The Elihu Thomson apparatus is a device that uses electro magnetism to launch an aluminum ring into the air. Mine cost a little under $80, but I bought everything brand new from the hardware store.
Step 1: Gather Supplies
To build your own ring flinger you will need:
-2 foot by 2 inch piece of PVC pipe
-200 feet of ceiling handing wire
-500 feet of 14 gauge single strand copper wire
-Push button able to handle 1A @ 350v ( or it may over heat)
-A spare extension cord
-Small piece of plexiglass (optional)
-A couple screws or nails
Step 2: The Core
The first step in constructing a Ring Flinger is to take the coiled up ceiling wire and cut it into two foot long sections, straightening the sections as you go. Don't worry if they aren't perfectly straight. Once all the ceiling wire is cut lay out the pieces and completely coat them with the enamel. I was able to get 3 coats out of one can of spray enamel. The enamel insulates the ceiling wire and prevents eddy currents in the core that will distort and weaken the ring flingers magnetic field causing the device to be less powerful.
Step 3: Winding the Solenoid Part 1
-While the enamel was drying I began winding the solenoid by removing the 14 gauge copper wire from the spool. To do this I made a jig from scrap wood and a broom to wind all the wire onto as shown in the second picture.
-Next I split the plastic spool in half with a hack saw. If you take the PVC and insert it into one end of the spool you will see it has a much wider opening than the outside diameter of the PVC.
-You will want to wrap enough duct around the bottom of the PVC pipe so that one of the spool openings fits snuggly around it and tape the spool half in place.
-Now take the other half of the spool and drill a 2 inch diameter hole in the center of it. Slide it down the PVC until it the top (flat half) is 20cm from the bottom and mark the location of the top of the spool.
-Wrap duct tape just as before (so the spool fits snuggly) just below the marked line. Slide the unattached half of the spool over the duct tape and tape it in place.
-When this step is done you should have something similar to the first photo in this step.
Step 4: Winding the Solenoid Part 2
Clear your schedule cause this took me ~3.5 hours. You may want to wear work gloves so your hands don't get sore and you can take breaks by just taping the wire in place where you leave off.
-On the bottom spool half there should be a hole of some sort. Pull about 12 inches of the copper wire through this hole coming in from the top and tape it off on the bottom of that half of the spool.
-Now wind the wire from the bottom spool half to the top spool half. You may fill the gap between the spool halves with tape or anything nonconductive to make your solenoid look nicer. Keep the windings as tight and as close to each other as you can. It makes a huge difference in the ring flinger's power.
-When you reach the top spool half bring the wire down to the bottom spool half in one wrap.
-Keep doing this until you don't have enough wire to wind an entire length of the solenoid.
-When you finish winding, tape the wire in place and cut off the excess leaving a tail about 1.5 feet long.
Step 5: The Switch Box
-To do this simply build a box! I built mine with a plexiglass lid because I had some laying around. I also left a gap in one end of the box to pull the wires attached to the button through.
-To attach the button connect 6 inch long pieces of wire to the button leads. then drill a hole in the top of the box and attach the button with the leads hanging out.
Step 6: Hooking It All Up.
In this step everything comes together.
-Begin by cutting the outlet part of the extension cord off.
-Now split the wires of the extension cord (the side that plugs into the wall) so they're not right next to each other. This step will depend on what you use for a power cord.
-Attach on end of the split extension cord to the bottom of the solenoid with a wire nut. Attach the other end of the split extension cord to one of the button leads with another wire nut. I attached the outlet end of the extension cord for my own experiments in electromagnetism (completely unnecessary).
-Next attach the open lead of the button to the top of the solenoid.
-Finally insert the enamel coated ceiling wire into the PVC pipe. To do this try to shove the whole bunch of ceiling in all at once as far as you can by hand. When you can't get the ceiling wire in any farther hold a piece of wood on top of the bunch and hit the wood with a hammer shoving the ceiling wire into the PVC pipe. Be careful not to break the pipe. I also wrapped my solenoid in duct tape in an effort to minimize energy losses through vibration.
Step 7: Ammo!
-I found that the best ammo for the ring flinger was an aluminum ring as shown in the first picture above. The steel ring was too heavy and the copper wire coil had too much friction. The second to last photo shows the aluminum coil levitating the with the steel coil on top of it. The last photo is a blurry picture of the aluminum ring on mid flight.
-Some simple improvements to the design include using magnet wire instead of the 14 gauge single strand wire and/or using a solid iron core. Either of these will increase the ring flinger's ring flinging ability.
-If you want to control the power of the ring flinger simply hook it up to a variac to control the voltage supplied to the device.