Step 9: Charge Shuttle Asembly
Drill a 1/4" hole in each 1" dia sphere. Insert spheres onto each end of the pen cartridge; secure w/glue. Locate and mark the balance point of the assembly. Carefully stick a push pin through this point to make the shutle axle entry hole.
Straighten a paperclip to make the charge shuttle axle. Insert one end of the clip perpedicularly through the hole. I made bases for the shuttle mounts from 1/2" x 1/2 dia wood plugs cut from a dowel and inserted into one end of each straw.
Important Note: the shuttle assembly must be equidistant from upper and lower electrodes so that each sphere of the shuttle contacts a stationary sphere simultaneously (it's embarrassing to say how long it took to [almost] achieve this requirement! :> o). Once you determine the optimum shuttle height and repositioned the stationary electrodes as needed, hold the mounts in position and mark the location; drill a 1/16" hole in each straw to accommodate the axle. Glue mounts to the base. Lastly, insert the shuttle-axle assembly between the mounts and lock the in place by bending axle ends at 90 degree angles.