What happens when a DJI Geo-based altitude limit is reached during a Litchi mission.

[joeruby]

What happens when a DJI Geo-based altitude limit is reached during a Litchi mission with a Mavic 2? 1) will it fly thru it? 2) will it stop and hover? 3) Will it crash into the mountain side it was trying to climb? 4) Will it RTH? The altitude limit in this area is 150 meters (492 feet) above takeoff, and the mission flight plan always stays 102 feet above the ground as it fly's up the mountain side to 582 feet above takeoff. I would sure like an answer to this question from someone that knows the correct answer.
Thanks
Joe Ruby

 

[Facherty]

I'm not sure if I "know the answer", but I did post something relevant here:

Litchi Height Restriction

I couldn't find a simple and modern Mavic Air answer to the conundrum below, despite a wide search. Simply, I had made a Litchi mission to stay within 30m of the ground as the drone climbed and then descended a hill. After I hit the 'play' button and the mission was 100% transmitted to the...

mavicpilots.com

Hope this helps.

 

[joeruby]

I'm not sure if I "know the answer", but I did post something relevant here:

Litchi Height Restriction

I couldn't find a simple and modern Mavic Air answer to the conundrum below, despite a wide search. Simply, I had made a Litchi mission to stay within 30m of the ground as the drone climbed and then descended a hill. After I hit the 'play' button and the mission was 100% transmitted to the...

mavicpilots.com

Hope this helps.

Thank you Facherty. Yes I had the same problem several years ago, so I leave my maximum altitude at the maximum limit (500 meters). You can set that in DJI go4 or in Litchi. So I have to be careful that I don't make a mistake when planning a mission.

My question is related to a limit in the DJI Geo data base (at this location) of 150 meters (492 ft). The ground area under this 150 meter limit varies in elevation by about 150 meters too. So it depends where you take off from.

So here is an even more basic question: What is the reference elevation for the 150 meter limit given in the DJI Geo data base. See the attached photo. I need to answer this even more basic question first. Is it from where you take off? Or is it from the elevation of the airport runway? I have not really thought about this before now.

Maybe I will understand this in stages.

 

[joeruby]

What happens when a DJI Geo-based altitude limit is reached during a Litchi mission with a Mavic 2? 1) will it fly thru it? 2) will it stop and hover? 3) Will it crash into the mountain side it was trying to climb? 4) Will it RTH? The altitude limit in this area is 150 meters (492 feet) above takeoff, and the mission flight plan always stays 102 feet above the ground as it fly's up the mountain side to 582 feet above takeoff. I would sure like an answer to this question from someone that knows the correct answer.
Thanks
Joe Ruby

I now have the answers to the two questions I posted:

• When I uploaded the Litchi mission to my AC while I was at home, there was no warning message displayed.
• When I uploaded the Litchi mission to my AC when I was at the takeoff location there was a warning displayed. “Flight restricted zone nearby” (or something similar). Since this was a test I OK the start of the mission.
• The mission started normally climbing the side of the mountain following the correct path, and when it reached 492 feet (150 m) the AC stopped climbing, but kept going forward along the mission path, the AC almost flew into the mountain side, but just before it hit (at 105 seconds into the mission), the speed reduced some, and then (at 124 seconds) the speed went to zero. Thus the AC did not slam into the mountain side. I was just about ready to hit the “pause” button, but I don’t think I did (need to verify). I think the forward obstacle sensor stopped the forward speed. See the attached file with the mode states, altitude, and speed plotted for your information.
• Now we know the answer to the second (more basic question) the 150 meter limit has a reference from takeoff elevation and not from the airport runway elevation. That is a compromise discussion for another day.
• Note that the mission did not end at this point. The AC stopped and hovered. Even though I had good strong signals to and from the AC, I could not control up, down, forward, backward, left, or right! I could only control yaw. There I am staring at the mountain side ever so close, so I yawed 180 degrees around and looked (FPV) the other way so I could relax and think. There I was, frozen in space, burning battery in a fixed hover!
• At 173 seconds (49 seconds later), my brain finally kicked in and I decided to enter sport mode momentarily to end the mission, and right back to GPS mode where I should have hover control and controls to get away from the nearby mountain side. I could have waited for the battery to burn down to engage the “Smart RTH” mode, but then if anything else happened I would not have any battery reserve left.
• Once in GPS mode, I was able to control away from the mountain and lower altitude down below 400 feet. Then at 203 seconds, I wanted to get back safely on the ground, so I engaged RTH directly, and started to relax a little watching carefully the path of the AC.
• I believe that if I had left the AC to hover until the battery reached the “Smart Return Home” SRTH point, that the AC would have come home safely by itself. Unless this had happened just around the corner of the mountain just out of sight. Then when SRTH, and the AC could not go any higher (because of the 150 m limit), The AC would not know what to do – go left or go right or go down. I think that when the battery reached 10% it would land on the side of the mountain and roll, and bounce, and crash.
• I learned a lot from this experiment.
• 
  
