How to Build a 15L Agricultural Spray Drone: Parts & Assembly
Build a 15–16 L agricultural spraying drone: frame, propulsion, 12S/14S batteries, pump, nozzles, radar, RTK and flight controller, with assembly steps, calibration, flight-time and coverage maths, and safety rules.
- Layout: four rotors on folding arms, about 1.6–1.7 m diagonal wheelbase, 15–16 L tank.
- Weight: about 38 kg maximum takeoff weight with a full tank in the example build.
- Power: 12S or 14S smart LiPo, around 22,000 mAh, with 34-inch folding propellers.
- Flight systems: agricultural flight controller, RTK GNSS, terrain-following and obstacle radar, handheld ground station.
- Budget tiers: frame kit plus individual parts for the lowest cost, an assembly kit for faster building, or a complete aircraft for the quickest start.
A 15–16 litre spraying drone is the class most often chosen for small and medium farms: big enough to cover about a hectare per tank at 15 L/ha, small enough for one crew to transport. This guide covers a four-rotor build around integrated propulsion units, from the parts list to the first water test.
Agricultural drone parts list
The table lists each part, what to check before you buy, and matching products. Choose 12S or 14S first and keep the propulsion, batteries, charger and pump on the same voltage.
| Part | What to look for | Matching products |
|---|---|---|
| Frame or assembly kit× 1Drone frames → | 15–16 L class, four folding arms, 40 mm arm tubes for X9-class units, tank mount, landing gear | |
| Propulsion units× 4Drone motors → | Integrated motor, ESC and folding propeller; 7–11 kg recommended takeoff weight per axis; 12S/14S | |
| Spare propellers× 1–2 setsDrone propellers → | Folding blades matched to the propulsion unit (MFP 34x11 for X9) | |
| Flight batteries× 3+Drone batteries → | 14S (or 12S) smart LiPo, about 20,000–22,000 mAh, AS150U-type connector | |
| Charger× 1 | 12S/14S support, 1,500–3,000 W, field generator compatible | |
| Flight controller× 1Flight controllers → | Agricultural firmware: AB and route spraying, flow and level inputs, radar and RTK ports | |
| RTK GNSS× 1Drone GPS & GNSS → | Centimetre-level RTK, ideally dual-antenna heading | |
| Terrain-following radar× 1 | Downward mmWave radar covering 1–10 m spray heights | |
| Obstacle radar× 1–2 | Forward (and rear) mmWave radar | |
| Pump× 1–2Spraying system components → | Brushless pump, 5–8 L/min, same voltage as the flight battery | |
| Nozzles× 2–4Spraying system components → | Centrifugal (adjustable droplet size) or pressure fan nozzles | |
| Flow meter× 1Spraying system components → | Measures applied volume for rate control and calibration | |
| Tank, filter and level sensor× 1Spraying system components → | 15–16 L chemical-resistant tank, inlet filter, empty-tank sensor | Usually supplied with the frame kit |
| Remote controller / ground station× 1 | Handheld Android ground station with integrated radio link and video | |
| Wiring and connectors× 1 set | High-current power distribution, battery connector matching the pack, waterproof signal connectors | — |
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Quote the full parts list →Quad or hex: choosing the layout
Four-rotor sprayers use fewer, larger propellers, which keeps the aircraft simple, light and quick to fold. Six-rotor sprayers spread the load over more, smaller units and give some redundancy if one unit fails, at the cost of more parts and wiring. The propulsion rating decides how many units you need: the Hobbywing X8 G2 is rated for 5–7.5 kg per axis, so six of them suit a 30–45 kg aircraft, while four X9 units at 7–11 kg each cover a 28–44 kg quad.
Frame kit, assembly kit or complete drone
A bare frame gives you the most freedom to choose every part, and the most integration work. An assembly kit such as the Hongfei HGS T16 Assembly Drone arrives as a 1,700 mm, 16 L airframe running on 12S power, folding to 870 × 870 × 750 mm, with the structure already matched to its tank. A complete aircraft such as the Hongfei HGS T16 or EAVISION EA-16X is ready to calibrate and fly, which suits buyers who need to start spraying this season rather than build.
Tools you need
- Metric hex and socket set, torque screwdriver and medium-strength thread locker.
- Soldering station for high-current connectors, heat shrink and waterproof sealant.
- Multimeter, cable ties and spiral wrap for the arm harnesses.
- Laptop or the ground station with the flight controller's configuration app.
- Measuring jug, stopwatch and clean water for pump and flow calibration.
Step-by-step assembly
1. Check the power system match
Before assembly, confirm that the propulsion units, batteries, charger and pump share one voltage (12S or 14S). Check the expected takeoff weight against the propulsion rating: four Hobbywing X9 units are rated for 7–11 kg each, which covers a 28–44 kg aircraft.
2. Build the frame and fit the arms
Assemble the centre frame, landing gear and tank cradle. Fit the arm tubes into the folding joints and check that every joint locks firmly. Mount the propulsion units on the arm ends so that all motor shafts are parallel, and tighten the clamps evenly with thread locker.
