This is a gattling gun for the Davincibot, which can be found here:http://www.thingiverse.com/thing:31496Squirt a bead of hot glue in the deep cylindrical recess and shove a #4 finishing washer into it. Center the washer as best you can.Hot glue a 5mm diameter magnet in the hemispherical recess on the front of the gun. Make sure the poles are properly aligned by holding the magnet in a spare finishing washer as you press it into the glue.Mount it on a Davincibot and make machine gun noises at your dog.For more details check out my instructable at: http://www.instructables.com/id/Davincibots-Create-a-3d-printed-modular-robot-toy/The scad file is included for your perusal. It should be easy enough to change sizes and number of barrels in case you wat to.