Autotune is divergent in pitch. 'Copter screws itself into the ground


I have what used to be a Quanum Nova / CX-20 with a genuine APM running firmware 3.2.1. The Autotune mode is set up to a combination of switches.

In Autotune a sequence of moving the stick to the left for two seconds, to the right for two seconds, etc., gives an improvement in roll; after a few similar movements in pitch the 'copter starts oscillating in pitch then becomes divergent, inverting and powering itself into the ground. Its almost as if the gain is being changed in the opposite direction to that in which it should be heading The APM is correctly oriented, magnetometer calibrated, accelerometers calibrated. External GPS and compass installed.

Any suggestions would be appreciated. I have been trying to get this to fly half decently for over a year on-and-off and am running out of patience. It flies but the loiter is terrible and even in stabilise it tends to wander off. I’m beginning to think it would be better to install a trained mouse and a joystick, shouting directions to it via a megaphone…

(Similar to this)

I recently built a 600-class all-aluminum quadcopter with an APM2.8 clone board running AC3.2.1. I actually found auto-tune to be a bit flakey and just about lost mine to a crash before I gave up on it and just tuned the PID’s manually, the old way. It flies beautifully after manually tuning the PID’s, but it is a bit more time consuming.

In Loiter, the default speed is set to 500 cm/sec. I’ve found that needs to be cranked up for decent Loiter performance or it won’t even hold itself in 10 mph wind. I cranked mine all the way to 2000 (44 mph) max speed in Loiter, which allows the aircraft to pitch to the maximum pitch setting and provides decent handling in Loiter mode.

In Stabilize your 'copter will always drift away. There is no horizontal positioning, except from pitch and roll input by the pilot. If it drifts in no wind conditions, and always seems to drift the same way, you need to set the X and Y trims in the Full Parameter List. You may have calibrated the accelerometer but the APM board may be mounted in such a way on the aircraft that it is not level with the props. Just a couple degrees, that you cannot see with the naked eye, makes the difference between an aircraft that will hover stable in no-wind conditions, vs one that drifts. That’s what those trim settings are for, and it is recommended to use those instead of the trim tabs on the transmitter, which should be centered. I’m not familiar with the Quanum Nova or its radio, as I use a FRSky Taranis and scratch build my aircrafts. But the trim settings should apply to all.

@Hugh_Neve Are you moving the sticks left and right to tune the quad?

Hi @Tim_D,

Yes, left and right for approx two seconds, as per here

Hi @ChrisOlson,

It always seems to wander off to the left in stabilise - too much to trim out.

I think I will reduce the pitch PID parameters by a chunk and then try and work upwards. In the UK at least this year has got to be the windiest year for ages. All I am waiting for is a break in the weather…



Drifting to the left while facing the rear of the aircraft should require a positive value for the X trim. I think autotune is more for Plane than 'Copter. My quad will easily do 28 m/s at full pitch. When I tried the Auto Tune it took off like a rocket sled on rails and rapid stick movements became absolutely dangerous with a powerful 2.5kg aluminum missile topped with 16" carbon fiber people slicers on it spinning at 6,000 rpm. So I stopped that procedure before something bad happened and set both the P and I to the same value and made repeated flight tests until I got the response I wanted, but without any twitching in hover. Then lowered the I values to about 75% of the P value. I ended up with a very responsive crisp handling aircraft, but stable in hover and am happy with it.

As I mentioned, in Loiter you also have to set the maximum speed allowed, which was set to 500 cm/sec by default. Even with the PID’s set to maximum in Loiter the aircraft was sluggish handling until I cranked up that maximum allowable speed. In Stabilize and Alt Hold, the maximum allowable pitch also has a bearing on how responsive the aircraft is. That was set to about 45 degrees if I remember correctly, and I changed it to 60 for a powerful, fast, snappy handling aircraft.

Those are some of the things you can check, and I went to making the adjustments in the Full Parameter List instead of using the sliders in the extended and advanced tuning tabs.

@Hugh_Neve Are you running copter or plane?

This is what you do for copter…

Your not doing the autotune right. With copter you dont move the sticks. The copter will twitch left and right by its self. No wonder your having issues.

Oops. :flushed:

Thanks for clearing that up. I now just need a calm day.