Help! Y3 VTOL Plane pitch oscillation

[mathirj]

I’m developing the Y3 tilt VTOL plane. I have encountered a problem with the pitch axis, which exhibits oscillations when the plane is flying in the air.
I have attempted to modify the PID values several times, but the oscillations remain. I would appreciate any help or guidance on how to resolve this issue.
I have included all the log files and videos for your reference.

Thank you so much for your time and support.

FC-Matek-F405-se
Motors - Tarot 3515 400 kv
Prop -15*5
Video&Log

 

[LitterBug]

What flight mode are you in during oscillations? Have you done an autotune? Do you have any pictures of your project? What version of ArduPilot are you running?
The more info you give us, the more likely someone can help.

LB

 

[L Edge]

Since the pitch is controlled by the tail, it has a large moment arm for any small change of RPM.

Reduce the sensitivity of the rear prop by decreasing the pitch or I'm guessing that a smaller dia prop/ low pitch should solve your problem. Put another way, a small RPM increase/decrease gives a large change in pitch and the gyro can't keep up with it and causes oscillations.

Another area could be you have a vibration problem. Are your props balanced? Last resort, check if you can change the frequency on the FC.

 

[mathirj]

What flight mode are you in during oscillations? Have you done an autotune? Do you have any pictures of your project? What version of ArduPilot are you running?
The more info you give us, the more likely someone can help.

LB

Thank you for your kind reply !

Firmware - Arduplane.

The test was performed using Qstabilize and Qloiter flight modes.

I have not tried the autotune yet because I am worried about the stability in Qstabilize mode.

You can find the videos and log files in the link below.

Flight test Video & Log file

 

[mathirj]

Since the pitch is controlled by the tail, it has a large moment arm for any small change of RPM.

Reduce the sensitivity of the rear prop by decreasing the pitch or I'm guessing that a smaller dia prop/ low pitch should solve your problem. Put another way, a small RPM increase/decrease gives a large change in pitch and the gyro can't keep up with it and causes oscillations.

Another area could be you have a vibration problem. Are your props balanced? Last resort, check if you can change the frequency on the FC.

Thanks for getting back to me so quickly! I really appreciate your fast and helpful reply
its giving me such useful information.

You are totally right about everything you said.

I will follow your suggestion and replace the propeller on the rear. I hope that will fix the problem. I'll let you know how it goes.

For the board frequency, I am using the Quadplane tuning guidelines from the arduplane wiki documents. But I am still not sure how to adjust it based on the log file. Could you please help me with that?

 

[L Edge]

Thanks for getting back to me so quickly! I really appreciate your fast and helpful reply
its giving me such useful information.

You are totally right about everything you said.

I will follow your suggestion and replace the propeller on the rear. I hope that will fix the problem. I'll let you know how it goes.

For the board frequency, I am using the Quadplane tuning guidelines from the arduplane wiki documents. But I am still not sure how to adjust it based on the log file. Could you please help me with that?

Can't answer your last problem for I used a different FC and software for my VTOL. But a lot of the problems are the same no matter which software you use. Litterbug and others should be able to guide you with your questions.

 

[mathirj]

Can't answer your last problem for I used a different FC and software for my VTOL. But a lot of the problems are the same no matter which software you use. Litterbug and others should be able to guide you in their answers.

I appreciate your help and suggestions, sir. Please let me know if I made any errors in the PID settings that I shared.

 

[JasonK]

I appreciate your help and suggestions, sir. Please let me know if I made any errors in the PID settings that I shared.

PID settings are a per craft ordeal, they need to reflect the performance characteristics of the motors, the mass, rotational inertia, placement of the motors, and a whole bunch more things.

there isn't a "single" correct set of PIDS (if there was, then they wouldn't be settings).

You need to go through a tuning process to figure out what the correct settings are for your craft.

