A 1-gram dual sensorless speed governor for micro-air vehicles

Embedding electronic control circuits onboard micro-air vehicles (MAVs) is a challenge in view of the stringent limitations in terms of mass, size, and power consumption. The propulsion unit is a cornerstone in the design of a MAV. In this study, we introduce a ´sensorless´ speed governor (regulator) for a propulsion unit composed of a miniature propeller (diameter 12 cm), a reduction gear, and a 8-gram coreless DC motor. In contrast with classical electronic speed controllers (ESC) designed for model aircraft, our speed governor operates in a closed-loop mode. Yet it does not require any tachogenerator. Experimental results show that our control strategy exhibits four main advantages: 1) it makes the rotor speed swiftly attain any new velocity set-point; 2) it makes the rotor speed virtually insensitive to aerodynamical (gusts) disturbances; 3) it makes the rotor speed largely insensitive to the drop in battery supply voltage; and 4) it makes the yaw autopilot of a miniature aerial robot act as a yaw damper. The two-channel speed regulator that we designed and built is used to servo the rotational speed of two propellers independently, without the need for any mechanical or optical tachometers. A new generation digital signal controller (dsPIC) allowed us to make this two-channel speed regulator small (13times15 mm), lightweight (1 g) and fully compatible with the 100-gram OSCAR II aerial robot developped at our laboratory.