Hi Geoff,
That should work. It looks like you have 165 pwm from MID to MAX. And that may be all your linkages will accommodate.
A 450 heli will probably be more responsive than larger ones by its nature. All you can do is turn up the P gains .01 at a time until you get undesirable oscillations set in, then turn it down to the last known “good” setting so that goes away, and make sure it’s stable in Stabilize mode. Just make sure to do that at low altitude maybe a 1/4 meter off the ground because if the heli goes into a rapid roll oscillation it may be uncontrollable.
Then try Loiter and see how well it performs there. If you can’t get P gains up in the .1 range you’ll have to increase the feedforward (VFF) and I gains to get it to perform decent in Loiter.
Headspeed plays a role too. The helicopter will be more responsive and “twitchy” with higher headspeed than lower. So tuning with the headspeed you intend to use for normal flight is the best thing to do.
Once everything is tuned so it flies nice I adjust the AHRS trim values:
AHRS_TRIM_X,0
AHRS_TRIM_Y,0
to get the heli to hover pretty much hands off in Stabilize in no wind. Those settings are in radians, so .017 is one degree. Positive values will make it nose up and roll right, negative values the opposite. It is possible you have a perfect installation with your autopilot perfectly level and true, but I notice they are zero. So if it tends to want to drift one way or another in Stabilize you can adjust those to make it to stay stationary in no-wind conditions. That compensates for your autopilot being mounted in the frame a few degrees off.
And then there is this setting also, which adjusts for tail rotor “side blow” that makes a helicopter drift away from the direction of tail rotor thrust.
ATC_HOVR_ROL_TRM
I do not know the correct procedure to set that. I assume that when you calibrate your accelerometer the AHRS trim values should be calculated and automatically entered in the params during that procedure. And in theory, you should have a heli that hovers perfectly except for the tail rotor side blow. And then you can adjust that parameter to get it to hold stationary. However, I’ve never done that. Mainly because my flight controller never seems to get mounted exactly perfect, nor is the accel calibration exactly perfect in coming up with the right AHRS trim values. So I adjust the AHRS trims until the heli stops drifting and leave the ATC_HOVR_ROL_TRM at the default of 300. And that seems to work fine.
I do know that adjusting the AHRS trims makes takeoff far less dramatic because the heli just lifts off pretty much straight up instead of taking off in the direction of being out of trim. After adjusting those AHRS trims this is an example of a hands-off takeoff with my 500 in Acro flight mode. I did not touch the cyclic at all until a few seconds after the heli was airborne and it takes off really nice even sitting on unlevel ground. Adjusting those also makes it less work to hover the heli because you’re not constantly fighting it to keep it in one spot in hover.
Since your AHRS trims are all zero, I thought I’d mention that.
Editing to add a WARNING:
DO NOT take off in Acro flight mode by trying to “fly” the heli on the ground before liftoff. Just like most FBL units, the Pixhawk will “store up” stick inputs on the cyclic before liftoff in Acro mode and it will cause a very interesting few first moments of flight. You could even flip your heli over if you get carried away with it and don’t catch it right away on liftoff. Just leave the cyclic alone in Acro for takeoff until the skids leave the ground, and everything will be fine. I would not try any takeoff’s in Acro until you get the heli tuned, trimmed and know it flies fine in the other flight modes.
This is not necessarily a “flaw” in the software - it is the way flying in rate mode works with a helicopter.