The Brennan torpedo, invented in 1877 by Louis Brennan, was one of the first (if not the first) guided torpedoes of a practical design. Amazingly, it had no internal power source but it did have a very clever and counter-intuitive mode of operation: a cable was pulled backward to propel the torpedo forward.
If the idea of sending something forward by pulling a cable backward seems unusual, you’re not alone. How can something go forward faster than it’s being pulled backward? That’s what led [Steve Mould] to examine the whole concept in more detail in a video in a collaboration with [Derek Muller] of Veritasium, who highlights some ways in which the physics can be non-intuitive, just as with a craft that successfully sails downwind faster than the wind.
The short answer is gearing, producing more force on the propeller by pulling out lots of rope.
If you were in Tunisia in October, you might have caught some of the Morse Code championships this year. If you didn’t make it, you could catch the BBC’s documentary about the event, and you might be surprised at some of the details. For example, you probably think sending and receiving Morse code is only for the elderly. Yet the defending champion is 13 years old.
Teams from around the world participated. There was stiff competition from Russia, Japan, Kuwait, and Romania. However, for some reason, Belarus wins “almost every time.” Many Eastern European countries have children’s clubs that teach code. Russia and Belarus have government-sponsored teams.
Back in 2018 we saw [Carl]’s earliest versions making their first spins and it was clear he was onto something. Since then they have only improved, but improvement takes both effort and money. Not only does everything seemingly matter at such a small scale, but not every problem is even obvious in the first place. Luckily, [Carl] has both the determination and knowledge to refine things.
Hardware development is expensive, especially when less than a tenth of a millimeter separates a critical component from the junk pile.
The end result of all the work is evident in his most recent test bed: an array of twenty test motors all running continuously at a constant speed of about 37,000 RPM. After a month of this, [Carl] disassembled and inspected each unit. Each motor made over 53 million rotations per day, closing out the month at over 1.6 billion spins. Finding no sign of internal scratches or other damage, [Carl] is pretty happy with the results.
These motors are very capable but are also limited to low torque due to their design, so a big part of things is [Carl] exploring and testing different possible applications. A few fun ones include a wrist-mounted disc launcher modeled after a Spider-Man web shooter, the motive force for some kinetic art, a vibration motor, and more. [Carl] encourages anyone interested to test out application ideas of their own. Even powering a micro drone is on the table, but will require either pushing more current or more voltage, both of which [Carl] plans to explore next.
Getting any ideas? [Carl] offers the MotorCell for sale to help recover R&D costs but of course the design is also open source. The GitHub repository contains code and design details, so go ahead and make them yourself. Or better yet, integrate one directly into your next PCB.
Got an idea for an application that would fit a motor like this? Don’t keep it to yourself, share in the comments.
Although a lot of tools have been digitized and consolidated into our smartphones, from cameras, music players, calendars, alarm clocks, flashlights, and of course phones, perhaps none are as useful as the GPS and navigational capabilities. The major weakness here, though, is that this is a single point of failure. If there’s no cell service, if the battery dies, or you find yourself flying a bomber during World War II then you’re going to need another way to navigate, possibly using something like this Astro Compass.
The compass, as its name implies, also doesn’t rely on using the Earth’s magnetic field since that would have been difficult or impossible inside of an airplane. Instead, it can use various celestial bodies to get a heading. But it’s not quite as simple as pointing it at a star and heading off into the wild blue yonder. First you’ll need to know the current time and date and look those up in a companion chart. The chart lists the global hour angle and the declination for a number of celestial bodies which can be put into the compass. From there the latitude is set and the local hour angle is calculated and set, and then the compass is rotated until the object is sighted. After all of that effort, a compass heading will be shown.
For all its complexity, a tool like this can be indispensable in situations where modern technology fails. While it does rely on precise tabulated astrometric data to be on hand, as long as that’s available it’s almost failsafe, especially compared to a modern smartphone. Of course, you’ll also need a fairly accurate way of timekeeping which can be difficult in some situations.
If you’re new to the world of circular math, you might be content with referring to pi as 3.14. If you’re getting a little more busy with geometry, science, or engineering, you might have tacked on a few extra decimal places in your usual calculations. But what about the big dogs? How many decimal places do NASA use?
NASA doesn’t need this many digits. It’s likely you don’t either. Image credits: NASA/JPL-Caltech
Thankfully, the US space agency has been kind enough to answer that question. For the highest precision calculations, which are used for interplanetary navigation, NASA uses 3.141592653589793 — that’s fifteen decimal places.
The reason why is quite simple, going into any greater precision is unnecessary. The article demonstrates this by calculating the circumference of a circle with a radius equal to the distance between Earth and our most distant spacecraft, Voyager 1. Using the formula C=2pir with fifteen decimal places of pi, you’d only be off on the true circumference of the circle by a centimeter or so. On solar scales, there’s no need to go further.
Ultimately, though, you can calculate pi to a much greater precision. We’ve seen it done to 10 trillion digits, an effort which flirts with the latest Marvel movies for the title of pure irrelevance. If you’ve done it better or faster, don’t hesitate to let us know!
If you ask around a wood shop, most people will agree that the table saw is the most dangerous tool around. There’s ample evidence that this is true. In 2015, over 30,000 ER visits happened because of table saws. However, it isn’t clear how many of those are from blade contact and how many are from other problems like kickback.
We’ve seen a hand contact a blade in a high school shop class, and the results are not pretty. We’ve heard of some people getting off lucky with stitches, reconstructive surgery, and lifelong pain. They are the lucky ones. Many people lose fingers, hands, or have permanent disfiguration and loss of function. Surgeons say that the speed and vigor of the blade means that some of the tissue around the cut vanishes, making reconstruction very difficult.
Modern Tech
These days, there are systems that can help prevent or mitigate these kinds of accidents. The most common in the United States is the patented SawStop system, which is proprietary — that is, to get it, you have to buy a saw from SawStop.
For home computer users, the end of the 1980s was the era of 16-bit computers. The challenge facing manufacturers of 8-bit machines through the middle of the decade was to transfer their range and customers to the new hardware, and the different brands each did this in their own way. Commodore and Atari had 68000-based powerhouses, and Apple had their 16-bit-upgraded IIGS for the middle ground below the Mac, but what about Acorn, makers of the BBC Micro? They had the Archimedes, and [RetroBytes] takes us through how they packaged their 32-bit ARM processor for consumers.
The A3000 was the computer you wanted if you were a geeky British kid at the end of that decade, even if an Amiga or an ST was what you got. Schools had bought a few of the desktop Archimedes’, so if you were lucky you’d got to know Arthur and then RiscOS, so you knew just how fast these things were compared to the competition. The video below the break takes a dive into the decisions behind the design of this first ARM consumer product, and along the way it explains a few things we didn’t know at the time. We all know what happened to Acorn through the 1990s and we all use ARM processors today, so it’s a fascinating watch. If only an extra two hundred quid had been in the kitty back then and we could have bought one ourselves.
If you have never used an Archimedes you can get pretty close today with another Cambridge-designed and ARM-powered computer. RiscOS never went away, and you can run it on a Raspberry Pi. As we found, it’s still pretty useful.
