Spray and commercial drones: parts, fixes and upkeep

• Flush the system the same day. Fill the tank with clean water and run the sprayers until it's empty, and repeat so the lines are rinsed about three times. Chemical left to dry is what clogs nozzles and corrodes parts.
• Clean the tank strainer and the nozzles. Take them off and clean them properly instead of just rinsing them in place.
• Wipe down the aircraft. Take dust and chemical off the motors, propellers and heat sinks with a damp cloth, then dry them. Keep the radar and vision sensors clean so flight and spraying stay accurate.
• Clean the battery ports and pins. Use 95% alcohol and a cotton swab or microfiber cloth. DJI says to check and do this daily.
• Store it dry and out of the sun.
• Keep a log. Note flight hours, what you cleaned and anything that felt off. It makes problems easier to spot and explain to a dealer.

• Inspect a centrifugal nozzle. Check the motor sealing ring and the valve rubber pad for corrosion, pinching or buildup. Spin the shaft by hand. Look at the solenoid plug for damage or corrosion, and clear any buildup in the nozzle.
• Leak-test the tank. Take it off, fill it with water, and look over the seams and the seals at the top and bottom.
• Check hoses, connectors and the tank for leaks, cracks and wear, especially after high-pressure cleaning or transport.

This is DJI's own checklist for the Agras T40. Other models differ in the details, so check your manual.

• Arms. Lock them open and wiggle each one at the motor base. A loose arm needs its nut tightened (DJI names a 16 mm socket wrench for the T40). The arm locks should snap into place: too loose and they can open on their own, too tight and they can stress the carbon fiber. Look over the arms for cuts and scratches, which can become weak points.
• Motors and propellers. Open each propeller pair. There should be some resistance, and the adapter screws shouldn't be loose. Run a finger along the blade edges for cracks, chips or dents. Cracked propellers must be replaced before takeoff, in pairs, with new prop gaskets. Spin every motor by hand: roughness usually means coil corrosion or a broken bearing, so take it to your dealer.
• Spraying system. Recalibrate it. In the Agras app, open Spraying System Settings, add a liter of water, tap Clear Trapped Air, then run Flow Meter Calibration. Empty the tank and tap Tare Calibration. Fill it with 20 L of water, check that the payload reads between 16 and 24 L, then run Weight Calibration. Finally, run the sprinklers at full flow (12 L/min on the T40) and look for leaks.
• Batteries and chargers. Inspect the charging ports for corrosion, such as green-tinged rust on the pins. Check that each battery holds a charge and powers the aircraft, and that fast charging still works.
• Test flight. Power up and check for errors. Hover gently, then fly manually with 180 and 360 degree spins, listening for whining motors. Test the radar against a pole and check the altitude readings going up and down. Run a route, then fly a couple of full tanks manually.

DJI recommends keeping spares for parts you can swap quickly in the field: motors, ESCs, propellers and prop gaskets. That's the difference between a 5 to 10 minute delay and losing the day. Dealers also suggest a set of nozzles plus gaskets and sealing rings for the spray system.

After a crash, DJI says a full damage assessment is needed, and a part swap at the field isn't recommended.

Dealer guides citing DJI's maintenance schedule give about 700 flight hours for replacing the pump motor, the nozzle motors and cylinders, and the spray tank on the T50. Check the maintenance table in your own manual for your model.