Well I feel better now. I'm always a little nervous to fly a new ship until the first crash. You never know how she'll deal with adversity.
I was flying FPV in loiter at ~15m when it suddenly pulled hard right and back making a nice arc into the ground at about 20kph according to the telemetry log. The current jumped from the ~30A normal to over 60A in the few seconds of the death plunge. When I got there the motors were spinning and wouldn't react to transmitter commands including disarm. All the props were broken of course.
Looked through the logs a bit, but I can't tell what happened. If anybody cares to take a glance and give me some insight, I would be very grateful. I don't mind when things go terrible if I can at least understand why it happened.
The damage seems to be limited to a couple of cracked arms and a few other frame bits. The GoPro was fine thanks to the waterproof housing. Not even a broken antenna on the 3dr radio or video Tx! I'm taking it all apart tonight and checking the electronics, they got covered in snow, but no physical damage that I can see so far. I'll upload some pics once Iphoto stops crashing every time I try to get them off my camera. There must be weird solar weather or something going on today, I've never had a problem getting pics off of my camera before, really strange...
I'll have to upload my tlogs from the windows machine, just a minute.
: )
Comments
I have everything disassembled at this point. I'm going to just rebuild into MkII with some fundamental layout changes.
I will definitely do more testing in the future. I have been a fool for not using this excellent logging and tuning capability. Having flown RC for so long I think that I tended to rely on in flight tuning methods almost exlusively. With this telemetry stream and a tuning stand I could have really eliminated a lot of potential issues, it won't eliminate crashes, but diagnosing fault could be a lot easier if there weren't so many possible causes on the list.
I just checked mp hud, bearing stays rock solid even with the APM tilted to extreme roll. Of course this is out of the airframe now just held in my hand with USB connected.
I'm using the uBlox LEA-6 and the auto-learn tune.
In this build all the ESCs and their power distribution were ~35mm above the APM with the mag on the daughter board, I have ferrite on everything, but I worry that messes with the poor mag even more.
I'm rebuilding in a new configuration with everything spread out much further.
I get that nav reacted to correct it's position in a too aggressive way, that's probably my fault for flying in loiter without tuning the nav PIDs enough. This machine is fairly powerful (4s/770kv/12x4.5 prop).
Why did it go against my stick inputs though? I don't understand why it thought the loiter point was somewhere else?
Here's the ESC layer which sits above the flight control layer-
Oops..little typo above.
5. AC dev team will make loiter less aggressive when far from the loiter point. Really the response needs to be non-linear....when you're close in it needs to try to blance aggressively but we need to back off that aggressiveness a bit when you're far from the target.
Joshua,
Yes, the MP always shows a + configuration even if your copter is in the x configuration.
I've been thinking about this a bit more and I think we have a combination of things we need to do to solve this:
All this together has surely got to solve the issue completely.
Emile, disregard my above comment about the video not being aligned with flight log, starting at :43 it's a continues clip with no edits until the touchdown , so yes, even with the .5 sec lag it's obvious that actual heading was almost 90deg counterclock to what the nav_bearing graph shows in last part of the flight.
Also, it's not shown in the above photos, but I had a small 10A v-reg giving 5v into the minimosd on the video side, it was fed by the 3s battery powering the vid- Tx, and was mounted between the Tx and the minim board. One more source of noise in the picture.
I put ferrite everywhere, some are just token attempts as I only have a couple of wraps on them. My intention was to remake the short cables with a reasonable number of wraps on the next version, just wanted to get everything laid out. It's tight especially when the upper ESC plate is mounted. I really need an external mag(early APM 2 adopter penalty).
I looked at the "magfield" log and see a change during the crash event, but I assume that is just because the craft is moving. If the current jump to 60A caused interference that makes sense, but why did the auto pilot ask for this dramatic increase in a direction opposite my inputs? I assume that in loiter my stick inputs are supposed to be constantly changing the desired loiter position.
If my GPS lag is only .5sec then the nav bearing graph is definitely off from what was actual. Am I correct that the icon in the MP flight data map is + even if config is set to x?
The video has been truncated in a few spots so it will not match up with the flight log in real time.
I am using the power module which should be able to supply the gimball servos. Next time I will use the BEC rail to power the servos
Joshua,
Ah right. The nav_bearing is the direction towards the waypoint so that's the direction it thinks it needs to go in to get to the target point. So really it's recognising that the direciton of the target is changing...but it really wasn't successful getting there.
The GPS lag is about 0.5sec on the ublox and about 1sec on the mediatek. We don't use the gps for heading in anyway but it would be involved in the nav_bearing in the graph.
My guess is that it got confused about it's heading because the sudden throttle up of the motors interferred with the compass. We've got some code on the way, probably for 2.9.1 that will help compensate for that.
Randy, I think the heading deviation I was commenting about is just normal GPS lag after researching a little, is this correct?
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