Agricultural Spray Drone

Overview

The Agricultural Spray Drone is a multirotor unmanned aircraft built to apply liquid fertilizer, pesticide, and herbicide across row crops, orchards, and paddy fields. It carries a Liquid Payload Tank of roughly 40 L and lays product down in a swath of 4 to 9 m depending on flight speed and altitude. A full machine in this class has a maximum takeoff weight near 65 kg, with the tank making up most of the payload. The aircraft flies a planned path generated from a field boundary survey, holds a fixed height above the canopy using radar, and meters product against ground speed so that the applied dose per hectare stays constant even when the drone slows in a turn.

The eight-rotor layout gives lift margin and keeps the aircraft controllable if one motor fails. Arms fold inward for transport, so a machine with a 2 m+ span across the props collapses to a footprint that fits in a pickup bed. The major subsystems are the Airframe, eight Propulsion Unit units, the Spray System, the Flight Controller, the RTK GNSS Navigation receiver, the Obstacle and Terrain Sensing radar suite, the Power System, and a Telemetry Datalink for telemetry.

Airframe and propulsion

The Center Frame Body is a pair of carbon fiber plates separated by aluminum spars, with an enclosed bay for avionics that keeps electronics away from chemical mist. Eight Foldable Carbon Arm tubes attach through an Arm Folding Hinge with a cam lock and detent spring, so each arm swings out and locks without tools. Two Landing Gear Skid skids set the aircraft high enough to clear the tank and the underslung nozzles.

Each Propulsion Unit pairs a large Lift Motor (BLDC Outrunner) outrunner with a Folding Carbon Propeller and an 80 A ESC. The motor runs on a Stator Assembly and Rotor Assembly turning on two Ball Bearing races. Folding blades let the props stow against the arms. The ESCs run field-oriented control for smooth thrust at the low RPM where these big props are most efficient.

Spray system

Product flows from the Liquid Payload Tank, a roto-molded HDPE shell with a strainer filler cap and an Ultrasonic Level Sensor that reports remaining volume to the flight controller. Two Diaphragm Pump diaphragm pumps, each driven by a BLDC Motor, push liquid through the Plumbing and Hoses to four Spray Nozzle Assembly units mounted under the outer arms. Each nozzle uses a Centrifugal Atomizer Disc spinning disc rather than a pressure tip, which gives a tight, uniform droplet size and resists clogging.

A Liquid Flow Meter with a magnet-tagged turbine measures actual delivery, and a Pressure Regulator with a Pressure Sensor holds line pressure steady as pump load shifts. Total flow runs 6 to 12 L/min, which empties a tank in a few minutes of continuous spraying. For dry product the Granule Spreader Attachment swaps in: a hopper feeds a Broadcast Spinning Disc broadcast disc through a servo-controlled gate.

Flight control and navigation

The Flight Controller carries two Microcontroller processors and two IMU (6-axis) sensors for redundancy, plus a Barometer for coarse altitude. Position comes from the RTK GNSS Navigation subsystem, an RTK GPS Module with two GNSS Antenna antennas that yield centimeter accuracy and a true heading. Centimeter positioning is what lets the drone fly parallel passes with no skipped strips and no double coverage.

The Obstacle and Terrain Sensing suite adds four Radar Module units for obstacle detection around the aircraft and a downward Terrain-Following Radar that holds the spray height constant over rolling ground and rising crop. An FPV Camera Module feeds a live view to the operator. Together these let the drone follow terrain at low altitude where spray drift is lowest.

Power and data

The Smart Battery Pack is a swappable 14S smart pack built from LiPo Cell cells with an onboard BMS Board, rated near 30 Ah. It mates through an XT60 Connector to the Power Distribution Board, which uses Power MOSFET switches and Gate Driver IC drivers to feed the eight ESCs and the pumps. Because flight time is roughly 10 min on a pack, crews hot-swap batteries between fills and keep several charging at the field edge. The Telemetry Datalink streams position, tank level, and flow data to the ground station over a redundant radio link.

Variants and use

A four-rotor version of this aircraft trades lift for a lighter folded size and suits small orchards, while six and eight-rotor builds carry the full 40 L tank for broadacre work. Operators plan a job by walking or flying the field boundary once, then the drone runs the mission with the human watching for obstacles and managing battery and chemical resupply. Field rates reach about 16 hectares per hour, which is why these machines have displaced backpack sprayers and some ground rigs in paddy and terraced regions where wheeled equipment cannot go.

Maintenance centers on the wetted parts. The Spray Nozzle Assembly discs, the Diaphragm Pump diaphragms, and the strainer in the Liquid Payload Tank filler all see abrasive product and need regular cleaning and periodic replacement. The carbon Foldable Carbon Arm tubes and the Folding Carbon Propeller blades are inspected for cracks after hard landings. Chemicals are corrosive, so crews rinse the Plumbing and Hoses and tank with clean water at the end of each day to stop residue from drying inside the lines. Software handles the rest: the flight controller logs every pass, flags any strip where flow dropped below target, and lets the operator re-fly a missed section the next morning.