Collective pitch output on Tx defined in plane mode

Hi ARDU user’s,

I mounted a Pixhawk on an heli Tirex500. I defined the Tx in Accro mode as recommended. The question is: Because in that mode the receiver does not provide a “pitch” output; So, which output of the receiver may I connect to the “pitch” input of the Pixhawk?
May be the response is basic, because I have not found this question treated along the discussions!

I would strongly appreciate any kind user take tiem to reply to me.
Many thanks

Did you look at the wiki on for traditional helicopters? Here is a link to the radio set up

The short answer is that arducopter uses the throttle channel (channel 3) of the transmitter as the collective (pitch) input. The throttle or engine control is on channel 8 of the transmitter. Is your heli electric or nitro powered?

Hi Bill,
Thanks a lot for your kind reply.
Yes, I read several and many times the Ardu wiki related to the radio set-up for a traditional Heli. Unfortunaly, I did not understand clearly which output of Rx goes to which input of the Arducopter, particularly for the pitch signal.
Sorry, I confess I am still confusing about your indication: Do you mean : chanel 3 “throttle” of Rx goes to input 8 “throttle” of Ardu. Because Ardu processes this signal as Collective Pitch, there is nothing to plug into the input 3 “Pitch” of the Ardu?
Should my understanding is wrong, would you kindly spend time to indicate input and output concerning Pitch and Throttle of both Rx and Arducopter.
My heli is electric.
Yours sincerely,

So I need more info on your setup
I’m assuming you are using the built in governor feature of the ESC to maintain the rotor speed.

What make and model is your transmitter? Sounds like you already have it set up to use a plane model in the transmitter which is fine.

How Does the receiver link to the pixhawk? SBus thru RCIN port or PPM encoder thru RCIN port or spectrum satellite into spkt port? If you are using the SBus or the spectrum satellite receiver then the receiver channels are mapped directly to the same channel inputs of the pixhawk. If you are using a PPM encoder then you can change them around but I would recommend just mapping the channel of the receiver to the corresponding channel on the pixhawk.

The throttle stick on your transmitter which is output as channel 3 on the receiver will be input on the pixhawk as channel 3. The arducopter software will read this as the collective input.

Channel 8 on your transmitter which will be output as channel 8 on the receiver and input to the pixhawk as channel 8. The ardupilot software will read this as the throttle input or your esc governor input. So the ESC will be connected to channel 8 output of the pixhawk.

Elevator control on your transmitter is channel 2 output from receiver and channel 2 input to the pixhawk
Aileron control on your transmitter is channel 1 output from receiver and channel 1 input to the pixhawk
Rudder control on your transmitter is channel 4 output from receiver and channel 4 input to the pixhawk

Do you understand how to make all of the connections from the pixhawk to the servos?

I think the confusion stems from regular flybar heli setup where Aileron is on channel 1, elevator on channel 2, throttle is on channel 3 and pitch is on channel 6. The aileron servo is LF, pitch RF, elevator rear. And CCPM mixing is done in the radio.

ArduPilot uses no mixing in the radio, similar to most FBL units. FBL units use pitch on Channel 6 and throttle on channel 3. ArduPilot uses pitch on channel 3 and throttle on channel 8. I’m pretty sure this was done for compability with multi-rotor code so throttle on Channel 3 for multi and collective pitch on Channel 3 for heli do kind of the same thing.

This causes confusion for people familiar with helicopters because ArduPilot doesn’t name any channel “pitch” like like a normal flybar heli, or a FBL unit does. ArduPilot insists on calling the pitch channel “throttle”. We should get rid of all reference to “throttle” on Channel 3 in the heli setup wiki and rename it “pitch”.

Hi Bill,

I am really impressed by your prompt reply and appreciate your nice will to help me.

  1. yes I use an ESC but without governor activated
  2. My Tx is the JR XG8. I have “on shell” another Tx, the Spektrum DX8
  3. the Rx links to the Pixhawk RCIN trough a PPM encoder. I can select which Tx channel to be cconnected to the Pixhawk channel
  4. On my Tx the outputs are mapped like hereunder
    channel 1: Throttle
    channel 2: Aileron, Roll
    channel 3: Elevator
    channel 4: Rudder
    channel 5: Gear
    channel 6: Flap
    channel 7: Aux 2
    channel 8: Aux 3
  5. If I translate your connections indication, according to my Tx output mapping, I would writte:
    Trottle of Rx (channel 1) is connected to channel 3 (Pitch) of Pixhawk
    Channel 8 of Rx (Aux3) is connected to Channel 8 of Pixhawk which is read as Throttle input!
    Elevator, Aileron and Rudder of Rx ae connected to the relevant channels of Pixhawk.
    Wah, how could I guess those connection by myself!
  6. Yes I understand how to connect the servos, unless some hidden tricks would happen to me!
    Please confirm or correct what I understood as above. Can you explain how the channel 8, which is an auxiliary output without any signal unless mixed with another channel, can be considered by Pixhawk as the Throttle input.

