AltHold drift issue

I’m trying to tune a copter which flew nice (even autotune worked) in 3.3.3. Autoanalysis gave me an error “Empty log… throttle never above 20%”, my thr_mid value is set correctly at 300 and it flys decent in stab. When entering althold the copter slowly climbs or descends it can’t hold alt (this did work in 3.3.3). Barometer readings are clear and vibrations are also within reasonable levels. copter can be considered as pretty light with 245g.
Can you please have a look at my LOG and point me in the right direction.
I can provide also a log with autotune where it twitches ever so lightly but this has been already posted by a lot of people already.


Not sure at all… But the height innovations look relatively high (not an expert…)
So, since the baro looks good and even thought the GPS should not be used in Althold it seems to be related. Btw, I am wondering why you had no Sats in the beginning. Maybe you can make a test under good GPS conditions.
Best regards,

Thank you Thorsten for having a look into the log. Unfortunately this issue also appears if there are enough sat (hdop ~1.4). I had no sats because i was too lazy to wait for full lock (and even with lock no difference). Could you explain to me what do you mean by “height innovations” --> height corrections? Will try to get a log with full gps lock as soon as the wheater permits… :frowning:

There is known bug in 3.4 that means that unless the EKF is operating in GPS mode, it’s height outputs are not being scaled correctly when they are passed to the controller. The way to avoid this is to not take off until GPS arming checks pass, ie you need to be able to arm in loiter mode. The fix for this has been submitted and will be included in the next release candidate.

thank you, checked again today and it seems much better with gps lock. still some climb/descent ~1 m but okayish i would say… hdop was 1.4. next issue autotune :smiley:

Hi, I’ve had the same issues w/ alt_hold in 3.4.
Even under ideal conditions, it always drifts up and down a meter or so.
Same copter w/ 3.3 stays in one spot… (maybe a couple inches drift up and down).

yup, i wonder why. put the testing currenlty on hold as there are too many issues in rc1 for me to use it confidently. autotune is not that important to me it just popped up as i try to do the full cycle of tuning from scratch when updateing.