I’m kinda new to the Pixhawk but the other morning I had somebody testing out a new aircraft on manual mode and everything was working well.
In the afternoon I took it out again and a few seconds after the pilot had made a successful take-off the aircraft decided to do a couple of loop the loops before plunging nose first into the ground. While this was happening the motor could be heard slowing down then speeding up again all whilst the throttle was set at 100% on the transmitter.
I’ve looked through the log and can see RC In and RC Out for the throttle drop down to zero almost right away then increase to roughly 5% then zero again over and over again. This was not what happened on the transmitter! The timeframes don’t seem to match up against the actual flight either (Please see the video - https://www.youtube.com/watch?v=87sfS37V_Uc).
Now obviously that’s just the throttle but that can’t explain the manoeuvres the plane made either. I’m totally confused why it all happened and I can’t work out why.
I think you had RC dropout. There are 2 graphs below one for the RCIN which is what the pixhawk see’s coming from the RC receiver and the other is RCOUT which is what the pixhawk sends to the servos. Because you were in manual mode both were identical which is good. However, notice how when you throttle (blue line) goes to min PWM all your other RC channels “flat line”. I think you will find that’s the default behaviour of your receiver to put throttle to min and output the last known value when it loses contact from the transmitter. Look at the end when they flatline and the plan goes up slightly then heads straight for the ground.
So you might need to do a range check, see where you have placed the receiver in case of interference. Not sure how you powered the receiver but was the battery low? Was your transmitter battery low?
Hope this helps.
Thanks, Grant.
I had suspected a range issue but it couldn’t have been more than 70m away from us when it happened.
I had a battery which goes to the motor speed controller and then into the Pixhawk for power and for control.
The battery was quite new and had only flown one flight beforehand (perhaps 1-2mins in length). I haven’t had a chance to test the battery yet but I should be able to tomorrow. Would you not expect some other indication from the log that there was a loss of power?
At the crash site we did a quick test with the operator standing in the same position as he was before and the servos moved without issue. I’ll perhaps try another test.
Just seen in the last few seconds of your video that you had your transmitter antenna pointing at the plane.
This is a big no no, the tip of the antenna has the weakest signal strength. Try and keep the antenna bent so that the side of the antenna is towards the plane.
Not sure if (in the log) RSSI and RemRSSI are actual RSSI values but, if they are, it would indicate a massive signal loss which could be explained by the antenna orientation.
My friend has a new Spektrum DX7g2 with the antenna fixed in the upright position. It can barely manage a range test if you point it at his plane, but as soon as you change the angle of the transmitter so the side of the antenna points at the plane, the range test is increased by at least double.
[quote=“MarkM”]Just seen in the last few seconds of your video that you had your transmitter antenna pointing at the plane.
This is a big no no, the tip of the antenna has the weakest signal strength. Try and keep the antenna bent so that the side of the antenna is towards the plane.
Not sure if (in the log) RSSI and RemRSSI are actual RSSI values but, if they are, it would indicate a massive signal loss which could be explained by the antenna orientation.
My friend has a new Spektrum DX7g2 with the antenna fixed in the upright position. It can barely manage a range test if you point it at his plane, but as soon as you change the angle of the transmitter so the side of the antenna points at the plane, the range test is increased by at least double.[/quote]
Doubled? I’d never would have guessed that! I honestly didn’t think it would make that much difference. I assumed the reason the antenna folded was for transportable reasons more than anything.