Hi everyone I have a question on pid tuning suppose i have a copter with mtow 4kg and i tuned it and later i changed the mtow to 2kg then
Will my copter become overtuned?
Will my copter oscillate?
Do i have to tune again by switching to original values first and then tune?
The question is likely not in the right category, I assume it’s a quad or other multirotor, not a helicopter.
I assume that MTOW is the actual weight of the flying copter, not the theoretical maximum take-off weight. In the latter interpretation, it’s theoretically possible to only change the characteristics that impact tuning very slightly.
Assuming your previous tuning is tight enough, it will become overtuned. A twofold decrease of mass is a very significant change. The particular behaviour depends on the circumstances, from sound change and current increase, to visible quick oscillations, to burning your motors and/or ESCs right at the start.
Assuming you have not rebuilt everything from scratch using diferent parts, I would recommend not to switch to the original values (which original values? the defaults that are only good for one particular copter?), but by downrating the existing tuning and starting from there. If you follow something like Ardupilot Methodical Configurator by @amilcarlucas, you may note that a lot of initial steps are not affected by the weight, and if you went far enough with the tuning of the original machine, you probably know some of the features of your frame (resonances etc). My approach would be to:
ATC_RAT_{PIT,RLL,YAW}_{P,I,D});ATC_ANG_{PIT,RLL,YAW}_P);ATC_ACC*, the names have changed a bit for these in 4.7) by a factor of 1.5;and to do a quick test flight. 2.5 is 2 with a safety margin, and 1.5 is also 2 with a safety margin. If everything goes well, it should fly okay-ish, maybe with a bit less precision than the original one, but likely without any severe oscillations, and should then be ready for autotune, that in turn can finish quite quickly and with few surprises. But obviously some care should be exercised.
Hi thanks for the reply
Talking about my setup it’s a 24inch Copter which original weight weight was 7.2kg but later it crashed because of shorting in esc. And now I reconstruct the drone with weight 5.2kg(because first one has 2 batteries with weight 3kg and payload weight 1kg & Now I have removed my payload and only using 1 battery with weight 1.5kg).
And yesterday when i was flying with this less weight then drone was oscillating a lot in loiter and was taking off at 70percent throttle.
Now i don’t understand why this drone is oscillating.
We would need to see an exact description of the parts (battery details, motors, props, ESCs) and a .bin flight log.