That NASA EM Drive Paper: An Expert Opinion

A week or two ago we featured a research paper from NASA scientists that reported a tiny but measurable thrust from an electromagnetic drive mounted on a torsion balance in a vacuum chamber. This was interesting news because electromagnetic drives do not eject mass in the way that a traditional rocket engine does, so any thrust they may produce would violate Newton’s Third Law. Either the Laws Of Physics are not as inviolate as we have been led to believe, or some other factor has evaded the attempts of the team to exclude or explain everything that might otherwise produce a force.

As you might imagine, opinion has entrenched itself on both sides of this issue. Those who believe that EM drives have allowed us to stumble upon some hitherto undiscovered branch of physics seized upon the fact that the NASA paper was peer-reviewed to support their case, while those who believe the mechanism through which the force is generated will eventually be explained by conventional means stuck to their guns. The rest of us who sit on the fence await further developments from either side with interest.

Over at Phys.org they have an interview from the University of Connecticut with [Brice Cassenti], a propulsion expert, which brings his specialist knowledge to the issue. He believes that eventually the results will be explained by conventional means, but explains why the paper made it through peer review and addresses some of the speculation about the device being tested in space. If you are firmly in one of the opposing camps the interview may not persuade you to change your mind, but it nevertheless makes for an interesting read.

If EM drives are of interest, you might find our overview from last year to be an illuminating read. Meanwhile our coverage of the NASA paper should give you some background to this story, and we’ve even had one entered in the Hackaday Prize.

Bitbanging VGA Fits In under 1 kB

Don’t throw those old VGA monitors away, turn them into works of art with [danjovic] and VGA Blinking Lights. This circuit uses a PIC16F688 to generate VGA video. Not just a random spray of monochrome dots either. VGA Blinking Lights puts up an ever-changing display of 48 colored squares.

blink-thumbOriginally created for the square inch contest, VGA Blinking Lights could hide behind a quarter. [Danjovic] dusted his project off and entered it in The 1 kB Challenge. The code is written in PIC assembly. The final hex used to generate the squares clocks in at 471 words. Since the PIC uses a 14 bit word, that’s just over 824 bytes. Plenty of space for feature creep!

Video is generated with a twist on the R2R DAC. [Danjovic] tweaked the resistor values a bit to obtain the correct voltage levels for the VGA standard. The color of the squares themselves are random, generated using a Galois Linear Feedback Shift Register (LFSR).

With only a handful of components, and a BOM cost under $5, this would be a fun evening project for any hardware hacker.

1kb-thumb

If you have a cool project in mind, there is still plenty of time to enter the 1 kB Challenge! Deadline is January 5, so check it out and fire up your assemblers!

Hacking Your Way Through NASA

The 2016 Hackaday SuperConference took place last month in sunny Pasadena, California. Also calling Pasadena home is the Jet Propulsion Laboratory, the place where Mars rovers are built, where probes are guided around the solar system, and where awesome space stuff happens.

JPL had a large contingent at the SuperCon and two of them teamed up to present their talk: Charles Dandino and Lucy Du. Lucy is a mechatronics engineer at JPL and already has a little bit of fame from fielding a Battlebot in the last two seasons of ABC’s series. Charles is also in mechatronics, with experience with Curiosity, the Mars 2020 rover, and the (hopefully) upcoming asteroid redirect mission.

In their talk, Charles and Lucy uncovered some of the hacks happening in the background at JPL. There’s a lot of them, and their impact goes much further than you would expect. Everything from remote control cars to keeping spacecraft alive on the other side of the solar system.

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Sensing a Magnet with Local Sourcing

I had a small project going on–never mind exactly what–and I needed to detect a magnet. Normally, that wouldn’t be a big problem. I have a huge hoard of components and gear to the point that it is a running joke among my friends that we can be talking about building something and I will have all the parts we need. However, lately a lot of my stuff is in… let’s say storage (again, never mind exactly why) and I didn’t have anything handy that would do the job.

Options

If I had time, there are plenty of options for detecting a magnet. Even if you ignore exotic things like SQUID (superconducting quantum interference device) there’s plenty of ways to detect a magnet. One of the oldest and the simplest is to use a reed switch. This is just a switch made with a thin piece of ferrous material. When a magnet is nearby, the thin piece of metal moves and makes or breaks the contact.

