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What is the benefit of RTK for sUAS's when conducting Bridge Inspections?

jaja6009

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Hello,

I am trying to get all of the information possible about how an sUAS like the Matrice 300 RTK benefits from having an RTK fix when flying under a bridge. I do get the precise location benefit, but what is the benefit in regards to the sUAS losing signal.

We lost a Mavic 2 Dual due to being under a bridge. The Dual had very strong signal to controller strength but GPS satellites dropped down to 7 and the drone flew backwards at a high speed with no controller input and hit a column placing it out of service indefinitely.

I do realize that RTK will involve more constellations such as GPS, Glonass, Beidou and Galileo so you will have more satellites available.

I was just wondering what other benefits I am missing.

Thanks!
 
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Hello,

I am trying to get all of the information possible about how an sUAS like the Matrice 300 RTK benefits from having an RTK fix when flying under a bridge. I do get the precise location benefit, but what is the benefit in regards to the sUAS losing signal.

We lost a Mavic 2 Dual due to being under a bridge. The Dual had very strong signal to controller strength but GPS satellites dropped down to 7 and the drone flew backwards at a high speed with no controller input and hit a column placing it out of service indefinitely.

I do realize that RTK will involve more constellations such as GPS, Glonass, Beidou and Galileo so you will have more satellites available.

I was just wondering what other benefits I am missing.

Thanks!
Sorry about your drone loss.

Out of curiosity how big/wide was the bridge (width as in how many lanes, not span length)? Just trying to get an idea of how far from the edge/clear sky view when it dropped some of the satellites. I’ve flow inspections under small wood deck over steel girder bridges without any issues but they are truly “baby” bridges in size.
 

R.Perry

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I have flown my Mavic Pro in underground garages where I had no GPS and it flew perfectly. Were you doing a autonomous flight under a bridge, if so, that won't work, you need at least 10 satellites for autonomous flights.

Maybe someone else has other opinions but I see no need for RTK to do bridge inspections. Actually I'm wondering if RTK is really worth it unless your a licensed surveyor.
 

jaja6009

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Sorry about your drone loss.

Out of curiosity how big/wide was the bridge (width as in how many lanes, not span length)? Just trying to get an idea of how far from the edge/clear sky view when it dropped some of the satellites. I’ve flow inspections under small wood deck over steel girder bridges without any issues but they are truly “baby” bridges in size.
Its not a particularly large bridge, but it is a 4 lane concrete and metal bridge.

There was work being performed under it and I was preplanning it for our Fire Department since there were high angle rescue and water rescue implications.

I was under the bridge for about 1 minute when satellite count got under 10 and down to 7, then when satellites went up to 8 or 9 again the aircraft lurched backwards at full speed into the column marked in the image included.
The excellent members on the MavicPilots forum looked at my flight logs and came to a consensus.
It was similar to people who have had Phantom 4's flying indoors where they suddenly went from not enough satellites to greater than 10 only to have the drone fly into a wall with no stick input.

I too have flown indoors and have never had a problem, but something happened and the aircraft "jumped". The flight log shows that there were no stick inputs. The flight log also shows the sheer confusion the aircraft had as it shows it flying forward in circles, when in reality it flew a perfect straight line backwards into the column.

I think RTK would of helped as there would of been more satellites available. My non-RTK drones show far fewer satellites than my Phantom 4 RTK.

My inquiry here is more about how RTK is inferred in marketing for something like the Matrice 300 RTK for bridge inspections.

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Dave Pitman

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Did you have obsticle avoidance on? And if you did, did you have the "back up" function turned off?

Sorry if you've already gone through all of this. I know of others that have had their craft back up and make contact with something else when obstacle avoidance kicked in. And I think that aspect is turned on by default.
 

Dave Pitman

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My inquiry here is more about how RTK is inferred in marketing for something like the Matrice 300 RTK for bridge inspections.

I believe the advantage of RTK is that you can fly automated misssions much closer to objects because of the precise known location of the craft. Have you seen marketing where they say it is better for instances where gps is limited, like under a bridge deck? If so, like you said, it may be just because there are more constallations available to it but that is just a guess.
 

jaja6009

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I believe the advantage of RTK is that you can fly automated misssions much closer to objects because of the precise known location of the craft. Have you seen marketing where they say it is better for instances where gps is limited, like under a bridge deck? If so, like you said, it may be just because there are more constallations available to it but that is just a guess.
Obstacle avoidance was on. I was probably 20 feet in front of the column when the aircraft then shot backwards.

I have not seen it directly state in marketing that the reason is constellations, but it was my guess as I thought about why it is better.

It has been the only time any drone I am familiar with has done anything that myself and others cannot fully explain. I assume the aircraft met criteria from its sensors that it was unable to deal with. There was also the fact that it was over water which can confuse the Opti-Mode vertical sensor, and the compass could of been confused with the sheer amount of metal that made up the bridge. While Mavic Pilots crash gurus gave their valuable opinion, there was no consensus on why the aircraft did this. I used their findings in my official work Accident Report and that along with the flight log showing a very professionally conducted mission, and this made it so there were no disciplinary issues. This more served as a lesson learned and made it so more focus was made on all of our pilots having to fully understand satellite counts, GPS, Opti and Attitude modes.
 
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MikeA

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Obstacle avoidance was on. I was probably 20 feet in front of the column when the aircraft then shot backwards.

I have not seen it directly state in marketing that the reason is constellations, but it was my guess as I thought about why it is better.

It has been the only time any drone I am familiar with has done anything that myself and others cannot fully explain. I assume the aircraft met criteria from its sensors that it was unable to deal with. There was also the fact that it was over water which can confuse the Opti-Mode vertical sensor, and the compass could of been confused with the sheer amount of metal that made up the bridge. While Mavic Pilots crash gurus gave their valuable opinion, there was no consensus on why the aircraft did this. I used their findings in my official work Accident Report and that along with the flight log showing a very professionally conducted mission, and this made it so there were no disciplinary issues. This more served as a lesson learned and made it so more focus was made on all of our pilots having to fully understand satellite counts, GPS, Opti and Attitude modes.
Not to beat a dead horse, but I am interested in the incident. Were you in normal flight mode or atti?
 

jaja6009

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I was in P-Mode and the drone did not appear to go into Attitude mode. It was hovering rock steady. Without warning it went straight back into the column at a high rate of speed with no stick input. It almost survived. After impact it fell onto the base of the column, bounced and then went into the water. For a second though it teetered on the edge before falling in. I did recover it, but her flying days are over.

I am not sure if this will work, but I uploaded the text flight log to Phantom Help. Here is the link. But as I said I do not know if this will work.

 
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R.Perry

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Looking at the flight log you may have experienced an IMU failure. Reason I say that is because you will notice a loss of VPS for 0.3 seconds and then NA at the last recording. You had satellite connections but were dropping connections as well. I don't believe 9 links is enough for navigation, or the IMU had issues because of the loss of links. Also notice the IMU warning that was displayed.
So why not have it repaired? Or at least see what it would cost to repair it.
 

jaja6009

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The great members who do the crash assistance on Mavic Pilots, stated the IMU error was from after the crash. If you view the log, everything that is in the log after the last stick input (13 min 14.1 s) is not in any way indicative of what the aircraft did. It never moved forward or in the erratic path. It only flew straight back into the column, then fell and tumbled.

The aircraft went into salt water where it sat for 45 minutes until waders were brought on scene to recover the aircraft. We will never trust this aircraft for public safety missions again. We did replace it with an aircraft with a much better payload in the Autel Evo 2 Dual. But I do miss the Mavic 2 Enterprise Dual, it was rock solid until it wasn't.

Meta4's expert opinion:

How close to the bridge column do you think the drone was immediately before this happened?
Also could the Right Front Motor high RPM and no current be from the crash?
It will be as a result of propeller damage from the collision.
I am currently trying to write up an after action report with all findings about contributing factors to the accident and crash. I have already documented bad pilot decisions on going under the bridge, not aborting when satellites dropped in number
You had 5 seconds of flight (13:09.3 - 13:14.4) where the bridge blocked enough of the skyview to affect satellite reception significantly.
The flight controller was not confident in the location data for that period and the drone would have effectively been in atti mode for that period.
That is not necessarily a problem and just requires additional caution if flying close to obstacles.
The drone was safe and stable during that 5 seconds of the flight.

But after satellite numbers returned the data shows a discrepancy between indicated speed and GPS speed.
It's a bit hard to explain but it looks like the drone may have "jumped" to catch up with where it thought it was, which would account for the sudden unexpected movement.

The drone collided with something at 13:17.1.
Any error or warnings after that are a result of the collision, not indicating a cause.
In 0.3 seconds the pitch angle went from +65° to -77° while the drone rolled over 169°.
that was the cause of the IMU warning.




Link to full thread, and again I say, thank you to those great members who put in their time to help me come to a conclusion that went into an official Accident report as well as an After Action report.

Read through the whole thread, it is very interesting to watch these guys pick apart the flight log and come to a conclusion.

I take responsibility for the decision to go under the bridge, but I needed to be under it to capture the underside directly under the bridge lanes as well as where the drone was pointing pre-crash as that was the temporary stairs to reach the temporary walkways under the bridge. I log training hours flying in Attitude mode and am pretty decent in being able to recognize when entering into the mode, fly in this mode or hold a somewhat steady position.
No one at first believed me when I stated that I had zero stick input and the aircraft just jumped. People assumed that I must of been playing around or of been BVLOS. I am in an associates degree program for sUAS Field Technician and by far have the most flight hours of anyone in our program and due to that I have seen and been part of multiple accidents and crashes. Others seem to think that sUAS aircraft are perfect and can never have an incident unless it was from pilot error. I unfortunately have seen 5 different manufacturer's sUAS do all kinds of crazy things and am no longer surprised when something happens.
 
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Dave Pitman

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No reason why you should not have flown under the deck when you had good situational awareness and were prepared to fly in ATTI mode. These craft are very good but certainly not perfect.
 

Dave Pitman

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He was in the P mode the entire flight.
Sure. But the craft drops into ATTI when it looses gps lock. You don't have to manually flip the switch. Although that might have been a good idea when heading under the deck. Apparently it only lost lock for a few seconds and got.confused. Had it just stayed in ATTI it could have been okay.
 
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