VTOL design with servo motors

Hello, my vtol plane disign has:
motor 1, motor 2, motor 3, motor 4, Pusher motor
Right elevon, Left elevon, Rudder, Throttle
It’s small vtol for academic needs.

I want to use with Pixhawk PX4 Flight Controller PIX 2.4.8 32 Bit

In the ardupilot documentation I found this warning:
Do not connect any servos or other devices to the PWM outputs of your receiver. The RCIN port on the Pixhawk is designed for low power devices only, and a servo or relay may draw a lot of current from the receiver. If you connect a servo directly onto your receiver while the receiver is powered from the RCIN port of your Pixhawk you may damage your Pixhawk.
In this page - https://ardupilot.org/copter/docs/common-pixhawk-wiring-and-quick-start.html

My question is how I connect servo motors for two Elevons, Rudder and Throttle.
Is servo motors needs to be with some kind of special connections?


There is no special connection. Plug servos to the outputs directly. Wiki says that do not connect the servos to the receiver directly because you are connecting the receiver to the rcin. Rcin has its own 5v with limited current rate which cannot supply for higher current demands. If your escs has bec, servos can be supplied from servo rails. Pins on the Plus row at the servo rail are all shorted so if one of these has 5v other pins are also have 5v.

Thank you!
I am newbie in drone designing, so my question is about voltage.
In case I want to use this servo for 15kgf/cm and it needs 7.4V.

from here https://www.aliexpress.com/item/1005001530980323.html?spm=a2g0o.cart.0.0.1f623c00HKMXPh&mp=1

Is it possible to use it as a servo motors with Pixhawk PX4 Flight Controller PIX 2.4.8 32 Bit ?

How “small” ist your VTOL ? thats a 62g servo !

Servoconnection and Pixhawk Servo Rail read the wiki


The wingspan will be 650mm, following my calculations the servo motors for the elevons need to be able to move maximum on 14kgf/cm.
I found that this servo is suitable for my needs…

I don’t think you need this much big servos on your vehicle.
ES08MDII will do fine.

Mustafa, thank you!
I wrote before not correct information, sorry for that.
To be more clear the MTOW need to be around 9 kg.
And the wingspan will be around 650mmx2 = 1300mm.
Because of it following my calculations the servo motors for the elevons need to be able to move maximum on 14kgf/cm.

What do you think about that?

Thank you!

I have never worked with VTOLs, but you might need strong servos during conversions from vertical to forward flights.
I am not an aerospace engineer first of all, but don’t you have too much weight?
Wing loading seems to be too much, at least from my knowledge.
The vertical flights may be fine if you have enough thrust at the 4 motors but from my experiences, you may face difficulties at forward flights.
I designed a plane and it is ready to fly. The wingspan is 210cm and the chord is 35cm.
MTOW will be around 6kg, which gives 0.816gr/cm^2 wing loading.
Assuming you have a 30cm chord at your wings, so you have 2.308gr/cm^2 wing loading.
This is purely my opinion but you should reduce the wing loading around to the 1 (if possible, less than 1).

1 Like

Thank you very much!

I want to back to my original question, how to enable servo motor with 7V in maximum load needs?

Following Rolf answer I need to use ESC or alternatively a separate source such as a BEC because
Pixhawk does not supply power to the servo rail

So what parts I need to buy for my Pixhawk PX4 Flight Controller PIX 2.4.8 32 Bit to connect and use this powerful servo motors ?

I would recommend you to use an adjustable voltage regulator to power up your servos like this one.
You can set the output voltage as you like.

Does one voltage regulator enough for all 4 servo motors in my design ?
Or for every servo motor need to be one voltage regulator ?

Those regulators are stable up to 2amps. I could not be able to see current draw of the servos at the web page. Test the servos with multimeter. If overall current not exceeds 2amps, one regulator is enough.

Thank you!

One more question,
What is the connection of the servo motors to the FC and to the power using this voltage regulator?

I found this wiring diagram but for Raspberry Pi PX4 Autopilot - Flight Controller

(from here https://pnghut.com/png/x3yw8zP7B0/airplane-ardupilot-wiring-diagram-raspberry-pi-px4-autopilot-flight-controller-transparent-png)

Also I found this diagram with 4 motors

But can not understand how the servo motors are connected in VTOL Plane design …

Is there some diagram\example for connection servo motors with Pixhawk PX4 Flight Controller PIX 2.4.8 32 Bit ?

Thank you!