I have a large octo With powerful motors. It's been in the air many times.
I did some work on it today, changing the camera gimbal. I also installed a New 5,8ghz video tx and a trigger Circuit for operating the shutter on the camera. The shutter and video tx were both Connected to the camera. Shutter was Connected to ch6 on the receiver.
I decided to Power it up in the office to adjust the camera shutter channel and test that everything worked. The telemetry system(Frsky Taranis) warned about low RSSI. Since the only new Connection I had made to receiver/apm was the shutter cable, I removed the servocable from the receiver ch6. The telemetry system stopped warning about low RSSI. So, just to check again, I reconnected the servo cable to ch6. I know I should not do this kind of stuff on a live machine With propellers, and luckily I was taking precautions by keeping out of Reach of propellers. Then all hell broke loose...
8 Heavy lift motors With large APC propellers, capable of lifting a total of 20kg went into full throttle. I just let it go and took shelter, while the machine was doing its thing to the ceiling and Office Furnitures, before shutting Down. Most of the propellers and one motor destroyed. Glad to be alive With all my body parts intact. I've been working on multirotors since "the beginning", and had my share of propeller cuts, but thats a long time ago.. It's obvious I needed a reminder again... :)
So... what happened? I'm not concluding With anything, this may not be related to the APM at all. I suspect that the camera shutter in some way made the receiver bring channels high/low. Logfile Attached. Anyone care to do some analyzing?
Replies
Ok. Starting to believe this logfile is not the correct one. It's the only possible log. Other logfiles are from previous flights.
What a horrible story. I'm glad you came out of it without injury. I learned the hard way never to have props on inside as well. Like you it was a case of just doing a quick check on something before going out to fly. I was also lucky with just a couple of stitches required. Thanks for sharing as it will probably prevent someone else from taking a shortcut that they will regret as well. I have never powered a copter inside with props since that event. Of course that makes sense and we all know it, but sometimes we do stupid things.
Thanks. Accidents always happen when you don't expect it. I usually don't do any work on the kopters With props on. But the plug I pulled out and connected was related only to the camera shutter switch, did not expect this kind of issue at all. I think I've learned now, an hopefully, as you say, other who reads this wil also think twice.
Did u accidentally plug it back in reversed?
Yeah I had similar experiences with smaller copters. One with an APM1 leapt off a table and kamikazed into the costliest enemy installation around, my laptop. Turns out that under some circumstances, it floats some signals (nothing rules, just random noise) and this is then amplified and sent to the ESCs. Later is compensated for it by switching off everything mid air.
This was an APM and not a PX4/ Pixhawk?
Regards
Soren
I believe I Connected it the correct way, at least at startup. I'm usually very careful With looking at color codes on wires. But of course,, I can't be sure.
It's a APM.
It's possible that the camera has a very dirty ground or otherwise pulls a large current through the shutter. Tell us more about that shutter cable, do you connect it direct apm->camera or do you use an optical isolation inbetween? The optical isolator reduces the current and removes the need to share the dirty camera ground with the AP.
Can you draw a quick diagram how it's all connected?
Surprised that something actually happened though, because you'd expect the arm sequence would hold the receiver output? Or did you actually arm the machine in the process?
The shutter cable is a no brand type. It has worked for more than a year on another multirotor running a DJI wookong. The shutter cable was Connected to the receiver, not the APM. There is no Optical isolation.
Yes, I've also been thinking about the common ground could cause problems. But I did not arm the APM.
Attaching a diagram.
diagram.jpg
So lets see you were making a change indoors with the props on for what reason?
Indeed. The bigger the props, the bigger the reason to remove them on the bench.
Actually I'm very glad this happened indoors. Outdoors the machine could have flown away, doing some real damage to someone.
Seriously, I explained what happened, don'r need moral pointers. Not saying I did not make a mistake, the evidence is very visible. But I need to figure out what exactly happened, so I can make sure it won't happen again.
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