Simple Variable Pitch for Brushless Motor

With a brushless motor and a TRex tail rotor mechanism I could assemble a simple variable pitch system. I measured and it generates 700g with the TRex 500 tail rotor blades.

I tried the Trex 250 blades from the main rotor but although they are longer the thrust is smaller, just 400g. This is probably because the motor doesn't have enough torque.

This could be used for a variable pitch quadcopter or with an airplane.

Motor: Hextronik DT750
ESC: Plush 25A
Battery: Turnigy 2200mah 25C
Tail rotor: HK-500GT
Wood to support the tail mechanism: 38mm tall

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  • Thanks Bernardo.
    I guess you might also need a clutch on the prop otherwise or will be trying to turn the motor during autorotate.
  • Matthew, to do the autorotation, first you need to invert the pitch so as you go down the air that passes thru the blades accelerate them. Although you are not creating lift the blades generate drag, like a parachute so you have a controled descent. When you are near the ground, you invert the pitch so that you can create lift from the kinectic energy of the spinning blade ;). The main problem is to know that if 4 rotors like these would generate enough lift because they seem to have low inertia.

    The blades are symmetrical, if we use a different one it would perform better in just one direction. During my tests I've put an aluminum board in front of my chest and i wore safety glasses hhehehe

    hauhhauhauha, thanks for the tip andrew

    Valeu Guto! ;)

  • Distributor

    Show de bola Bernardo!



  • Turn your rig through 90° for testing so it doesn't chop your head off when it explodes...

  • Bernardo,

    I have a question on the autorotation on which I am far from expert.  Autorotation converts potential energy into lift by way of kinetic energy.  My question is where that kinetic energy comes from to make lift for the final  flareout?

    In the first phase of autorotation, height is traded for forward speed which keeps the blades spinning.  As you get close to the ground, speed is reduced.  In the final moments before touchdown, the only energy you have is the rotating blades.  Do the four small diameter blades have enough energy to autorotate?

    Are the tail rotor blades a symmetrical section?  If you can find equivalent size blades that are non-symmetrical then you might get better lift/drag at lower rpm.

    Having quickly scanned through Joe's blog, failure of the assembly is likely if you overstress it with larger blades or more rpm.  You might prepare for that my running your experiment in a safe enclosure. If you have a blade off it might do more than slice your finger.

    Have fun with your innovation.  I hope you prove some skeptics wrong.


  • There is already a solution for 3d flight including inverted hovering without mechanics. The ultraESC[1] can inverse the rotation direction of an brushless motor. It includes also live monitoring of the esc[2]

    Have a look at this nice demonstration:



  • Been there, done that, but tried to be bigger and smarter...ended in tears...Take a look at my blog

    A Large Scale Variable Pitch Tilt Quadrotor implementation.


    The Nampilot.

  • Hhahuhauahah thanks for the advice Maxime, i'll take one

    Good luck! ;)

  • Sweet jesus, please buy C-Clamp instead :D (okay I did that and finish night at the hospital) but I think think that give a chance :D

    Nice setup, I want to do something like that for a special quadcopter setup but existing material almost doesn't exist. I wanted to use helicopter part but doesn't know exactly how to fit it but your video help.
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