Enabling a future full of insect-scale robots will require progress on a huge number of fronts, one of which is the development of mobility platforms designed to operate beyond the scaling frontier of commercially available solutions. The vast majority of researchers seeking to create functional centimeter-scale flying robots have turned towards biomimeticpropulsion mechanisms, specifically flapping wings. In this work I take a very different tack, investigating a propulsion mechanism with no natural analogue — electrohydrodynamic thrust.
Electrohydrodynamics (EHD), specifically in the context of corona discharge based systems, has been a long studied and, until relatively recently, often poorly understood phenomenon. The beginning of this dissertation focuses on the theoretical underpinnings of the thrust mechanism. The bulk of my work has focused on developing proof of concept demonstrators for EHD at the meso-scale. Starting with rapidly prototyped materials and quickly moving to microfabricated electrodes, a series of prototypes elucidate the potential for EHD to yield high thrust-to-weight ratio fliers. Initial demonstrations have been backedup by more rigorous investigations of electrode geometric and density effects.
Quadrotor systems begin to suffer from decreased performance at and below the centimeter scale, especially with regards to increasing demands on durability of rotory components (which may not exist at scale), efficiency of available DC motors, and propeller figures of merit . Simply replacing the rotors with EHD thrusters, however, allows us to side step some of the unfavorable scaling laws of propeller-based propulsion while maintaining theability to transfer domain knowledge from the rich world of quadcopter design and control. Demonstrating repeatable takeoff and rudimentary (open-loop) attitude control is trivial with external power supplied to the simple quad-thruster design. Through a combination of design and methodology (e.g., with regards to assembly) improvements, functional EHD-based “ionocraft” can now be built in about half an hour, with near 100% success rate. Controlled flight is now within reach.
Merely hovering with tethered power and an off-board controller is only the beginning. The final sections of this work outline a variety of paths forward, towards better performance of a meso-scale ionocraft, autonomous operation, and further miniaturization. Ultimately, I believe the future is bright for ionocraft. While electrohydrodynamics may not be the most power efficient mechanism, nor the easiest to grasp conceptually, it is certainly the simplest to design; put two asymmetric electrodes close to eachother, apply a high voltage, and awayit goes! In the words of a respected professor, how hard could it be?
December 31, 2018
Drew, D. S. (2018). The Ionocraft: Flying Microrobots With No Moving Parts. United States: University of California, Berkeley.