3. Place CW and CCW units correctly
Integrated units come as clockwise and counter-clockwise versions. Install them on the arms shown in the flight controller's frame diagram, and fit the matching blades. Do not swap phase wires on integrated FOC units.
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4. Route power and signal wiring
Run the power leads through the arms to the central power distribution, observing polarity, and fit the battery connector. Route throttle, radar, GNSS and pump signal cables apart from the high-current leads, and leave slack at each folding joint so cables are never pulled tight when the arms fold.
5. Mount the flight controller, GNSS and radar
Mount the flight controller near the centre of gravity on its damping mount, arrow forward. Mount the GNSS or RTK antennas on their masts, away from power wiring and pump motors. Fit the terrain radar facing straight down and the obstacle radar facing forward with a clear view.
6. Install the spraying system
Connect tank, filter, pump, flow meter and nozzles with chemical-resistant hose and secure every joint. Mount centrifugal nozzles under the rotors or on booms as the frame design specifies, and connect the pump and nozzle control cables to the flight controller outputs.
Setup, calibration and test flights
- Throttle: integrated units such as the Hobbywing X9 series need no stick calibration; set the flight controller's output range to the unit's specification.
- Sensors: level the aircraft and calibrate the accelerometer; calibrate the compass outdoors, away from vehicles and steel structures.
- Radio: bind the ground station, check every stick and switch, and set the failsafe action (hover or return home).
- Motors: with propellers removed or secured, run the motor test and confirm each position and direction.
- Spraying: fill a known volume of water, purge air from the lines, run the flow calibration and enter the measured volume.
- Flight tests: hover with an empty tank first and check stability and temperatures, then repeat with clean water before ever loading chemicals.
Pre-flight checklist for every working day
- Arms and propellers: every folding joint locked, no cracks or chips on the blades, blade bolts tight.
- Battery: fully charged, cell voltages balanced, latch closed, connector clean and dry.
- Positioning: RTK fixed (or enough satellites for GNSS), compass healthy, home point recorded.
- Radar: the ground station shows a sensible height reading over the take-off area.
- Spraying: filters clean, no leaks at hose joints, flow rate and swath set for the label rate.
- Field: boundaries and obstacles mapped, people and animals clear of the work area, wind within the product label limits.
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Calculations: thrust, flight time and coverage
The example uses the Hongfei HGS T16 figures (38 kg maximum takeoff weight) with four Hobbywing X9 units and one 14S 22,000 mAh battery.
- Weight budget: 38 kg maximum takeoff weight minus 16 kg of liquid leaves 22 kg for the airframe, propulsion, electronics and battery together; this 22 kg is the empty weight used in the hover-time figures below.
- Load per axis: 38 kg ÷ 4 = 9.5 kg, inside the X9's 7–11 kg recommended range.
- Thrust-to-weight ratio: 4 × 22 kg maximum thrust = 88 kg; 88 ÷ 38 ≈ 2.3:1. That is more than twice the thrust needed to hover, which leaves margin for wind, sloshing liquid and climbs over rising ground.
- Battery energy: 51.8 V × 22 Ah = 1,139.6 Wh. Using 80% leaves about 912 Wh.
- Hover power ≈ takeoff weight ÷ system efficiency. Assuming 8 g/W at full load, 38,000 ÷ 8 = 4,750 W, plus about 150 W for pump and electronics, gives about 4,900 W.
- Hover time ≈ usable Wh ÷ power × 60: 912 ÷ 4,900 × 60 ≈ 11 minutes full. The same formula at 22 kg empty and an assumed 9 g/W gives about 22 minutes. Real work flights include acceleration and turns, so plan on less.
- Coverage per tank: area (ha) = tank volume (L) ÷ application rate (L/ha). At 15 L/ha, a 16 L tank covers about 1.07 ha.
- Pump flow needed (L/min) = rate (L/ha) × swath (m) × speed (m/s) × 60 ÷ 10,000. At 15 L/ha, 5 m swath and 5 m/s: 2.25 L/min, so one 5 L/min pump is enough and the tank empties in about 7 minutes of spraying.
- Batteries needed for continuous work ≈ 1 + charge time ÷ (flight time + turnaround). At 3,000 W, recharging 1,140 Wh takes at least about 23 minutes; with roughly 12 minutes per sortie including refilling, that is 1 + 2 = 3 batteries. With a 1,500 W charger, plan on about 5.
Safety and regulations
- Read the pesticide label first: it sets the application rate, the conditions such as wind and temperature, and the protective equipment. Wear the specified gloves, mask and eye protection when mixing and loading.
- A 14S 22,000 mAh pack is over 1,100 Wh, far above the 160 Wh limit for passenger baggage. Ship these batteries as dangerous goods cargo, at a reduced state of charge, with packaging and documents arranged through the carrier.
- In the US, dispensing chemicals from a drone requires a Part 137 agricultural aircraft operator certificate, a remote pilot certificate, aircraft registration, and for aircraft of 55 lb or more an FAA exemption and authorisation.
