It does not take a great deal of technical knowledge or imagination to realize drones require a varied array of sensors, not only for control, but to maintain safe operation. People and property on the ground need to be safe from high-speed, low-flying aircraft crashing into them. Obviously, a drone can be an expensive equipment investment. Any form of accident could cost a brick of cash.
Depending on the size and application of the drone, a set of sensors for basic drone operation includes accelerometers, current sensors, tilt sensors, magnetic sensors, position sensors, inertial and measurement units. Then there can be several for minding the engine such as pressure, temperature, air flow, and fuel and power sensors.
The next level of sensors is dependent on the drone application. For example, a spy or surveillance drone may be equipped with one or several optical sensors as part one or more cameral modules. If the drone is intended to observe a large fire, be it consuming a residential or business domicile or a forest, it will most likely carry a thermal-imaging camera or two. For agricultural or weather observation chores, the drone may be carrying dedicated humidity, temperature, wind, gas, and chemical sensors. These are just a few of the applications drones may be enlisted for.
There are two types of drones that take off straight up, vertically, like a helicopter. The most common drone is the helicopter type, usually lifted up via four propellers spaced in a square or rectangular pattern atop the drone.
Standard drones find great use in consumer, hobbyist, and commercial applications. Commercial-goods delivery is an application that looms on the horizon. They are also used quite extensively in law enforcement and security work.
Vertical takeoff and landing (VTOL) drones are somewhat larger and come with their own set of requirements. They are smaller versions of vertical takeoff jet fighters without the same amount of engine power. One example is Sony’s VTOL that achieves speeds up to 105 mph after a vertical takeoff. It can carry up to 22 lbs. of cargo.
Primarily used for military and other heavy-duty apps, VTOL drones travel at higher speeds and offer somewhat more sophisticated maneuverability than standard drones. Therefore, sensor requirements differ. One example is airspeed sensors.
The PX4 Story
Airspeed velocity is a critical parameter of all drone types, more so in VTOLs travelling at higher speeds than most. An accepted and open-source auto-pilot solution is used for drone control, a solution that is easily customized to meet the needs of the designer.
Sensirion addresses one parameter of VTOL design with its SDP3x, initially introduced as the smallest differential pressure sensor on the market. It is now offered as part of an airspeed sensor development kit for VTOL and fixed-wing unmanned aerial vehicle (UAV) applications. The reference design is the fruit of collaboration with PX4 Pro, which means it’s a fully open-source solution with an aerodynamic software compensation model for the sensor and pitot tube, i.e., plug-and-play.
One problem the SDP3x sensor claims to overcome is the need for airspeed-sensor calibration before each flight. The sensor is completely calibrated and temperature-compensated, enabling calibration-free setup. This translates into instant launches and high sensitivity at low airspeeds, which reportedly translates into greater reliability and safety.
The SDP3x sensor is based on Sensirion’s CMOSens sensor technology. This entails an integration of the sensor element, signal processing, and digital calibration on a compact CMOS chip. Differential pressure is measured by a thermal sensor element with flow-through technology. This may be a kit to consider if you are heavily involved in VTOL drone development. ~MD