Recoil 6" (2017)

6 inch lightweight racing copter with F80 motors

Recoil XL (2017)

4 inch racing copter with xnova 1407 motors

Recoil (2017)

3 inch racing copter (AUW < 125g)

derbe evo (2016)

First aeropod in the world! Has served me a long time on many competitions!

0815 (2015)

Standard 250 racing frame

DERBE (2015)

Tilted body, vertical arm racing copter

QRC5 (2015)

First-ever tilted body, vertical arm racing copter

The QRC5 is a 5 inch (250 class) tilted-body FPV racing quadrotor. It incorporates some ideas that I had when I was designing the GEMiNi and the HEXO+. First of all, it's not a hex- or trirotor anymore, it is one of my first quadrotors... Personally, I think quadrotors are a bit boring. But there are many FPV racing events coming up, and I am sure that most of them will have several different regulations and limit the battery voltage, the amount of motors or the rotor diameter. The most 'standard' racing copters are quadrotors with 5" props. I am sure that they will get their own racing class. I would like to be able to compete with them, therefore I decided to design a copter for this standard class, even when I am not the biggest fan of quadrotors or racing rules and classes.
QRC5 in the 2015 FPV Airrace in Bexbach

Tilted propellers have become popular since the GEMiNi was presented, and in my opinion they really have an advantage. The aerodynamic drag is reduced quite a bit in fast forward flight. And, also important, the drag is increased in slow flight and during braking. This part becomes important on racetracks with sharp corners.
The QRC5 does not really have tilted propellers, but a tilted body (which is very similar). When only the body is tilted, there is little vertical offset between the propeller disks, which seems to be advantageous for the flight control.
The body is tilted 30° backwards, leaving the propellers on a relatively similar plane

The arms that connect the motors with the body are flat plates that are aligned with the dominant flow direction: Below the rotors, the flow will be 95% perpendicular to the rotor disks, no matter how fast we fly. The flat plates have very little drag, which will increase the maximum flight speed. Each of these plates are made from a three-layer sandwich (glass fibre, end grain balsa, glass fibre). This results in extremely rigid and lightweight arms.
Top view: The flat arms are parallel to the main flow direction
I'll again use the 'CCD-Killer' CMOS camera by Fatshark. For me, this is still the best camera, even much more expensive CCD cameras don't give such a great image. The camera is tilted 13° up (with respect to the propellers).
The CCD-Killer sits between the arms

It flies really great and has tons of power (4s motors + 2300 kV motors drawing 12.5 Amps each at full throttle). Due to some modifications in the code of my flightcontroller, it is more smooth and responsive (sounds like a contradiction, but is isn't!) than ever before...: I am using kiss escs with "oneshot" enabled. That means that these set the speed of the motor according to a 125 - 250 microseconds PWM input pulse. My code automatically determines how long the calculations of the control loop take and then synchronizes itself with the PWM pulse. This results in a minimum lag between reading the sensors and reacting to them. Furthermore, I also calculate the velocity of the throttle stick and add it to the motor output. This gives a very good response to throttle commands (something like feed forward). I will soon also include the accelerometer to further enhance this.

I had the chance to fly a few batteries in FPV mode, and it's really great fun. The top speed and throttle response is very good, the inertia in tight turns is also not too high although the copter weighs around 400g.

Here's a short Dom HD capture video:

And here is a video from the 2015 FPV airrace in Bexbach, shot from a different quadrotor. It was an intense battle and the video ends with a nice midair collision...:


  1. Hello,

    any other external video?
    or true picture?
    and about the price?


    1. Hi, here's an "external" video of it:
      That video ends with a crash. The QRC5 is currently still damaged and waits for me finding some free time to repair it...

    2. ...and there's no price, because this is my hobby...

  2. Hi william. Congratulations for the whole project. I do not know if you have already pubblished your firmware with GPS and pressure transducer. I am interested to take a look in it if you do not mind. Thanks in advance for your prompt reply...
    Iannis Iliopoulos (Electronic engineer)

  3. do you have any plans that you're willing to share or sell?
    i still haven't decided on the frame that i'll start this hobby with, but i'm sure its gonna be a 250 frame. there is overwhelming number of frames out there, from tilt arms to fixed. this and Derbe is in the top 5. when i finally finish up my cnc machine i want to be make the frame myself...

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