Yours Sincerely,

I have taken some time off work over the holiday’s so I have some spare time on my hands :grin:

So I have used the PPM encoder and was not that impressed with it. I like using a Futaba radio with an SBus receiver or the spektrum radio I think it would be better for you to use the Spektrum radio. unplug the satellite receiver from the main receiver of your spektrum receiver. Plug the satellite receiver into the Spkt/DSM port on the pixhawk. Hopefully this is not too much trouble for you.

I would recommend using the governor feature of your ESC. if that is not possible, we can still make it work but in my opinion using the ESC governor is best. Let me know what you decide and I will then explain the channel 8 setup

Hi Bill,

Unfortunally my Tx Spektrum is not associated with a sattelite receiver. So, with this Tx, I still need to pass through the PPM encoder that gave me satisfaction when used with Pixhawk on quadricopter. So, I am condemned to work with PPM.

I am not sure to be able right now to feature the ESC on Governor mode. I have to find out the related programming board.
I am going immediately to proceed with the connections you indicated in order to go further in the setting of the system Tx-Rx-Pixhawk-Heli! Obviously, I will keep you informed of every succes and …mistakes. Hope I can still take profit from your expertise.

Yours Gratefully,


Hi Chris,

The confusion rises up because in Accro mode, as recommended by Ardu, Tx does not offer a “Pitch” output corresponding to the “Pitch” input of the Pixhawk. In the Ardu Wiki, a Strange Futaba receiver is showed up with a pitch output on its channel 6! A rare specimen or swiched on heli mode?
Thanks for your comments,

Hi Bill, I forgot to ask if any change in the connections you indicated if ESC is not in Governor Mode?

Ok. That is fine.

Yes then this sound right.

So what are your plans for this heli? Do you plan to do acrobatics? OR just explore the autonomous flight and non acrobatic manual flying? I need to know this in order to walk you through the next part.

by the way, here is a great video on setting up the pixhawk using mission planner and the Config/tuning - full parameter list page rather than the Config/Tuning -Heli setup screen in mission planner. It is recommended that you use the method in this video. I will have some minor adjustments on your collective settings based on your response to my questions above.

Hi Bill,
I am a beginer on heli, even though i began to discover the heli almost 5 years ago, when stabilization electronics assistant was not as efficient as now. So, I broke plenty of heli and become very very prudent and I never over pass beyond the hover mode with light movments. So, to answer to your question, I intend to experience with my heli 500, powered with the Pixhawk, the same mode of flight. Hope you are not disappointed.
Thanks again for the video you transfer to me.


This is the Pixhawk input mapping as Bill noted:
Channel 1 - aileron
Channel 2 - elevator
Channel 3 - pitch
Channel 4 - rudder
Channel 5 - flight mode selection
Channel 6 and 7 - assigned functions
Channel 8 - throttle

You are using Mode 1 channel mapping in your transmitter instead of Mode 2. Normally ArduPilot is set up with Mode 2 in the transmitter so left stick is collective, right stick is aileron and elevator. Yours will be reversed because you are using Mode 1 setup.

If you are used to flying Mode 1, Bill can probably help you map it with the RC map parameters.

No, that is not a strange Futaba receiver. All heli setups I’ve seen use channel 6 for pitch and Channel 3 for throttle. ArduPilot is the one that is strange, using Channel 3 for pitch, and Channel 8 for throttle. That is why the crossover is shown. The wiki is showing the crossover for a Heli H1 swash setup in the Tx.

The confusion arises from the fact that in FBL unit setup, the Tx is set to Heli H1 swash mode, and not airplane mode. Throttle is tied to the collective pitch with a throttle/pitch curve in the Tx. And you have a throttle hold switch with one more “Conditions” or idle up throttle curves. You will have “Normal”, “Idle up 1”, “Idle up 2”, etc.

ArduPilot uses one of three throttle modes tied to a switch on Channel 8.

This is what makes it very confusing to set ArduPilot up for throttle control for an electric using no governor. ArduPilot’s system of assigning throttle to a on/off switch is so far removed from what FBL units use, that unless you use the MODE 2 with a governor you are in for a confusing experience to set it up.

If your ESC does not have a governor in it, then you will have to use MODE 3 if you want to fly Auto flight mode. The caveat there is that MODE 3 was designed for piston engines with a governor where the governor “falls back” to the throttle/pitch curve and the throttle servo goes to WOT if the engine “lugs” on full collective climb-out causing the governor to drop out. So it is difficult to set up for an electric because electric doesn’t work that way.

