As part of its in-house Bionic Learning Network, Festo has been exploring the fascination of flight for more than 15 years. Since then, the tinkerers in Esslingen have researched and technologically implemented numerous other flying objects and their natural principles – and learned from the biological models. In this context, autonomous swarm behaviour represents a particular challenge. With the BionicBee, Festo Bionics has now developed a flying object that can fly in large numbers and completely autonomously in a swarm.

Ultralight flying objects with a delicate design

At around 34 grams, a length of 22 centimetres and a wingspan of 24 centimetres, the BionicBee is the smallest flying object from the Bionic Learning Network to date. Unlike previous projects, the developers of the BionicBee used the methodology of generative design for the first time. After entering just a few parameters, software finds the optimal structure based on defined design principles, using as little material as necessary to create the most stable construction possible. This consistent lightweight construction is essential for good manoeuvrability and flight duration.

Functional integration in a small space

The bee's body contains the compact design for the flapping wing mechanism, the communication technology and the control components for wing flapping and the adaptation of the wing geometry. A brushless motor, three servomotors, the rechargeable battery, the gearbox and various circuit boards are installed in a very small space. The intelligent interaction of motors and mechanics allows, for example, the frequency of wing flapping to be precisely adjusted for the various manoeuvres.

Natural flight manoeuvres with four degrees of freedom

The artificial bee flies with a wing flapping frequency of 15 to 20 hertz. The wings flap back and forth at a 180-degree angle. The brushless motor drives the wing flapping without play via a precisely guided and extremely lightweight mechanical construction. The higher the speed, the higher the flapping frequency and lift. The three servomotors at the wing root change the geometry of the wing in a targeted manner, thus increasing effectiveness in certain wing positions and leading to a targeted variation of the lift generated.

A question of geometry

If the bee is to fly forwards, for example, the geometry is set so that the lift in the rear position of the wing is greater than in the front position. This causes the body to tilt forward and the bee to start flying forward. If the geometry is set so that the right wing generates more lift than the left wing, the bee rolls to the left along its longitudinal axis and flies off sideways. Another possibility is to adjust the geometry so that one wing at the front generates more lift and the second wing at the back generates more lift. This causes the bee to turn around its vertical axis.

Autonomous flight in a swarm

The fundamentally new, almost revolutionary thing about the BionicBee, however, is its ability to fly in a swarm. To enable up to ten bees to interact autonomously with each other in the air, the developers used an indoor localisation system with ultra-wideband technology (UWB). To do this, eight UWB anchors were installed on two levels in the room, enabling precise runtime measurement. This enables the bees to locate themselves in the room. The UWB anchors send signals to the individual bees, which can independently measure the distances to the respective transmission elements and calculate their own position in the room using the time stamps.

High spatial and temporal accuracy

To fly together in a swarm, the bees follow the paths specified by a central computer. A high degree of spatial and temporal accuracy is necessary for a safe and collision-free flight in close formation. When planning the path, possible mutual interaction through air turbulence (‘down-wash’) must also be taken into account.

Automatic calibration function for each individual bee

Since each bee is built by hand and even the smallest manufacturing differences can influence flight behaviour, the bees also have an automatic calibration function: after a short test flight, each bee determines its own individually optimised controller parameters. In this way, the intelligent algorithms can calculate the hardware differences between the individual bees, and so the entire swarm can be controlled from the outside as if all the bees were identical.

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