Two views of a motor are shown. On the left, a ring of copper-wire-wound stator arms is visible inside a ring of magnets. Inside this, a planetary gearbox is visible, with three mid-sized gears surrounding a small central gear. On the right, the same motor is shown, but with the internal components mostly covered by a black faceplate with brass inserts.

A Budget Quasi-Direct-Drive Motor Inspired By MIT’s Mini Cheetah

July 14, 2025 by Aaron Beckendorf 16 Comments

It’s an unfortunate fact that when a scientist at MIT describes an exciting new piece of hardware as “low-cost,” it might not mean the same thing as if a hobbyist had said it. [Caden Kraft] encountered this disparity when he was building a SCARA arm and needed good actuators. An actuator like those on MIT’s Mini Cheetah would have been ideal, but they cost about $300. Instead, [Caden] designed his own actuator, much cheaper but still with excellent performance.

The actuator [Caden] built is a quasi-direct-drive actuator, which combines a brushless DC motor with an integrated gearbox in a small, efficient package. [Caden] wanted all of the custom parts in the motor to be 3D printed, so a backing iron for the permanent magnets was out of the question. Instead, he arranged the magnets to form a Halbach array; according to his simulations, this gave almost identical performance to a motor with a backing iron. As a side benefit, this reduced the inertia of the rotor and let it reverse more easily.

To increase torque, [Caden] used a planetary gearbox with cycloidal gear profiles, which may be the stars of the show here. These reduced backlash, decreased stress concentration on the teeth, and were easier to 3D print. He found a Python program to generate planetary gearbox designs, but ended up creating a fork with the ability to export 3D files. The motor’s stator was commercially-bought and hand-wound, and the finished drive integrates a cheap embedded motor controller. Continue reading “A Budget Quasi-Direct-Drive Motor Inspired By MIT’s Mini Cheetah” →

A 3D printer is in the process of printing a test piece. The printer has two horizontal linear rails at right angles to each other, with cylindrical metal rods mounted horizontally on the rails, so that the rods cross over the print bed. The print head slides along these rods.

An Open-Concept 3D Printer Using Cantilever Arms

July 12, 2025 by Aaron Beckendorf 13 Comments

If you’re looking for a more open, unenclosed 3D printer design than a cubic frame can accommodate, but don’t want to use a bed-slinger, you don’t have many options. [Boothy Builds] recently found himself in this situation, so he designed the Hi5, a printer that holds its hotend between two cantilevered arms.

The hotend uses bearings to slide along the metal arms, which themselves run along linear rails. The most difficult part of the design was creating the coupling between the guides that slides along the arms. It had to be rigid enough to position the hotend accurately and repeatably, but also flexible enough avoid binding. The current design uses springs to tension the bearings, though [Boothy Builds] eventually intends to find a more elegant solution. Three independent rails support the print bed, which lets the printer make small alterations to the bed’s tilt, automatically tramming it. Earlier iterations used CNC-milled bed supports, but [Boothy Builds] found that 3D printed plastic supports did a better job of damping out vibrations.

[Boothy Builds] notes that the current design puts the X and Y belts under considerable load, which sometimes causes them to slip, leading to occasional layer shifts and noise in the print. He acknowledges that the design still has room for improvement, but the design seems quite promising to us.

This printer’s use of cantilevered arms to support the print head puts it in good company with another interesting printer we’ve seen. Of course, that design element does also lend itself to the very cheapest of printers.

Continue reading “An Open-Concept 3D Printer Using Cantilever Arms” →

Four brown perf board circuits are visible in the foreground, each populated with many large DIP integrated circuits. The boards are connected with grey ribbon cable. Behind the boards a vacuum fluorescent display shows the words “DIY CPU.”

Designing A CPU With Only Memory Chips

July 11, 2025 by Aaron Beckendorf 14 Comments

Building a simple 8-bit computer is a great way to understand computing fundamentals, but there’s only so much you can learn by building a system around an existing processor. If you want to learn more, you’ll have to go further and build the CPU yourself, as [MINT] demonstrated with his EPROMINT project (video in Polish, but with English subtitles).

The CPU began when [MINT] began experimenting with uses for his collection of old memory chips, and quickly realized that they could do quite a bit more than store data. After building a development board for single-chip based programmable logic, he decided to build a full CPU out of (E)EPROMs. The resulting circuit spans four large pieces of perfboard, weighs in at over half a kilogram, and took several weeks of soldering to create. Continue reading “Designing A CPU With Only Memory Chips” →

A blue 3DBenchy is visible on a small circular plate extending up through a cutout in a flat, reflective surface. Above the Benchy is a roughly triangular metal 3D printer extruder, with a frost-covered ring around the nozzle. A label below the Benchy reads “2 MIN 03 SEC.”

