Virginia T. Norwood passed away earlier this year at the age of 96, and NASA’s farewell to this influential pioneer is a worth a read. Virginia was a brilliant physicist and engineer, and among her other accomplishments, we have her to thank for the ongoing success of the Landsat program, which continues to this day.
The goal of the program was to image land from space for the purpose of resource management. Landsat 1 launched with a Multispectral Scanner System (MSS) that Norwood designed to fulfill this task. Multispectral imaging was being done from aircraft at the time, but capturing this data from space — not to mention deciding which wavelengths to capture — and getting it back down to Earth required solving a whole lot of new and difficult problems.
A thermoelectric generator (TEG) can turn a temperature difference into electricity, and while temperature differentials abound in our environment, it’s been difficult to harness them into practical and stable sources of power. But researchers in China have succeeded in creating a TEG that can passively and continuously generate power, even across shifting environmental conditions. It’s not a lot of power, but that it’s continuous is significant, and it could be enough for remote sensors or similar devices.
Historically, passive TEGs have used ambient air as the “hot” side and some form of high-emissivity heat sink — usually involving exotic materials and processes — as the “cold” side. These devices work, but fail to reliably produce uninterrupted voltage because shifting environmental conditions have too great of an effect on how well the radiative cooling emitter (RCE) can function.
The black disk (UBSA) heats the bottom while the grey square (RCE) radiates heat away, ensuring a workable temperature differential across a variety of conditions.
Here is what has changed: since a TEG works on temperature difference between the hot and cold sides, researchers improved performance by attaching an ultra-broadband solar absorber (UBSA) to the hot side, and an RCE to the cold side. The UBSA is very good at absorbing radiation (like sunlight) and turning it into heat, and the RCE is very good at radiating heat away. Together, this ensures enough of temperature difference for the TEG to function in bright sunlight, cloudy sunlight, clear nighttime, and everything in between.
As mentioned, it’s not a lot of power (we’re talking millivolts) but the ability to passively and constantly produce across shifting environmental conditions is something new. And as a bonus, the researchers even found a novel way to create both UBSA and RCE using non-exotic materials and processes. The research paper with additional details is available here.
The ability to deliver uninterrupted power — even in tiny amounts — is a compelling goal. A few years ago we encountered a (much larger) device from a team at MIT that also aimed to turn environmental temperature fluctuations into a trickle of constant power. Their “Thermal Resonator” worked by storing heat in phase-change materials that would slowly move heat across a TEG, effectively generating continuously by stretching temperature changes out over time.
That altitude is considerably short of what would be called “space”, but it’s still an awfully long way up and the air there is very thin compared to on the surface. Space is generally (but not universally) considered to be beyond 100 km above sea level, a human-chosen boundary known as the Kármán line. 35 km is a long ways into the stratosphere, but still within Earth’s atmosphere.
Even so, that doesn’t mean there haven’t been efforts to go considerably higher. There was a Japanese proposal to drop airplanes made from special heat-resistant paper from the International Space Station, roughly 400 km above Earth. Success would show that low-speed, low-friction atmospheric reentry is feasible — for pieces of paper, anyway. But one of the challenges is the fact that there is no practical way to track such objects on their way down, and therefore no way to determine where or when they would eventually land.
There have been many other high-altitude paper plane launches, but the current record of 35,043 meters was accomplished by David Green in the United Kingdom as part of a school project. Such altitudes are in the realm of things like weather balloons, and therefore certainly within the reach of hobbyists.
As for the airplanes themselves, the basic design pictured here probably won’t cut it, so why not brush up on designs with the Paper Airplane Design Database? Even if you don’t send them into the stratosphere (or higher), you might find something worth putting through a DIY wind tunnel to see how they perform.
[Emupedia]’s work to preserve computer history by way of making classic and abandoned games and software as accessible as possible is being done in a handy way: right in your browser with EmuOS.
A few moments of BIOS startup kicks off EmuOS right in a browser window.
Doing things this way has powerful “Just Works” energy. Visit that link in a modern browser and in no time at all you’ll be looking at a Windows 95 (or Windows 98, or Windows ME) desktop, filled with a ton of shortcuts to pre-installed and ready-to-run classic software. Heck, you can even keep it simple and be playing the original Microsoft Solitaire in no time flat. There is also a whole ton of DOS software waiting to be fired up, just double-click the DOSBox icon, and browse a huge list. The project is still in development, so not everything works, but the stuff that does is awfully slick.
Quick references are handy, but sometimes it’s nice to have a process demonstrated from beginning to end. In that spirit, [Darren Stone] created a video demonstrating how to model a twisted part in FreeCAD, showing the entire workflow of creating the part as a blend of surfaces and curves that get turned into a solid.
FreeCAD is organized using the concept of multiple “workbenches” which are each optimized for different tools and operations, and [Darren] walks through doing the same jobs in a few different ways.
This twisted bracket is a simple part that is nevertheless nontrivial from a CAD perspective, and that makes it a good candidate for showing off the different workbenches and tools.
The video below is also pretty good overall demonstration of what designing a part from a mechanical drawing looks like when done in FreeCAD. As for mechanical drawings themselves, we’ve seen FreeCAD can be used to make those, too.
If you’ve ever looked into CNC cutting tools, you’ve probably heard the term “feeds and speeds”. It refers to choosing the speed at which to spin the cutting tool, and how fast to plow it into the material being cut. They’re important to get right, and some of the reasons aren’t obvious. This led [Callan Bryant] to share his learned insights as a first-timer. It turns out there are excellent (and somewhat non-intuitive) reasons not to simply guess at the correct values!
A table of variables and how they relate to one another (click to enlarge).
The image above shows a tool damaged by overheating. [Callan] points out that as a novice, one might be inclined to approach a first cutting jobs conservatively, with a low feed rate. But doing this can have an unexpected consequence: a tool that overheats due to spinning too quickly while removing too little material.
CNC cutting creates a lot of heat from friction, and one way to remove that heat is by having the tool produce shavings, which help carry heat away. If a tool is making dust instead of shavings — for example if the feed rate is too conservative — the removed pieces will be too small to carry significant energy, and the tool can overheat.
[Callan] makes a table of variables at work in a CNC system in order to better understand their relationship before getting into making a formula for calculating reasonable feed and speed rates. Of course, such calculations are a reasonable starting point only, and it’s up to the operator to ensure things are happening as they should for any given situation. As our own Elliot Williams observed, CNC milling is a much more manual process than one might think.
ChatGPT is an AI large language model (LLM) which specializes in conversation. While using it, [Gil Meiri] discovered that one way to create models in FreeCAD is with Python scripting, and ChatGPT could be encouraged to create a 3D model of a plane in FreeCAD by expressing the model as a script. The result is just a basic plane shape, and it certainly took a lot of guidance on [Gil]’s part to make it happen, but it’s not bad for a tool that can’t see what it is doing.
The first step was getting ChatGPT to create code for a 10 mm cube, and plug that in FreeCAD to see the results. After that basic workflow was shown to work, [Gil] asked it to create a simple airplane shape. The resulting code had objects for wing, fuselage, and tail, but that’s about all that could be said because the result was almost — but not quite — completely unlike a plane. Not an encouraging start, but at least the basic building blocks were there. Continue reading “ChatGPT Makes A 3D Model: The Secret Ingredient? Much Patience”→
