Jan 1, 2015 | By Alec

It seems as if 3D printed quadcopters have been filling the skies everywhere in recent months, but are they already outdated technology? Or are regular helicopters, for that matter? A brand new design, developed by the Modlab (University of Pensylvania) student James Paulos, who is studying under professor Mark Yim, could very well be relegating them to museums and history books.

So what's so revolutionary about this brand new design? To be completely honest, it isn't even that brand-new, as it relies on simple 3D printed parts and store-bought components. But what it does is utterly simplify the standard design of a helicopter, doing away with numerous different motors and parts, and could thus be paving the way for more cost effective, reliable and affordable helicopter technology.

So how is this design different? Well, the difference is in the number of motors and moving parts are necessary to make a helicopter airborne. As James explained in a paper presented at a 2013 conference in Japan, traditional helicopters rely on a large propeller motor and two or three small servomotors to control thrust, pitch, and roll forces and moments. Quadcopters, meanwhile, need four separate blades to achieve the same effect. 'Broadly speaking, thrust comes from the average speed and angle of attack of the propeller blade, and attitude moments are derived from an added cyclic oscillation in the angle of attack through each revolution. This cyclic pitching blade motion is ordinarily proscribed by a swashplate linkage driven by two or three additional servomotors and is sometimes augmented by the dynamics of a stabilizing flybar.'

This presents a number of design challenges; 'A swashplate-controlled coaxial helicopter must find room in its mass, size, and cost budget for four actuators (two big rotor motors, two swashplate servo motors) and a complex linkage assembly. A quadrotor must similarly support four motors and face the practical problems of rapidly shrinking rotors.' Not only does this increase assembly costs, it also means that there are more parts that can break.

But the design James came up with cleverly maintains all those control advantages of regular helicopters, while significantly simplifying its system. 'We derive thrust, roll, and pitch authority from a single propeller and single motor through an underactuated mechanism embedded in the rotor itself. This allows new types of conventionally-capable micro air vehicles which only require two motors for practical control. This contrasts with the many servos and linkages of conventional helicopters or the many drive motors found in quadrotors.'

This main motor directly powers the helicopter's propeller hub, which is in turn attached to the propeller blades through two cleverly designed inclined hinges. 'The hinge geometry couples blade lead-and-lag oscillations to a change in blade pitch. Instead of only driving the motor with a steady torque, we add a sinusoidal component in phase with the rotation of the rotor to induce a cyclic pitch variation. The amplitude and phase of this control signal determines the magnitude and direction of the vehicle response.'

This means that the helicopter is capable of flying with a single motor, that generates attitude moments through selectively elevating and decreasing its blade. 'By changing the magnitude of the driving sinusoidal modulation the magnitude of the control moment is adjusted, and by changing the phase of the signal relative to the airframe the direction of the control moment in the pitch and roll plane is affected.'

This necessary linkage can be achieved by adding a simple and affordable modification, made from a flexibile joint and a plastic blade. And this is exactly where 3D printing comes in handy; 'Forming the blade from a low cost material like polypropylene with good fatigue properties would allow it to withstand many repeated cycles of small angle bending.'

All this does mean developing a complex control system filled with unusual components, but James was almost entirely able to rely on store-bought components and 3D printed parts. 'The drive motor is a Park 400 12-pole,740 Kv brushless motor suitable for direct drive of large propellers. The three part propeller hub was manufactured on an Object 3D printer from a plastic polymer. The fixed hub interfaces with the motor shaft using a commercial aluminum mandrel, and two custom plastic blade clamps connect to the central hub along steel wire hinges.'

Of course this whole set-up makes the controls much more complex than is generally the case with conventional helicopters. While saving money on motors and other components, this does mean that other costs will unavoidably rise. But this is exactly the region where, or so James and his professor argue, time is an advantage. 'Cost is removed from the physical device and shifted to the control. We can then exploit the advances in computational power, reduced size, power consumption, and cost for these electronic systems.' Isn't that clever?

Most importantly, it works. While James submitted his clever device to a lengthy series of aerodynamic tests and analyses (see his conference paper for those), most of us will be content watching the interesting clip of his revolutionary helicopter in action below.

So what's next for James and his cool contraption? Well, it'll likely be some time before he'll seek to bring his design to market, as he's currently looking into techniques for 'determining optimal geometric design parameters for power-efficient operation given application constraints on required moments, thrust, and rotor size.' Ultimately, however he hopes to contribute to reducing system complexity and actuator count in helicopter technology and pave the way for a whole generation of low cost micro air vehicles.

Posted in 3D Printing Applications


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biniyam tamiru wrote at 12/13/2016 11:28:37 AM:

It is so beautiful! (Howit work)

S. Kim (my work was referenced in his paper :) wrote at 11/2/2016 3:56:06 PM:

Noble design, but this could induce vibration as the cyclic control requires intentional blade lead-lag action. More testing may be necessary at different rotor sizes and configurations.

IKE wrote at 7/15/2015 7:47:22 PM:


JB wrote at 1/2/2015 8:27:40 PM:

Does the distance between motors play an important roll. Could a coaxial brushless setup be used like this. http://www.hobbyking.com/hobbyking/store/catalog/CR28M.gif Underslung battery and FPV gear is my liking.

Bob wrote at 1/2/2015 5:33:23 PM:

Waleran, I think you totally missed the point that this design is linkage free and cyclic is accomplished by motor control software and an offset flapping hinge for the upper rotor blades. As far as I know that is unique, can't wait to see this in commercial models.

Bob wrote at 1/1/2015 10:37:56 PM:

LOL, should have read your conference paper

Waleran wrote at 1/1/2015 9:55:11 PM:

Very clever but 2 blade UAV's/duocopters are already possible with standard motor/propeller setup and an off the shelf, cheap, controller. But 3D printing the chassis for one of these.....hmm.

Bob wrote at 1/1/2015 7:22:56 PM:

James, use a hollow shaft motor (drill the existing motor shaft) on the lower, arrange the undercarriage through the motor to reduce weight. Very nice work on this design by the way.

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