Author: Jenny List

3308 Articles

Rapid-Fire Hail Of Chopstick Arrows Makes Short Work Of Diminutive Foes

November 20, 2018 by 9 Comments

Many Hackaday readers may also be familiar with the Discworld series of fantasy novels from [Terry Pratchett], and thus might recognise a weapon referred to as the Piecemaker. A siege crossbow modified to launch a hail of supersonic arrows, it was the favoured sidearm of a troll police officer, and would frequently appear disintegrating large parts of the miscreants’ Evil Lairs to comedic effect.

Just as a non-police-officer walking the streets of Ank-Morpork with a Piecemaker might find swiftly themselves in the Patrician’s scorpion pit, we’re guessing ownership of such a fearsome weapon might earn you a free ride in a police car here on Roundworld. But those of you wishing for just a taste of the arrow-hail action needn’t give up hope, because [Turnah81] has made something close to it on a smaller scale. His array of twelve mousetrap-triggered catapults fires a volley of darts made from wooden kebab skewers in an entertaining fashion, and has enough force to penetrate a sheet of cardboard.

He refers to a previous project with a single dart, and this one is in many respects twelve of that project in an array. But in building it he solves some surprisingly tricky engineering problems, such as matching the power of multiple rubber bands, or creating a linkage capable of triggering twelve mousetraps (almost) in unison. His solution, a system of bent coat-hanger wires actuated by the falling bar of each trap, triggers each successive trap in a near-simultaneous crescendo of arrow firepower.

On one hand this is a project with more than a touch of frivolity about it. But the seriousness with which he approaches it and sorts out its teething troubles makes it an interesting watch, and his testing it as a labour-saving device for common household tasks made us laugh. Take a look, we’ve put the video below the break.

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The (UV) Writing’s On The Wall

November 18, 2018 by 15 Comments

[Michael Karliner]’s Belshazzar, named for the Biblical character upon whose wall the writing appeared, is a unique light painting machine, that tracks an array of UV LEDs across a glow-in-the-dark background to paint transient dot-matrix letters in light. It was one of many cyberpunk-themed art pieces in Null Sector at the 2018 Electromagnetic Field hacker camp this summer.

The row of LEDs hangs down from a carriage that traverses a tubular rail, and is edged forward by means of a stepper motor driving a roller. This arrangement delivers the benefit that it can be scaled for displays of any length. The LEDs are driven from an Arduino via a Texas Instruments TLC5940 PWM driver ship.The result can be seen in the video below the break, and those who saw it at EMF may remember it tracing suitably dystopian phrases.

Continue reading “The (UV) Writing’s On The Wall” →

The Kilogramme Will Cease To Be A Physical Entity

November 16, 2018 by 72 Comments

One of the most illuminating high school courses no doubt for many readers as much as for your scribe, was the series of physics lessons during which the SI units were explained. That glorious sense of having the order of the universe unlocked into an interlocking series of units whose definitions could all be derived in terms of a series of base units was mind-blowing in those early teen years, and even though the explanations might have been at a for-the-children level that has been blown out of the water by later tiers of learning it’s still a bedrock that will serve an engineer or scientist life-long.

The definitions of the SI base units have evolved with scientific advancement to the point at which they are no longer tied to their original physical entity definitions. Of all the base units though there is still one that has resisted the urge to move away from the physical: the kilogramme (giving it its French spelling to preserve context) is still defined in terms of a metal cylinder in a laboratory just outside Paris. Kg diehards have not much time left to cling onto their platinum-iridium alloy though, for a new definition has been adopted in which it is derived from Planck’s Constant. From next May this will become the official kilogram, at which point concerns over microscopic erosion of the metal standard become irrelevant, and an SI kilogram can be replicated by any laboratory with the means to do so.

The piece of apparatus that makes this definition possible is the Kibble balance, a balance in which the force required to overcome the effect of gravitational force on a given mass is measured in terms of the electrical power required to do so. The gravitational force at a given point can be measured accurately and is defined in terms of the other SI units, while the electrical power can be derived from a Josephson junction, a superconducting junction whose current is defined in terms of Planck’s constant. As a result, the kilogram can be measured solely in terms of the constant and other SI units, consigning the metal cylinder to history.

This high-end metrology and physics make for interesting reading, but it’s fairly obvious that the de facto kilogram we all use will not change. Our everyday measures of everything from sugar to PLA filament will be the same today as they will be next May. But that’s not the point, everyday measurements do not need the extreme accuracy and reproducibility of a laboratory. The point of it all comes in as yet unforseen applications, as an example would the ability to synchronise timing to create GPS or digital radio have been possible were the second to be still defined in terms of astronomical movements rather than atomic states?

Standard kilogramme replica picture: Japs 88 [CC BY-SA 3.0]

An Apollo Guidance Computer Laid Bare

November 12, 2018 by 42 Comments

An Apollo Guidance Computer probably isn’t a machine that’s likely to come the way of most Hackaday readers. The device that played such a vital role in taking astronauts to the Moon and bringing them home again is hardly a common find, even if it is one of the most iconic machines of its type and era.