Managing Temperatures For Ultrafast Benchy Printing

July 8, 2025 by Aaron Beckendorf 13 Comments

Commercial 3D printers keep getting faster and faster, but we can confidently say that none of them is nearly as fast as [Jan]’s Minuteman printer, so named for its goal of eventually printing a 3DBenchy in less than a minute. The Minuteman uses an air bearing as its print bed, feeds four streams of filament into one printhead for faster extrusion, and in [Jan]’s latest video, printed a Benchy in just over two minutes at much higher quality than previous two-minute Benchies.

[Jan] found that the biggest speed bottleneck was in cooling a layer quickly enough that it would solidify before the printer laid down the next layer. He was able to get his layer speed down to about 0.6-0.4 seconds per layer, but had trouble going beyond that. He was able to improve the quality of his prints, however, by varying the nozzle temperature throughout the print. For this he used [Salim BELAYEL]’s postprocessing script, which increases hotend temperature when volumetric flow rate is high, and decreases it when flow rate is low. This keeps the plastic coming out of the nozzle at an approximately constant temperature. With this, [Jan] could print quite good sub-four and sub-thee minute Benchies, with almost no print degradation from the five-minute version. [Jan] predicts that this will become a standard feature of slicers, and we have to agree that this could help even less speed-obsessed printers.

Now onto less generally-applicable optimizations: [Jan] still needed stronger cooling to get faster prints, so he designed a circular duct that directed a plane of compressed air horizontally toward the nozzle, in the manner of an air knife. This wasn’t quite enough, so he precooled his compressed air with dry ice. This made it both colder and denser, both of which made it a better coolant. The thermal gradient this produced in the print bed seemed to cause it to warp, making bed adhesion inconsistent. However, it did increase build quality, and [Jan]’s confident that he’s made the best two-minute Benchy yet.

If you’re curious about Minuteman’s motion system, we’ve previously looked at how that was built. Of course, it’s also possible to speed up prints by simply adding more extruders.

A plywood box with a clear plastic front is shown. Three needle gauges are visible on the front of the box, as well as a digital display, several switches, and some indicator lights. At the right of the box, a short copper tube extends from the box.

Building An X-Ray Crystallography Machine

July 7, 2025 by Aaron Beckendorf 10 Comments

X-ray crystallography, like mass spectroscopy and nuclear spectroscopy, is an extremely useful material characterization technique that is unfortunately hard for amateurs to perform. The physical operation isn’t too complicated, however, and as [Farben-X] shows, it’s entirely possible to build an X-ray diffractometer if you’re willing to deal with high voltages, ancient X-ray tubes, and soft X-rays.

[Farben-X] based his diffractometer around an old Soviet BSV-29 structural analysis X-ray tube, which emits X-rays through four beryllium windows. Two ZVS drivers power the tube: one to drive the electron gun’s filament, and one to feed a flyback transformer and Cockroft-Walton voltage multiplier which generate a potential across the tube. The most important part of the imaging system is the X-ray collimator, which [Farben-X] made out of a lead disk with a copper tube mounted in it. A 3D printer nozzle screws into each end of the tube, creating a very narrow path for X-rays, and thus a thin, mostly collimated beam.

To get good diffraction patterns from a crystal, it needed to be a single crystal, and to actually let the X-ray beam pass through, it needed to be a thin crystal. For this, [Farben-X] selected a sodium chloride crystal, a menthol crystal, and a thin sheet of mica. To grow large salt crystals, he used solvent vapor diffusion, which slowly dissolves a suitable solvent vapor in a salt solution, which decreases the salt’s solubility, leading to very slow, fine crystal growth. Afterwards, he redissolved portions of the resulting crystal to make it thinner.

The diffraction pattern generated by a sodium chloride crystal. A slide is shown with a dark black dot in the middle, surrounded by fainter dots. — The diffraction pattern generated by a sodium chloride crystal.

For the actual experiment, [Farben-X] passed the X-ray beam through the crystals, then recorded the diffraction patterns formed on a slide of X-ray sensitive film. This created a pattern of dots around the central beam, indicating diffracted beams. The mathematics for reverse-engineering the crystal structure from this is rather complicated, and [Farben-X] hadn’t gotten to it yet, but it should be possible.

