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Suggestions how to setup Pixhawk + FBL-system

Here are some suggestions how to setup Pixhawk to work with FBL-systems like VBar, Microbeast, GT5.2, etc.

Arducopter Heli Version 3.3.3

Tip: calibration of accelerometer is much easier before you put the Pixhawk in the helicopter.

WARNING !!! Remove blades or pinion or motor wires NOW.

Insert the Pixhawk between RX and FBL. RC1 = aileron, RC2 = elevator, RC3 = collective pitch, RC4 = rudder, RC8 = ESC, RSC, throttle

If necessary change the TX output (channel number, servo direction) to achieve the correct movements in Radio Calibration. TX must send 100% on each channel, trim at 0.
In Radio Calibration make sure the bars move with your stick left and right for aileron and rudder.
The collective pitch is called throttle and should correspond to your stick movement as well.
The elevator must go down (lower numbers) for helicopter nose down stick movement and must go up (higher numbers) for nose up stick movement.

WARNING !!! MissionPlanner tries to help you and changes your input to the recommended minimum or maximum value. Unfortunately These values are most of the time for multicopters and not for helicopters. Therefore it is recommended to use Full Parameters List/Tree, Write and Refresh commands to check if the value is what YOU want.

ACRO_TRAINER = 0 (this gives the FBL-unit full control in ACRO mode)
H_SV1_POS = 90 (aileron)
H_SV2_POS = 0 (elevator)
H_SV3_POS = 180 (collective pitch)
HS(1,2,3,4)_TRIM = 1500 (adjust as needed to trim the input of your FBL to center,
DO NOT trim the swash plate !
Any trim of the swash plate must be done in the FBL-unit !)
The Pixhawk should act now similar to a RX, Main Out 1 = aileron, Main Out 2 = elevator, Main Out 3 = collective pitch,
Main Out 4 = rudder, Main Out 8 = ESC for H_RSC_MODE = 1

These Main Out signals are the input for FBL-units that understand Standard RX. Some newer FBL-units only read ‘Singlewire’ signals.
For these FBL-units you can provide SBUS signals from the Pixhawk SBUS port.
If you use SBUS, set BRD_SBUS_OUT = 1 (or higher ?) and RSSI_PIN = 103 (needs power cycle) to get SBUS signal from Pixhawk to FBL-unit.

In your FBL-unit you must be able to make channel assignment. For standard input you switch wires until it fits, for SBUS input you need to set it with the software of your FBL-unit (check manual before you buy it).
Once the channels are assigned you need to scale the amount of input for your FBL-unit either by doing it with the software of your FBL-unit or by controlling output of Pixhawk.
H_CYC_MAX = 4500 (this is your aileron + elevator input to the FBL-unit, you can adjust this to limit the output to your FBL-unit)
H_COL_MAX = 1900, H_COL_MIN = 1100 (this is your collective pitch input into the FBL-unit, you can adjust this to limit the output to your FBL-unit)

Check the input channels of your FBL-unit to show the correct direction of aileron, elevator, collective pitch and rudder.
Adjust as needed using HS1/2/3/4_REV = 1 / -1 (1 or -1 to change direction)
DO NOT use the TX to reverse servo direction !
All trim settings must be done in the FBL-unit, disable trim on your TX !!!
The Expo settings on your FBL-unit should be 0, use your TX to set Expo because this is for your fingers, Pixhawk needs linear response.
Check rudder and swash movement (collective, aileron, elevator) and adjust as needed using your FBL-unit. Basically do a FBL-unit Setup according to the manual (just as you would without the Pixhawk and a RX instead).

You must not have two control Loops - as you have the FBL-unit, you must disable the Pixhawk PID loop.
RATE_PIT_P/I/D = 0, RATE_RLL_P/I/D = 0, RATE_YAW_P/I/D = 0 … we have external FBL, therefore everything 0
RATE_PIT_FF = 0.05, RATE_RLL_FF = 0.05, RATE_YAW_FF = 0.05 … we want manual input in Stabilize etc., adjust to your taste 0.05 - 0.25 should be o.k… Check for similar stick reactions in Acro and Stabilize mode !

ACCEL_Z_P = 0.3 (adjust as needed, many helicopters oscillate on collective using standard value 0.5)
H_LAND_COL_MIN = 300 (adjust to your taste, should give you about 3°-4° negative collective using symmetrical blades. If the H_LAND_COL_MIN is set too high, such that the helicopter cannot descend at the target landing rate, then it will think it has landed and might disarm in the air.)
Edit read:
DISARM_DELAY = 0 (only if you can’t arm because after arming software disarms and other settings don’t work, otherwise keep this safety feature)
RC1,2,3,4_DZ = 5 (if your TX is good and you like small inputs), RC_SPEED = 125(?), RC_FEEL_RP = 50 (adjust to your taste)

WARNING !!! Remove blades or pinion or motor wires NOW.

