Yesterday I ran into this web extra from back in 2007 when we were working on MAKE Volume 09, and it brought back some fond memories. We were deep in production, and one of our major slotted projects was the “Antigravity Lifter.” The dilemma was whether to publish this cool but really high-voltage and potentially really dangerous project. Enter the MAKE Advisory Board. Our editor-in-chief Mark Frauenfelder sent a message out to the members of the board, and a lively discussion ensued. We shared the whole thing online.
To give you a little background on lifters, here’s the description that was going to run with the article:
“Lifters (aka ionocraft) are a simple assembly of wire and foil that acts as an asymmetrical capacitor. The thin wire runs parallel to and above a length of aluminum foil, with the two attached and held apart by a lightweight nonconductor such as balsa wood.
When you apply a voltage across the lifter, negative to the wire emitter and positive to foil ground, static charge builds up on both sides. At high voltages, electrons from the wire leak into and ionize the surrounding air molecules — mostly the oxygen, since nitrogen requires more energy to ionize. These negatively charged molecules are pulled downwards into the foil, which has a positive static charge. In this way, the lifter constantly pulls air downward, producing an “ion wind” which results in upward thrust. (Many enthusiasts believe that additional forces also contribute to the lifter effect.) Typical home-built lifters will fly at around 20kV at 0.4 milliamps.
At such high voltages, surplus electrons from the wire can also jump the gap down to the foil directly. This shortcut reduces both the amount of charge that can ionize the air and the force with which the ions are drawn downward. When this happens, energy goes into producing a spark rather than producing lift, so in order to fly, the lifter must be “tuned” to eliminate arcing.
Like air purifiers and electrical storms, lifters generate ozone, nitrous oxide, and other gases which may enhance the invigorating feeling of experimentation.
Many strange and poorly understood phenomena are manifested by high voltages, and some investigators believe that this area has never received the research attention it deserves. Common wisdom attributes this bias to Thomas Edison, who used his considerable influence to steer scientific inquiry and respect away from the high-voltage ideas of his rival Nikola Tesla.”
And here’s the first part of the dilemma discussion:
DANGER: HIGH VOLTAGE! Do not attempt this project without expert assistance unless you are an adult experienced in working with extremely high voltage power sources. This project is intended only for very experienced adults. Severe injury, death, or property damage may result from failure to use adequate safety gear and precautions.
What’s more important: empowering readers to take control of technology, or protecting them from the risks? A spirited discussion between MAKE’s editors and technical advisory board ultimately led us to cancel publication of the high-voltage “Lifter” project in Volume 09.
The piece was written by John MacNeill, a well-known illustrator whose work appears frequently in publications such as Popular Science. MacNeill is also a “lifter” hobbyist who has made several of the mysterious levitating devices, and the how-to project he submitted was excellent. We were very excited to run it. However, MAKE’s technical advisory board, consisting of engineers, how-to book authors, and researchers, deemed the project to be unsafe, due to the project’s high voltage conducted across exposed wires in a flying object. Would strong warnings suffice, or did we need a full primer on high voltage? We also worried about recommending reuse of a TV tube (CRT) as a power supply, due to the dangers of capacitance discharge, and the unknown voltage and current. But even with a store-bought DC power supply, could the current of 0.4 milliamps be deadly? (Probably not.) Would the current-limiting knob protect makers? (Probably so.) Was the project too tempting for inexperienced teens? Isn’t it MAKE’s mission to empower people to handle technology? And, having established an email thread of world-class makers questioning safety, what about legal liability?
The article that almost was…
We made a tough call. Tell us what you think at in the talkbacks below.
Mark Frauenfelder, editor-in-chief: Dear MAKE technical advisory board members: Attached is the layout for one of the projects in MAKE Volume 09 — a high-voltage “lifter.” The instructions call for a high-voltage DC power supply, but offer the alternative of using an old (pre-Energy Star) CRT monitor to supply the power:
Using an Old CRT as a Power Supply
Here’s how to adapt an old (pre-Energy Star) CRT monitor into a high-voltage power supply that’s adequate for a small lifter. Unplug the monitor and let it sit for at least an hour to allow residual charge to dissipate. Open up the monitor, and locate the large wire that leads to a rubber cup at the back of the tube. This wire supplies the tube’s electron gun. Lift up the cup and find a metal contact for the wire.
Run one insulated wire to the electron gun contact and another insulated wire to the metal spring framework that holds the CRT. These will feed the lifter’s emitter and the ground, respectively. Position the 2 wires as far apart as possible, close up the case, and you’re ready to go.
I’m a little concerned about these instructions because I’ve heard CRTs can hold powerful charges almost indefinitely. I guess you could drain the charge by shorting the leads with a screwdriver, but that makes a scary spark and noise.
What I’d like to know is (a) whether my concern is valid, (b) if it is, is there a safe way to dissipate the charge? and (c) is there anything else important that’s left out from this? Thanks for your help!
Now read what members of the MAKE Advisory Board advised, and let us know what you think.