Nathan Chronister with S-1 Robotic Bird.

The revolution had its earliest beginnings in 1985. Paul MacCready was the legendary co-creator of the Gossamer Condor airplane, along with Peter Lissaman. It was the first human-powered airplane to fly a figure-eight course totaling one mile. In 1985, Paul MacCready’s company, Aerovironment, was funded by the Smithsonian Institution to build a half-sized replica of the giant pterosaur, Quetzalcoatlus northropi. It was featured in an IMAX film called On the Wing. Even at half scale, the robotic pterosaur had an 18 foot  (5.5 meter) wingspan. It was the first ornithopter to use an onboard computer to provide active stabilization of an otherwise unstable aircraft. The wings were driven by a powerful, custom-built servo, which provided variable flapping amplitude and computerized control of the wing movements. Although the QN replica was a milestone, the technology developed in the $4 million project did not find its way into common use in the ornithopter field.

Over the years, some people did begin to experiment with servo-powered ornithopters. Initially, we used the same servos that are used to move the control surfaces in radio-controlled airplanes. This new task of flapping the wings would require far more power. But we gave it a try anyway, because it seemed like a much easier alternative than trying to build our own ornithopter gearboxes completely from scratch. At the time, we didn't fully appreciate the other benefits that would follow.

Early servo-powered ornithopter attempts.
Bob Hoey's bird glider		Georges Chaulet		Nathan Chronister

Bob Hoey was among the first to try servo-driven wing flapping. He built a series of realistic bird-shaped gliders. The birds were carried aloft by an RC plane, and then they glided down from a height. Some of the models could move their wings up and down. Hoey knew the servos he had were not powerful enough for full flapping-wing flight, but it gave the appearance.

Georges Chaulet, around 1997, made an effort at powered flight using hobby servos. He connected the servos to the wings using a linkage, just as we had been doing with our gearboxes. He built one RC bird with wings hinged at the body, and another with hinges part way out on the wing. In this second model, a single servo was used to flap both wings, and an additional, smaller servo was provided for steering.

My own first attempt was a simplified, lightweight design, with one servo for each wing. To eliminate excess weight and friction, the wing spars were attached directly to the servo arms. The wing spars were secured with rubber o-rings, allowing their easy removal. The servos were controlled directly by a small RC receiver. I launched the model many times from a hill, and this allowed me to gain some appreciation for the difficulty of controlling wing movements in this manner. Despite considerable effort, my first servo-powered ornithopter could not maintain its altitude, and the servos would get quite hot in the attempt.

Mike Dodd also made an early contribution, with the servo-powered blimps that he began building in 1994. Freed of the restrictions of gravity, Dodd (aided by John Piri of West Coast Blimps) was able to fully develop a servo-powered drive system with electronic control. That is, a programmable microchip onboard the model does all the work of moving the servos back and forth. It even incorporates steering movements from the RC receiver. This avoids the need for repetitively moving the RC control stick back and forth to flap the wings. It provides much more accurate wing movements, for a more stable flight. While he was working on these models, we still didn't have any servos powerful enough to fly without helium.

Nathan Chronister's 2005 "Raven" ornithopter with powerful, custom-built servos.

In 2005, I built a new type of ornithopter using a hybrid approach. Called the “Raven” due to its onboard intelligence, it had separate motors driving the left and right wings. Each motor and gearbox was constructed in the conventional way, but I incorporated a potentiometer into each wing hinge, to sense the position of the wing. This information went to a microcontroller, which could vary the amount of power to the two motors. The positional feedback system amounted to a custom-built servo, and it offered some benefits never before imagined in an ornithopter: The two wings could be controlled independently, for a wide range of different flight maneuvers. The wings provided all flight control functions, and the tail was fixed. The wings could be stopped at a favorable glide position. Unlike the hobby servos available at the time, the dual motor drive system provided easily enough power for flapping-wing flight. Unlike hobby servos, the motors ran always in the same direction. This was thought to provide better efficiency and power output. However, this system does not allow varying the amplitude of the wing flapping. It was also very elaborate to build.

