Completely bad flight behavior of a new helicopter


I have a Vario Bell230 with 1.8 meter rotor. I bought this second-hand and had flown it with a normal FBL system.

Now I have installed a Pixhawk 4 mini with GPS and adjusted it carefully.

For the parameterization I took the parameters from the tuning pages and the improvements from Bill.
I only set ATC_RAT_RLL_P and ATC_RAT_PIT_P to 0.024.
I also use this value in my TREX600 with Pixhawk 4 mini. This woks in the Trex.
Do not know where I have read to these.

The Bell has an H4-90 linkage, but I only use three servos. Servo1, 2 and 5.

Everything works fine on the workbench. The FC counteracts correctly.

A few days ago I made my first test flight in almost windless weather.

I took off in “Stabilize” mode. The helicopter was very restless. I then switched to “AltHold” mode and then to “Loiter” mode. In “Loiter” mode, the helicopter immediately nodded and rolled back and forth wildly. After a few seconds I switched back to “Stablize” and landed the helicopter shortly afterwards.

I tried to find out via the logs what the cause of the behavior is.

With my little knowledge, however, I have not found anything.

I’m probably looking in the wrong place.

Here the parameter file
and the log file.!AjSq727ChpJzdGSrLpnjg1n5Ktg?e=gNT24A!AjSq727ChpJzc9l4abMaDedweXE?e=nrpWuH

I need your help. Thank you in advance for that.



I found some points that i will look after and sort it out.

Why did you only use 3 servos. Are you sure that 3 servos have enough power to control the swashplate. If you are concerned about binding of servos due to the 4 point connection, there is a linearize servo feature that allows 4 point servo setup with no binding.
Read about the linear servo feature in the swashplate set up section of the tradheli wiki.

I might expect this type of behavior if your servos were not powerful enough to move the swashplate under in-flight loads. I do apologize though that I have not looked at your log yet. I just wanted to point this out.

hello Heri

Looked briefly at your logs, your pitch and yaw are not tuned correctly, and it looks as if you’re also having a bit vibration on roll…
You have to refine the tuning, it is not advisable to fly in loiter mode before finishing the tuning.
The data on your log is partial, no battery information, please add it to the logging.


Hello bill,

The VARIO Skyfox mechanics usually have four servos.
Until recently I had used 4 analog Futaba servos. They had 4kg of torque and weren’t that fast. But that was enough to fly with a scale helicopter.

Before installing the PH4 mini, I flown the helicopter with a normal FBL system (Bavarian Demon 3SX). That worked.
When I installed the PH4 mini a few weeks ago, the old Futaba servos couldn’t handle the PH4 mini. Although I left the frequency at 50 Hertz.

That’s why Holger @picoflug recommended servos to me, which he uses in his tandem helicopters. These are digital servos with 11kg torque. And are much faster than the old futaba servos.

Unfortunately, four of them do not fit into the framework of the Skyfox mechanics. Therefore I only use 3 servos. Holger also said that 3 servos are sufficient.

I am familiar with linearization and have already performed it. But thanks for your hint.



Hello @ZvikaF

thank you for looking into the logs.

I do not use the drive battery to power the FC. For this I would have had to re-solder all the connections. Therefore, no log entry is created for this. Log entries are only available for the board’s power supply.

Thought you are flying electric .


yes, I am flying electric.

The helicopter is not new. Only the installation of the PH4 mini is “new”. I have probably expressed myself incorrectly.

To use the power board, I would have had to re-solder all the connections. I do not use XT60 connectors in all models. That’s why I solved it differently. But I don’t think the bad flight behavior has anything to do with it.

I have already looked at my log file myself. The parameter RATE Rdes and R.

I am still a beginner in interpreting the log files.

However, I notice that the RATE R values oscillate. Basically the RATE R value seems to follow the RATE Rdes.

Should I change the VFF values or the "ATC_ACCEL_x_MAX " value? What is your opinion. I think, the ACCEL Max is too high for a 800size helicopter.

