I finished building my 3DR Y-6 kit last weekend and was excited to get out an fly it. I flew it a couple of times at my house and it seemed to be okay so I took it to a local park so that I could check it out more. For the first three flights at the park it seemed to fly okay for the first few minutes but then it seemed to drop out of the sky and crash. Luckily the altitude that it dropped from was only a couple of meters and the park has thick grass and relatively soft dirt so it did not damage the hexacopter. After it crashed I checked it out and seemed to be okay so I flew it again for a few minutes and it crashed again. I checked it out again and it did not seem to be damaged so I tried it again. It again flew okay for a few minutes but then crashed again. This time it broke one of the props and I did not have any spares so I was done flying it.
I took everything home and decided that because I have a lot of the APC 10 inch props I would change the lower props to all of them being APC 10 inch ones so that I could go flying again.
After changing the props I flew it again at my house and it seemed to fly okay so I took it to the park again. I started off with a flight of about nine minutes at a maximum altitude of about two meters to see how it would do. It seemed to fly really well so I continued with three more flights with each flight going higher and farther from the launch point. The maximum altitude was about 20 meters and the maximum distance from the launch point was probably about 75 meters. The hexa really seemed to fly very well without any apparent glitches. I was still concerned that I did not find a reason for the previous crashes so I would continue to fly and hopefully it would not have any issues.
Later that day I flew the hexa and after a few minutes it crashed from an altitude of about 5 meters. This time it came down on a hard asphalt road and broke the bottom tail motor off as well as breaking more props and some of the landing leg parts.
I have been trying to think of commonalities that could help find the cause of the crashes but I have not been able to conclusively come up with anything yet. Looking at the Data Flash logs it seems that the power shuts off abruptly without me lowering the throttle. The battery voltages seem to be okay with the last crash occurring at a battery voltage (under load) of 10.5 volts. During the flight immediately before the crash flight the battery voltage (under load) was in the high 9 volt range and the Hexa flew wonderfully.
I have attached the logs from several of the flights so that others can review and see if they can come up with any possible causes of the crashes. Log #13 is the last log for the flight that crashed. Log #12 is the log of the flight before the crash that was a wonderful, long flight without any issues. I have also attached a PDF of some screen shots of the data plots that I was looking at to try to determine what the problem is.
I am really interested to see what the community may come up with on this.
Thanks,
Replies
Looking at the .log files, it looks like all of the motors are shutting down at the same time but then sometimes they seem to come back on but by that time the Hexa has fallen and does not seem to be able to recover. Looking back over the several crashes I seem to remember that at least some of the motors where running when the Hexa hit the ground.
The battery voltage has been okay during the crash sequences as well as the supply voltage to the APM. What could cause the motors to be commanded to go to no power?
Any help from the community would be greatly appreciated as I do not have any confidence to fly the Hexa at this point.
Thanks,
Hello Oliver,
I received the replacement lower motor (to replace Motor #1) and various spacers on Friday from 3DR and installed the parts. I replaced the neccessary props and checked everything out. I also set the Datalogs to collect the data for the motors (MOT) as you suggested.
I did a check flight at my house and then went out to the park. I took my computer so I could get the tlog files. For the first flight I started off flying at about 2 meters so that if the Hexa crashed it would not hurt it too much. I flew the whole battery which was about 10 minutes without any issues. Through out the rest of the day Saturday, I flew nine or so more batteries of about 10 minutes each and did not have any issues. During those flights I flew quite high (up to about 27 meters) and fast (up to about 17 meters/sec.). I also tried agressive yaw inputs to see if that would cause any problems. All of the flights were good and I was beginning to think that maybe the replacement of the motor solved the problem.
On Sunday morning I went out to the park to do some more flying and on the first flight, less than one minute after take-off, the Hexa crashed. It crashed the same way that it had done before. The motors just seemed to pretty much shut off and the Hexa fell out of the sky.
The Hexa fell from about five meters onto the grass and dirt. The crash broke one prop and two of the landing gear. I took the Hexa home and was able to repair the Hexa so that I could fly it.
I took it out to a smaller and closer park so I could fly it to see if it would crash again. I was able to fly the Hexa for two batteries of about 10 minutes each with no problems.
I have attached the log and tlog files from the crash and the log file from the flight after the crash. I hope that we can figure out what the problem is.
Thanks,
Dale
2013-11-03 08-54-08.tlog
2013-11-03 20-12 25.log
2013-11-03 20-14 27.log
There are five errors in the log :
- Battery failsafe trigerred (line 7265)
- i2c bus errors (starting at line 7349)
- Compass read error (line 7352)
- GPS data lost (line 7367)
- GPS failsafe trigerred (line 7441)
The last four errors are certainly caused by a disconnected or broken GPS module during the final impact. The first is simply a battery low event. Battery failsafe is disabled so it has no effect except logging.
The real cause in certainly a motor stopped on the left front arm or a propeller not fastened enough on the hub or a problem with an ESC.
You can see that in the Roll / Pitch graphs around line 7320. You did ask a strong pitch input (full stick), but the copter did pitch the opposite, and it did roll at the same time to the left, when you did not ask that.
Did you remember why you did ask for a strong pitch command ?
I would check each motor a few times on the ground during a few minutes at a high throttle (be careful, strongly attach the frame to the ground to do that and stay away) to find where is the faulty component.
For next flights it could be useful to enable motor logging.