My daughters and I have a custom-frame aluminum quad rotor that uses the standard Arducopter electronics and software. Last evening, in an act of piloting stupidity, I accidentally crashed the quad into my swimming pool with a spectacular, high-speed, spinning splash. As soon as it happened, my heart sunk. I thought "I just ruined our quad. This is going to be a TOTAL LOSS."
We ran over to the pool. The quad was sitting on the bottom of the pool in four feet of water. To our utter amazement, the water was glowing with blue light. The quad was still on and functioning under water. All the LEDs were lit and acting normally.
After taking half a second to get over my stunned disbelief, I ran into the pool, grabbed the quad, and pulled it out (hoping that a 11.1 volt LIPO mixed with a pool of salt water wouldn't give me a jolting surprise).
"That's so cool, Dad, we invented a quadrotor-submarine!" my daughter said as I went into the pool.
When I finally got the quadrotor onto the deck, the lights were still on. I yanked the Deans battery plug, thinking I should kill the power ASAP. We took the quad rotor into the house and tried to dry it off with towels and a blow dryer. We then let it dry overnight.
This is a "salt water" pool, which means you add salt pellets to it rather than chlorine sticks, and then an electronic "Chlorintor" converts the NACL to chlorine. This results in a pool that is about 1% salt and a chlorine level of about 1.0.
This morning we inspected our quadrotor-submarine for damage. Again, I was expecting that none of the electronics would even power up much less function as designed. I assumed they would all be ruined. To our great surprise, we powered it up and it came on. Here are the details so far:
1. The battery was functional and doing its job fine, but it was wet and soggy, so we disposed of it and replaced it with a new one. (No sense taking any chances when it comes to Lithium-Polymer).
2. The Futaba receiver comes on and appears to function normally. It locks onto the Transmitter and responds to commands.
3. The Battery Alarm comes on and appears to function normally.
4. Astoundingly, the ArduPilot Mega and IMU come on and appear to function properly. They boot up normally, show the normal lights, respond to the RC Transmitter, and power the motors. When I rock the quad back and forth, it changes the motor speeds, so that indicates the IMU board is at least alive and that the Arduino software is running on the APM. Obviously, we'll do more tests, but this seems promising.
5. The MediaTek GPS comes on, blinks the normal amount of time, and then locks on satellite signal.
6. One of the motors runs fine (although it seems a bit hoarse in tone as compared to before, as if it's filled with salt particles or something). Three of the motors (or their ESCs) are twitching and beeping like they need calibration. They are all getting power, but they aren't acting normally. I'm not sure if it's the motors or the ESCs yet.
7. I can't tell at first glance whether the Magnetometer and Sonar are functional. We're going to test those a bit later.
8. There were no cameras or telemetry electronics on board at the time.
So, that's the damage assessment at this point. We were amazed.
The next step is to go through careful diagnostics to determine exactly what is working and what isn't. It could be that certain components are coming on and appear to be functional but will have problems that aren't immediately evident. It looks like the motors or ESCs need some work or replacement. But other than that, I don't see any obvious damage.
I officially nominate myself as the president of the DIY quadrotor-submarine society.
My daughters have changed the name of our quad from "Flyer 1" (their original name for it) to "The Nautilus". :)