These used to be common in alarm systems to detect an open or closed door. However, a trip to Radio Shack revealed that they no longer carry things like that as–apparently–it cuts into floorspace for the cell phones.

I started to think about robbing a sensor from an old computer fan or some other consumer item with a magnetic sensor onboard. I also thought about making some graphene and rolling my own Hall effect sensor, but decided that was too much work.

Browsing

I was about to give up on Radio Shack, but decided to skim through the two cabinets of parts they still carry just to get an idea of what I could and could not expect to find in the future. Then something caught my eye. They still carry a wide selection of relays. (Well, perhaps wide is too kind of a word, but they had a fair number.) It hit me that a relay is a magnetic device, it just generates its own electromagnetic field to open and close the contacts.

I picked up a small 5 V reed relay. They don’t show it online, but they do have several similar ones, so you can probably pick up something comparable at your local location. I didn’t want to get a very large relay because I figured it would take more external magnetic field to operate the contacts. You have to wonder why they have so many relays, unless they just bought a lot and are still selling out of some warehouse. Not that relays don’t have their use, but there’s plenty of better alternatives for almost any application you can think of.

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Absolute Power

We recently noticed a very cool-looking series of power supply modules on a few of the Chinese deal web sites. Depending on the model, they provide a digitally-controlled voltage with metering. You need to provide at least a volt or so over the maximum desired output voltage. You can see a video from [iforce2d] below. The module in the video is rated for 5A at 50V maximum, but there are other sizes available. For those interested in graphs and numbers [lgyte] did a lot of characterization of these modules.

There was a time when importing goods from far away places was somewhat of an art. Finding suppliers, working out payment, shipping, and customs meant you had to know what you were doing. Today, you just surf the web, find what you want, pay with PayPal, and stuff shows up on your doorstep from all four corners of the globe.

There is one problem, though. We see a lot of cool stuff from China and some of it is excellent, especially for the price. Frankly, though, some of it is junk. It is hard to tell which is which. What’s more is even though in theory you might be able to return something, usually the freight charges make that impractical. So when you get a dud, you are likely to just eat it and chalk it up to experience. So the question is: how good (or bad) or these power supply modules?

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Measuring High Voltage in Millimeters (and Other HV Probe Tricks)

I work a lot with high voltages and others frequently replicate my projects, so I often get asked “What voltage is needed?”. That means I need to be able to measure high voltages. Here’s how I do it using a Fluke high voltage probe as well as my own homemade probe. And what if you don’t have a probe? I have a solution for that too.

How Long Is Your Spark?

The simplest way to measure high voltage is by spark length. If your circuit has a spark gap then when a spark occurs, that’s a short-circuit, dumping all your built up charge. When your spark gap is at the maximum distance at which you get a spark then just before the spark happens is when you have your maximum voltage. During the spark the voltage rapidly goes to zero and depending on your circuit it may start building up again. The voltage before the spark occurred is related to the spark length, which is also the spark gap width.

The oscilloscope photo below shows this changing voltage. This method is good for a rough estimate. I’ll talk about doing more precise measurements when I talk about high voltage probes further down.

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This Old Mouse Keeps Track of Filament Usage

Keeping track of your 3D-printer filament use can be both eye-opening and depressing. Knowing exactly how much material goes into a project can help you make build-versus-buy decisions, but it can also prove gut-wrenching when you see how much you just spent on that failed print. Stock filament counters aren’t always very accurate, but you can roll your own filament counter from an old mouse.

[Bin Sun]’s build is based around an old ball-type PS/2 mouse, the kind with the nice optical encoders. Mice of this vintage are getting harder to come by these days, but chances are you’ve got one lying around in a junk bin or can scrounge one up from a thrift store. Stripped down to its guts and held in place by a 3D-printed bracket, the roller that used to sense ball rotation bears on the filament on its way to the extruder. An Arduino keeps track of the pulses and totalizes the amount of filament used; the counter handily subtracts from the totals when the filament is retracted.

Simple, useful, and cheap — the very definition of a hack. And even if you don’t have a 3D-printer to keep track of, harvesting encoders from old mice is a nice trick to file away for a rainy day. Or you might prefer to just build your own encoders for your next project.

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