I also noticed the vibration values. I checked the mechanics again and mounted another swashplate driver.
Somehow I have the feeling that the vibrations are also influenced by the FC controls.



I would recommend fast attitude and PID logging in addition to what you already have. That will give logging rates of 400 hz and allow you to see rotor vibrations. I recommend you determine the freq of your vibrations and use the harmonic notch to remove the rotor vibrations.
Once I see a log with the PID logged then I can tell more about your tune but it does seem that you might need more VFF based on your plot.


Should I activate “ATTITUDE_FAST” and “PID” in the Log bitmask?

Just to make sure I understood you correctly?

The “harmonic notch” thing is still higher math for me, if you know what I mean by that. :smirk:

Yes activate “ATTITUDE_FAST” and “PID”

ok, I will do that.

I will also set the ATC_ACCEL_x_MAX to 52000.

At the moment it is still at 110000, which is more suitable for a 450 helicopter.
I had not read to change this value for an 800 helicopter.
What do you mean, should I do this too?

Hello @heri

The battery info adds to the understanding on the power demand of the helicopter.

This will happened if the installation of the FC is not dumped as a reaction to the vibration.

That’s OK… you have to start somehow :slight_smile:

VFF and RAT_xxx_P are the first parameters to adjust in order to get the heli react accordingly.
to my understanding ACCEL_x_MAX effect the agility, and should be adjusted to the characteristic of the heli.

Bill knows best :slight_smile:

Please excuse me, I learned English at school here in Germany. That’s enough on vacation.

I do not understand your comment, however.
Would you be so nice and would you formulate your statement in more detail. It would be very helpful to me. I want to understand. Many Thanks.

Yes, to see the consumption of the engine is definitely interesting. And I will take this into account for a new helicopter to be built. And take advantage of the possibilities of the power board.

Bill recommends increasing the VFF values.
After looking at the log files, I would have thought I would have to reduce the VFF values.
I believe Bill, but I don’t understand why I should increase the values.
That is exactly the problem with beginners. I read the tuning instructions carefully and take a close look at the log files, and yet I still draw the wrong conclusions.



Sorry for that, let me try to simplify…
what I meant is that the AutoPilot should be installed on shock absorbing installation, as the vibration affects the accelerometers and gyros and excite reaction …


I use the pads, which were in the set from Holypro. And I fixed them like the manual told me. But, maybe I have to much Vibes from the frame.

I made a new flight today, with the extended logging activated. I will upload the log file.
So, you and Bill can see more hopefully :heart_eyes:

You can read in the wiki about how to set the harmonic notch for helicopters but I am more than happy to assist if you have questions.


sometimes the pads are not enough, and you have to use such an installation:

sounds great :slight_smile:

Bill, I searched for the harmonic notch and found the Wiki. Thank you for giving me the link. That is hard to understand. I have to read it after and after.

Here is the new log with many data.!AjSq727ChpJzd18fCYiV1qGzUr0?e=Ppy1sU

The only parameter I changed before flight was the atc_accel_x_max from 110000
to 100000

I started in “Stabilize” and changed to “AltHold”, that was much easier. But I did not changed in “loiter” anymore. I tried to keep the helicopter at one point in the air, just watching what it makes.
The yaw was oszillating slowly.

When I steered Pitch in one direction, the helicopter teetered. I didn’t see this while rolling. But that may also have been due to my observer position.

I’ve already looked at the log myself. RATE Rdes and RATE R.

The graph of the RATE R value is now just a single thick bar.

I hope you can see more

Sounds good. Thank you for searching the www. Only the long delivery time to Europe.
Maybe can build myself.
You could use two CFK plates and 3M adhesive pads in between.
I had already made it up myself.

I found this here in Germany

But maybe the vibrations are only part of my problem.

My TREX, which flew well with the PH4 mini right away, has similar vibration values ​​when I look at the Vibex, y, z in the log.

I need to adjust the tuning parameters properly. But I can’t interpret the logs correctly. So I don’t know in which direction to adjust this.