Why did my drone hit a tree?

I’m trying to create a mission where my drone flies a loop on the side of a relatively steep mountain. In order to make this safe, I enabled “Use Online Elevation” and then programmed the mission so the first waypoint was 2 m above the ground, the second waypoint is approximately in the same location but 30m up, and then all the subsequent waypoints were 30 m above the ground.

This all goes well until it passes Waypoint 10. At Waypoint 10, the drone reports that it’s 95’ above the ground which is darn close to perfect. The ground elevation at Waypoint 11 is 21m higher than Waypoint 10, and 40m away, but as the drone leaves Waypoint 10 it never increases altitude. By the time it reaches Waypoint 11, it’s actually slightly lower than it was at Waypoint 10, and that’s about where it impacts the tree. Took me 90 minutes of hiking and bushwhacking up a 30 degree slope at 9,400’ altitude to get to the drone’s landing spot.

And yes, after that I did look up to find out how you tell the drone to stop what it’s doing. I went home, adjusted the mission to fly at 50m above the ground, and went back to try it again. It headed straight for the same tree! This time I did abort the mission and bring it back home safely.

Here’s what’s really strange - in both cases (the first mission at 30m above the ground, and the second mission at 50m above the ground) the “height above takeoff” never exceeded 500 feet, even though the limit is supposed to be 500m. Is it possible the drone thought it had hit some ceiling, and so refused to go higher?

I am flying a DJI Mini 2 using Litchi v4.24.1-g.

Do not trust online ground settings. And set the height of the points yourself about the take-off points.

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I came close to crashing my Mavic Pro into a palm tree and thereby learned that when the elevation of the terrain over which the drone is programmed to fly Litchi waypoint missions happens to be HIGHER than the launch point elevation, the drone may wind up flying as much as 50 feet BELOW the altitude the user set for the drone to fly above each successive waypoint.

In other words, for DJI drones under Litchi control which are launched from any location that is lower in elevation than the flight path’s course, it is essential for the altitudes above each waypoint to be increased significantly at the flight planning stage using Litchi Mission Hub, to ensure adequate terrain clearance as the drone heads uphill.

Conversely, when launching a DJI drone on a Litchi mission from a point that is of higher elevation than the terrain over which the flight path is vectored, the drone will actually fly between 20 and 50 feet higher above terrain than was intended during the flight planning stage.

This sounds like a major bug in the Litchi software. Is there anyone from Litchi monitoring this forum? Can you verify this is a known bug that is being fixed?

This is a user error that everyone is trying to repeat.

@paxxa - If you are aware of a user error, I’m sure both Mad_Pup and I would be thrilled to learn what we have done wrong. Or, if you are willing to help Mad_Pup or I figure out what went wrong, that would also be greatly appreciated.
If, on the other hand, you are just making something up because it sounds good, please refrain from posting. You are not helping anyone by doing this.

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I’m not trying to help you, you read how to use online terrain information, but you assume that mini2 will do everything for you. Litchi has everything right with the height algorithm.

I find it odd that you are not trying to help people, but are posting in the “Help” forum. In any case, you have helped me in a way, which is to convince me that dealing with trolls like you makes this forum useless. Please do reconsider your life choices.


Your toppic:
What is default maximum altitude?

First of all, why would you program a mission using metrics, then viewing the flightlog using imperial?

Post #1
but when I look at the log in AirData, the maximum altitude is 497.7’. Is it possible the drone uses a max altitude of 500’ when the units are set to imperial?

No, that’s were you stopped the mission.
It’s also the height YOU programmed at WP9 (146m=497’).
“the drone was heading straight into a tree (close to waypoint 9) and I quickly aborted the mission and brought it home.”

Post #5
Does “at maximum distance” mean that’s the furthest away from home the drone got on this mission, or that it was reaching the limit of its radio communication?

It means furthest away from homepoint the drone got.

Since you like to cunfuse yourself by jumping between the metrics and imperial system, are you sure you entered the number 500 in Litchi’s AIRCRAFT SETTING ‘Maximum Altitude’ while GENERAL SETTING ‘Units’ was set to metrics and NOT imperial.

To calculate Above Ground altitudes, it is assumed the first waypoint is in the same location as the take off.

This might also explain Mad_Pup’s story (Take off & WP1 NOT in same location).

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It is not any fault with Litchi.

It is Google Earth elevation data, which the drone and Litchi uses.

Google Earth elevation accuracy becomes extremely confused and unreliable
when very close to cliff edges and rapid changes of elevation. eg. deep river valleys.

Probably explains why bridges crossing rivers in Google Earth seem to have melted
down to the river level.

You should set your mission heights relative to take off point, not above ground,
and prefferably fly the route
manually first to check roughly what height the drone should be at what ever waypoint.


Have a look at this topic:

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Excellent, the content of the answers on the topic has finally reached my first answer in this thread, the author would have to learn to read and draw conclusions.