We’ve got mixed feelings about a new video from [AndysMachines] that details how he makes custom ball screws. On the one hand, there’s almost zero chance that we’ll ever have an opportunity to put this information to practical use. But on the other hand, the video gives a fantastic look at the inner workings and design considerations for ball screws, which is worth the price of admission alone
The story behind these ball screws is that [Andy] is apparently in cahoots with SkyNet and is building a T-800 Terminator of his own. Whatever, we don’t judge, but the build requires a short-throw linear drive mechanism that can be back-driven, specs that argue for a ball screw. [Andy] goes through the challenges of building such a thing, which mainly involve creating threads with a deep profile and wide pitch. The screw itself wasn’t too hard to cut, although there were some interesting practical details in the thread profile that we’d never heard of before.
The mating nut was another. Rather than try to cut deep internal threads, [Andy] took a sort of “open-face sandwich” approach, creating half-nuts in a single piece of brass using a CNC machine and a ball-nose mill. The threads were completed by cutting the two halves apart and bolting them together — very clever! [Andy] also showed how the balls recirculate in the nut through channels cut into one of the half-nuts.
Whether the results were worth the effort is up to [Andy], but we were just glad to be along for the ride. And if you want a little more detail on lead screws and ball screws, we’ve got just the article for that.
It’s not often that the passing of a medium sized company on an industrial estate on a damp and soggy former airfield in southern England is worthy of a Hackaday mention, but the news of hypersonic propulsion company Reaction Engines ceasing trading a few weeks ago is one of those moments that causes a second look. Their advanced engine technology may have taken decades to reach the point of sustainable testing, but it held the promise of one day delivering true spaceplanes able to take off from a runway and fly to the edge of the atmosphere before continuing to orbit. It seems their demise is due to a failure to secure more funding.
We’ve written about their work more than once in the past, of their hybrid engines and the development of the advanced cooling system required to deliver air to a jet engine working at extreme speeds. The rights to this tech will no doubt survive the company, and given that its origins lie in a previously canceled British Aerospace project it’s not impossible that it might return. The dream of a short flight from London to Sydney may be on hold for now then.
This week, Jonathan Bennett and David Ruggles chat with Sylvestre and Brian about Firefox! What’s up in the browser world, what’s coming, and what’s the new feature for Firefox on mobile that has Jonathan so excited? Watch to find out!
In the last two articles, I talked about two systems relying on audio notifications. The first one is the Alt-Tab annihilator system – a system making use of my window monitoring code to angrily beep at me when I’m getting distracted. The other is the crash prevention system – a small script that helps me avoid an annoying failure mode where I run out of energy before getting myself comfortable for it.
I’ve been appreciating these two systems quite a bit – not only are they at my fingertips, they’re also pretty effective. To this day, I currently use these two systems to help me stay focused as I hack on my own projects or write articles, and they are definitely a mainstay in my self-hacking arsenal.
There is a particular thing I’ve noticed – audio notifications help a fair bit in a way that phone or desktop notifications never would, and, now I have a framework to produce them – in a way that calls for a purpose-tailored device. It’s just wireless headphones, Pi-powered, connected through WiFi, and a library to produce sounds on my computer, but it turns out I can squeeze out a lot out of this simple combination.
Here’s a pocketable device I’ve developed, using off-the-shelf hardware – an audio receiver/transmitter with extra IO, paired to my laptop. And, here’s how I make use of this device’s capabilities to the fullest.
Audio Output
In the “producing sound out of a Pi” article, I’ve mentioned USB-C 3.5mm soundcards. You can use them with a USB-C host port, and you don’t even need any sort of resistors for that – the soundcard doesn’t try and detect state of the CC pin, and why would it, anyway? Get VBUS, GND, D+, and D-, and you got yourself an audio card with high quality output.
We’ve been fans of the Yosys / Nextpnr open-source FPGA toolchain for a long while now, and like [Michael] we had no idea that their oss-cad-suite installer sets up everything so that you can write in Verilog or VHDL, your choice. Very cool!
Verilog and VHDL are kind of like the C and ADA of the FPGA world. Verilog will seem familiar to you if you’re used to writing code for computers. For instance, it will turn integer variables into wires that carry the binary values for you. VHDL code looks odd from a software programmer’s perspective because it’s closer to the hardware and strongly typed: an 8-bit integer isn’t the same as eight wires in VHDL. VHDL is a bigger jump if you have software in your brain, but it’s also a lot closer to describing how the hardware actually works.
