Little enigma of physics that I asked myself

[Dislashed]

Hello,

I had thought of a physical problem that I did not know how to solve. My colleagues have not been able to answer either.
Here's the problem :

I own a drone and be on a moving train. I decide to fly my drone 1 meter higher from the ground, in stationary mode.
Will the drone crash?

I know that when you're on a moving train and I throw a ball in the air, the bullet will take the acceleration of the train.
But the problem is different, right? I need answers because it takes my head.

Thanks

 

[rfc]

I’m not sure what you mean by “stationary mode”, but if your assumption is that the drone will maintain its position using gps, then ( unlike the ball), It will Head to the back of the train car at a speed equal and opposite of the train’s, and likely smash into the back of the car.

If it is in ATTI mode it will act more like the ball horizontally, but still maintain its height, unlike the ball, which will not resist gravity.

 

[RichieGG]

Where'd the bullet come from?

 

[sar104]

A simple way to look at this, and similar problems, is to note that as far as the laws of physics are concerned, all constant-velocity frames of reference are equivalent. In other words you, the ball, and the aircraft, cannot tell the difference between a moving train and a stationary train, since those velocities are, themselves, defined in an arbitrary frame of reference - the surface of the earth. It only makes a difference if, as was mentioned above, those frames of reference cease to be independent, for example if the aircraft on a moving train uses the GPS system that defines a stationary frame of reference.

 

[RadioFlyerMan]

Yup, GPS will zap you!

 

[FlyGuy8675309]

Nice experiment. Yes, if you are inside a train car and launch your quad the back wall of the car will smash right into it. You would have to fly forward at the same speed of the train to keep it "stationary".

 

[sar104]

Nice experiment. Yes, if you are inside a train car and launch your quad the back wall of the car will smash right into it. You would have to fly forward at the same speed of the train to keep it "stationary".

That raises an interesting question - is there a solution to the problem in P-GPS mode. Left to its own devices, with sticks centered, the FC will perceive the situation as a forwards wind with a windspeed equal to the speed of the vehicle. It will therefore apply backwards tilt to try to hold against that wind. Forwards elevator could be used to remove the backwards tilt provided that the speed is less than the aircraft maximum, thus holding the aircraft perfectly level, which is what is required to keep it steady in the still air in the vehicle frame of reference.

 

[DanMan32]

Even ATTI mode, the IMU might also try to compensate.

 

[Splashy]

Within 50m of a railway !!!! Tut Tut

I would not think you would get a GPS lock and so the visual sensors would take priority and so it would be ok to use your AC on a train.

 

[Mossiback]

If you got a GPS lock, even momentary, it would try to maintain it's GPS position. It would appear to fly to the rear of the car but in reality the car would move into it.

The same thing happens when someone launches from a moving boat. They claim that the Mavic flew into the boat but it was the boat moving into the stationary Mavic.

 

[DanMan32]

Good point, VPS and GPS do tend to work together and system gets confused when they don't agree. I swear that's why many of us get problems flying low over bodies of water, particularly with winds causing surface ripples.
Anyone have a treadmill?

 

[sar104]

Even ATTI mode, the IMU might also try to compensate.

Compensate for what?

 

[FlyGuy8675309]

Even ATTI mode, the IMU might also try to compensate.

The IMU doesn't do anything but collect and transmit data to the main processor. It can not "compensate" for anything.

 

[abtocmeptb]

Now try to understand motorcycle counter-steering. Steer left to turn right.

 

[draver]

Good point, VPS and GPS do tend to work together and system gets confused when they don't agree. I swear that's why many of us get problems flying low over bodies of water, particularly with winds causing surface ripples.
Anyone have a treadmill?

I think that's only for airplanes...

 

[Jackcutrone]

Now try to understand motorcycle counter-steering. Steer left to turn right.

Huh? Not on any motorcycle I ever rode.

 

[draver]

Huh? Not on any motorcycle I ever rode.

That is surprisingly true. Next time you're going faster than 10-15 mph, you'll see. Very odd, but true.

Edited to add: Just watch some videos of flattrackers or road racers and you'll see their bars turned opposite the curve direction.