Algodoo

Note: try dragging the UFO with the drag tool, or hitting it with anything until it goes far.

In this scene, you can test a prototype of a RCed UFO.
Use WASD to controll the UFO.
It's controlled via visible light, therefore you need be within
the range (circa 10 meters).
When the UFO is short time out of range, it'll get into the
"last valid position" mode, so it'll return to the last "connected"
position.
When the UFO is a long time out of range, it'll try to reach the
remote control.
Both alternative modes are immediately inactived once ir crosses
the range boundaries.

It's useful in those situations when the RC device (example: drones)
go out of the range, and they "fall" because of the lack of signal.
This code allow your RC device to go back to a position where it's able
to receive the control signal again.

Physic comments:
In the real-life models, the signal is transmited through a EM wave
(radio, for example), so the signal is able to go around obstacles
(difraction effect). In this simulated model, the signal is transmited
using laser beans, and they don't undergo difraction.