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, thanks. I agree,. No, I don't think the APM is to blame either. I think dere is some kind of Brownout, short Circuit, common dirty ground problem or something going on here.
This is an opto isolator that I used to drive my camera and I never had any such problems. On the HV side on the other end, I use a very small 2S battery to provide power:
https://www.sparkfun.com/products/9118
Can you still post a circuit diagram how you connected the vtx and the shutter cable? It sounds as if you power the lot from the APM board, which would not be advisable.
I posted a diagram earlier: http://diydrones.com/forum/attachment/download?id=705844%3AUploaded...
The vtx is Powered from straight from the battery. The shutter cable is getting Power from the receiver, who in turn gets Power from the APM. I think the shutter cable should use very little current, so it should be acceptable. But you gave me an idea, I will check how much current the shutter cable draws.
Ah ok, sorry. I think your issue is actually a ground loop. The ground after the vtx or at the camera may not be at the same potential as the apm's, so current starts flowing through the ground that can be disastrous. The loop isn't there when the vtx isn't there, neither when the shutter is.
Ok, thanks. So, the solution would be a shutter cable where the part that Connects to the camera is isolated from the rest?
Personally, I would optically isolate the circuit right after the shutter, so you'd have the apm+rx+shutter running as one branch and the tx+camera as another branch on the same battery. When you do that however, you also need another battery right after the opto-isolator going into the camera. If the camera has a 5V out, then maybe that can be used (that's the proper ground to use anyway), otherwise you need to add a very small battery. Another disadvantage is that opto-isolator are limited in the current they provide on the HV side (going into the camera), so sometimes that's not enough to perform the actual trigger, then you'd need some more electronics to amplify.
if the Canon + shutter work out of the box, it could be that the vtx is the issue, maybe that regulator is a bit wonky, so switching to a different tx could also help.
Another thing that could work is to give the vtx its own battery and leave the circuit as is.
I'd wait this thread out and see if anyone else has a better solution.
The thing I said about the RSSI was Critical low With the shutter Circuit Attached to receiver. Maybe the APM had a constant brownout and was just not handling anything at all?
Just ordered 2 New replacement motors, props and a New camera shutter. Will keep props off when testing..
I see no increase in current, or ThrOut - wrong log ?
since you have no log of RCIN enabled on your APM, I guess it may be too little data anyway. -
The current sensor is not used. I'm only just using the volt/current sensor to supply the APM With 5V. The ESC's get the Power directly from the battery, not through the sensor. The multirotor is using to much current to Draw it through the current sensor.
then there is no sign of APM commanding that PWM.
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