On 2/24/06, Jake Brownson wrote: > For now I think I'll go w/ a canned system due to time constraints. Use the two axis compass module, and attach it to your unit with a pendulum. It will always remain level with respect to ground (some swinging shouldn't affect the output drastically). A universal joint is fairly inexpensive and can be found at most tool stores in the socket wrench accessories area:: http://www.mcmaster.com/catalog/112/gfx/small/5521ap11s.gif Combine that with a two axis accelerometer to determine angle with respect to ground and you'll have a fairly straightforward and complete knowledge of exactly where the nerf gun is pointing. The advantage to these methods is there is no accumulated error - you're measuring a fixed gravitational field, and a fixed magnetic field. Of course, the accuracy and precision of your sensor readings is the key to getting adequate aim, and is where you're going to run into the most trouble. Alternately, make the gun barrel about 300ft long, and attach GPS devices to both ends. Good luck! -Adam -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist