How to Build a Wimshurst Influence Machine – Part 4

Sep

2009

Building a Wimshurst Influence Machine - sparkyspark

This is part four in a series of articles describing how to build a Wimshurst Influence Machine with parts and materials available at your local home center and hardware store. In this part I detail the construction Leyden jars and the final assembly. If you missed the beginning of the series start here. This article was originally published in Make: Magazine volume #17.

Building the Leyden Jars and Final Assembly:

Incorporated into Wimshurst's machine are a pair of Leyden Jars which store the electric charge produced and provide for much bigger and more spectacular discharges. Leyden jars were initially invented in 1745 by Ewald Georg von Kleist. However, Pieter van Musschenbroek in Leiden independently developed the same device about a year later and went on to present his discovery to the scientific community. Thus this storage device is commonly known today as the Leyden Jar rather then the Kleist Bottle, though that term is still used occasionally in Germany.

The Leyden jar is the granddaddy of the modern day capacitor. It consists of inner and outer layers of aluminum foil separated by a dielectric or insulator. The amount of charge that a Leyden Jar can hold is determined by the area of these two plates, their distance from each other, and the dielectric or insulating capability of the material used to separate them. The original Leyden jars were made with silver or lead foil and glass. However, plastic is far a superior insulator due to glass' propensity to absorb some water molecules thus reducing is dielectric properties.

Our Leyden Jars are large enough to give you quite a jolt, but not so large as to be capable of actually harming a healthy person. However, Leyden Jars capable of administering a lethal shock are quite easily built – so be sure you fully understand their properties if you decide to construct larger jars. In fact, the first generally acknowledged accidental death by electrocution occurred in St. Petersburg in 1783 when a Professor Richman brought his head a bit too close to a charged bank of Leyden Jars, killing him instantly.

Making the Leyden Jars:

Cut the Leyden jar body:

Using the miter box and fine tooth hacksaw, cut two 7 1/2" lengths from the fluorescent lamp protector sleeve.

wimshurst-layden-cut-tube.jpg

Cut and affix the inner plate:

Cut (4) 5" by 6" sheets of heavy duty aluminum foil.
Form one sheet by wrapping it around the tube and then rolling it so it can be inserted. Roll along the 6" axis so the foil cylinder ends up being 5" high.
Insert the foil into the tube so that it is 1" from one end. Use a couple of rolled up sheets of paper to hold the foil firmly against the inside of the tube while you tape it in place. The tighter you can make it to the inside of the tube the better.

wimshurst-layden-plate-inner.jpg

Affix the outer plate:

Wrap another piece of aluminum foil around the outside and tape it in place. Again, the tighter the better, but don't wrinkle the foil.

wimshurst-layden-plate-outer.jpg

Make the bases:

Snap the tube ends onto the opening that is 1" from the foil
Make the Leyden jar bases from a pair of plastic closet pole mounts. Drill out the center hole to 5/16".

Note: These are Stanley brand and I had to trim some reinforcing ribs off with an X-acto knife to make them slide into the tubes.

wimshurst-layden-plate-bottom.jpg

Final Assembly:

Mount the disks and drive line:

Slide the disk axle into a support and put on a 5/16" set screw collar, an O-ring belt, the two disks, the other belt, and another collar.
Attach the casement window crank to the drive shaft, insert the bushings in the supports if you are using them and slide the shaft through the pulleys. The pulleys should be a tight fit and you will have to twist the shaft back and forth to get it through. Don't forget about the belts hanging from the top shaft, one will need a twist so that the disks rotate in opposite directions. A collar goes on either end of the drive shaft.
Once both shafts are in place, stretch the belt around the pulleys. (In the picture, the belt with the twist is hidden behind the disk. What you are seeing is a reflection of the untwisted belt.)

Note: 5/16" set screw collars can be found at the hardware store but I made my own by drilling out a 5/16" nut and threading a #6-32 screw into the side.

Note: I found that my machine became difficult to turn once it was fully charged due to the electrostatic attraction of the disks. I cut a 2 ½" washer from a plastic milk jug and placed it on the shaft between the disks to remedy this problem.

wimshurst-axle-collars.jpg

Align the disk and collector supports:

Cut two 11" lengths of fiberglass rod and press them into the holes made earlier in the base.
Loosen the screws that hold the two supports to the base and slide them around to adjust the disks so they line up with the charge collector supports.
Re-tighten the supports.

wimshurst-lineup-collectors.jpg

Install the Leyden jar base and inner plate contact:

Slide the Leyden jar bases onto the fiberglass charge collector supports.
Slide the charge collector assembly over the fiberglass supports.
Using about 6" of 14 AWG solid copper wire, form the inner plate contact. Wrap it once around the brass tube and form two loops in the ends.
Using a scrap of the plastic tube as a guide, adjust the inner plate contacts so they apply even and gentle pressure. You want good contact with the foil but you don't want to rip the foil when you install the Leyden jars.

wimshurst-layden-contact-inner.jpg

Epoxy the charge collector assembly in place:

Apply epoxy to the end of the rod and slide the brass charge collector assembly down onto the fiber glass support rod.
Set aside while the epoxy cures.

wimshurst-collector-epoxy.jpg

Install Leyden jar and assemble collector:

Slide the Leyden jar onto its base, being careful not to tear the foil as makes contact.
Line up the charge collector comb and trim the prongs. Test spin the disks to see if there is any wobble and trim the prongs to come as close as possible to the disks without touching.
Assemble the charge collectors.

wimshurst-layden-complete.jpg

Install discharge electrode:

Insert the discharge electrodes into the lamp finial on the charge collector and tighten the screw to hold it in place.
The finial should be tight enough to hold the collector comb but allow the discharge electrode to move back and forth. If it's too tight, or not tight enough, the support rod can be twisted in the base to accommodate.
Wrap a small bit of tape around the end of the electrode and screw on one of the small ball nuts; this will prevent charge from bleeding off the sharp end.

wimshurst-collector-inplace-2.jpg

Install neutralizing brushes:

Slide the neutralizing bars onto the upper shaft and adjust them to be about 45 degrees from the collector combs.
Sectors should pass through a charge collector, encounter a neutralizing bar after about 1/6 of a rotation, and then encounter the other charge collector after a further 1/3 of a rotation.
Tighten the set screw to secure.

wimshurst-neutralizer.jpg

Position brushes:

Clip (2) 1 ½" lengths of Solder Wick™ to the ends of the neutralizing rods so they make good contact with the disk.

wimshurst-neutralizer-brush.jpg

Mount the Leyden jar shunt and add optional finials:

Use small brass wood screws to attach the (2) acrylic brackets to the front disk support, leave them a little loose at first.
Place the Leyden jar shunt in the brackets and line them up so the balls on the shunt lean comfortable against the Leyden jars.
Tighten the brackets.

The two tops of the disk supports looked a little bare to me so I raided my junk box for more lamp parts and came up with these decorative finials. The wealth of finial and cabinet knobs at the typical home center means that there are infinite opportunities for creativity here!

That's it! Your Wimshurst machine is done!

wimshurst-complete-front.jpg

wimshurst-complete-back-2.jpg

Painting is optional but I decided that my machine would look better in black and gold so I completely disassembled it and painted the base and supports with black lacquer. I also painted the plastic pulleys with Krylon Fusion, but that turned out to be a mistake. If you do paint your pulleys, make sure to mask the area where the belt contacts the bottom of the pulley groove to prevent the belt from peeling off the dried paint.