Synchropter project

Just decided to show off this 2 years project.
Reasons: build a tailless helicopter because they look bad@$$ and just because I can.

I don’t take a lot of note and photo, These are all pics I have.

Project start: ‎July ‎19, ‎2015
Some line drawings (initially designed to use 4 servos)

‎September ‎3, ‎2015
Decided to start with the most difficult part, the custom bevel gears that mesh at 25 degrees.
This pair of gears proved countless people wrong about capability of 3 axis CNC

September ‎13, ‎2015
More details in

‎September ‎20, ‎2015
Made a prototype frame from acrylic

September ‎24, ‎2015
Bearing blocks

‎October ‎12, ‎2015
Came up with more practical design

‎October ‎18, ‎2015
Access to “real” CAD software

November ‎12, ‎2015

‎November ‎24, ‎2015
The finalized design

‎December ‎21, ‎2015
Getting real!

March ‎8, ‎2016
2nd most difficult part: Rotor heads
The blade grips need angled arm to avoid blade strike = custom made

Table top CNC isn’t going to make them like magic
This is Fail compilation, total of 4 failed attempts (3 are human error :stuck_out_tongue_closed_eyes: )

A pair needs to be made on the same Al block to ensure that they are identical and balanced

April ‎3, ‎2016
Finally usable grips!

April 5, ‎2016
Now, the center hub

I consider this the trickiest part to make on 3-axis machine…and they all failed

None of these hubs work,
Loose on shaft,
shaft won’t fit,
spindle not perpendicular.
no matter what tools I used to flip the work piece, there are coordinate errors
It’s impossible to make without 4th axis :weary:

August ‎22, 2016
“If you can’t flip it, mill both sides at the same time!”

//Run out of photo uploading space
continuing next reply


What the rotor heads look like:

The curved mixing arms fix non-linearity of angled grip arms.

‎July ‎21, ‎2016
Made an upgraded version of bevel gears: “Zerol Bevel Gears” with metal bushing

August ‎28, ‎2016
“The Grand Assembly”

‎September ‎4, ‎2016
The landing skids (legs) no photo available

Til this date, I still had no idea what flight controller I could use

September 19, 2016
Joined :sparkles:
See my discussion here: Synchropter build need help

‎December ‎1, ‎2016

‎December ‎24, ‎2016
First Lift Off

Video nowhere to be found

‎January ‎24, ‎2017
Telemetry set

‎May ‎6, ‎2017
Testing Here GPS
By mounting GPS on top in Cube’s former place, Cube got moved below the frame.

This was when the magic happened
Vibration level halved

May ‎8, ‎2017
Decided to make new lower frame that allow Cube to be mounted inside.

Final Design

May ‎17, ‎2017
Start working

‎May ‎23, ‎2017

May ‎31, ‎2017
“I wanna mount a camera”

‎June ‎29, ‎2017
First Loiter

‎July 2‎4, ‎2017

To be continued


Fail Compilation
These are either defective, outdated, incompatible or broken parts


that’s an amazing job and project!

In the end, waht firmware are you running on this baby?


I’m using modified 3.4.5 right now.
Will move to 3.5 as soon as it is stable.
I just don’t want to work with code everytime 3.5 rcxx is out.

Outstanding and truly exceptional, thanks for sharing!
You first loiter is also amazingly stable.

Btw, 3.5 is out now :wink:

This is a super cool helicopter. I’ve seen the video before I think, really impressive!

Hi, I’m working on the same project and I have a basic questions about the software:

I’m using the PX4_2.4.6 with the APM-Copter V3.5.5 heli; frame 11; mission planner and QGround Control.
Do I need any other software?

Many thanks!


This is awesome! And there I was complaining to myself this morning that I have to solder wires to an ESC to get flying…

What are the upsides and downsides of this kind of copter? Why isn’t it more popular?

The upside is symmetric control response, and importantly, they’re basically immune to retreating blade stall (which in a normal helicopter is nasty).
The main downside is mechanical complexity.

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Just seen this and would like to say I think it’s AWESOME! Congratulations @PittRBM!

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Only requirements are AC 3.5 or above. So APM can’t be used.
However the official firmware only supports Tandem style (fore-aft or left-right) not intermeshing style.

The code needs small modifications to yaw mixer. Aside from that, it’s like normal heli.

Also, obviously, no need for tail rotor and the cool look.

Complexity is not the real problem, it’s about as complex as tandem style (synced rotors) but shorter drive train and angled shafts.
The real problem IMO is lack of controller, the physics, and the dangerous look of it.
For physics part, I didn’t do much analysis or math, cascading 2 CCPM rotors just worked.

Many thanks! Now I’m using AC V3.6… Is it possible to get the modified code? THX

This is my code based on 3.5.4.

There have been few changes to these files since 3.5.4 so you can’t simply copy these 2 files to 3.6.x but I believe these changes won’t conflict.
I’m no expert at coding and git thing, you may find it poorly written.

Thank you for your interest. :slightly_smiling_face:

@PittRBM the dual heli frame was meant to support both tandem or side-by-side/syncropter heli’s. What changes are necessary for 3.6 to support synchropter? if the changes can be made so that the dual frame supports synchropter, I’m all for it. If you can suggest how to modify dual frame motors library to support this, then I’ll be sure to make it happen.


The only changes from transverse heli are yaw and roll mixer.

Roll: differential collective -> uses cyclic pitch only

Yaw: differential cyclic -> adjustable combination of differential cyclic + collective
*In my experience, differential collective is much more responsive but it induces undesirable sideway movement.
**the responsiveness and undesirable-sideway movement (in theory) varies with rotors angle and separation distance so I made my yaw mixer adjustable

That’s cool. I am too in the process of designing a whole new drone. But I’m stuck in the firmware part.
I’ve written about the design, which though has some clarifications yet to be made in detail, with images attached here :
The concept is this: Adding a third propeller spinning perpendicular to ground as a torque-reaction balancer.
Forget about the aerodynamics of air being pushed on one side that would make the drone spin unbalanced.
It can be rectified by adding another one coaxially and which spins pushing the air in opposite direction. The thing is that the other free side is now free for payload which in my case is a cutting arm. It’s a drone that operates semi-autonomously in harvesting coconut, much to the aid of farmers. If you are interested, please join me!
I saw all the code in ArduPilot regarding this (Ap_Motors etc.,) and I see that a lot and lot of cpp files need addition and integration with one another which is an overwhelming task for me. Can you look into this? Is it possible to create an entirely new design in this existing setup of libraries?

It’s alot easier to modify one of the existing frame type that’s the most similar to your design.(heli_dual in my case)
You skip the step of intoducing the new frame type (not recommended if you are planning to share to the world)

Better start your own topic, you’ll get more attention.

This concept is similar to the Russian Mil V-12, which is a transverse helicopter and already supported in heli in ArduPilot. Unless it uses collective cyclic pitch mixing it is not a helicopter and would be another multi-rotor frame type.

The synchropter being discussed here is a variation of the transverse helicopter and uses CCPM.