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Autosentry

The autosentry breaks the first law of Asimovs three laws of robotics: A robot may not injure a human (...).

Hooked to a laptop with a high speed videocamera this monster can automatically track persons on a sup'air paintball playfield and shoot at them. This includes compensation of the paintballs trajectory, calucation of the players speed and compensation to hit them even if they are far away and fast moving.

It's done via a simple frame-to-frame comparison. The resulting grey-scale picture (dark=no movement, bright heavy movement) is mathematically reduced to the least possible number of boxes that cover all bright areas. These boxes are compared (only those that are near to each other), and by the distance a movement-vector is calculated. Because of the framerate, the movement-vector is only a small fraction of the players real movement vector. Thus this vector is scaled, it grows very fast, overshoots the real margin, but quickly adjusts to the real movement vector. By doing this the system can react very fast on movement, and the overshooting of the vector results that the gun is shooting some meters in front of the player. Because paintballs travel very slowly (280 feet per second) they will reach the targeted point just by the time the player has reached the point, hitting him. A very nice sideeffect that i had to do no extra-calculations for. The autosentry selects the biggest object it can see moving, fires for 10 seconds, selects the second-biggest object, fires for 10 seconds and so on. Areas that have a steady but too slow movement (like the trees you see on the screenshot) are filtered out by simply counting up a variable everytime something moves. After a special treshold is hit the box is no longer taken into account. The servos are controlled by a microcontroller (hooked to the laptop via rs232) that takes care of soft start/stop, zero calibration, fire and so on.

There are some tricks you can fool this system, for example by a very fast start and an abprupt stop. But if you really play paintball, you have no time to fool around like this to trick the autosentry. By the way: The first time someone hit the videocamera, the cmos-chip of the sensor was teared from its circuit board by the g-forces resulting from the impact. Wow.



The mechanics for version 2 (below, version 1 was built around 2000) are used for a
different project and are now out of my reach. The main intention was never to shoot
at people, this is only a sideeffect (a "party gag", but a very cool one if i may say so).















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