We would recommend a great deal of caution to anyone considering replicating this – a few clips of X-rays inducing flashes in the camera sensor made us particularly concerned – but we do have to admire any hack that coaxed such impressive results out of such a rudimentary setup. If you’re interested in further reading, we’ve covered the basics of X-ray crystallography before. We’ve also seen a few X-ray machines.

A man’s hand is visible holding a large, potato-shaped object in the foreground. A short, white, cylindrical structure is on the top of the potato, with black wires bending back into the potato. A smaller rectangular structure is to one side of it, and a red alligator clip connects to a nail protruding from the potato.

Building A Potato-based GLaDOS As An Introduction To AI

July 6, 2025 by Aaron Beckendorf 5 Comments

Although not nearly as intimidating as her ceiling-mounted hanging arm body, GLaDOS spent a significant portion of the Portal 2 game in a stripped-down computer powered by a potato battery. [Dave] had already made a version of her original body, but it was built around a robotic arm that was too expensive for the project to be really accessible. For his latest project, therefore, he’s created a AI-powered version of GLaDOS’s potato-based incarnation, which also serves as a fun introduction to building AI systems.

[Dave] wanted the system to work offline, so he needed a computer powerful enough to run all of his software locally. He chose an Nvidia Jetson Orin Nano, which was powerful enough to run a workable software system, albeit slowly and with some memory limitations. A potato cell unfortunately doesn’t generate enough power to run a Jetson, and it would be difficult to find a potato large enough to fit the Jetson inside. Instead, [Dave] 3D-printed and painted a potato-shaped enclosure for the Jetson, a microphone, a speaker, and some supplemental electronics.

A large language model handles interactions with the user, but most models were too large to fit on the Jetson. [Dave] eventually selected Llama 3.2, and used LlamaIndex to preprocess information from the Portal wiki for retrieval-augmented generation. The model’s prompt was a bit difficult, but after contacting a prompt engineer, [Dave] managed to get it to respond to the hapless user in an appropriately acerbic manner. For speech generation, [Dave] used Piper after training it on audio files from the Portal wiki, and for speech recognition used Vosk (a good programming exercise, Vosk being, in his words, “somewhat documented”). He’s made all of the final code available on GitHub under the fitting name of PotatOS.

The end result is a handheld device that sarcastically insults anyone seeking its guidance. At least Dave had the good sense not to give this pernicious potato control over his home.

An aluminium frame is visible, supporting several connected pieces of chemistry equipment. At the left, there is a tube containing a clear solution, with a tube leading to a clear tube heated by a gas flame, with another tube leading to a clear bottle, which has a tube leading to a bubbling orange solution.

A Miniature Ostwald Reactor To Make Nitric Acid

July 3, 2025 by Aaron Beckendorf 13 Comments

Modern fertilizer manufacturing uses the Haber-Bosch and Ostwald processes to fix aerial nitrogen as ammonia, then oxidize the ammonia to nitric acid. Having already created a Haber-Bosch reactor for ammonia production, [Markus Bindhammer] took the obvious next step and created an Ostwald reactor to make nitric acid.

[Markus]’s first step was to build a sturdy frame for his apparatus, since most inexpensive lab stands are light and tip over easily – not a good trait in the best of times, but particularly undesirable when working with nitrogen dioxide and nitric acid. Instead, [Markus] built a frame out of aluminium extrusion, T-nuts, threaded rods, pipe clamps, and a few cut pieces of aluminium.

Once the frame was built, [Markus] mounted a section of quartz glass tubing above a gas burner intended for camping, and connected the output of the quartz tube to a gas washing bottle. The high-temperature resistant quartz tube held a mixture of alumina and platinum wool (as we’ve seen him use before), which acted as a catalyst for the oxidation of ammonia. The input to the tube was connected to a container of ammonia solution, and the output of the gas washing bottle fed into a solution of universal pH indicator. A vacuum ejector pulled a mixture of air and ammonia vapors through the whole system, and a copper wool flashback arrestor kept that mixture from having explosive side reactions.

After [Markus] started up the ejector and lit the burner, it still took a few hours of experimentation to get the conditions right. The issue seems to be that even with catalysis, ammonia won’t oxidize to nitrogen oxides at too low a temperature, and nitrogen oxides break down to nitrogen and oxygen at too high a temperature. Eventually, though, he managed to get the flow rate right and was rewarded with the tell-tale brown fumes of nitrogen dioxide in the gas washing bottle. The universal indicator also turned red, further confirming that he had made nitric acid.

Thanks to the platinum catalyst, this reactor does have the advantage of not relying on high voltages to make nitric acid. Of course, you’ll still need get ammonia somehow.