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How to install a second tilt servo motor

(Etienne Demers) #1


I am trying to install a Second tilt servo motor but I can’t seem to figure out where to plug it and what function to assign to te joystick button.

On the pixhawk, the present tilt motor is connected to RC8 main output. Only Aux 1-5 remain available.

I have been trying to find documentation that will explain what is what but no joy.

Can anyone help out?


(Jacob) #2

Is this for a second camera mount? If so, this is how to proceed:

You will need to plug the servo into one of the available outputs on the pixhawk (let’s use aux1), then you will need to configure the MNT_2* parameters so that you can use it.

You will need to set the MNT2_RC_IN_TILT to RC9 (this is hard coded).

Then you will have to set the SERVO9_FUNCTION parameter to mount2_tilt. Aux1 = servo 9, Aux2 - servo 10 etc.

The last thing you will need to do is to configure some buttons for the second mount in the joystick config tab.

Almost all of the settings on the Vehicle Setup page are adjusting parameters stored on the autopilot. You can adjust parameters directly using the ‘Parameters’ tab.

(Etienne Demers) #3

Hello Jacob,

Yes this is for a camera tilt. I cannot view these parameters until I am connected to the BR2 again. Hopefully they are not too hard to find.

So when I assign a button I will find MNT2_RC_IN_TILT in the list?

What if I want 2 more camera tilts?


(Etienne Demers) #4

Hello Again,

I can’t find MNT2_RC_IN_TILT or anything else pertaining to MNT2. Is there something I have to do to get it to appear in the MNT section?

I have 2 tilt servo motors plugged in, I even reversed the motors to test my wiring.

No luck.

Here are some grabs from QGC.


(Jacob) #5

Hi, I was mistaken. The second mount is not enabled in the current ArduSub builds.

What you can do in the meantime is use the generic servo* button functions. These control the Aux9-11 outputs, and the only setup you need to do to use them is to assign the functions to joystick buttons.

(Etienne Demers) #6

Hello Jacob,

Being there is not much litterature on the subject, would you mind providing more detailed explanation?

Where can I find Aux9-11?


(Jacob) #7

Hi @etienne, there are some labels on the edge of the pixhawk, one says “Main” (8 outputs), and one says “Aux” (6 outputs). Aux1 is the output nearest to the edge of the board.

I made a mistake in my previous post, it should have read “Aux1-3”.

(Etienne Demers) #8

Hello Jacob,

Thanks for your patience. Turns out it was really simple when you know what to look for.

For my tests I just use the same servo tilt unit. The one that comes standard with BR2.

I found that all 3 AUX servo outputs are very jerky and quick compared to MNT1 (where tilt is usually connected)

Is there a way to slow down/make the tilt motion as smooth with the Aux outputs?

Secondly, the range of the tilt is very limited. Can I use the full span of the servo motor?

QGC says the limits are 800 to 2200 why is that?

Lastly when fully tilted down, there is a noticeable “hum” coming from the motor until I jerk it up a bit. This hum is also present if connected to MNT1 output but MNT1 is less noisy.

I am wondering why this hum is present, how much current it wastes and if it is damaging to the servo.


(Jacob) #9

There are a few differences between the MNT outputs and the servo outputs.

The mount output is velocity controlled while the regular servo output is only position controlled, hence the jerkiness.

There is currently not a way to smooth the regular servo output.

Most servos have physical limits. these usually coorrespond to PWM signals between 800-1000 microseconds and 2000-2200 microseconds, but there are differences from model to model. The endpoints you are using for control signals are defined by the SERVOn_MIN and MAX parameters. Some servos are dumb, they will break themselves if you send them a control signal beyond the physical limit; they will attempt to execute the action. This might be the hum you are referring to. Some servos are just noisy and hum a lot of the time in arbitrary positions while they are ‘servoing’.

One last important point, the pwm frequency on the MAIN outputs is defined by the RC_SPEED parameter (default 200Hz), the pwm frequency on the Aux outputs is always 50 Hz. Many analog servos can’t accept pwm frequencies above ~50-100 Hz and may be damaged with higher pwm frequencies.