Slow-Mo tip over after landing

[DroneRanger]

Been flying my TH for years and this was my first crash. Uneventful video mission and returning to home manually. After gently touching down and holding the throttle down fully, the motors never slowed but seemed to pulse and then increase RPM slowly. The H started to tilt to starboard and the port gear leg came off of the ground. It continued this motion while I was keeping the throttle held fully down and now I pressed the motor stop/start switch. It continued tilting slowly until a prop hit the ground and then the H just skittered across the ground on its side. The motors would not quit no matter how long I held the button down, but they eventually shut off after a couple of props broke off. So it evidently detected the imbalance or the weird attitude and killed the power to the motors. Damage was limited to some scuffing, 4 broken props, and the camera snapped off, requiring the body mount to be replaced.

Has anyone seen or heard of this behavior before? Is there a log I can access on the H or ST16 that might shed some light on what happened? I keep going over the incident in my head and cannot figure out what went wrong except for some electronic failure or hardware issue.

Thanks!

 

[Vaklin]

Very possible the right (rate) slider is with some problems. You can check it on the available monitors in the ST16. There also you can find the log file. The topic is widely discussed in the forum. Also important for us to know is do you are equipped with RealSense or not.

 

[WTFDproject]

..... Is there a log I can access on the H or ST16 that might shed some light on what happened? ....

Yes. It's called FlightLog and it is stored on the ST16,
Use the instructions below to upload the file to the forum for review. DO NOT open the original file before uploading it. Opening the file corrupts it in a way that it cannot be opened by the program created by @h-elsner.

Dropbox

www.dropbox.com

 

[Vaklin]

Just to add some advice for future situations like this one. Any flight apparatus has two safety places, on the air and landed and steady. All transition maneuvers are more dangerous than these two stable positions. Landing is the most sophisticated, so everyone should be ready to reject it and return to the air, where safety is more. RTH in this situation will have to save the drone, but if it was airborne before.

 

[DroneRanger]

Just to add some advice for future situations like this one. Any flight apparatus has two safety places, on the air and landed and steady. All transition maneuvers are more dangerous than these two stable positions. Landing is the most sophisticated, so everyone should be ready to reject it and return to the air, where safety is more. RTH in this situation will have to save the drone, but if it was airborne before.

Understood and agreed. However, in this case performing an emergency liftoff with the aircraft (AC) at an ever increasing angle would, in my opinion, introduce even more variables and issues than continuing to try for a safe motor shutdown while still on the ground. Rejecting the landing was not an option because the AC had already landed and, other than the spinning props, was motionless......at least it was motionless for a moment after touchdown before the tilt started.

I keep wondering if I was inadvertently touching the right stick after touchdown and I caused the issue. I certainly hope not, but that is what I am hoping the flight log will show, or not.

 

[DroneRanger]

Thank you everyone! (and in particular WTFDproject for the comprehensive flight log retrieval instructions). I will hopefully extract the file later today and then post it here for analysis.

Much appreciated!

 

[DoomMeister]

Please be aware that we need the Telemetry, Remote, and RemoteGPS files for that flight to do a proper analysis. For the issue you are having the Remote.csv is going to be a must along with the Telemetry.csv.

Keeping the folder structure by following the instructions gives us more than that flight, but also allows us to see a trend in control issues from previous flights that can occur with the ST16.

The attached document gives some background into factors affecting control.

 

[Vaklin]

Understood and agreed. However, in this case performing an emergency liftoff with the aircraft (AC) at an ever increasing angle would, in my opinion, introduce even more variables and issues than continuing to try for a safe motor shutdown while still on the ground. Rejecting the landing was not an option because the AC had already landed and, other than the spinning props, was motionless......at least it was motionless for a moment after touchdown before the tilt started.

I keep wondering if I was inadvertently touching the right stick after touchdown and I caused the issue. I certainly hope not, but that is what I am hoping the flight log will show, or not.

Tested by me in the same condition and the bird goes up very well. Lift power gives stability. The copter was H+ but this doesn't matter relative to the topic.

Check the ST16 controls in the HW monitor as well as in the final output monitor. You'll find the source of the problem there I guess.

 

[DroneRanger]

Please be aware that we need the Telemetry, Remote, and RemoteGPS files for that flight to do a proper analysis. For the issue you are having the Remote.csv is going to be a must along with the Telemetry.csv.

Excellent advice. I will be sure to include that. Thanks!

 

[DroneRanger]

Tested by me in the same condition and the bird goes up very well. Lift power gives stability. The copter was H+ but this doesn't matter relative to the topic.

Check the ST16 controls in the HW monitor as well as in the final output monitor. You'll find the source of the problem there I guess.

Copy that. I had tested with the HW monitor prior to flight, but did not do so with the final output monitor. Good advice.

