RTL: Landing problems

Hi!

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.

Jonas  

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

Tags: Landing, RTL

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Permalink Reply by Eddie Weeks on August 16, 2012 at 10:01am

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


Eddie


DeveloperPermalink Reply by jasonshort on August 16, 2012 at 12:28pm

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.

Jason

Permalink Reply by Jonas Bohlin on August 16, 2012 at 1:03pm

@Eddie I thought the APM needed the sonar to do RTL landings, and it would be nice to get it to work.

@Jason I dont think it is anything blocking it, and it works fine when I have it connected to the USB and run test\sonar (APM board only powered by usb). Could it be something in the initiation that sometimes fail? 

I also have a problem of the compass showing 180 degrees off when started with out USB but when it is connected to missionplanner via USB it seems to be right? 

Jonas

Permalink Reply by Dave on August 17, 2012 at 6:55pm

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.

Permalink Reply by MaxBotix Inc on August 27, 2012 at 12:49pm

Hello Dave and the DIY community,

Thanks for comment. During the engineering phase, our sensors are subjected to the full temperature range of -40c to +85c to characterize performance and ensure the sensors operate.  During this original testing, the MB1200 sensors did not exhibit any issues and passed all testing as designed.  After we received a technical support request, we evaluated the behavior of the sensors over temperature and found this rare anomaly (only effecting a very small percentage of sensors) in the temperature performance. We have made a minor firmware and hardware changes to completely prevent the issue.  Since this discovery,  we have issues any replacements we believe that may be related to this temperature performance.  MaxBotix Inc is glad to help anyone requiring support.  Please feel free to send me an email for any of your support requirements. 

Please let me know if you have any questions. Have a great day!

Best regards,

Scott Wielenberg
Technical Support & Sales
of MaxBotix Inc.
Phone: (218) 454-0766
Fax: (218) 454-0768
Email: scott@maxbotix.com

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