Automatic Paintball Gun

With all of the newfangled, high-tech paintball guns floating around these days, I decided to convert my 98 Spyder SE into a fully automatic model. Although they sell automatic trigger frames for about $80, it is always more fun to do things by yourself. This project turned out to be a fairly simple modification; I sawed off the bottom half of the trigger, attached a paper clip to the top nub of the trigger about where it contacts the spring, and then ran the paper clip down through a hole and attached it to a solenoid. The trigger frame was made of fairly soft aluminum, so it was easy to drill and tap mounting holes for everything.

One novel addition to this project was my electronic trigger mechanism. In paintball, you generally want as light and as short of a trigger pull as possible. I decided that the best way to do this was to use a metal "touch" plate, and simply have no trigger pull at all. I attached a metal plate where the trigger would be and ran a wire from the plate to an analog input on my microcontroller. I then grounded the plate using a 5 megaohm resistor. Two screws wired to 5 volts were also mounted at the back of the grip and contact your palm when you grip the gun. Because the trigger plate is grounded with such a large resistance, when you touch the plate with your hand at 5 volts it causes a considerable increase in voltage. The microcontroller would detect this and trigger the gun accordingly. I also added a switch to change from single fire, 3 round burst, and fully automatic operation.

Note that the trigger plate is mounted with a black, nylon screw. I started off with a steel screw which grounded the plate to the entire gun. This was not ideal because the gun would fire if you touched it anywhere!

Image of the trigger and with the solenoid removed:

View of the solenoid:

The electronics in the grip:

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