 

[DroneRanger]

Very possible the right (rate) slider is with some problems. You can check it on the available monitors in the ST16. There also you can find the log file. The topic is widely discussed in the forum. Also important for us to know is do you are equipped with RealSense or not.

Sorry that I didn't answer this earlier, but the H is not equipped with RS.

 

[phoonflyer]

Been flying my TH for years and this was my first crash. Uneventful video mission and returning to home manually. After gently touching down and holding the throttle down fully, the motors never slowed but seemed to pulse and then increase RPM slowly. The H started to tilt to starboard and the port gear leg came off of the ground. It continued this motion while I was keeping the throttle held fully down and now I pressed the motor stop/start switch. It continued tilting slowly until a prop hit the ground and then the H just skittered across the ground on its side. The motors would not quit no matter how long I held the button down, but they eventually shut off after a couple of props broke off. So it evidently detected the imbalance or the weird attitude and killed the power to the motors. Damage was limited to some scuffing, 4 broken props, and the camera snapped off, requiring the body mount to be replaced.

Has anyone seen or heard of this behavior before? Is there a log I can access on the H or ST16 that might shed some light on what happened? I keep going over the incident in my head and cannot figure out what went wrong except for some electronic failure or hardware issue.

Thanks!

Ive had every kind of weird landing in a 480 you can name. I read somewhere, after my 3rd or 4th landing like you described, that landings should be done in rabbit mode as opposed to turtle. I know it doest answer why, and it seems counterintuitive.....but it works!

 

[Vaklin]

Turtle mode is designed only to face slow-motion pictures or video taken over/near the people which, from their side, is needed due to rules requirements. This should not affect the throttle but the reality is slightly different. The situation is even worse with an RS installed.

 

[Vaklin]

Just took one more look at the throttle behavior in a turtle position. The full down left stick position should not produce a landing scheme execution in the FC, because the turtle is strictly related to a flight near the people. With the RS the copter stays 2+ meters over the ground and has no force that can land it. Without it, landing is possible in some conditions, such as a very calm wind, but every burst will turn over the copter.

BTW the pilot can override this landing scheme, which I do almost the time, but this is not related to the discussed crash.

 

[Steve Carr]

I've experienced these types of landings many times on the H480 and twice with the H Plus.

As @phoonflyer mentions, always take off and land in Rabbit mode. There can be several causes or a combination of causes. Unlevel ground, slight wind or wind gust, movement of the right stick or yaw input, ground effect from the prop airflow hitting the ground and lifting the H.

Anytime the Flight Controller is fighting a bad touchdown (tilt), it will try to level the aircraft. When this happens it will ignore stick input or the red button. The exception is full throttle. So it will take off and level itself if you immediately go full throttle for just a couple of seconds.

The best method to avoid a bad landing is to press and hold the red button right before touch down. The H will land and shut off the motors very smoothly. I do this often when the landing conditions are not ideal. It works every time I use it. By pressing the red button before touch down I believe the Flight Controller aborts it's auto-level function and goes into the shut down routine.

 

[Vaklin]

As the real aircraft. Full throttle plus instinctive buttons (AP & auto trust off).

Pressing the red button is not the best decision. If the landing goes not as expected, the right solution is full-throttle, safe altitude, enough time to resolve the situation, and the next attempt to land.

 

[DoomMeister]

Ive had every kind of weird landing in a 480 you can name. I read somewhere, after my 3rd or 4th landing like you described, that landings should be done in rabbit mode as opposed to turtle. I know it doest answer why, and it seems counterintuitive.....but it works!

The document I attached explains why. With the Rate slider in turtle the full down throttle does not give an output low enough to idle the motors so the aircraft is still buoyant. Once the aircraft tilts past a certain point the motors arm/disarm switch is disabled by the onboard F/C.

 

[DroneRanger]

Just to be perfectly clear, this was not a "bad" touchdown or landing per se. There was no wind, the landing surface was level concrete, and upon touchdown the AC did not rebound or bounce, but settled as it normally does. Prior to touchdown I was in hover around 1-1.5 ft. over the surface and pulled left stick slowly down as normal and held it down after touchdown. Several seconds elapsed before the erratic motor behavior and the tilt started to occur.

 

[DroneRanger]

Please be aware that we need the Telemetry, Remote, and RemoteGPS files for that flight to do a proper analysis. For the issue you are having the Remote.csv is going to be a must along with the Telemetry.csv.

Keeping the folder structure by following the instructions gives us more than that flight, but also allows us to see a trend in control issues from previous flights that can occur with the ST16.

The attached document gives some background into factors affecting control.

Thank you for that additional data document. I will upload those files shortly.

 

[Vaklin]

Prior to touchdown I was in hover around 1-1.5 ft.

This one kills the automated touchdown sequence. My opinion is defective potentiometer is on the right slider but let us see the logs. Also, keep in mind any path command (right stick moved in any direction) is not recommended near the ground. To stabilize the bird the best solution is full throttle.