• 
  
• Joe
• KC7GHT

 

[Chip D]

That's actually what I discovered. It made no difference where I created the route (on my computer at the office Omaha, NE) and then flew the mission (on the North side of the Columbia River along the Broughton log chute). The MP uploaded my route, and took off on my great series of waypoints that scaled up the side of a mountain, but when I hit 400' above my takeoff point, it just stopped. Fortunately it was about to hit a Doug Fir. Popped it into Sport mode and returned it to my takeoff point. The only way I can see to do the side of a mountain is to be on top, fly down quickly to a lower elevation, hope you don't burn batts too much, and then start the route. It will always climb back up to your takeoff point, and even another 400' above.
Chip D

 

[joeruby]

That's actually what I discovered. It made no difference where I created the route (on my computer at the office Omaha, NE) and then flew the mission (on the North side of the Columbia River along the Broughton log chute). The MP uploaded my route, and took off on my great series of waypoints that scaled up the side of a mountain, but when I hit 400' above my takeoff point, it just stopped. Fortunately it was about to hit a Doug Fir. Popped it into Sport mode and returned it to my takeoff point. The only way I can see to do the side of a mountain is to be on top, fly down quickly to a lower elevation, hope you don't burn batts too much, and then start the route. It will always climb back up to your takeoff point, and even another 400' above.
Chip D

Hi Chip D,
You might note that my problem was at nearly 500 feet (492 feet , 150 meters), and this was a ceiling limit near an airport. Could you please check and see if you had your "Set max flight altitude" set to 120 or 122 meters (400 feet) for the flight you described. I just want to make sure I understand what happened in my experiment. I think you might have just run into this set max limit, which would happen at every location. Note that for your flight, in the future, you can set this max limit as high as 500 meters (1640 feet above take off)

Thank you for the help.
Joe
KC7GHT

 

[joeruby]

I now have the answers to the two questions I posted:

• When I uploaded the Litchi mission to my AC while I was at home, there was no warning message displayed.
• When I uploaded the Litchi mission to my AC when I was at the takeoff location there was a warning displayed. “Flight restricted zone nearby” (or something similar). Since this was a test I OK the start of the mission.
• The mission started normally climbing the side of the mountain following the correct path, and when it reached 492 feet (150 m) the AC stopped climbing, but kept going forward along the mission path, the AC almost flew into the mountain side, but just before it hit (at 105 seconds into the mission), the speed reduced some, and then (at 124 seconds) the speed went to zero. Thus the AC did not slam into the mountain side. I was just about ready to hit the “pause” button, but I don’t think I did (need to verify). I think the forward obstacle sensor stopped the forward speed. See the attached file with the mode states, altitude, and speed plotted for your information.
• Now we know the answer to the second (more basic question) the 150 meter limit has a reference from takeoff elevation and not from the airport runway elevation. That is a compromise discussion for another day.
• Note that the mission did not end at this point. The AC stopped and hovered. Even though I had good strong signals to and from the AC, I could not control up, down, forward, backward, left, or right! I could only control yaw. There I am staring at the mountain side ever so close, so I yawed 180 degrees around and looked (FPV) the other way so I could relax and think. There I was, frozen in space, burning battery in a fixed hover!
• At 173 seconds (49 seconds later), my brain finally kicked in and I decided to enter sport mode momentarily to end the mission, and right back to GPS mode where I should have hover control and controls to get away from the nearby mountain side. I could have waited for the battery to burn down to engage the “Smart RTH” mode, but then if anything else happened I would not have any battery reserve left.
• Once in GPS mode, I was able to control away from the mountain and lower altitude down below 400 feet. Then at 203 seconds, I wanted to get back safely on the ground, so I engaged RTH directly, and started to relax a little watching carefully the path of the AC.
• I believe that if I had left the AC to hover until the battery reached the “Smart Return Home” SRTH point, that the AC would have come home safely by itself. Unless this had happened just around the corner of the mountain just out of sight. Then when SRTH, and the AC could not go any higher (because of the 150 m limit), The AC would not know what to do – go left or go right or go down. I think that when the battery reached 10% it would land on the side of the mountain and roll, and bounce, and crash.
• I learned a lot from this experiment.
• 
  
