Design and Implementation of EPM Based Modular Micro-UAVs for Autonomous Midair Docking

Abstract

This letter presents a modular micro-UAV system based on electro-permanent magnet (EPM) technology, addressing the critical challenges of energy-constrained docking mechanisms in resource-limited micro aerial platforms. Built upon the Crazyflie 2.1 platform, our 75 g modular design (with battery) features an EPM docking mechanism that combines high holding force (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\approx$</tex-math></inline-formula> 1.5N) with zero static power consumption, making it particularly suitable for micro-UAVs with severe energy and payload constraints. Unlike existing approaches that rely on either uncontrollable permanent magnets or power-intensive electromagnets, our EPM mechanism achieves controllable docking/undocking through short current pulses while maintaining connections with no continuous power draw. Each EPM unit weighs only 1.5g while providing a 100:1 force-to-weight ratio. To accommodate the binary switching characteristics of the EPM mechanism, we implement a tailored two-phase control strategy that ensures smooth docking transitions. Experimental validation demonstrates a successful docking dynamic flight. This work provides a practical hardware solution for self-reconfigurable modular UAV arrays, with significant potential for collaborative aerial missions requiring frequent reconfiguration.