In the video, Rob will refer to the following Parameters
HSX_TRIM where X is the servo number 1, 2 or 3
These parameters are now
and SERVOX_REVERSED (normal = 0, Reversed=1)

Before doing the set up procedure that Rob shows in the video I would suggest doing the radio calibration under the initial setup menu in mission planner. So the sticks are the easy part, what may not be so obvious is channel 5 and channel 8. So channel 5 of your transmitter which should be plugged into channel 5 of the pixhawk tells the Arducopter software what flight mode you want. Set this to a switch of your choosing. may be use a 3 position switch so you can make use of three different flight modes. set channel 8 to a switch, typically I use the throttle hold switch that you would use on a gas/nitro heli or electric for doing autos. Be sure to move the channel 5 and 8 switch to every position when doing the calibration. As far as reverse settings for channels 1-4, I typically set these as normal. all the reverse settings can be done in the pixhawk.

Get through your servo set up and then we can talk about the Mode 3 setup for the rotor speed control (channel 8).

Yeah I hadn’t thought about that. I didn’t know if that automatically was accounted for in the transmitter output. I thought for futabas whether is was mode 1 or mode 2 transmitter, the channels were as I listed them. I thought his different channel listing was a JR thing.

Guy, let me know about the transmitter mode type you are using.

Bill, just a suggestion for Guy. He is new to heli’s and wants to practice. This is GREAT for setup with an ESC with no governor. The thing with the channel mapping in the Tx using Mode 1 instead of Mode 2 needs to be figured out. You can use the RCMAP params to change that if he’s only used to flying Mode 1 in the Tx.

But for the RSC MODE I would use MODE 1. And set up the head with only -2 deg of negative pitch instead of -8 or -10. Set up a mix in the radio with a switch as the slave on channel 8, and using the collective lever as master to mix the throttle signal to channel 8.

That way Channel 8 is like a traditional “throttle hold”. Guy obviously wants to practice hovering, maneuvering, nose orientations, and learn collective pitch management when making turns, etc… Common for new pilots is to panic if something goes wrong and drop pitch. Using a mix automatically shuts down the heli’s engine, plus won’t slam the heli into the ground with the engine running at full throttle if the pitch is dropped into the negative range.

MODE 3 does not provide smooth enough throttle control from full negative pitch and throttle off to hover collective because it is only a three-point curve. The radio has infinite adjustment of the throttle curve and will be much smoother for learning. ArduPilot’s linear throttle curve between the points on MODE 3 sucks. That should be at least a four-point curve corresponding to full neg, 40%, 60% and 100% so the throttle curve could be flattened a bit around hover collective.

One other thing I forgot to mention about the video. Rob talks about setting H_COL_MAX, H_COL_MID, and H_COL_MAX. I recommend, since you are not planning on doing any aerobatics, to set these so that H_COL_MAX corresponds to a collective blade pitch of 11 deg, H_COL_MID corresponds to a collective blade pitch of 4 deg and H_COL_MIN corresponds to a collective blade pitch of -3. Then you set your IM_COL_1 to 0, IM_COL_2 to 400, IM_COL_3 to 600 and IM_COL_4 to 1000. These might need to be adjusted slightly once we find out what your hover collective is.

I was going to use mode 3 but adjust it like a 3 point throttle curve for collective from -3 to 11 rather than -10 to 10. What do you think?

I think you would have a problem with this if he ever decides to use an auto mode

What happens is the same thing that happens with a V-throttle curve in your transmitter. If you have equal pitch range on each side of 50% the V curve works pretty good. If you have only -3 collective and set the throttle curve to be zero at that point (to shut off the engine like most FBL units do in “Normal” flight mode with limited neg collective), the ramp is not smooth.

You can make it really smooth with the transmitter’s curve mixes, or even a linear mix with 10 point settings. ArduPilot only has 3 settings. We could improve that immensely and make it possible to fly no-governor with ArduPilot as well as any modern radio can.

The downside to MODE 1, as you note, is that in Auto flight if the RC signal is lost there will be no throttle correction for pitch. It is locked at whatever the last received PWM value was. MODE 3 continues to control the throttle with no RC signal.

So that’s why I suggested the MODE 1 setup, which is what I used for my wife when she started learning how to fly heli’s earlier this summer. It worked good for her, and after about two months when she had progressed to basic sport aerobatics we went to MODE 3 and enough negative pitch to do loops and rolls. She never became interested in doing Auto flights. She has a new 516 now and we put a Vbar in it instead of a Pixhawk because she only wants rate and attitude modes, and just do general flying.

So not all people want to do Auto mode flying. That will depend on the user. You can set up MODE 3 so it maintains say 30-40% throttle at full negative collective, and then it will be smoother on throttle advance as you pull pitch. But it will require snapping the Channel 8 “throttle hold” to shut it down if the pilot suddenly drops pitch and slams the heli into the ground.

Hi Chris,
I am using the Mode 2 (gas stick at left) on my transmitter.
Oh! so huge tide of advices and accurate précisions concerning my subject. Thanks.
I am reading each detail of advices coming from both of you and Bill.
Prior going further I would like to proceed with the radio and servo output settings according to the connections indicated by Bill.
Best Regards,