Throttle control (Ch 8) for Align 450 running Revo full size FC

Revolution became one of the FCs recently supporting ardupilot FW.
I just flashed arducopter heli fw to an Open Pilot Revolution FC which only has 6 sets of output pin. This Revo FC replaces my earlier Pixhack 2.8.4 which has 8 sets of output pins. The BEC from ESC was connected to Output 8 of Pixhack.
I can see Ch 8 PWM output in the Radio calibration and Failsafe pages of MP as I turn the knob which is set up to control the rotor rpm.
Where should I connect the BEC to Revo FC ? I tried output 6, which is the last output pin set of Revo, but it did not work.
Revo Output Ch 1 and 2 – the front 2 servos
Ch 3 — the rear servo (elevator)
Ch 4 — rudder servo

PPM output from encoder goes to RC in of Revo FC.

Appreciate your help.

Hi Frankie,
To get the rotor speed control to output to channel 6, you will have to change the SERVO6_FUNCTION to 31. That will then output the signal for the ESC to channel 6 on your servo rail.
Hope this helps!

Hi Bll,

It works. Thanks.


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This is a coincidence! I’m setting up a sub 200 size microcopter with the radiolink minipix controller to research a smaller platform than my trex 470. After pouring over the documents and forums I was pointed right back to the ardupilot.discuss forum here and I found an old post asking about a pixracer, so I changed SERVO6_FUNCTION to 31 but nothing I could do would cause the ESC (CC talon 15) to arm! I then spent about 2 days searching and trying different setups as well as my fullsize pixhawk and coudlnt figure out why the minipix wasnt outputting on position 6. I finally found an obscure post somewhere about board pwm count and sure enough the BRD_PWM_COUNT parameter was set to 4 pwms lol, changed it to 6 and all was well, now to tune!

After I read your reply, I checked the value of BRD_PWM_Count, it is set at default value of 8.

Strange, the option for this param is up to 7, and it still works.

My Open Pilot Revolution FC has only 6 sets of output pins, so can connect the BEC of ESC to this channel.

Hello Bill and fellow pilots,

Not sure if I should have started a new thread…but part of my confusion is partially addressed in the above reply. I’m in the process of setting up mRo R15 PixRacer with a 450 traditional flybar heli. Trying to get the RC Channels and PixRacer PWM pin outs straight. Because I have only 6 PWM pin outs, I’m following your recommendation in your post to set RotorSpeedControl as: SERVO6_FUNCTION to 31 (Haven’t decided on which RSC Mode to use yet).

Here’s where I need help…(using QGC nightly build & FW 3.6.12)

  • SERVO6_FUNCTION doesn’t offer “31” for an option but it does offer RCPASS THRU and HELI RSC as options. Should I select “HELI RSC” option for SERVO6_FUNCTION ?
    BRD_PWM_COUNT parameter was correctly set to 6 automatically. Related PixRacer config questions…
    Using Spektrum DX 8 Gen 1. Currently QGC shows my DX8 outputs as:
    CH1 ROLL
    CH2 PITCH ( I suspect PITCH and elevator are synonymous here)
    CH 4 YAW
    CH 5 Gear (Have successfully configured 6 flight modes as Wiki outlined using mixes with Gear and FM switch)
    CH6 Flap & Aux 1 - a 3 position switch
    CH7 AUX 2 - a 3 position switch
    CH8 AUX 3 - Knob

PixRacer PWM pin outs for Pins 1 thru 4 will be per Wiki
1 Left Front Servo
2 Right Front Servo
3 Rear Servo (Elevator RC Channel 2…I think)
4 Rudder servo (Getting YAW signals from Channel 4)
5 PWM Pin 5 Not connected to anything
6 ESC (THROTTLE?) connection (PWM pin 6 getting throttle signals from Radio Channel 3)

Does that check out OK with you?

Can you correct me on configuring or re-mapping any channel if needed? A top concern of mine is getting a FAILSAFE switch functional. From the Wiki, it seems like that should be on CH8. Could you walk me through setting a FAILSAFE switch up?
What do you recommend for the KNOB…if anything.

Thank you,

HeliRSC is what the 31 option is called for throttle. So that is the correct selection for the throttle output channel.

This is correct, as well. Channel 2 is elevator (fore/aft cyclic) control. Channel 3 is pitch (collective) control. Channel 8 is throttle.

Your throttle control will be on a knob on this model. Depending on which RSC mode you choose, you may want to put Channel 8 on a two-position switch instead.

There is actually a mixer in the code that will apply the signal to all three servos for the cyclic control. But this is correct.

The ESC is getting throttle signal from channel 8, not channel 3. There is confusion in the ArduPilot code on this. They call channel 3 control “throttle”, and it is actually collective pitch.


Just a general question - On the bench, while testing the cyclic and rudder output’s, just noticed that when we give a rudder stick i/p, the o/p continues to increase or decrease until it hits the limits, it this normal on the bench ?


Well Chris did not answer…

Yes it is normal, in stabilized mode the yaw controls the position and not the rate.
it is like heading hold on gyro control.