Check FAIL SAFE, what happens with TX off, what happens with RX off and Pixhawk on (no connection Pixhawk to RX), what happens if you loose connection Pixhawk to FBL-unit, etc.
SBUS sends Failsafe flag, PPM input is usually best handled using OFF (no signal) in the fail safe settings of the RX. Walk with your heli around (away from home) to see RTL or LAND servo movements etc.

Check stick movements before EVERY flight !
Check ACRO mode FBL correction direction before EVERY flight !
Check STABILIZE mode correction direction before EVERY flight !


Thank you for paying so much attention to sorting out these instructions!

I have tried to use Pixhawk with Mikado miniVbar several times to try this Pixhawk + FBL program, in the FW AC3.3.3 conditions.

In accordance with this step adjustment, in front of the settings can be successfully achieved. But the final problem to stop the set-up work. That is, in any case to adjust the channel reversal, or servo reversal, or try to reverse the TX channel, can not solve the miniVbar and Pixhawk Pitch direction of the action and correction is the same!

Because the Pixhawk output channel does not allow the setting of positive and negative parameters, and miniVbar channel positive and negative direction and correction direction is the initial channel calibration, AHRS on the way to determine the installation can not be set by the back of a channel of the revised Positive and negative.

Therefore, the problem is very distressing, I tried a few times, had to give up. As far as I know, the use of SK720, SK540 FBL system set up successfully, because the SK720 / 540 can be set to channel positive and negative direction and correction of positive and negative.

I did not find the parameters set up, or where there is no connection correct, the following links are my attempts and questions to discuss the content:



Hi Zhangsir,

I can promise you it works, because I used this setup with GT5.1, GT5.2, original MiniVBar and VBar Neo.

In accordance with this step adjustment, in front of the settings can be successfully achieved.

Do the ‘Radio Calibration’ and make sure the direction of the green bars is correct by reversing the channel in the TX. Left, right for aileron and yaw needs no explanation. Nose down is lower numbers than nose up and ‘Throttle’ is collective pitch and up gives higher numbers.
Can you confirm you have the correct TX-setup in ‘Radio Calibration’ ?

But the final problem to stop the set-up work. That is, in any case to adjust the channel reversal, or servo reversal, or try to reverse the TX channel, can not solve the miniVbar and Pixhawk Pitch direction of the action and correction is the same!

Never ever reverse the TX channel to reverse servo direction !!!

Because the Pixhawk output channel does not allow the setting of positive and negative parameters…

Servo direction is controlled by HS1_REV = 1 or -1 for aileron, HS2_REV = 1 or -1 for elevator, HS3_REV = 1 or -1 for collectiv and HS4_REV = 1 or -1 for yaw. Remove the blades and go to ‘Failsafe’ screen, arm in ‘Acro’ mode using ACRO_TRAINER = 0. Confirm correct movement of green bars in RADIO IN 1,2,3,4 and make sure you have reasonable output values (same size as input).
At this point treat the Pixhawk like a RX. Connect the FBL-unit to accept SBUS. Do the channel assignment according to the manual of the FBL-unit. Change channel direction using HSx_REV. Do the complete setup for the FBL-unit, just as you would with a normal RX, but do not change any setting on the TX !!! If you need to change direction or value of a channel, do it according to the instructions above in the Pixhawk (MP) !
In ‘Acro’ mode using ACRO_TRAINER = 0 the heli must show correct reactions to stick input and the FBL must do the correct counter movements when you move the heli !!!
If everything works fine try to simulate Stabilze, AltHold, PosHold, Auto…on the ground, walking around.

Try all kinds of failsafe Scenarios (without blades) !

Thank you very much!

I try to re-set!

The main problem is that the MP out of control to protect the page channel monitoring, the pitch of the channel signal display, and the rocker is the opposite direction! This is normal in multi-axis flight.

It does not matter, I carefully from beginning to end in accordance with the steps set!

Thanks again! ultrafuge


thank you very much!

Try again carefully to follow the steps to set up, and finally succeeded!

The original problem occurred in the H_SV1 \ 2 \ 3 \ 4 Rev settings, through this setting, Vbar channel positive and negative, and Pixhawk the same!

Previously ignored this! It is their careless …

thk you ,@ultrafuge

Hi Zhangsir,

I am glad that I could help you.

