Duocopter Does it With Two Fewer Propellers

Quads are a great ‘copter design. The paired blades counteract each others’ torque, and varying the relative speeds of the four motors makes it easy to steer. But what if you could get by with fewer blades, substituting a significantly fancier control algorithm?

[Dirk Brunner]’s DuoCopter drone uses two propellers that counter-rotate, and it steers by increasing and decreasing the speed at which the blades rotate within a single revolution. Spinning faster on one side than the other makes it tilt. Saying this is one thing, but getting the real-time control algorithms up and running is another. From the video embedded below, it looks like [Dirk] has it working. (He also holds the world’s record for fastest quadcopter ascent, FWIW.)

Of course some of you out there won’t be satisfied until your ‘copter has only one propeller. Or maybe you’d prefer a third prop. Whatever your taste, we’re stoked to see people pushing the boundaries of copter design.

[via Heise Online]

15 thoughts on “Duocopter Does it With Two Fewer Propellers

  1. I understand the attractiveness of VAV/rev (Variable Angular Velocity along a Revolution) ant this is quite a remarkable achivement! *Hat-Off*

    But then I would like to also see a study on power consumption modeling/measurement because of the ripple in acceleration and how it compares to symmetrical propellers (which I suppose do run “smoother”). This will not be easy due to prop diameter vs. prop efficiency and related interdependencies.

    Another interesting aspect I am curious about is how the additional jitter in forces do affect MTBF/overall life of the motors, their bearings and the whole support structure w. all the fasteners.

    I do admit that I’m neither a mech.eng. nor even a copter owner :-) but at least an old chap in some e-powered RC stuff from once upon a time when brushless did not yet exist.

      1. I saw this from ETHZ already back in spring last year.
        Both concepts -Monocopter, Duocopter- are surely worth to be thoroughly analyzed so the open questions of my post above can be answered. [1]
        I have not made my opinion yet on neither systems and I do look forward on more details on topic. My post above was not meant to be discrediting at all but to pursue research!

        [1] my educated guess for the ETHZ monocopter tends toward expecting jitter in the forces being of lower frequencies (so possibly similar to what goes on in a multirotor system) an possibly with less harmonics as what happens in the Duocopter system.
        My curiosity still waits for facts and figures – guesstimations and speculatius are of no help here.

    1. On the power consumption side: I’m sure there’s something smart you could do with a regenerative braking type thing within each cycle, swapping between driving the motor and driving the generator. For moderate tilt-accelerations, it might even come close to breaking even.

    2. Good comment. There are also experimental single propeller asymmetrical designs that seem to work. The real interest in these minimalist designs are in weaponization. The design requirement is a least cost in mechanical design yet fully controllable in a one-time-use “fire-and-forget” weapon that can target and hit the enemy precisely. Stabilization in-flight is NOT a goal with these weapons, no on-board cameras for-example. The trajectory is either pre-programmed using real-time battlefield geo-location data, and/or guided using some form of radio control (e.g., something like GPS but better).

      The result is a low-cost yet dynamically targeted and simple to deploy weapon that entirely replaces something like a traditional mortar round.

      The problem is who will get there first? ISIS with a total outlay of thousands of dollars using off-the-shelf parts over a one year period, or the U.S. Military who will spend Billions of dollars and take 20 years to develop the thing?

    1. Good link!

      But as for “superior”, I’d go “maybe”. It has the weakness of requiring variable blade pitch, which is a serious mechanical complexity. This duocopter design does it all in the electrons, which may be more reliable, and is certainly cheaper.

      1. It’s superior in every way except mechanical complexity, and ‘mechanical complexity’ is the sum total of 4 hinges.

        It doesn’t require variable blade pitch; it uses fixed pitch blades, and uses the lead-lag flapping motion of the blade to alter the pitch of the blade – which in my mind is a more effective solution than purely pulsing thrust, because it requires less rotor RPM for control authority. Other than that, it uses the same technique as this example to actuate control.

        It also allows for two blades per rotor, giving more thrust for the same rotor diameter, and dispenses with the superfluous dead weight required to counterbalance the single blade rotor systems.

        I’m willing to bet that with a little testing, the hinges could be implemented ‘solid state’ too so as to require no maintenance – either through a living hinge, a flexure, or an elastomer.

        In short, so long as you don’t actively fetishize the pure (regardless of its practical efficacy) ‘solid state’ nature of this solution, the solution I posted is in every way better. It’s also far more ingenious and much more of a hack. That solution is clever. This solution is brute forcing the problem.

    1. One bladed propellers are actually more efficient, at least from an aerodynamics point of view. Having only one blade means less “crashing” into the various vortices created by the trailing edges and tips of the blade.

      The main inefficiency of this design will come from the constant acceleration/deceleration, which makes the motor work much harder.

      1. It might not be that bad – since you have to add and remove power each half rotation you could have a capacitor bank for each rotor. so you could do “regenative” braking. Actually how about just not powering the rotor for half a rotation?
        The motor wouldn’t work “harder” overall unless you wanted to keep the current height of the drone while also going in one direction.

    2. As already mentioned, they’re not inherently less efficient. In fact single-blade propellers have been used in some RC modelling categories where every bit of performance counts. They’ve been used in top-level “control-line” championships and for setting speed records.

  2. What a time to be alive. Next thing you know, they will have copters with only one set of propellers. I have no idea what they would even call them “unocopter” or some such but everyone will probably default to “drone”.
    *too sweet- I couldn’t resist.
    Good work :)

  3. I want to see one of these methods put to use making a working version of the drone used in “Runaway”. The technology all exists now to make one that looks and functions exactly as in that movie.

  4. It’s worth clicking through to the vertical speed record link, too. Some amazing footage (including magic smoke and on-board camera view of an ESC failure tumble). I bet there were quite a few UFO reports the day they were doing that. :-)

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