Reality of Tricopter on PX4

Hi every one,

I am Charles, french guy who want to try to use PX4 on a Tricopter on a Dropix (same as Pixhawk). I been trying for a week to make work the yaw of my tricopter with the servo on the tail. I did a lot of research and I never found someone who has a tricopter with PX4 and a Pixhawk (and I don’t speak about the Dropix…). I am wondering if it’s possible ?

I use an analog servo, and when I arm it goes all the way to the left. If I put all the mains output at 50Hz (I can’t change juste the channel of the servo) the servo work better but not correctly. It respond to the radio and the gyro.
I have a esc with a BEC plug on the servo rail, so the servo power is simply connect to the servo rail too.

  • Do I need to use a digital servo because I can’t change only the channel 4 frequency in the mixers ?

  • Does Tricopter frame style is really ok to fly today with PX4 or not ?

  • Any one have experience on Tricopter on PX4 ?

Thank you,
CBB.

I have no tricopter but I don’t see why it wouldn’t work.

However you pointed out a valid problem with the update frequency of the outputs. What you can do is adding an empty mixer entry between the motor and the yaw mixer. That will shift the yaw servo to channel 5 which means you can use 400Hz for 1-4 and 50Hz for the rest.

HTH
ada

# Tricopter Y-Configuration Mixer
# Yaw Servo +Output ==> +Yaw Vehicle Rotation

# Motors
R: 3y 10000 10000 10000 0

# Empty
Z:

# Yaw Servo
M: 1
O:      10000  10000      0 -10000  10000
S: 0 2  10000  10000      0 -10000  10000

Thank you very much Andreas !

It seems to be a good idea. I am not a good coder but I can understand. I found the source code here : https://github.com/PX4/Firmware and some information here https://dev.px4.io/en/concept/mixing.html

Now I did the modification I have to build this code to my Dropix and I will be able to change the frequency of my channel 5 in the settings ? I did not know that the different channel were group (why) and I can adjust the frequency of each group if I understand ? It’s possible to do that on QGC in settings or in the code only?

I will try tomorow :wink:

Thank you for your help.
CBB.

Hi - I fly Tricopter on PX4.
I just used default settings. Just had to pick the correct Tricopter +/- model
i am using old analogue servos and ESC with this. Maybe I am lucky and servioc will break :slight_smile:
It needs tuning, but flies OK for me as I am still learning PX4

OOOOOOh really ? Ahah YES ! Do not go away please :stuck_out_tongue: .

So can you give more information on your setup ? Where the servo and esc are connected ? Why I have to choose the right Tricopter +/- model ? For me it is the same ?

I am sure you have the solution of the mistake I made :slight_smile:

Thank you,

CBB.

Uuuup :smiley:

I need to know your secret Shikra !

Hi - it is no secret!!!

i only set it up same as the diagram in qgroundcontrol.
I had to change tricopter +/- because yaw direction of servo was wrong. I do not know it this is correct way, but it worked for me.
Everything else I have set at default settings. Nothing special. What issues do you have?

Ahah, Ok I believe you !

I am going to do a video test to show you what’s happen :wink:

Hi,

Finally, the tricopter worked, but I decided to stop using tricopter. The servo for the yaw is not perfect for me.

@shikra Your method worked for me too. I was using tricopter Y+ airframe and had my copter spinning around the Yaw axis on take off. I couldn’t fly it at all. I had tried reversing the servo etc. but it was still not working. On reading this thread, I decided to switch to tricopter Y- airframe and viola, I can hover, even though there is high vibration but at least all I need to do now is tune.

Thanks

Great - glad it helped! I have some vibes in mine too! One day I’ll get round to sorting it out

@shikra do you by any chance understand how to reproduce the flight log plots using the px4 ulogs? I have been able to extract the logs from sd into csv using pyulog. However, I don’t really understand what columns are what, and the sampling rates etc.

Thanks for your help.