I promised to tell more about the DJI Mavic that I crashed into Skagerak during our trip to Norway 2018.
It was a perfect day for some drone footage of Sally while broad-reaching in 15 knots of wind from the northeast.
I have searched YouTube for videos of how to start a drone from a boat but at that time I didn’t find any, there were some videos of how to land a drone on a moving platform. So that part of the flight was pretty clear, fly parallel with the boat and catch the drone from below. But what about the takeoff?
The takeoff strategy was simple, place the drone on an as open and free spot as possible and go up as fast as possible to get free airspace around the drone.
So I placed the drone on the roof of the aft cabin, start it up, and then full throttle straight up. As soon as the drone got airborne like 5 cm above deck, it breaks hard and fly into the upper lifeline on the aft deck, loses control and fell upside down into the water behind the boat, and sank like a stone.
Think it must have been one of the shortest drone flights ever, all was over in less than 2 seconds.
I have tried to figure out what gone wrong and I think the reason is that the software of the drone flight control system isn’t built to start from a moving platform. When I tell the drone to go straight up it wants to be on the same spot and since it was moving forward with the same speed as the boat (around 12 km/h) it tries to brake as hard as it can to come to a stop. At the same time, the boat continues forward with 12 km/h so I think the drone actually hit the aft lifeline with 24 km/h (around 6 m/s). So the 2 m of the distance between the start point and the lifeline took about 0.3 seconds. I have no chance to react at all, just stood there completely amazed at what just happened.
I’m still not sure of the best takeoff strategy, have seen two different ways of doing it.
- Hold the drone from below and takeoff into free airspace.
- Start the drone and throw it up in the air into free airspace.
If there will be next time I will use method 1, it feels most secure.
I have found this YouTube clip where they put a short fishing line with a small weight, in the end, hanging down under the drone and then use that line when the drone is retrieved. Think I will practice it while on land to see how it works.