This idea came to me on a winter’s day as I paced around the studio wondering what to do next. I was wearing a pair of polyester sweat pants and as I walked back and forth they developed a severe case of static cling. It was then that I had an idea. What if I could use static electricity to make kinetic or even interactive sculpture?
I immediately hopped in the car and went to the fabric store armed with a balloon I found lying around the studio. I blew up the balloon in the store, rubbed in on my head and began testing out fabrics. This was really a process of trial and error as not all materials are labeled with their exact content. Some plastics are great dielectrics and others are not. The color of dye on a feather can effect how well it holds a charge, and so on.
After some research I decided to build an induction based electrostatic generator. This is similar in principal to a Wimshurst Machine, which is named for its inventor, James Wimshurst. This well-known version was build between 1880 and 1883. Electrostatics is a vast subject but there are basically two types of generators, Friction based and induction based. An example of a friction-based generator, invented in 1929 by Robert J. Van de Graaff is the Van De Graaff Generator. For a fairly concise summery of early discoveries in electrostatics visit this link.
To learn more about electrostatics and building induction based generators I highly recommend this book: Electrostatics: Exploring, Controlling and Using Static Electricity by A.D. Moore.
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Step 1: What Exactly Is Going on Here?
This type of machine works by mechanically separating electrostatic charges. These charges can build up high voltages but they have very low current and are generally not dangerous to humans, but can destroy your cell phone. You may also get a little bit of a shock!
The diagram above shows a simplified version of the rotating wheel with inductor/collector plates on either side labeled C-1 and C-2. A second set of brushes labeled N contact the rods where they stick out the back of the wheel. These back brushes are connected by a wire and placed in such a way that they will contact two rods at the same time on opposite sides of the wheel and connect them through the wire. When this happens, those same two rods are close to but not touching the inductors. One inductor is positively charged and the other is negatively charged. Electrons (-) in the rods and wire will be attracted to the positive (+) inductor and will move in that direction. When the wheel turns, the rods are isolated and carry either a positive or negative charge. As the wheel turns these same rods contact the front brushes, attached to C-1 and C-2 and drop off their charges, increasing the separation of charge with every turn.
Step 2: The Design
I used the following materials to make the parts you see above:
Base and mounting plates: 1/4" Black Acrylic (sandwiched to make 1/2" for some parts)
Corona Shields: 1/8" clear acrylic
Inductor and collector plates: Aluminum Sheet
Rods: 1/4" aluminum rod, cut and beveled.
Collector brushes: Conductive tape made by Laird
I started with a sketch on paper and then created an Illustrator file for laser cutting. Before I designed my acrylic parts to be cut, I ordered my shafts and bearings from McMaster-Carr. In this case I wanted a press fit for the bearings, which can take some experimentation and getting to know your laser cutter.
I based my design off of a combination of machines I had seen, prototypes I made and suggested designs from the book I mentioned in the introduction. You can have fun with the aesthetics but I recommend prototyping and testing before settling on your design for the moving parts.
Step 3: Fabrication
Inductor/collector plates: I cut the parts from sheet on a table saw with a blade specifically for aluminum, rounded the corners on a belt sander, drilled the mounting holes, gave them a finish with an oscillating sander and then bent them in a finger bender.
Next I sandwiched the acrylic parts with double stick tape and rounded the edges with a router. I then used a plastic polisher to bring them to a polish. Note: It's important to leave the paper on during these processes to protect the surface. I drilled and taped the holes for attaching the inductor plates and rear brushes in the next step. Note: You must use nylon or other plastic machine screws for this to keep charges from passing to the other side of the acrylic.
The rotating wheels are made from two pieces of acrylic. This was a last minute change since the 1/4" sheet was not thick enough to hold the rods in place and they didn't want to stay parallel. The rods should be perpendicular to the surface of the acrylic wheel.
A note about plastic polish: Most plastic polishes and plastic cleaners contain anti-static agents. I'm not sure what these are but they will make your machine not work at all. Be sure to clean your parts with either simple green, vinegar or a damp rag, nothing else. In dire circumstances you can use denatured alcohol but this and other solvents can sometimes cause crazing in acrylic. I used plastic polish in the vicinity of the first machine I assembled. Apparently the polishing wheel spread some dust from the polish around the work area and it took me 3 days to figure out what was wrong with my generator!
Step 4: Assembly
Once all the parts were ready I did a quick assembly test before getting into gluing.
Gluing acrylic is a one shot deal. If you spill on any surface that will be seen, the acrylic cement will damage the surface. Always prepare carefully before beginning. Mock up your pieces and have a plan for holding them in place once they're glued. You can use clamps or in this case I used heavy machinist blocks.
I used blue painters tape to both mark where the vertical acrylic pieces would sit on the base as well as to protect the surface from spills. I used a more viscous type of acrylic cement, which makes assembly a bit easier. I put a bead of glue on the part, gently rested it down into place and steadied it with the blocks. Once the cement had cured I could then move on to the next glue joint. Gluing requires patience and planning. Take your time and build jigs if necessary. For instance, the first couple of wheels I assembled were a bit wonky so I ended up making extra acrylic disks to hold the rods steady while the epoxy cured.