I have been meaning to ask this for ages. I think I know the answer. What would happen in the following scenario ignoring the obvious fact that nobody would likely ever do this:
You board a train at a station and turn on your drone. The train is static. The drone finds satellites, home point and is ready to fly. The train pulls away from the station with the drone sat on a table in the carriage, and travels at a general speed (could be anything but lets say 50mph).
You then start the propellers, and press lift to take the drone up in the carriage. (But the train is moving so the point which it takes off from is moving at 50 mph beneath it). Does the drone remain in place and if so how because it is technically travelling at 50mph? Or does it take off and instantly fly backwards smashing into the end of the carriage? Or do the ground sensors tell it that it is stable to prevent this?
A drone inside a moving vehicle will presumably be flying in ATTI mode, and therefore ‘unaware’ that the train/bus/van/ship/aircraft is moving. The space it is in is it’s entire universe, and the rest of everything is moving but the vehicle is stationary. If it’s made of paper by origami it is also stationery, but that’s another story…
If you fly from a table near the window it is presumably possible for the drone to access GPS satellites and position itself according to those, but once the train starts moving the home point is updated. My understanding of this is that the drone will attempt to follow the updated home point, or you can fly it in the same direction that the train is moving in. Eventually, the train’s speed will increase beyond what the drone is capable of and it will appear to fly backwards towards the rear wall of the compartment, which will eventually catch up and hit it, and it will probably crash unless the prop guards are fitted.
It will add to the weight of the train by the extent of it’s own weight even when it is flying, because it will displace air of exactly that weight within the enclosed carriage.
Logically (Captain):
If the drone has gained a GPS lock, it will take off and attempt to maintain its GPS position, just as if it took off in windy conditions and immediately had to lean into the wind. Therefore, I believe it will intantly smash into whatever is behind it.
However, if the drone is depending only on optical flow positioning, it will maintain position above whatever it sees beneath it, and it will stay put relative to the vehicle its in.
However (again), if it is using a mixture of GPS and optical, the behaviour will depend on the software.
However (yet again), on GPS it may fail to get a lock on a location due to the vehicle’s movement, and revert to using optical flow, and remain stable.
P.S. Please get someone to video your experiment, we would love to see the result.
In reality, drones and the train will follow Newton’s first and 2nd law of motion and will maintain their inertia.
Newton’s second law of motion states that the acceleration of an object is directly proportional to the force applied to it, and inversely proportional to its mass: ie Forcce = mass x acceleration.
The drone would sit stationary in the mass of air in the carriage until it, or the train, exerts their own force on said mass.
The drone will attempt to maintain its GPS lock if available and therefore exert its own force overcoming the mass of air it is sitting in, or the train accelerates to the point where it affects the mass of air within it.
I wasn’t expecting these answers I thought satellites were the sole source of location pinpointing for the drone. What system, or tool on the drone, permits it to allow itself to move and possibly at speed, whilst it can also see that it is moving rapidly away from the H or fixed point it thinks it was at? Or is it that it can see it is moving without any prop inputs therefore works out that it is in a moving vessel?
Absolutely Chris, unlike the genius of Tex Avery and Chuck Jones’ Warner Bros. Cartoons! Loved Bugs Bunny and the way he avoided certain death by stepping out of a falling elevator at the last second (for one example… there were so many).
Surely if it has a satellite lock and is simply hovering, ( with no stick inputs) as the train moves forward the drone with try and maintain its GPS position and move in the opposite direction of the train ? I’d have thought that once it has a satellite lock, with no stick inputs it’s surely going to try to maintain its position in relation to its GPS coordinates ?
I’m not sure it will be able to lock GPS reliably on a train anyway. Most modern trains are double-glazed, and many have tinted windows, some electrically heated, that will tend to interfere with the very weak GPS signals, and that’s before cuttings, tunnels, bridges, buildings close to the track, interference from the overhead electric wires &c are taken into account. Chances are a drone in a railway carriage will be in ATTI mode most of the time. It will therefore hover steadily inside the carriage no matter how fast the world outside is passing the window.
Still, I wouldn’t put it past our DJI friends coming up with something, look at LiDAR!