Please add a link in you old discussions how it works.

Well, I’ll do it right away

Thanks again!


@ultrafuge : Have you tried latest trade heli with the parameters you are referring to?

I am tempted to try as I do have a 500 scale working perfectly with microbeast…

Thank you in advance…

No, I stopped using helicopters for UAV mapping (only using planes at the moment). I never tried a Microbeast, but all the other FBL-units I tried worked without a problem. At that time it was the most reliable solution.

Hi - May I ask how you made the connection between the autopilot and the FBL? Was it using s.bus out on the autopilot to s.bus in on the FBL? Or was it autopilot main PWM output to FBL PWM input?

I was using both, one autopilot didn’t output the SBUS signal and therefore I used the aileron, elevator, etc. PWM outputs and connected those wires to the FBL. On the other helicopter the autopilot provided the SBUS signal and the FBL could handle only single wire input therefore I used SBUS. If both is possible I would use the SBUS.

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Thank you. I was looking at the Durandal FC for a T-Rex 550x I’m building as a first time autopilot setup and wanted the comfort of an FBL that I’m familiar with. That being said, if I’m not planning any 3D flying on this machine, is there any reason to include the FBL or would I be ok with just the Durandal?

I don’t know the Durandal and I don’t know how reliabel the current versions are - sorry can’t say anything about it. The advantage of using a FBL is the added safety. If your autopilot goes crazy you can flip to manual (Rx signals are not modified by the autopilot) and use the rescue function of your FBL or just fly it like you would without the autopilot.
When I used ardupilot you couldn’t fly 3D, don’t know if this changed in the meantime.

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I’m trying to follow the instructions on the following thread but I still not get it to work.

I’ve tried to follow the instruction here as well and still have problem.

I’m using the following HW:

  • Pixhawk 1
  • Mini VBar
  • FrSky RC with ch1 = ail, ch2 = Ele, ch3 = Thr, ch4 = Rud configuration (No mixing at all)

I’ve changed the following parameters:

Param Original Value --> Change to

H_SW_TYPE 0–>1
ATC_RAT_PIT_VFF 0.15–>0.35
ATC_RAT_RLL_VFF 0.15–>0.35
ATC_RAT_YAW_VFF 0.09–>0.35
H_SW_TYPE 3–>1
ATC_RAT_PIT_D 0.0008–>0
ATC_RAT_PIT_I 0.35–>0
ATC_RAT_PIT_P 0.04–>0
ATC_RAT_RLL_D 0.0005–>0
ATC_RAT_RLL_I 0.32–>0
ATC_RAT_RLL_P 0.035–>0
ATC_RAT_YAW_I 0.3–>0
ATC_RAT_YAW_P 0.22–>0
ATC_RAT_YAW_D 0.003–>0

Before connecting the Pixhawk, when I moved the Heli (roll & pitch) the FBL system by default is trying to stabilized the Heli so after connecting the Pixhawk and I move the Pixhawk in my hand the swash plate moved as well which means the Pixhawk trying to stabilize the Heli as well so I don’t really know how to check if the setup is correct.

Another thing is when I’m moving the roll pitch stick, the servos are moving very slow (Stabilized FM) and not as fast as they were connected directly to the FBL system.

In addition, while looking at the Vbar GUI, when moving the Ail stick, the Ele moves as well, and when moving the Rus stick the Ail & Ele are reacting as well (Not the entire movement)

I’I appreciate some help here.

Thank you very much


Hello @rotems

Is there a special reason you are using the mini vbar ?
If not, dump the unit, and allow the pixhawk do all the work, it is easier to manipulate this way…


Yes, the FBL systems PIDs are much better tuned to the helicopters.
I spent hours on hours to try to tune the Pixhawk and all the time there is something to tune, like bouncing tail, vibrations mounting, PIDs and more.

Thank you

What is your setup ?
Do the tuning according to the wiki and the heli should be fine.
start in a calm non windy days.
You are falling in between two stabilization systems that interfere with each other.

I have trex 700 and tried pixhawk 2.1 and pixhawk 3 pro, and as I mention before, there is all the time something to tune and I would like to try the external FBL way.

Can you help?

Thank you

As i wrote before, had bad experience with using both systems, and better luck with using only the Pixhawk.
Alas, the system is tricky to adjust, and it takes time to get it work properly.
You have to start with rates adjustments as mentioned in the wiki.
By now, I have three 450 and one 550 flying quite well.
you have to provide recorded telemetry .bin file in order to check your situation.
There are no short cuts.

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