- Monospinner is an innovative drone that completely overlays the working principle of aerial vehicles
- The design of this monospinner drone proves that simplicity can absolutely be a strong point when it comes to drone engineering and design
The Institute for Dynamic Systems and Control at ETH Zurich have developed a new mono spinner. This mono spinner is a type of drone. According to the makers, mechanically, it is the simplest and controllable flying machine ever made. It has only one moving part (the rotating propeller) and it can control its position in space using that part. The vehicle features no additional actuators or aerodynamic surfaces.
The aim behind this creation was to fabricate a vehicle that has only one moving part. The principles behind this idea are based on the study of previous works on quadrocopters. The theory states that a quadrocopter can maintain flight despite the complete loss of one, two, or three propellers.
The need for a cascaded controller
The theory summed up into the following argument,
” To do this, we redefined the definition of “to hover”: now the vehicle may rotate at a constant angular velocity as long as it remains approximately at the same point in space. Of course, the vehicle then has to be controlled near this hover solution, to allow it to track trajectories and reject disturbances. ”
As the rotor had only one input or thrust force, a cascaded controller was designed to control the motor. The cascaded controller worked on the principle that the faster inner loop controls the thrust direction while the slower outer loop controls the vehicle’s acceleration.
The decomposition of controller
In general terms, the conclusion was to decompose the system into two parts. The first part is the average part of the thrust (calculated by the outer loop). It determines the acceleration of the Monospinner. The second part is the calculated deviation from the average thrust (calculated from the inner loop). This calculation helped in controlling the orientation of the vehicle.
After the theoretical analysis, the practical fabrication challenge was to build an aerodynamically stable design for such a complex system. In addition, there were some uncertainties such as the mass distribution or the position of the vehicle’s centre of mass.
For countering this problem, the design was built with the help of Monte-Carlo algorithm. In this algorithm, different perturbations from the uncertainties are sampled . Simulations are used to test if the controller can be synchronised with the drone. These tests resulted in achieving a configuration that works in most situations.
The control algorithm
For control strategy, hovering is used to manoeuvre the device. The vehicle spins about 4 revolutions per second. To get the vehicle near the operating angular velocity, a passive platform is built for the rotor. It consist of a vertically oriented bearing. This bearing allows the monospinner to rotate freely.
The rotation is achieved through the reaction torque of the propeller, and the thrust is slowly ramped up from zero. Once the vehicle is sufficiently near the hover angular velocity, the controller is switched on and the vehicle jumps off the platform. The platform ensures that the take-off condition is near the hover solution. This allows the monospinner to move like a Frisbee.
Needs start assistance
Since this drone is fitted with a single rotor system, it does require quite a bit of help flying up and actually getting into the air. Hence it requires assistance to get started. Once it gets into the air, it uses its innovative rotor system to balance its torque in such a manner that it can keep flying along.
This drone uses a complex mechanical structure and showcases a rugged tech innovation in the field of unmanned aerial vehicles.