NOT maintain Altitude in AltHold & Loiter Mode if RC3 in Central stick

ARDUCOPTER 4.3.6 running on CUAV V5+ .below is the system used
Hobbywing X9 propulsion system.
12S power system . 34 inch propeller.
Skydroid T12 Rc system

As per the Tuning instruction i have made all the setting and collected flight log with INS_LOG_BAT_MASK = 1 & INS_LOG_BAT_OPT =4

as per above FFT log i have found
INS_HNOTCH frequency as 30
INS_HNOTCH BW as 15 with

i have attached log below also in google drive;
i have changed Althold flight mode and copter is not maintain height as if i increase the RC3 height of the drone keep increase in height even i keep the RC3 to center position to stop the drone i have to down the RC3 and again Centre to stop the drone. Similarly for height downwards also.
I have seen RC3 while flying its well Centre position. this is happend in Loiter mode too.
here is the log: Hobbywing X9 Propulsion System Agri - Google Drive

Note: i have another drone with same FC and propulsion system but that drone doesn’t have this issue. only change is firmware AC 4.3.3

The problem is there’s slightly too much vibrations, making the attitude control and motor outputs just a bit too noisy for there to be a consistent hover state. Have you got a photo of the flight controller and mounting?

Other than that, it looks like you are doing everything right so far.

I’m a bit worried about the battery type - is it Lipo or Li Ion?
I assume there is a generator since the voltage stays around 51 volts during flight.
This could be too high for Li Ion batteries and you might have to adjust that maximum generator voltage down to a maximum of 50 or 49 volts.
I would adjust the MOT_BAT and all BATT values based on the standard values for the battery type.

I would set these - even for “testing”

Yes its generator Powered hybrid drone with Lipo battery connected parallel to it for emergency land incase of generator failure.

The Flight controller mounted with rubber damper because of this is ICE engine based drone.

I would set these to suit your generator
but those wont change the hover performance unfortunately.

The problem appears to be the rangefinder altitude, which differs greatly from the baro altitude and GPS altitude (which do correlate)

Sorry to forget to say that i don’t installed any rangefinder and main altitude source is GPS bacause the baro is affecting too much .


Then why don’t you set RNGFND1_TYPE to 0 ?

@dkemxr have you seen my parameter has any RNGFND parameters enabled ? i have checked my parameter file after @xfacta clarification there is no rangefinder parameter enabled.
if i enabled it i would get prearm error that not getting any data from it since no sensor i was attached.

Sure it’s enabled. As an analog rangefinder.

And, it doesn’t just mysteriously show up in a log if one is not enabled:
Rnfdr log

But you are right about one thing. The barometer looks like shit.

Since this is a large copter and possibly flying missions at relatively low altitude, I would invest in a different GNSS unit like the CUAV Neo 3 Pro which has a barometer built in, M9N chipset which supports up to 4 simultaneous constellations and CAN connection.
If you have it mounted on the nice stand these come with the Barometer should be above most prop wash and should be much more reliable.
There are other similar units but without the barometer (from Holybro for example) and even having the higher-end or more modern GNSS chipsets (M9N, F9P) could give improved altitude accuracy.

This drone has CUAV Neo 3 which same Ublox M9N but it serial version not CAN version.

Yes, but the Pro has the barometer too, and putting the baro up high in the GNSS unit out of the prop wash makes a big difference.
You could probably get a standalone baro and put it somewhere out of prop wash, but it wont be as neat and tidy as the Neo 3 Pro

If i use neo 3 pro over top of the prop wash area will it work? I have one doubt that if baro on openly placed with direct sunlight will have poor performance?

The Neo 3 Pro has the baro properly mounted inside and it’s not subject to sunlight as far as I know.
I’ve seen logs using the Pro and the baro readings where particularly good.

If you use a separate baro you would have to find a way of housing it, maybe in the existing GNSS case, or probably on the under-side of the GNSS unit. Maybe it could even be connected to the existing I2C wires.

The standard baro within the flight controller should actually be OK if you’ve got a suitable cover over the whole area to minimise prop wash.

The CUAV shop might be indicating the Neo 3 also has a baro - I’ll try and contact them and find out for sure, because yours is not showing a baro.

I got a reply from Lindy at CUAV which linked to the documentation

The CUAV Neo 3 Pro has

  • MS5611 barometer
  • RM3100 compass
  • STM32F412 (probably for integration and CAN comms)

The CUAV Neo 3 just has

  • IST8310 compass

You might accidentally enable the Range Finder 0

The range finder input is analog pin and it is propably the noise, then the Attitude controller will try to keep up with desired terrain altitude even when the drone was staying at the same position.