Soon after that, I learned that Hitec had introduced a whole new type of servo. Their digital robot servo, HSR-5990TG, had some advanced features that I thought might make it suitable for driving the wings of a robotic bird. First, the new servo used a better type of transistor, called MOSFETs. They switch the motor cleanly off and on, with very little energy wasted as heat. This would allow more efficient operation and a higher power output. The new servos were also designed to operate at a higher voltage, and they could produce far more power, for their weight, than any previous hobby servo. It remained to be seen if this would be enough power for flight. I had the idea of launching a contest, to see who could come up with the first ornithopter powered by these new servos. I thought it would be a fascinating challenge, which could bring new enthusiasts into the hobby. I thought it would stretch people to come up with more efficient ornithopter designs, to utilize what I still saw as a marginal power source. In 2011, I proposed the idea to Debra Cleghorn, at Model Airplane News, and also to Hitec as a potential sponsor. Although there was great interest in the concept, Cleghorn suggested that I ought to build a test model first, to validate the concept. I felt that it defeated the purpose of holding a contest to see who could do it first. However, Hitec was kind enough to donate a pair of the digital robot servos, to facilitate the development of a prototype.

My first ornithopter with the digital robot servos was not quite successful. I tried to use a biplane configuration, based on the classic Luna design. Many other researchers (and a few toy companies) had adopted its scissor-wing design. The balsa wing spars kept breaking, and even intact, the ornithopter didn’t really want to fly. Biplanes were thought to require about half as much power to fly, compared with the monoplane type, but even so I decided that I would try again, with a monoplane design. I had one ace in the hole, which was a new wing design that could dramatically improve the performance over conventional membrane wings, reduce the weight, and allow it to fly with less power.

The S-1 Robotic Bird in flight.

The S-1 Robotic Bird began its first test flight with a very simple program and no radio control. Not sure what to expect, I set it to flap the wings only five times and then go into a glide. I waited for a perfectly calm morning, drove to the flying field at the nearby elementary school, and stood there with the model in my hand, trying to mentally prepare myself to deliver a suitable hand launch without any way of knowing how the model was going to behave. I connected the power and positioned the giant bird for launch, while the programmed time delay slowly elapsed. When the sleek robotic bird finally took off, it darted forward from my hand and accelerated across the field with startling vitality. After the planned five wing beats, it went into a graceful glide and landed gently in the grass.

I found out the model would fly even better with some of Hitec’s newer servos. The digital robot servo that I started with is no longer made, and Hitec now sells a faster titanium-gear, digital brushless servo that brings performance up to the level of conventional RC ornithopters. Hitec has even incorporated a regenerative braking system, which recaptures momentum at the end of each wingstroke and makes the flight more efficient.

Subsequent flights with radio control allowed me to vary the flapping amplitude and experiment with some different steering methods. Servo-powered ornithopters allow multiple steering methods, without any additional servos, without any mechanical linkage, and without any separate control surfaces. With only the two servos that flap the wings, you can have four or more independent control functions. You may also enjoy the challenge of experimenting with various wing movements to see what kind of aerobatic maneuvers you can perform. I am excited to get this new platform into the hands of some other hobbyists, and see what ideas they come up with. I created a new online forum, accessible from BirdKit.com, where people can share programming ideas and code for robotic birds. Other than the programming, I didn’t have to make any major changes between the original prototype and the production model kit. This shows the versatility of these new servo-powered ornithopters. Keep an eye out for updates, as significant new developments are likely to unfold at a rapid pace.

Discover Flapping-Wing Flight!

An ornithopter is a device that flies by flapping its wings.

How is it different from an airplane or helicopter? Those machines are driven by rotating airfoils. In an ornithopter, the driving airfoils have back-and-forth motion instead. This imitates nature, because no animals have any rotating parts.

Leonardo da Vinci did not invent the ornithopter.

The idea of the ornithopter goes back to ancient times. Assyrian stonecarvers depicted God flying in a winged chariot or ornithopter at least 3,000 years ago. Ornithopter attempts were made before Leonardo's time, and Leonardo himself never actually built one -- he only drew sketches. The first successful flight of a manned ornithopter took place in 1942.

Build your own ornithopter!

Experience the challenge of building your own ornithopter, with model kits from BirdKit.com. Bird kits range from simple models powered by rubber band, to advanced robotic birds. They are all great flyers and perfect for school projects!