Bug #30

ultrasound malfunction when flying over grass

Added by Some Body 1716 days ago. Updated 1326 days ago.

Status:New Start:21-08-2010
Priority:High Due date:
Assigned to:- % Done:


Target version:-


Today i'm flying with the drone in my garden.
After a few seconds flying over 20cm high grass,
the ARDone display an ultrasound alert and ascend into heaven.

Any sink commands from the iPhone App were ignored from the Drone.
After the drone was 40 - 50 Meters over the ground the landing command reached the drone and she survives this bug.
(the altitude lock was on)

Bug reproduce:
- Fly over medium high grass (20cm -30cm)
- ascend to 3-5 meters
- "ultrasound alert" comes up
- drone go's up in the air

Any idea what's wrong?


Updated by jean charles mammana 1711 days ago

I had exactely the same problem with the impossibility to landing without pressing emergency shutdown...
Conclusion: He brokes into crashing to the ground....

Updated by Martin Schleusener 1711 days ago

same problem here.

Updated by Philipp Reichart 1708 days ago

Happened to me, too, today: Flying in a park over grass, configured for outdoor shell, outdoor flight with height limit enabled. Suddenly the app displays "ultrasound alert" and the drone starts rising to about 20m and drifts with the wind over some trees --- any landing or emergency signals were ignored. After passing the trees it landed 100m away rather rough on another patch of grass.

This behavior is really bad, it should decrease altitude in case of error, not rise :/

Updated by M FJ 1708 days ago

Same here indoor: my advantage: the drone was trying to lift the roof of my house :-) so I was able to capture the drone with the landing command. I agree with Phillipp, that looks like a sign error or the wrong action code in case of a lost sonic signal.

Software 1.4

Updated by Tommy Kammerer 1697 days ago

I am able to reproduce this too.

Updated by Antoine Ferran 1697 days ago


Could you give us a little more details about this, to help us understand?

What commands were you sending when this happened? Did you ask the drone to go up? Was it hovering?
How fast did the drone went up?
Did you try to press the landing button? the emergency?
Did you ask the drone to go down? If yes, How long have you been pressing the button?
Was there some wind? how strong?

When ultrasounds are not available, the AR.Drone is controlled by accelerations because it has no way to know if it's going up or down.
That means that if you ask the drone to up and release the button, it will continue on it's momentum for a time. You have to ask the drone to go down and hold the command until the upward acceleration is canceled and the downward acceleration starts.

We are investigating this issue, and the more details we have the better.



Updated by jean charles mammana 1696 days ago

Hi Antoine,
So, I broke two drones because of this problem :/
Each time I was over 50cm/60cm high grass and then I ascend to 3 meters (with altitude limit activated) I had "ultrasound alert" and the drone start to goes up really fast.
All my tries to ask the drone to go down or landing failed and the drone continue to goes up until 20/30 meters (six floors building).
As he started to drift near the trees I had to press the emergency button.

Maybe it could be usefull to add a manual override gaz control to avoid this kind of problem...


Updated by Henning Theune 1693 days ago

Hello Antoine,

my two drones behave the same way, even indoor about 2,3 m high over short pile carpet (carpet with short fibers). I got the ultrasound alert and the drones try to lift the ceiling. Sometimes they do that while I adjust the altitude.


Updated by Paul Nevins 1687 days ago

Same issue here as well.

Indoors and outdoors, it has to do with sudden changes in elevation, grass, or very thin carpet? I have vaulted ceilings at my place, so I can stop it most of the time from flying away when I pass over a couch or carpet. But I agree, no upward movement on ultrasound error would be nice, I would sugges at least a slow decent instead, if not a complete stop in vertical movement until time out tells the drone to decend.

Updated by Philipp Reichart 1684 days ago

When flying the drone with maximum vertical speed settings, it's easy to get past the height limit --- there's just not enough time for the ultrasound sensor to notice and for the firmware to rectify the height.

I suspect this is also what happens when flying over tall grass and other ultrasound-unfriendly ground: It makes the drone rise too fast, effectively jumping above the ultrasound/height limit before the firmware can react --- above that, it obviously can only be controlled by rotor speed like Antoine said above. And due to the "jump" rotors are already running at max speed, so it keeps rising.

I'd like to see the next firmware updated to decrease rotor speed when both (height limit is enabled) and (ultrasound alert is received).

At best, this would prevent any fly-offs and at worst would land the drone.

Updated by Joseph Colson 1662 days ago

I had the same problem. Flying in my front yard which is 180 ft wide by 800 feet long going east to west. The south side is a tree line with heights around 70ft. Grass is cut with a height around 2 to 3 inches. The outdoor shell was attached with height limit enabled. No Wind because of the trees all around me.

Flying with no problem when I decided to take it up a bit. It went up a little and leveled out. When i went up again it jerked up and took off climbing. I did not notice any warnings as I was freaking out watching it climb into oblivion. When it cleared the tree line the wind up there was blowing to the south and pushed the drone towards the trees while climbing. I attempted to turn the drone into the wind and tried to bring it back but that lasted for a second or too before I lost all control. I pressed the emergency button but it was too late. The drone stopped responding and continued to fly south climbing. I lost site of it and didn't hold much hope. Well I must be pretty lucky because I ended up finding it on the ground only about 2 feet from a canal approximately 300 feet away. The unit sustained minor damage to the blades which I can only assume was from falling through the trees.

So what is one to do? If I want to get some height for some nice house shots it will take off out of control? How is this useful? What settings would be best to avoid this behavior? I got real lucky I didn't lose my $300 toy the first day!

Updated by Hai Tran 1643 days ago

I had the same problem last week resulting in a crash and a broken Central Cross.

The bigger problem is that Parrot won't ship the replacement part to Australia, and whilst Amazon ships the drone, the Central Cross is NOT available for order.

Updated by Bob Meyers 1642 days ago

You can add my experience last week to exact same conditions and symptoms. I was out in my pasture of tall grass when it suddenly, rapidly ascended almost out of sight. I could not stop ascent but the emergency cutoff button still worked.

Updated by Martin Lefebure 1621 days ago


The ultrasonic sensor has limitations. When flying over non-reflective ground like some grass surfaces or non-planar surfaces like trees, as no ultrasonic measure is available the user no longer controls vertical speed but vertical acceleration. Hence going back down is reached when downward input has been maintained long enough to zero upward speed and then accelerate downward.


Updated by Normen Hansen 1598 days ago

In my opinion the drone shouldn't do anything when the ultrasound connection gets lost, especially not accelerate (which seems to be happening for some reason in these moments). If this behavior is due to some peak in the ultrasound metering when the connection gets lost it should simply compensate these errors. I was trying around with my drone, aware of these problems and in fact it was just about to shoot in the sky when two seconds later I was pressing the "landing" button which saved my drone.

Updated by MAPGPS . 1491 days ago

jean charles mammana wrote:

Maybe it could be usefull to add a manual override gaz control to avoid this kind of problem...

Command "AT*PWM" is supposed to be a manual override gaz control, but disabled.

Updated by Tuxette - 1326 days ago

I have broken two drones, in an environment with ultrasonic motion sensors. The maximum height was set to 2 meters, and the ceiling is at 3 or 3 1/2, so its attempt to fly and vanish into the heavens is always twarted. Still, on landing, both have broken, and neither has obeyed the landing command (emergency had to be triggered)

So, if there's any advance on this issue, it'd be good to know.

Also, I have got to agree with Normen Hansen, that if it loses its ultrasound, the Drone shouldn't accelerate up (or down or in whichever direction it wants to go); it has broken far too many Drones, as indicated by this bug issue.

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