We learned Verilog, because it’s what Yosys supported. But thanks to GHDL, a VHDL analyzer and synthesizer, and the yosys-ghdl-plugin, you can write your logic in VHDL too. Does this put an end to the FPGA-language holy wars? Thanks, Yosys.
[Michael] points out that this isn’t really news, because the oss-cad-suite install has been doing this for a while now, but like him, it was news to us, and we thought we’d share it with you all.
Want to get started with FPGAs and the open-source toolchain? Our own [Al Williams] wrote up a nice FPGA Boot Camp series that’ll take you from bits to blinking in no time.
The London Underground is an iconic piece of Victorian era engineering. What started in 1863 quickly became a core piece of infrastructure that would define the modern character of the British capital. It’s grown and changed immensely in the many years that have passed. Sadly, increasing patronage and more trains have created problems that the original designers never envisaged.
Deep in those London tunnels lies an engineering challenge. The Tube is literally cooking itself. Every day, millions of commuters descend into a network of tunnels that have been absorbing heat since the reign of Queen Victoria. Those clay-lined tubes have been soaking up excess thermal energy like a giant underground radiator, and now they’re giving it back with interest. The tunnels are simply too hot, and cooling them down is inordinately difficult.
The Perfect Storm of Thermal Chaos
The Tube’s heat problem isn’t just about one thing gone wrong – it’s about everything gone wrong at once. When Victorian engineers designed these tunnels, cooling wasn’t a major consideration. The tight, compact tunnels were built deep, nestled in the clay beneath London. In the early days, temperatures in the Underground were considered comfortably low.
“The Underground’s the only spot for comfort when the days are hot; it is cooler below.” – London Underground poster, 1926
Originally, the clay surrounding the tunnels sat at around 14°C, acting as a heat sink for the network. However, over the years, with more trains coming and going and more heat pouring in, the temperature has risen. It now typically sits anywhere from 19° to 26 °C. That’s just the earth around the tunnels, though. Air temperatures are worse—hitting as high as 47°C during a 2006 heatwave. The problem has been a continual bugbear of the beloved Tube, with concerns that future heatwaves could see temperatures rise ever higher.
Victoria and Central have been the hottest lines in recent years, according to TfL data.
The problem varies depending on which part of the Tube you’re on; some lines are worse than others. The Central Line is worthy of the nickname “The Central Heat Line”, with temperatures historically reaching 35°C. That’s not just uncomfortable – it’s approaching the limit of what the human body can handle efficiently. Much of this is due to the tunnel’s design. Opened in 1900, it featured two compact tunnels buried over 20 meters underground with minimal space for ventilation. It’s one of the so-called “deep-level” lines on the Underground network. Meanwhile, the Victoria line hit 31°C at its peak in 2023, and actually overtook the Central line as the hottest line, recording an average temperature of 28°C last year. Contrast that with the newer Jubilee line, which recorded an average temperature of just 22°C—far more comfortable.
To understand the problem, we need to know where the heat is coming from. A breakdown of heat sources was provided by Rail Engineering in 2007. Trains using their brakes, converting kinetic energy to heat, contributed 38% of the total heat input to the underground. The rest was put down to mechanical sources (22%) and the drivetrain (16%)—because those big electric motors get hot in operation.
As we wrap up for cooler temperatures outside, remember to remove coats whilst travelling to prevent overheating. 🧥
TfL at times has to remind customers that the Underground is warm even when it’s cold outside.
The rest of the heat came from a variety of sources, with train auxiliary equipment and tunnel support systems making up 13% and 4% respectively. The human factor can’t be ignored—each passenger is basically a 100-watt heater on legs. Multiply that by the millions of commuters that pass through each day, and you can see the scale of the problem. Indeed, passengers contributed the final 7% of heat generation in the Tube system. Of all the heat generated in the Tube, 79% passed into the tunnel walls, with 11% going into the tunnel itself. The remainder—just 10%—was removed via ventilation.
While the Tube had been slowly getting hotter for some time, the problem really started coming to a head in the mid-2000s, particularly when the European heatwave hit in 2006. Solutions were demanded, but the Underground wasn’t going to make it easy. The oldest parts of the network presented the greatest challenges, with precious little space to fit additional equipment for cooling. Many lines were simply too tight to allow for air conditioners to be retrofitted to existing trains, for example. Even if they were fitted, there would be a further problem of how to remove the additional waste heat generated from the tunnels, which were already too tight to ventilate effectively.
