Glitched trapdoors are one of the most useful tools in drone mapmaking. They were most famously used and popularized by player_03, a few examples of which are here:

http://numa.notdot.net/map/96160
http://numa.notdot.net/map/96371
http://numa.notdot.net/map/116921

Other uses have appeared in other maps, two of which are here:

http://numa.notdot.net/map/115125
http://numa.notdot.net/map/121283

Making a glitched trapdoor is rather simple; using one is not. To make one, simply change the third number of the code into an 'Nan', as shown below.

9^384,540,0,1,16,22,0,0,0
9^384,540,NaN,1,16,22,0,0,0

This creates a seemingly random object that can be used for many purposes. To explore the ways in which the ninja interacts with a glitched trapdoor, press J in debug mode and add a ninja and the above code for a trapdoor onto the end.

The reason a glitched trapdoor is so helpful for drone maps is that it creates an invisible wall in certain directions, almost like a one-way for drones. To make a drone go downward into a wall, place a glitched trapdoor on the right hand side of the tile directly above the wall you want the drone to go into. Place the key in an unattainable place. The tiles to the left and right of the trapdoor must be filled, or at least to the drone (half-filled works as well). This way, when the drone enters the tile with the trapdoor, it will form a wall above the drone, and as the drone cannot go left or right, it goes down into the wall.

To make a drone stop, do the exact same process as you did for letting the drone into the wall, except place the glitched trapdoor one tile to the left of where you want the drone to stop. This is the trick that was used in two maps listed above to make the drones stop.

Similar maneuvers may be used to cause the drone to stop at or go into walls in other directions, though down is the most common example. A rather thorough tutorial for this and more with trapdoors can be found on the forums.

I hope this helps.

VV What miyoser said VV

This is the code of a drone: 6^540,60,2,0,0,0
The last number in the code says how it moves (Surface follow, quasi random or dumb). If you put a NaN in stead of that number it stays still in it's place. Someone else is going to have to tell how to make them go in and out of tiles.

To make drones stand still, take the code of the drone and change the last number to NaN. For example, here is the code of a drone in this map and what it would look like after being stilled:

6^708,492,2,0,0,1
6^708,492,2,0,0,NaN

Another method of keeping drones still is surrounding them with doors, though this may cause lag and doesn't look as good. As for letting drones out of walls, they do that automatically. Place a drone in a wall and it will move in whichever direction you placed it. To make it turn when inside a wall, place normal doors where you want the drones to turn.

Getting drones to go into walls is far more difficult. This involves glitched trapdoors, and I can give a full explanation of this later when I am on a computer with N downloaded.

I hope this helps!