Copter took off at full throttle in PH

[SuperSharpShooter]

I've just spent some time trying to tune altitude hold. I had been making reasonable progress, until my copter took off at full throttle while in position hold. At the time, I had PH engaged, and I was flying it back towards me, but it was going quite slowly, so i think I ended up giving it full pitch stick, and it just took off full speed upwards. I flipped it back into manual to save it and bring it back and land. I'm very keen to try and understand how and why this happened to make sure it cannot happen again. I have a serious lack of trust in this thing at the moment.

Just before this flight I changed the throttle factor to be in line with the formula to make it hover at 700 on the radio. (Corrected Factor Throttle = Current Factor Throttle * Value read from graph / 700). My previous throttle factor was 0.53 which made it more or less hover in manual mode (~830 on the radio channel), and pretty much hold altitude in PH, whereas following the formula it suggested 0.63, which makes the copter climb rapidly if I switch out of position hold back to manual, but brings my radio hover throttle to 700 in manual mode. I still needed to have the throttle at about 860 on the radio to hold alt in PH after changing this.

My alt hold PIDS are:
Nav Alt Speed P = 200
Nav Alt Speed I = 3
Nav Alt Position P = 0.2

Here's the clip of the log which shows it. You can see while in position hold earlier it made a single large jump in altitude that I caught (around 10k in the log).

Please help!

[SuperSharpShooter]

It just did it again. Looks to happen when a large pitch stick input is given while in PH.

[Max]

I'm a bit confused about your throttle setting. Basically what happens in AH/PH mode is that the throttle channel value is taken and 700 is subtracted from it. Any deviation from zero, which is outside the set throttle deadband, becomes the climb/sink command to override held altitude. In your log, the throttle channel is is ~870 while in PH. So either you have a very high deadband set, or it should have been climbing most of the time.

In the log it kinda looks like a lot of vibrations got set up as you were pitching the craft back towards you. The gyro and accel sensor magnitudes start fluctuating more and more while you're holding the pitch stick back, and eventually those get too high and it starts to climb. At that point the vibrations and your motor roll/pitch values go nuts. There's even a strange radio_quality dip in there (possibly from Rx vibrations?).

I can't state the cause, those are just my observations.

-Max

[SuperSharpShooter]

OK thanks for looking at this. Yeah I have the deadband set to 100, but I'll try cutting that back to 50.

When in PH, I need to have the throttle at that level so that it will hold the altitude relatively stable, otherwise it sinks. I've never been able to get it to exactly hold altitude, it's always slowly climbing or sinking.

I've just double checked my radio settings. I have it set so that the travel is from 0 to +1400, but mid stick on my remote shows up as 870 in qgc with the throttle factor set to 0.53. Just testing now, changing the throttle factor to 0.63 doesn't change the mid stick value in the radio setup screen at all.

So I'm not quite sure how to get the throttle value to be 700 at mid stick?
Edit: have just put an offset of -25% on the throttle channel so now mid stick is at 700, but the max tops out at 1350. I'll recalibrate the ESCs and see if this helps.

[Max]

If it's sinking in altitude hold mode when your throttle is within the deadband, you have something else going on. Possibly a poorly calibrated board. Keeping the throttle above the deadband isn't a real solution.

If your tx range is 0-1400, how come 700 isn't the center? Do you have a throttle curve set up? In my Tx I can set the high/low/mid points separately (actually I use 5 points for throttle to give a bit of expo around hover position). You definitely want a value of 700 for middle position (as seen in QGC radio values). You will not see the effects of throttle factor in the reported radio values, since it does not directly affect the radio input value itself.

Lastly, your ESCs should be calibrated to the AQ output, not your Tx. Specifically, they should be calibrated to the range specified by Motor Start and Motor Max parameters (Special Settings in QGC, 1125/1950 by default).

-Max

[DUKE40]

Hi Max,
How Do You calibrate the ESC's to the range of the AQ?
I could Not find a procedure for this in the documentation.

[Max]

Duke, read this post and mine right below it.

viewtopic.php?f=33&t=1446#p5869

And yes this needs to be in the docs... keeps coming up.

-Max

[SuperSharpShooter]

Max, I'm not sure why 700 wasn't in the centre of my stick with the limits set to 0 and 1400 at the extremes. When I set it up I figured 700 would be in the middle if the start was 0 and range was 1400, but not so. There were no curves or anything applied.

I'm going to hook my tx up to my APM2 board so that I can see the PWM values and adjust the limits of the throttle channel to be 975/1950, and then calibrate the ESCs with that.

The AQ board is back in the freezer. I'm going to start from scratch (again!) with the calibration and see if I can get this f*cker to finally perform.

[Max]

[SuperSharpShooter]

Ah yes, oops.