Tricopter on Pixracer

Thanks to new mot_out library we are able to use pixracer on tricopters by assigning ch7 output to ch5 via a special function 39. This works great, however, IMHO it is a workaround as it occupies viable output ch5 which can be used for other things like RC pass through, camera trigger, gimbal control in auto modes, etc. I suggest permanently moving yaw control servo output to ch2. this will open up ch5 for other functions. right now only ch6 output on pixracer is usable.

Thank you.

is there a full work trough where is dokumentet how to change settings in the parameter list?

Thanks for testing.

My guess is the problem with moving the servo to ch3 (I think you said ch2 but that’s for the front left motor) is that the Pixhawk doesn’t support having different update rates on each output. So I think ch3 must have the same output rate as ch1,2 and 4. I think most servos won’t be happy with the 400hz update rate of those channels. I’m guessing a bit but I could be right.

Enhancement requests should go in the to-do list I think. I’ve created an issue to capture this request here.

Sorry, I see I never replied to this post which was made over 3 months ago!

@Zaaam, the tricopter wiki is here if that’s what you’re looking for. It looks like I should update this page to include the possibility to move the tail servo around as well so I’ll add that to the “update wiki” to-do item for AC3.4.

Thanks for the reply, I understand how busy you guys are since a lot of devs gad to quit due to the 3DR dropping diy crowd. Your explanation makes sense, yes I did typoed on the #2 vs #3.


Great, thanks for understanding.

By the way, most of the ardupilot devs have found new homes at other organisations and are continuing with ardupilot development. There were a lot of disruptions over the past year and that certainly had an effect on us. For example, I’m sure that I lost 3months of development time in 2016 but that’s behind us now. Anyway, thanks!


thx for response
in the wiki is not much to read about the pixracer and the chanel 7 problem and how to get it work.
thank you for the response. it is so grat to that you guys do this kind of job.
i think the pixracer and the design will have a big possibillety for smal mapping devices. if i can support you with testing i will do it on my smal trifactor nerby in time.

Just a small advice… Trifecta is a horrible frame… very flexy and has too many joints, this induces vibrations. I recommed david winderstal’s frame or mine:

Mine is optimized for pixhawk and its derivatives.

In both cases frame size is determined by the length of CF arms which you can cut as short as you like.

i know that the front arms are flexing a bit.can be replaced in cfk next time. The last secret now is where is the servo port in version AC 3.4 on the pixracer? do you have some information?
i would like to test it slight_smile:

btw the trikopter is only my “lerning” copter.

shown on your pictures from RCG it seems that you got the pixracer to work on your kopter. i am very helpless how to handle the pixracer in trikopter mode is in on output 3 or 4. i want to fly try to crash how get i the right pinout to check in the parameter list?
can i switch parameters on the rc out by hand?

Mission planner, full parameter list, RC function for #5 set to 39. This way you effectivelly set ch5 to output ch7. Do not forg to save.

Thanks Artemen for helping out here.

I’ve updated the tricopter wiki page with some advice on how to move the tail servo to another channel for the Pixracer. There’s also a new MOT_YAW_SV_ANGLE parameter in AC3.4 that should help reduce yaw-vs-pitch and/or yaw-vs-thrust coupling by increasing the rear motor speed as the servo angles the rear motor.

At this exact instant that I’m posting this the page hasn’t updated yet on the main server but I’m sure in 10min it’ll be updated.

Randy, no prob, always glad to share what I’ve learned. I had a fortune to be the first person to request this and the second one to try it out, the first one was Tridge :slight_smile:

May I add one more feature request: it is possible to know the exact angle of thrust of the rear motor by using a hall effect servo with position feedback wire, output can be read by any of the available ADC inputs. This feature is a must have for racing and is implemented in triflight (a brunch of cleanflight for tricopters). There are a few servos on the market which already come with a feedback wire. also, it is usually trivial to have this on most of the hall effect servos by adding the missing wire.
For APM crowd, it will be beneficial for fixed wing VTOLs where exact servo position at any given time is necessary for vertical to horizontal and back transitions. Currently i believe it is approximated.

Thank you!

i think you mean this comand?