The quagmire had even prompted then-Mayor Ken Livingstone to put forth a £100,000 bounty for anyone that could solve the problem. However, it went unawarded. Despite over 3,500 proposals, the Underground authorities found only unworkable or unaffordable solutions, or ones they were already considering.
As you might expect, the problem hasn’t just gone away. Indeed, British media have begun regularly putting out articles on the hottest tube lines each year, as well as updates on what is to be done. Looking ahead, climate change is only going to make this underground sauna more challenging to manage. TfL’s engineers are in a race against time and physics, trying to cool a system that was never designed to be cooled.
Transport for London’s engineers haven’t taking this lying down, however. In recent decades, they’ve thrown a range of complicated solutions at this difficult problem. Victoria Station saw major upgrades, with the successful trial of a groundwater-based cooling system and heavily-upgraded ventilation. On the toasty Central line, engineers realized there was an additional heat input into the system. Trains travelled above ground for part of their route, which would see them heat up in the sun and then bring that energy underground. Countermeasures included installing reflective material on train roofs and solar-reducing films on the windows.
Trials of a new panel-based cooling system have also taken place in recent years at the disused Holborn station, with TfL considering a rollout to various stations after successful trials. The system involves circulating cold water through a curved metal structure. Air is chilled by blowing it through the curved panels and into the station. The system is designed specifically to operate in stations on the deep parts of the Tube network, with an eye to keeping maintenance and operation of the system as practical as possible.
Subsurface lines have been running S-Stock trains, which feature full air conditioning to keep passengers comfortable. Credit: (c) Transport for London
Some Tube lines have been lucky enough to get air-conditioned trains, too. These can be found on the Circle, District, Hammersmith & City, and Metropolitan lines. The modern S-Stock trains run largely on the less-deep sub-surface Tube lines, where it’s possible to easily deal with the hot exhaust of the air conditioning systems. These trains also have regenerative brakes, which turn some kinetic energy back into electricity to feed into the tube network. This cuts the amount of kinetic energy turned into heat, which aids in keeping the network cooler.
The Picadilly line is due to gain air conditioning in 2025, when it abandons its 1973 Stock trains for newer models. Other lines will have to wait longer. Central Line is slated to receive new air-conditioned trains in early 2030, which will replace the aging 1992 Stock models operating on that line. Bakerloo, Waterloo and City, and Jubilee lines are slated to receive upgraded trains “within the next 20 years” according to a Transport for London statement late last year.
The Picadilly line will see its aging trains replaced with newer air-conditioned models starting in 2025.
Air conditioned trains will help to some degree by cooling passengers on the move. However, those air conditioners will necessarily pump heat out of carriages and straight into the tunnels the trains are travelling through, plus some waste heat to boot. That heat will have to be dealt with one way or another, lest the network heat up further. There’s also the problem that passengers on platforms will still be exposed to high temperatures. Ultimately, both the stations and the trains need to be brought down to reasonable temperature levels. Ideally, the tunnels would be, too, in order to protect any customers that get stuck in a tunnel on a broken-down service. TfL also needs to find a way to bring temperatures under control if it wants to increase services. More trains means more heat going into the system—so it’s important to find a way to pull more heat out, too.
Overall, the problem is still a long way from being solved. The fact is that the London Underground has 11 lines, 272 stations, and more than 4,000 trains. Upgrading all of those at once simply isn’t economically viable. Instead, it appears that Transport for London will keep chipping away at the issue, bit by bit, over the years to come. Ideally, this will outpace any increases in average temperatures brought on by our seemingly-ever-hotter climate. For now, London’s commuters will continue their daily descent into one of the world’s most interesting thermal management case studies. Just remember to bring a bottle of water and some breathable clothing– you’re going to need it.
The problem seemed to be that the battery pack was reporting that it was 100% charged at just 11.7 V instead of the correct 12.3 V. As it turns out, that 11.7 V figure is only slightly above what the battery should be when its run flat — so in reality, the battery was never actually getting a charge and would report that it was dead after just a few minutes of use. But why?
With a logic analyzer attached to the pins of the battery, [Shrinath] set out to sniff its communications with the ThinkPad. Even if it wouldn’t lead to fixing the battery pack, the information obtained would potentially be useful for other projects, such as creating a custom high-capacity LiFePO4 pack down the line.
