Servers by jDrones

New Co-Axial Heli?

I am wanting to build a coaxial helicopter that is just like the Sprite vehicle!

I saw that the PX4 code base supports this vehicle type… Does ardupilot support this? If so, can someone help me get this working? I would really appreciate any help. Thanks!!


Anything from you guys?


@hybrid-guy I didn’t see this post the first time. Is this a true constant speed rotor head with collective and cyclic pitch on both rotor systems. I am the code maintainer for the helicopter frame. I could help you get this working in arducopter but i will need some details.
Post on our traditional helicopter discussion topic under arducopter

@hybrid-guy Ryan,
I didn’t notice that this was actually in the single/coax Copter category on discuss. The frame type is supported and this is the Wiki page but I have never tried this frame type. I only fly traditional heli’s.
Hopefully you can follow the wiki and get your vehicle set up with ardupilot.

fyi the Sprite is running ArduPilot.

Ardupilot supports fixed pitch coax heli setups? I have 2 motors, and 2 servos setup like the sprite… Any help would be greatly appreciated!


James, where is the firmware for it? I am building one now, and need the firmware to flash to my autopilot… I haven’t seen anything online with details on it

The coax copter firmware should “just work”, as it doesn’t really matter whether you’re using a vane to vector the thrust, or vectoring the rotors

James, but how do I setup the swashplate with just two servos? It will think that I have 3 servos…

A bit hard to say without seeing your setup

2 motors in the middle for upper and lower rotor, 2 servos on swashplate

Thanks for responding quickly!


Might be some phasing you’ll need to work out, but it should pretty much “just work”.
I suspect that coupling your throttle to pitch and roll (ie a feedforward term) will help response, but @bnsgeyer or @Leonardthall are the controls gurus and would know better

James, Ok thanks! I got it starting to work but I need to see why my lower motor is not spinning up fully when I arm it and command it full throttle… I got the upper rotor (motor 5) working great, now working on (motor 6 lower). I think the swashplate is working correctly, I will let you know how I progress!


1 Like

Hello , I am looking for a coaxial heli solution with two swashplate of three servo(H3-120 ) ,I know a little about coax technology I already have a coaxial drone with my software, I want to switch to ardupilot software ,is it easier to use dual heli frame config with some modification in servos and mixing ?

@Tarek-H Are your swashplates ganged and mechanically mixed? If they are then you can just use the single heli frame type and use the H1 swashplate type. If not then you will have to describe your swashplate set up and we can got from there.

Thinking about this more, if you have independently controlled swashplates then we just added the intermeshing configuration to dual heli and that could also control a coaxial head

The two swashplates are controlled independently ,in total six servos , two independent brushless motors runs at a constant speed ! , the mixing ,servos outputs equation are developed by our team, generally I use ardupilot software for multicopter, no experience in the heli part , what i understand if i set intermeshing configuration in the H_DUAL_MODE: parameter it could work for coaxial without any change in the code !? i will check AP_MotorsHeli_Dual.cpp file to see how the servos are controlled.

This configuration was just added to master. It is not in 4.0.6. It will come out with the initial release of 4.1 which I believe will be in beta testing in the next month. So you will want to look at master if you look at the code.
@PittRBM is our expert with the intermeshing mixer code. The intermeshing has two ways of controlling yaw: differential collective pitch and differential longitudinal cyclic. For your coaxial config, you would set the parameter H_YAW_SCALAR to zero.
I’d be interested to get your feedback on this once you get it installed and flying. I will have to change the selection for DCP_MODE to add coaxial with intermeshing. Pretty exciting.

How does the feed forward term work? What do I look for when tuning it?


For my case i use the differential collective pitch to control Yaw , i dont know what mean H_YAW_SCALER =0 (Scaler for mixing yaw into roll or pitch.) and H_DCP_YAW parmameters , I started analyzing the 4.1 code of the Dual Heli part ,I will keep you posted when there is something new in this porject .

You’ll be using Intermeshing mode which uses both cyclic and collective for yaw. YAW_SCALER controls the cyclic part while DCP_YAW controls the collective part. You can set YAW_SCALER = 0 to disable differential cyclic so you have pure differential collective for yaw. Pitch and roll are synchronized for both swash plates, nothing throttle is the same with single heli.

Servers by jDrones