Introduction: Whimshurst Generator
I built this Whimshurst generator awhile back and I didn't take pictures through the build. But I thought I could share a few ideas to help others in a similar project of their own. I can through a nasty spark approx 2" on a dry winter day using the Leyden jars and has some cool demos I'll discuss later.
First some great resources are:
2. The Boy Electrician - by Alfred P Morgan
3. Homemade Lightening - by R.A. Ford
"The Boy Eectrician" is a collection of a number of projects if you haven't already heard of it - get it. Also "The Boy Mechanic - Vols 1, 2 & 3" are worth every penny for great project ideas. But back to the whimshurst...
Parts List Consists of:
a. Leyden jars - Spaghetti containers from the dollar store. I tossed the plastic caps and turned cherry lids on a lathe and used rubber bands from a roller conveyor to function as a gasket.
b. The lucite rods (3/4" diam) and the plexiglass disks (1/4" think) came from a local plastics supplier.
c. The brass fittings include drawer pulls of solid brass, solid brass rod from hobby store (K&S brand), and misc brass screws and inserts. NOTE: The drawer pulls are lacquered and need to have it removed for electrical continuity. Use a propane torch to burn it off and then scrub them with steel wool.
d. The sectors on the disk are aluminum flashing.
e. The grounding brushes are braided copper wire used for hobby racing slot cars.
f. The belt drives are rubber bands taken from a roller conveyor - these are really grippy and can be tightened up by cutting then melting them back together as they stretch.
Cut the disks as pairs and sand them as perfectly as possible so they rotate smoothly. I cut mine at 18" diameter. It makes a sizeable whimshurst and decent sized sparks. The edges are sanded then polished with fine steel wool.
Layout a scaled sketch of how the sectors will be epoxied onto the disks. The sectors must be an even number and exactly opposite of each other. Sand the surfaces of the sectors so they adhere well to the plexiglass and the exterior surface is very conductive ( no coatings anywhere is a very important theme her to make this work).
The hubs were turned in a lathe from solid cherry glued up in blocks. I then end bored a 1/2" hole in the center for the brass tube bushing to eventually be inserted and epoxied in each hub. I turned one piece first twice as long as one hub, then cut it in half on a bandsaw so I could ensure equal diameters as possible to make two hubs. The disks each have a notch for which the belt rides in it. The notch depth is not critical to be exact to the other but use a caliper anyway. The disks just need to spin in opposite directions. The hubs ride on an aluminum 1/2" solid shaft (K&S hobby) with NO grease or lube of any kind. I didn't want to risk contaminating any parts with something conductive then try to clean it off. The brass tube sleeve bushing on the aluminum is plenty slick for the low rpms such that a lube is not needed. A screw insert is located at the very top of the vertical shaft supports on each support to keep the shaft from spining with the disks and drilling into the support.
The Pick Up Combs:
You will need to drill a series of 1/16" holes through a brass rod (~ 3/16" diam) in a straight line that is approximately as long as the sector on the disk. To do this precisely as possible, cut a v-block out of a piece of scrap wood to nest the 3/16" rod in it so you can use it as a holder for a drill press to drill the holes. Evenly space the holes (aprox every 1/4") by marking each location by a small notch cut in it with a file. Once all the holes are drilled for BOTH ends of the rod, bend the rod around a piece of pipe to make a tuning fork type of shape.
Make the pick up pins with 1/16" brass stock and solder them into each hole. Then solder in the end extension rod at the base of the tuning fork shape.
The rear of the machine shows the hand crank that is built similarly to the top shaft: 1/2" aluminum rod run through the frame that is bushed with brass tubing. The lower drive shaft has two wooden pulley on it that I also turned out of cherry. These pulleys have a v notch cut into the edge to track the rubber drive bands. The pulleys have a small wooden hub screwed into the SIDE of the pulley which the hub has a insert in it where a screw runs through it and grips the shaft. File a small flat on the shaft to help land the screw.
Note that each of the leyden jars exterior aluminum foil surface is bonded to a brass strap which in turn is bonded to the other jar. This grounds the two jars exterior to help draw in charge to the internal foil surface. I used a very thin film of rubber cement in the jar then smoothed the foil onto it with a smooth wooden stick. Pre-cut & test fit the foil forst and pre-smooth it before fitting it inside.
This shows two demo units. The one on the left simulates a ion drive. It is a brass acorn nut with two copper wires bent at opposite angles to it with the ends grond to points. The electrons drain to these points and ionize the air and cause the unit to rotate. The acorn nut sits balanced on top of a rounded brass rod.
The two copper disks demonstrate discharge when a smaill ball bearing is suspended beteeen them (not shown). The ball will pick up cahrge from one plate then become repulsed due to being equally charged, then swing over to the other plate. When it contacts the other plate it drains off the electrons and then swings back to plate one to pick up more charge.
Again, sorry for no construction pictures but go to the references I mentioned and you will see all sorts of great ideas. But I hope you like my project and learned some new trick or idea.