Just been playing with my good old Funcopter.
I replaced long ago the gyro with a futaba GY401, but was still not impressed by the result as I had to bump the gain to 100% , which was still not enough and causing some troubles as I had to cut the gyro at full stick deflection in order to regain control of the aircraft in windy conditions.
I initially though I could use one of my retired flight controller as a yaw gyro using TxPID, but soon decided to give autotune a try... The funcopter is a "safe" heli : low head speed, extreemly stable out of the box which makes it a good candidate for a test that was likely to end-up in a crash!
Step1 : find a flyable set of PIDs with TxPID
As an initial step, I had to find a set of PIDs suitable for this heli. TxPID helped me a lot. Based on my experience on the GY401 I had no fear in bumping the Yaw rate (ended up with P=120 & I=40). Regarding the cyclic, dialling the inner loop was hopeless, but bumping the gain of the outer loop (P=110) helped me to regain control of the cyclic. Without this amount of gain, there was not enough authority (i.e aircraft not responding to stick input).
Step2 : play with autotune
Once the aircraft was somewhat flyable I went to the club and started the aircraft, with a custom flight mode (manual / manual / axislock) then tried horizon and finally lauched autotune. Total failiure... The aircraft was barely wiggling, but at least I knew autotune was flyable (i.e not dangerous) in my backyard. Back home I decided to increase the actuator effort for Roll and Pitch, little by little I ended up at 0,3 and finaly got a tune! You should have seen the big smile in my face when this heli started wiggling like my MiniOwl.
Roll tune is good (thanks guys for the graph in the autotune tab), Tail and Pitch were odd. Tail was mushy and Pitch was bouncing. So I decided to apply different damping and sensitivity on each axis: Roll with default settings, Pitch with Max damping and zero sensitivity, Tail with max sensitivity. DRonin is not providing the feature to apply different sensitivity and dampening on each axis, but this was just a mater of writing down the values for each axis while I was playing with the slider.
In the end the only wrong settings was for outer loop: suggested value was 24: I needed 110 in order to have enough "stick authority". Still have to find a sweet spot for this outerloop with TxPID.
15minutes of autonomy on a 2600mah battery and now flies like a huge quad: this opens tons of new possibilities