 

[mathirj]

PID settings are a per craft ordeal, they need to reflect the performance characteristics of the motors, the mass, rotational inertia, placement of the motors, and a whole bunch more things.

there isn't a "single" correct set of PIDS (if there was, then they wouldn't be settings).

You need to go through a tuning process to figure out what the correct settings are for your craft.

Thank you for your response.

I agree on your point.

I would be grateful if you could review the video and files and share any feedback on how to reduce the oscillation.
Video&Log

Thank you for your time .

 

[L Edge]

I appreciate your help and suggestions, sir. Please let me know if I made any errors in the PID settings that I shared.

PID settings are designed in to have the pilot's ability to match how they fly that aircraft. If your a beginner, auto level (autotune?) is important to setup to reduce crashes. So strong PIDS is important in pitch and roll(no wind). As you gain experience, you will adjust yaw and then learn how to adjust all three settings to cover gusty winds, maneuvers and pilot control that makes you comfortable in flying.

By the way, you did good to get this far looking at the video, rely on LitterBug and others who can give you tips with the matching software. Please share with them video and descriptions of what the problem is. Later on, try a bi-copter setup, all three axis movement come off the motor/props.

 

[mathirj]

PID settings are designed in to have the pilot's ability to match how they fly that aircraft. If your a beginner, auto level (autotune?) is important to setup to reduce crashes. So strong PIDS is important in pitch and roll(no wind). As you gain experience, you will adjust yaw and then learn how to adjust all three settings to cover gusty winds, maneuvers and pilot control that makes you comfortable in flying.

By the way, you did good to get this far looking at the video, rely on LitterBug and others who can give you tips with the matching software. Please share with them video and descriptions of what the problem is. Later on, try a bi-copter setup, all three axis movement come off the motor/props.

I appreciate your helpful response. It gives me a better idea of what's going on.

I'm going to test Autotune with different propellers and see if that fixes the problem.

Thank you for your time and support.

 

[mathirj]

Since the pitch is controlled by the tail, it has a large moment arm for any small change of RPM.

Reduce the sensitivity of the rear prop by decreasing the pitch or I'm guessing that a smaller dia prop/ low pitch should solve your problem. Put another way, a small RPM increase/decrease gives a large change in pitch and the gyro can't keep up with it and causes oscillations.

Another area could be you have a vibration problem. Are your props balanced? Last resort, check if you can change the frequency on the FC.

I'm so happy with the results of changing the propeller! The pitch oscillations are almost gone. The craft is now flying much better than before I really appreciate your kind and helpful suggestions, Mr L edge and everyone else who supported me. You saved me a lot of time and effort. Thank you so much for your valuable insights!

Test Flight Video

 

[L Edge]

I'm so happy with the results of changing the propeller! The pitch oscillations are almost gone. The craft is now flying much better than before I really appreciate your kind and helpful suggestions, Mr L edge and everyone else who supported me. You saved me a lot of time and effort. Thank you so much for your valuable insights!

Test Flight Video

Assuming you are going into transitional and then forward flight, suggest you spend time learning how to hover in and out of the ground effects first. Notice, when you up eye level or above, the plane reacts much smoother, go lower and its all over the place(ground effects),
So you need to spend flying time how to handle above and passing thru ground effects. You should be able to lift off, go thru the ground effects and hover(same procedure then with 5-10 mph winds) and then land almost in the same spot.

Now others would argue that you have autolevel and you don't need all the practice, but let's say your dare it, trying to return from forward flight to hover, up 25 ft and gusty 5 mph wind, and you are probably going to crash it, nor land it. So feel comfortable before trying the new stuff. It is the same approach to flying helis.

 

[mathirj]

Assuming you are going into transitional and then forward flight, suggest you spend time learning how to hover in and out of the ground effects first. Notice, when you up eye level or above, the plane reacts much smoother, go lower and its all over the place(ground effects),
So you need to spend flying time how to handle above and passing thru ground effects. You should be able to lift off, go thru the ground effects and hover(same procedure then with 5-10 mph winds) and then land almost in the same spot.