- In the EU, aerial spraying of pesticides is prohibited by default and allowed only in special cases approved by the national authority. In other countries, check both the aviation authority and the agriculture ministry before operating.
- Flush the tank, pump, hoses and nozzles with clean water after every working day, and store batteries at storage charge, away from chemicals.
Frequently asked questions
How do you calculate an agricultural drone's payload and flight time?
Takeoff weight = empty aircraft + battery + liquid, with 1 L of spray mix counted as about 1 kg. Hover power is roughly takeoff weight in grams divided by the propulsion system's efficiency in g/W. Flight time in minutes = usable battery Wh ÷ hover power × 60. For a 38 kg aircraft at 8 g/W and a 1,140 Wh battery used to 80%, that is about 11 minutes with a full tank.
How many batteries does a spray drone need?
For continuous work you need one battery flying and enough charging to keep up: batteries ≈ 1 + charge time ÷ (flight time + turnaround). With a 3,000 W charger such as the SkyRC PC3000H-12/14S and a 22 Ah 14S pack such as the Tattu Pro 14S 22000mAh, charging takes at least about 23 minutes, so three batteries cover 12-minute sorties. A slower charger needs more batteries.
How many hectares can a 15L drone spray per tank and per hour?
Area per tank = tank volume ÷ application rate: 16 L at 15 L/ha covers about 1.07 ha. While spraying, the work rate is swath × speed: a 5 m swath at 5 m/s is 9 ha per hour. Refilling, battery swaps and turns lower the real hourly figure. See complete agricultural drones for rated figures by model.
What tank size should I choose for a spraying drone?
10 L drones are lighter and easier to carry and suit small or terraced fields. 15–20 L drones, such as the Hongfei HGS T16, balance coverage and transport for small and medium farms. 30 L and larger drone sprayers cover the most per tank but need bigger batteries, chargers and generators. In the US, aircraft of 55 lb or more also need an FAA exemption to operate.
Is RTK necessary on an agricultural drone?
It is not required to fly, but it improves spraying accuracy. Standard GNSS positioning is accurate to about 1.5 m, which can leave gaps or double-sprayed strips between passes. RTK modules such as the CUAV C-RTK 2HP are rated at around 1 cm plus 1 ppm horizontally, and dual-antenna units also give a heading that is not affected by magnetic interference. Browse GNSS and RTK modules.
Do I need terrain-following radar on a spray drone?
Yes, if you spray over slopes, terraces or uneven crops. Spray drones fly only a few metres above the canopy, and a downward millimetre-wave radar such as the Topradar TR24DA100 (0.6–18 m range) keeps that height constant so the swath stays even. A forward obstacle radar such as the Topradar TR24DCA200 adds protection against trees, poles and wires.
Centrifugal or pressure nozzles: which is better?
Centrifugal nozzles spin liquid off a disc, so droplet size can be adjusted electronically and they resist clogging; the Hobbywing SPRAY 9L lists a 35–500 μm droplet range. Pressure fan nozzles are simpler and produce coarser droplets that drift less. Choose by crop, product label and drift risk; fine droplets drift further in wind. Browse spraying system components.
Which motors and propellers suit a 15–16 L quad sprayer?
A 15–16 L quad typically uses integrated propulsion units rated around 7–11 kg recommended takeoff weight per axis, such as the Hobbywing X9 with MFP 34x11 folding propellers or the JIYI CX9 Power Suit. Divide your full takeoff weight by four and pick a unit whose recommended range includes the result.
Should an agricultural drone use 12S or 14S batteries?
Both are common. What matters is that every powered part matches: propulsion units, batteries, charger and pump. For example, the Hobbywing X9 series and PUMP 5L both accept 12S and 14S, so either works if the batteries and charger match.
How long do agricultural drone batteries last?
Cycle life depends on depth of discharge, temperature and charge rate, so check the battery maker's rating on the battery page. Batteries last longer when they cool before charging, are not run flat, and are stored at storage charge between seasons.
How do you clean and maintain a spray drone?
After every working day, run clean water through the tank, pump, flow meter, hoses and nozzles until it comes out clear, then clean the filters. Wipe chemical residue off the frame, check propellers, arm joints and connectors for damage or corrosion, and dry the aircraft before storage.
What licences do I need to spray with a drone?
It depends on the country. In the US, you need a Part 137 agricultural aircraft operator certificate, a remote pilot certificate and aircraft registration, plus an FAA exemption for aircraft of 55 lb or more. In the EU, aerial spraying of pesticides is prohibited by default and allowed only in special cases approved by the national authority. Pesticide applicator licences may also apply.
Can I build an agricultural spraying drone myself?
Yes. The usual route is a frame or assembly kit such as the Hongfei HGS T16 Assembly Drone, four integrated propulsion units, an agricultural flight controller with RTK and radar, and a pump and nozzle set. Buying a complete aircraft such as the EAVISION EA-16X is quicker if you need to start spraying straight away.