[Carl Claunch] was approached to assist in the restoration of an AGC, and while he can’t reveal any information about its owner he is at liberty to document his progress. The result is a fascinating in-depth technical examination of the device over multiple blog posts, and is well worth a read for anyone with an interest in the Apollo program. It’s an ongoing progression of blog posts that are probably too numerous to list individually, but include the construction of a substitute for the DSKY control panel as well as looking at the device’s memory and construction. [Carl] then embarks on a series of posts looking at the restoration itself. This is where we see the computer in greatest detail, and learn the most about it.

If you think you might have seen [Carl]’s name here before, you’d be right. One of his past exploits was getting the first version of FORTH running on an IBM mainframe.

Belt Up With A Redundant Car Part

November 11, 2018 by 61 Comments

The toothed belt that turns the camshaft in synchronization with the crankshaft on many motor vehicle engines is something of an under-appreciated component. Unless you are unlucky enough to ave had one fail and destroy your engine, it’s probably something you’ve never given a second thought to outside of periodic service intervals.

For something to perform such a task over so many thousands of miles of motoring it must be made of pretty strong stuff. Even when a belt is life-expired it is still in good physical shape, and [Crispyjones] saw the potential in a used Subaru belt to make a different type of belt. After keeping his engine in sync for so long it would serve no less vital a purpose, and keep his pants from falling down.

You can of course buy the hardware for a belt from a decent crafting store, but he chose to recycle a buckle from a worn-out leather belt. Cleaning the timing belt and cutting it carefully so that the Subaru logo would be on show to the outside world in the finished article, he secured it round the buckle with some epoxy glue and a bit of stitching. The original leather retaining loop is not really appropriate, so one is fashioned from wire. Finally we see the process for measuring where the holes should be placed, followed by their creation with a hole punch.

Hackaday isn’t a crafting site, so we don’t often feature projects like this one. But the humble timing belt is a component that we’ve probably all replaced and thrown away more than once without really thinking what the properties of the thing we’re throwing away are. So we like this relatively simple project for its re-use of something few of us would otherwise keep, as well as for its delivering rather a cool belt. We’ve featured plenty of cambelts here doing their traditional job, but this is the first time we’ve had one as an item of clothing. We’ll leave you with a glimpse of a future without cambelts at all.

An Englishman’s Home Is His (Drone-Defended) Castle

November 9, 2018 by 24 Comments

Retiring to the garden for a few reflective puffs on the meerschaum and a quick shufti through the Racing Post, and the peace of the afternoon is shattered by the buzz of a drone in the old airspace,what! What’s a chap to do, let loose with both barrels of the finest birdshot from the trusty twelve-bore? Or build a missile battery cunningly concealed in a dovecote? The latter is what [secretbatcave] did to protect his little slice of England, and while we’re not sure of its efficacy we’re still pretty taken with it. After all, who wouldn’t want a useless garden accoutrement that conceals a fearsome 21st century defence system?

The basic shell of the dovecote is made from laser cut ply, in the shape of an innocuous miniature house. The roof is in two sliding sections which glide apart upon servo-controlled drawer runners, and concealed within is the rocket launcher itself on a counterweighted arm to lift it through the opening. The (toy) rocket itelf is aimed with a camera pan/tilt mechanism,and the whole is under the control of a Raspberry Pi

It’s understood that this is a rather tongue-in-cheek project, and the chances of any multirotors falling out of the sky are somewhat remote. But it does serve also to bring a bit of light back onto a theme Hackaday have touched upon in previous years, that of the sometimes uneasy relationship between drone and public.

All The Goodies You Need For Your RTL-SDR

November 9, 2018 by 14 Comments

When the RTL2832-based USB digital TV sticks were revealed to have hidden capabilities that made the  an exceptionally cheap software-defined radio receiver, it was nothing short of a game-changing moment for the home radio experimenter. The RTL might not be the best radio available, but remains a pretty good deal for only $10 from your favourite online supplier.

Having bought your RTL SDR, you will soon find yourself needing a few accessories. A decent antenna perhaps, an HF upconverter, and maybe an attenuator. To help you, [IgrikXD] has come up with a repository containing open-source implementations of all those projects and more. There’s an HF upconverter handily in both SMD and through-hole versions, as well as a wideband active antenna. A resonant antenna for a single band will always out-perfom a wideband device if your interest lies on only one frequency, but when your receiver has such a wide range as that of the RTL it’s irresistible to look further afield so the wideband antenna is a useful choice.

The RTL SDR is a device that just keeps on giving, and has featured innumerable times here since since its first appearance a few years ago. Whether you are into passive radar or using it to decode data from RF-equipped devices it’s the unit of choice, though we rather like it as a piece of inexpensive test equipment.

Via Hacker News.

Header image: Joeceads [CC BY-SA 4.0].