Now others would argue that you have autolevel and you don't need all the practice, but let's say your dare it, trying to return from forward flight to hover, up 25 ft and gusty 5 mph wind, and you are probably going to crash it, nor land it. So feel comfortable before trying the new stuff. It is the same approach to flying helis.

Thank you for your valuable guidance. I am grateful for your generous sharing of your experience and knowledge. I agree that mastering the skill of hovering and flying in different wind conditions and altitudes is essential, especially when transitioning from vertical to horizontal flight.
I need to practice more in the Q stabilize mode before transitioning. I have not tried auto tuning yet due to some technical issue and bad weather conditions.
I hope to overcome these challenges soon and improve my skills. As a beginner in this VTOL segment, I welcome your suggestions and advices in the future.

I sincerely thank you for your guidance and suggestions. I value your time and support.

 

[mathirj]

I have a problem with rear motor drop during the flight. I tried replacing the motor but it did not solve the problem. I would appreciate any advice or suggestions on how to fix this issue. Thank you for your time and attention.

Video & Flight Log

 

[L Edge]

If both motors are cutting out, did they overheat or is Esc hot? Vibrations or poor electrical connectors might be your problem. So recheck every electrical connector from battery to ESC to 3 wires into the motor which could cause a quick short?


Also, your battery C rating could be near the upper end and kick off one of the motors. I had a number of episodes with EDF's. Increased C rating and problem went away.

It said throttle disarmed? Could that caused it thru software not programmed properly? Maybe someone could comment on that if possible.
Thinking a quick acceleration(+ or -) of tail, program did not know what to do so it shut of motor?

 

[mathirj]

The front two motors are functioning properly and there is no problem with the motors or the ESC. The rear motor is the only one that is causing trouble. I checked all the ESC power connectors and signal connectors and they are fine.

Regarding the battery C rating, the whole system consumes 60 A in the bench testing. I am using a 25 C 8000 mAh LiPo battery that can deliver up to 160 Amps. So I don't think there is any issue with the battery C rating.

I still can't figure out what the issue is. When there is oscillation, the motor shut down happens most of the time.

Decreasing the propeller size reduces the oscillation significantly. But then the rear motor gets hot. When I switch to a larger propeller, the oscillation comes back and then the motor shuts down.

Can you help me figure out what's wrong and if it's a software or hardware issue?

I really appreciate your time and support.

 

[arslanwali]

Hello everyone, i was looking for answers for my VTOL’s problem and stumbled upon this thread. I’ve built a FT bronco with VTOL(that’s what I am for) i am using pixhawk2.4.8, front 2 motors tilt and are directly attached to emax ES 3054 digital metal gear servos. After arming when throttle is given the tilt mechanism jitters uncontrollably. Please guide how to correct it or find the fault.
video’s url is below for a better
understanding

IMG_4460.MOV

drive.google.com

 

[mathirj]

Hello everyone, i was looking for answers for my VTOL’s problem and stumbled upon this thread. I’ve built a FT bronco with VTOL(that’s what I am for) i am using pixhawk2.4.8, front 2 motors tilt and are directly attached to emax ES 3054 digital metal gear servos. After arming when throttle is given the tilt mechanism jitters uncontrollably. Please guide how to correct it or find the fault.
video’s url is below for a better
understanding

IMG_4460.MOV

drive.google.com

Hello @arslanwali

I had a similar issue with my servos. They were jittering because they shared the same ground pin from the power board with the ESC. I solved it by using separate ground pins for each servo and ESC.
If it not the case for you then try to use some high torque servos similar like RDS3115 MG Digital Metal Gear Dual Shaft 15 kg.

 

[arslanwali]

Thank you for getting back! What do you mean by sharing the same ground pin? I am using pixhawk 2.4.8 powered by the power module and using a 5v bec for powering the servo rail.