Fixing a drone after a water crash

That moment of horror when your custom-built drone crashes into the water. If it hasn’t sunk to irretrievable watery depths, you may have a chance to rescue it. Given water and electronics don’t mix, it’s down to the circumstance of your flight as to how much you can recover.

If you’ve managed to recover it, it’s likely not responding, but you can bask in the glory that you’ve saved your fancy carbon fibre frame, and that the GoPro probably works. It’s time to unplug the battery (and immediately flush it in fresh water if you downed it in the sea). Yes, this is perhaps the cleanest your drone has been for quite some time. Time to take it home and dry it out.

Step 1 – Dismantle, rinse and dry

The first step in recovery is to get the drone in a position where all the parts are clean and completely dry. It’s best to do this as soon as possible, otherwise everything starts to rust. Therefore, disassemble the drone, taking each part off of the drone, rinsing it in fresh water (or even better, deionised water), and dry out as much as possible with paper towel.

From experience, I find leaving everything on a tray to dry out for two days works well. Periodically shaking the parts and replacing the paper towel also helps you gauge just how much moisture is remaining. Important points to note:

  1. The motors should be dismantled. There is usually a central screw under the motor windings that detaches the bell of the motor from the motor chassis. At this stage you can put a drop of oil (e.g. WD40) on each of the bearings to prevent seizure and rusting
  2. The FPV camera can usually be dismantled; if possible, unscrew the back, remove the lens and extract the electronic MOS. Rinse and dry as for the other parts
  3. Only proceed after waiting for everything to completely dry out. If any of the electronics have residual moisture, you are increasing the chances of electronics shorting out and not working
Parts drying out

After the drone has fully dried out, you can reassemble the motors, applying a little oil to the bearings. After that, it’s time to incrementally check the components are working.

Step 2 – Check flight controller and radio receiver

Minimise the components connected to the flight controller. Most components have connectors, so this should be straightforward. No FPV camera, video transmitter, radio receiver, GPS, LED boards, etc.

Find a USB cable and USB charger and use this to test power the flight controller. Check if the LED lights come on. If they don’t, the flight controller is probably dead and you’ll need to purchase a new one. If the LED lights do come on, you can use the USB cable to connect the flight controller to your computer and Betaflight. In Betaflight, don’t forget to check:

  • Connectivity
  • Model settings
  • Gyro reacts when flight controller is moved

Power down the flight controller and connect the radio receiver. It’s normally possible to power the radio receive using the flight controller power, so it’s time to see if that works. Again, use a USB cable connected to a USB charger so you don’t inadvertently fry your computer. If both boards indicate LED activity, disconnect and reconnect to the computer and Betaflight. Power on your controller and see if Betaflight reacts to controller responses. Check:

  • Yaw, pitch, roll, throttle react correctly
  • Switches react correctly
  • Transmitter range

If all of the above works, it would appear your flight controller and radio controller are working! If not, you’re unlucky and will need to start sourcing components that have fried.

Step 3 – Check batteries and ESCs

Most of the drone requires power from the battery. Therefore, it’s time to connect the battery and check the motors and ESCs work together.

With 4-in-1 ESCS, you can do this without any of the other circuits attached – simply detach the flight controller ribbon cable. With separate ESCs, you’re going to have to immediately involve the flight controller.

Obvious safety points:

  1. Remove any props from the motors
  2. Don’t use the water-logged battery (dispose/recycle it). You’ve seen the exploding LIPOs on YouTube – don’t risk recharging or using a water-damaged battery
  3. If you have a smoke-stopper unit, this gives an additional layer of security against short circuits

Plug in the battery (ideally with smoke-stopper) and see if the ESCs respond and the motors twitch.

  • If the motors twitch, you’re in luck – the ESCs are operational
  • If nothing happens, add ESCs to your shopping list

At this point, if you have a 4-in-1 ESC, connect the flight controller and reconnect. The flight controller should also function.

Step 4 – Motor System Checks

We can now check the motors, ESCs, flight controller and radio receiver work in harmony. Preparation steps:

  1. Power on your radio transmitter
  2. Connect the radio receive to the flight controller
  3. Connect the ESCs to the flight controller
  4. Connect the computer USB cable to the flight controller and connect drone to Betaflight
  5. Don’t have props on the motors!

Now connect the LIPO to the drone. The drone should power up. Use Betaflight motor override and individually check each motor spins up in the correct direction and is associated with the correct position.

If the above checks out correctly, remove the LIPO, disconnect the USB cable and plug in the LIPO again. Arm the drone, and verify:

  • The the motors spin in their idle mode
  • Disarm/re-arm works
  • Gently playing with the controls results in motors responding

Your drone is now in a position to verify other components work correctly!

Step 5 – Component System Checks

Now is the time to check the other components. Namely:

  • The FPV transmitter
  • The FPV camera
  • A GPS
  • A buzzer, LED board or other components

It’s best to do them incrementally, to ascertain problem components. Remove the LIPO, and add a component. See if it works. Repeat for other components.

After adding all the components, perform a full system test on the drone. Treat it like a new drone build – verify all the switches work as expected, the FPV camera can be seen on the headset, the buzzer works, the emergency kill-switch functions correctly, and so on.

Step 6 – Test Flight

Now’s the time to head to an open field and perform a test flight. Add the props to the drone, observing the correct rotational direction for the props. Treat it like this is a maiden flight. This is usually accomplished by:

  1. Place the drone with plenty of distance from anybody
  2. Using line-of-sight flying, arm it, and bring to a hover, gently checking the controls. Bring down drone and verify disarm
  3. Perform a short, localised line-of-sight flight
  4. Perform a slow, gentle short FPV flight
  5. Perform a longer FPV flight, checking range, motor power and performance

If everything goes well, your drone is back to life. This doesn’t mean that components will not break later on, so treat the drone with caution for quite some time.

Ready for another watery adventure

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