RTL: Landing problems


I have problems with my RTL landing on most flights (~70%). The copter descends to about 8 m and then the altitude in the planner change to 0.21 m and it just drops to the ground. I have analysed the logs and it is obvious that something is wrong with the sonar, it shows the value 0.21 (distance from sonar to ground when on ground)  during the entire flight. So when the "mixed altitude" change from using the barometric alt to sonar alt, the altitude used for navigation change from 8m to 0.2 in a blink and the copter "thinks" its on the ground and drops to the ground. I have attach a log with this is showing.

Could this problem be something connected to initiating the arducopter over telemetry? If I use USB and test the sonar it always shows the right values.


Set up: APM 2, 3DR quad frame (official set up), 3DR-radio, Sonar: MB1200 XL-MaxSonar-EZ0, 

2012-05-15 21-48 22.log

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  • The sonar is very sensitive.  Mine reacts to a wire fence from 2m above.  You need to be sure the field of view of the sonar is completely clear of anything, including wires.

    There's also a possible bug in the sensor that causes it to stop working at low (near freezing) temperatures.  I had trouble where the sensor was outputing only the mimimum altitude reading (0.2m) in cold weather.  I warmed the whole quad over the heater (carefully) and it came back to life.  Contacted Maxbotix and they said they've encountered such problems and RMA'ed it.  The replacement is on its way.

  • Developer

    Yeah, your sonar alt showed 20cm the whole time. It's no wonder you had issues. Maybe it's getting a reflection from the landing gear? 

    BTW, the sonar is ignored above 8m because of exactly such an issue. If not the quad would have climbed indefinitely.


  • I would try it without the Sonar... My APM2 lands its self no problem... Sonar did strange things so I took it off


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Shivchand Jaysaval liked Shivchand Jaysaval's profile
Aug 25