Crash caused by exposed barometer

Just a reminder for those folk that are running their APM 2.5 without an enclosure. I ordered my APM unassembled as the assembled version was not available at the time. This was just on the transition from 2.0 to 2.5 and even though I ordered a 2.0, I received a 2.5 but with no case (as apparently they were still being manufactured). As a result I am running my APM as a bare board. I have had my quad in the air for about a week getting in as much air time as I can to improve my skills (about three 10 min flights per day).  Till today I have not had any problems and have been very impressed the the APM2.5.

I have previously read about potential issues with an exposed barometer due to direct wind both from movement and prop wash. Unfortunately I did not see reference to issues with the sensor in direct sunlight and this was the cause of my problem. I have my batteries mounted above the APM on my quad so they mostly protect the board. However, they certainly do not shield the board from ALL angles.

Yesterday I got out of the house nice and early and it was a nice bright sunny day. Due the the early hour, the sun was pretty low in the sky. I flew the quad for a few minutes in STABLIIZE mode with no trouble and then switched to ALT_HOLD at about 5m high. At first this was just fine and I was practising my nose in flying. All of a sudden the quad started randomly jumping up and down by a few meters or so. After doing this a couple of times it just dropped to the ground where it seemed to be dead. Unfortunately I did not have my wits about me and left the APM in ALT_HOLD mode. I took a couple of steps towards what I thought was a dead quad and all of a sudden, it took off down the field horizontally at about 1m high before crashing for good about 50m away. The end result was a broken motor mount and prop.

After looking the logs I see that the barometer has intermittent periods of 'noise' where the reported altitude fluctuates wildly by up to +/-300m. I did some research online and came up with a couple of cases where it is reported that direct sunlight can have an adverse effect on the barometer output. I tested this for myself by taking the quad outside while connected via USB and holding it at an angle that allowed direct sunlight to fall on the barometer sensor. Sure enough the altitude started going crazy. The fix was as simple as putting a piece of sticking plaster over the sensor. Needless to say, an AMP2.5 case is next on my shopping list...

I know this information is out there, however for the newby it is not that easy to find and easy to overlook. The consequences can be disastrous - in my case I was lucky and with spares on hand  I was flying again by the time I could re-charge the battery. Others may not be so lucky...

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Replies

  • T3
    Great post. I was not aware of the sun light issue. Thanks for sharing.
  • I experienced the same thing and I have my Baro shielded., I think there is an issue with APM 2.9.  I have the Min OSD where I can monitor the telemetry interlaced on my video from a gopro.  I was on the ground had not even started, and I was seeing +_400 foot swings in altitude on the ground.  Never experienced this before switching to APM 2.9.  It happened only once.  I reset the board and everything was normal.  I have not had it occur again but the odd thing is I never seen this on 2.8

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