As promised, here are the building instructions and program for the NXT Beam Weapon. BTW, the pieces are not limited to one retail kit - there are several more - so you may have to substitute pieces or modify the design. Anyway, for this robot, I decided to try using LDD. It worked quite well. I really like the auto-snap feature, although at times it makes it hard to get a piece where you want it. It would be nice if you had the option to move pieces manually (like MLCAD) in case the auto-snap wasn't working.
I also noticed a couple things with the gears. One of our forum members was having trouble with putting a gear on an axle, because the auto-snap feature kept putting the axle through the wrong hole in the gear. I worked around this by putting an axle in a gear separately, and then putting the combination into the correct spot. I also found a way to get gears to mesh - just use the hinge tool to rotate one or both gears in small increments until they fit. I don't know if this would work for all gear-connections, though.
Anyway, about the building instructions... the zip file I linked to above contains the LDD file for the robot. You can generate building instructions in the file, plus you can mess around with the model to help you see the exact placement of pieces.
Since LDD didn't have a gear track part which I used on the robot, I just made a photo instruction, which you can see below... you can do this step last. Note that the two 1x3 beams on the bottom, keeping the gear track-beam from sliding out, should actually be one peg further up.
This gear track allows the trigger motor to push the bolt into the magazine to fire a beam. Ten 1x5 beams are used for ammo, and are loaded into the magazine horizontally, each stacked on top of the previous one. Feel free to mess around with other ammo, such as 1x3 beams or even little bushes and pegs. I tried loading a bunch of little bushes (not the vegetation kind, the technical "bushes") into the magazine, and the result was pretty funny (spreadshot!).
If you build this robot, let me know how it works!
P.S. And no, I am not responsible for any deaths, broken bones, or any other injuries sustained from the use of this potentially lethal weapon. :P