• 
  
• Joe
• KC7GHTView attachment 101140

UPDATE:
I did in fact push the Pause Button at 123.7 seconds, and did not push it again to turn it back off. I was about to hit the mountain. See updated plot below.

 

[Chip D]

Hi Chip D,
You might note that my problem was at nearly 500 feet (492 feet , 150 meters), and this was a ceiling limit near an airport. Could you please check and see if you had your "Set max flight altitude" set to 120 or 122 meters (400 feet) for the flight you described. I just want to make sure I understand what happened in my experiment. I think you might have just run into this set max limit, which would happen at every location. Note that for your flight, in the future, you can set this max limit as high as 500 meters (1640 feet above take off)

Thank you for the help.
Joe
KC7GHT

Oops. You are correct, well almost. Yes, I didn't have it set to the max, but in this case, I could only climb 1000' or so as I did NOT have the max set in Litchi. So it went up about 1000' above the Columbia, but then it stopped, thankfully as I hadn't allowed for those Doug Firs.
Chip D

 

[joeruby]

Oops. You are correct, well almost. Yes, I didn't have it set to the max, but in this case, I could only climb 1000' or so as I did NOT have the max set in Litchi. So it went up about 1000' above the Columbia, but then it stopped, thankfully as I hadn't allowed for those Doug Firs.
Chip D

Thanks for checking Chip D. I appreciate that.
Joe
KC7GHT

 

[joeruby]

UPDATE:
I did in fact push the Pause Button at 123.7 seconds, and did not push it again to turn it back off. I was about to hit the mountain. See updated plot below.

View attachment 101149

UPDATE 2:

I have plotted the actual flight path taken from the data fed back to my tablet. Notice that the actual flight path deviates from the desired Litchi programed path very significantly as the altitude reaches the "airport" Geo 150 m limit! At the point where I pushed the "pause" button the desired path was about 85 feet higher than the actual path. I would have expected that the AC would have stoped when it had deviated that far from the programed path, but it didn't stop. It was still going 12 mph and starting to increase speed as noted on the speed curve near the "pause" time. See also the attached actual flight path file below. It sure looks like the AC would have hit the mountain. Maybe the forward sensor of the Mavic 2 would have stoped it.

Should I fly it again to see????

 

[DanMan32]

Height limits in AC is always relative to takeoff point.
The only spec that is not relative to TO but to MSL is service ceiling as that has to do with how thin the air gets at extreme altitudes.

 

[joeruby]

Height limits in AC is always relative to takeoff point.
The only spec that is not relative to TO but to MSL is service ceiling as that has to do with how thin the air gets at extreme altitudes.

Hi DanMan32,

Thanks for confirming that for me. However, that is a compromise discussion for another day.

Right now I am more interested in the surprising large path error during the Litchi mission where the altitude was 85 feet lower than the programmed altitude, and yet the speed was still 12 mph and slowly increasing (see the speed curve just prior to the "pause on" event). I would have expected (desired) the AC to stop, since it was grossly leaving the desired path.

I have flown many Litchi missions, and I have never had Litchi leave the desired programmed path by such a large error. (Litchi/DJI/SKD are you listening?) I am trying to learn as much as possible from this experiment as I can, and thus be prepared for unexpected events on future Litchi missions. Any insight into why Litchi/DJI didn't stop the mission and at least hover, would help me.

Thanks,
Joe
KC7GHT

 

[ratjr15]

WOW! I have had as much as a 30-34ft* variance at landing, but never as far off as you're talking! Then again, I suppose the problem is magnified going that high, as my missions are usually 60m and less.