ high. It uses 2 counter rotating tilting motors in the front, and 2 coaxial coaxial counter rota…

The vehicle seems stable in roll and yaw, but seems to have problems stabilizing in pitch. I tried hovering it a few days ago and the video and log file of the test are below. I need to know if the oscillation in pitch observed is operator error or an oscillation in the pitch PID controller that needs to be fixed?. I should mention that I tested the PID controllers for pitch, roll, and yaw by supporting the vehicle at its CG and manually giving it an impulse. At these low thrust levels, all the PID controllers seemed to work well except with a minor drift due to motor noise. This is how I determined the PID values when the vehicle flew well. I am currently using a FFT notch filter which lowered the noise by a factor of 10. Unfortunately I changed that reference level during the testing and forgot to recalibrate the reference level before the test flight. So this may have caused a slight nose down (1deg max) attitude during the test hover.

Looking at the log files I have noted several things:

The vehicle tilted nose down at lift off and I gave a series of up elevator pulses to correct the level of the vehicle to slow it down, since I have limited testing runway indoors. I can see the motors correctly responding to my commands and trying to correct the level of the vehicle. What concerns me is that the oscillation is growing as I give up elevator pulses.

The front motors are getting too close to their 2000 max limit in the test. I only charged the batteries to 80% and these high numbers tell me I need to charge the batteries to 100% charge to give the motors more headroom, especially in the front.

Link to video of test:

2 test_1 m height flight and crash.mp4

Link to log file of test:

6_test 2.bin

Do you think that if the vehicle’s level is recalibrated correctly, and if the batteries are charged to 100% that the vehicle is ready for another test, or do you thing there is a large oscillation in the Pitch PID controller that needs to be fixed? If so, do you have any suggestions?

Thank you, William Walker

[William_Walker]

Hi all,

I have confirmed the problem is an oscillation in the Pitch PID controller. I tested the vehicle on the ground with the vehicle with on top of a small board under the vehicles CG, while the motors were on trying to stabilize the vehicle: Here is a picture of the Pitch and DesPitch signals and the throttle signal to show the duration of the experiment:

https://drive.google.com/file/d/1eIiaYVKV6pDqBYbeKkQNyDZgOEdidzr4/view?usp=sharing

Here is a log file of the experiment:
https://drive.google.com/file/d/1NLmSRTzsO8arLLzYkmTNljLwauK0bJtm/view?usp=sharing

Now the question is how to get rid of this oscillation. I will now try playing with the Pitch PID parameters.

William