Whirling Shutters On This Field Mill Measure Electrostatic Charges At Distance

March 26, 2020 by Dan Maloney 34 Comments

Hardly a person hasn’t experienced the sudden, sharp discharge of static electricity, especially on a crisp winter’s day. It usually requires a touch, though, the classic example being a spark from finger to doorknob after scuffing across the carpet. But how would one measure the electrostatic charge of an object without touching it? Something like this field mill, which is capable of measuring electrostatic charge over a range of several meters, will do the trick.

We confess to not having heard of field mills before, and found [Leo Fernekes]’ video documenting his build to be very instructive. Field mills have applications in meteorology, being used to measure the electrostatic state of the atmosphere from the ground. They’ve also played a role in many a scrubbing of rocket launches, to prevent the missile from getting zapped during launch.

[Leo]’s mill works much like the commercial units: a grounded shutter rotates in front of two disc-shaped electrodes, modulating the capacitance of the system relative to the outside world. The two electrodes are fed into a series of transimpedance amplifiers, which boost the AC signal coming from them. A Hall sensor on the shutter allows sampling of the signal to be synchronized to the rotation of the shutter; this not only generates the interrupts needed to sample the sine wave output of the amplifier at its peaks and troughs, but it also measures whether the electrostatic field is positive or negative. Check out the video below for a great explanation and a good looking build with a junk-bin vibe to it.

Meteorological uses aside, we’d love to see this turned toward any of the dozens of Tesla coil builds we’ve seen. From the tiny to the absurd, this field mill should be able to easily measure any Tesla coil’s output with ease.

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“Who Is John Galt?” Finally Answered

November 22, 2015 by Bryan Cockfield 107 Comments

For those who haven’t read [Ayn Rand’s] philosophical tome Atlas Shrugged, there’s a pretty cool piece of engineering stuffed in between the 100-page-long monologues. Although fictional, a character manages to harness atmospheric static electricity and convert it into kinetic energy and (spoilers!) revolutionize the world. Harnessing atmospheric static electricity isn’t just something for fanciful works of fiction, though. It’s a real-world phenomenon and it’s actually possible to build this motor.

As [Richard Feynman] showed, there is an exploitable electrical potential gradient in the atmosphere. By suspending a tall wire in the air, it is possible to obtain voltages in the tens of thousands of volts. In this particular demonstration, a hexacopter is used to suspend a wire with a set of needles on the end. The needles help facilitate the flow of electrons into the atmosphere, driving a current that spins the corona motor at the bottom of the wire.

There’s not much torque or power generated, but the proof of concept is very interesting to see. Of course, the higher you can go the more voltage is available to you, so maybe future devices such as this could exploit atmospheric electricity to go beyond a demonstration and do useful work. We’ve actually featured the motor that was used in this demonstration before, though, so if you’re curious as to how a corona motor works you should head over there.

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Embed With Elliot: The Static Keyword You Don’t Fully Understand

August 4, 2015 by Elliot Williams 70 Comments

One of our favorite nuances of the C programming language (and its descendants) is the static keyword. It’s a little bit tricky to get your head around at first, because it can have two (or three) subtly different applications in different situations, but it’s so useful that it’s worth taking the time to get to know.

And before you Arduino users out there click away, static variables solve a couple of common problems that occur in Arduino programming. Take this test to see if it matters to you: will the following Arduino snippet ever print out “Hello World”?

void loop()
{
	int count=0;
	count = count + 1;
	if (count > 10) {
		Serial.println("Hello World");
	}
}

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3D Printed Wimshurst Machine

February 6, 2015 by Rick Osgood 23 Comments

Steampunk extraordinaire [Jake von Slatt] has released his latest creation. This time he’s built a Wimshurst machine from mostly 3D printed parts. The Wimshurst machine is an electrostatic generator and was originally invented in the late 1800’s by James Wimshurst. It uses two counter-rotating disks to generate an electrostatic charge which is then stored in two Leyden jars. These jars are also connected to a spark gap. When the voltage raises high enough, the jars can discharge all at once by flashing a spark across the gap.

[Jake’s] machine has a sort of Gothic theme to it. He designed the parts using Autodesk’s 123D Design. They were initially printed in PLA. Skate bearings were used in the center of the disks to ensure a smooth rotation. The axle was made from the fiberglass shaft of a driveway reflector. The vertical supports were attached the base with machine screws.

The Leyden jars were made from sections of clear plastic tube. The caps for the jars were 3D printed and are designed to accept a short length of threaded 1/8″ pipe. Copper wire was used for the interior contacts and are held in place with electrical tape. The metal sectors on each disk were made from pieces of cut aluminum tape.

You may be wondering how this machine works if it’s almost entirely made out of plastic. [Jake] actually painted most of the parts with a carbon paint. This makes them electrically conductive and he can then use the parts to complete electrical circuits. Unfortunately he found this to be rather ineffective. The machine does work, but it only produces sparks up to 1/2″ in length. For comparison, his other machine is capable of 6″ sparks using similar sized Leyden jars.

[Jake] actually tried rebuilding this project using ABS, thinking that the PLA may have been collecting moisture from his breath, but the result is still only 1/2″ sparks. He suspects that the bumpy surface of the plastic parts may be causing the charge to slowly leak away, preventing a nice build up. He’s released all of his designs on Thingiverse in case any other hackers want to give it a whirl.

Static Bleeder

December 17, 2009 by Caleb Kraft 31 Comments

When you are in the middle of the desert, pretty much every solution to a mechanical or electrical problem is a hack. [Sgt.M] who was deployed in Iraq sought out the help of radio guru [H.P. Friedrichs] about a static problem he was having. When dust storms would blow in strange things would happen in camp. Humming and crackling could be heard and [Sgt. M] actually had an electrical arc from a lamp to his hand at a distance of about 2 feet.

[Friedrichs] helped him find the problem. Their antennae were acting as static electricity collectors in the dust. All that dust friction in the dry air constantly built up a charge. The solution was simple, discharge the electricity at the antenna when it isn’t in use. Several solutions are outlined on the page, so check them out.