Levitating Magnet In A Spherical Copper Cage

October 13, 2024 by 21 Comments

Lenz’s Law is one of those physics tricks that look like magic if you don’t understand what’s happening. [Seth Robinson] was inspired by the way eddy currents cause a cylindrical neodymium magnet to levitate inside a rotating copper tube, so he cast a spherical copper cage to levitate a magnetic sphere.

Metal casting is an art form that might seem simple at first, but is very easy to screw up. Fortunately [Seth] has significant experience in the field, especially lost-PLA metal casting. While the act of casting is quick, the vast majority of the work is in the preparation process. Video after the break.

[Seth] started by designing and 3D printing a truncated icosahedron (basically a low-poly sphere) in two interlocking halves and adding large sprues to each halve. Over a week, the PLA forms were repeatedly coated in layers of ceramic slurry and silica sand, creating a thick shell around them. The ceramic forms were then heated to melt and pour out the PLA and fired at 870°C/1600°F to achieve full hardness.

With the molds prepared, the molten copper is poured into them and allowed to cool. To avoid damaging the soft copper parts when breaking away the mold, [Seth] uses a sandblaster to cut it away sections. The quality of the cast parts is so good that 3D-printed layer lines are visible in the copper, but hours of cleanup and polishing are still required to turn them into shiny parts. Even without the physics trick, it’s a work of art. A 3d printed plug with a brass shaft was added on each side, allowing the assembly to spin on a 3D-printed stand.

[Seth] placed a 2″ N52 neodymium spherical magnet inside, and when spun at the right speed, the magnet levitated without touching the sides. Unfortunately, this effect doesn’t come across super clearly on video, but we have no doubt it would make for a fascinating display piece and conversation starter.

Using and abusing eddy currents makes for some very interesting projects, including hoverboards and magnetic torque transfer on a bicycle.

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A VIC-20 With No VIC

October 13, 2024 by 7 Comments

[DrMattRegan] has started a new video series to show his latest recreation of a Commodore VIC-20. The core of the machine is [Ben Eater’s] breadboard 6502 design. To make it a VIC-20, though, you need a “VIC chip” which, of course, is no longer readily available. Many people, of course, use FPGAs or other programmable logic to fake VIC chips. But [Matt] will build his with discrete TTL logic. You can see the first installment of the series below.

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All System Prompts For Anthropic’s Claude, Revealed

October 12, 2024 by 5 Comments

For as long as AI Large Language Models have been around (well, for as long as modern ones have been accessible online, anyway) people have tried to coax the models into revealing their system prompts. The system prompt is essentially the model’s fundamental directives on what it should do and how it should act. Such healthy curiosity is rarely welcomed, however, and creative efforts at making a model cough up its instructions is frequently met with a figurative glare and stern tapping of the Terms & Conditions sign.

Anthropic have bucked this trend by making system prompts public for the web and mobile interfaces of all three incarnations of Claude. The prompt for Claude Opus (their flagship model) is well over 1500 words long, with different sections specifically for handling text and images. The prompt does things like help ensure Claude communicates in a useful way, taking into account the current date and an awareness of its knowledge cut-off, or the date after which Claude has no knowledge of events. There’s some stylistic stuff in there as well, such as Claude being specifically told to avoid obsequious-sounding filler affirmations, like starting a response with any form of the word “Certainly.”

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Solar Planes Are Hard

October 12, 2024 by 12 Comments

A regular comment we see on electric aircraft is to “just add solar panels to the wings.” [James] from Project Air has been working on just such a solar plane, and as he shows in the video after the break, it is not a trivial challenge.

A solar RC plane has several difficult engineering challenges masquerading as one. First, you need a solid, efficient airframe with enough surface area for solar panels. Then, you need a reliable, lightweight, and efficient solar charging system and, finally, a well-tuned autopilot to compensate for a human pilot’s limited endurance and attention span.

In part one of this project, a fault in the electrical system caused a catastrophe so James started by benching all the electricals. He discovered the MPPT controller had a battery cutoff feature that he was unaware of, which likely caused the crash. His solution was to connect the solar panels to the input of a 16.7 V voltage regulator—just under the fully charged voltage of a 4S LiPo battery— and wire the ESC, control electronics, and battery in parallel to the output. This should keep the battery charged as long as the motor doesn’t consume too much power.

After rebuilding the airframe and flight testing without the solar system, [James] found the foam wing spars were not up to the task, so he added aluminum L-sections for stiffness. The solar panels and charging system were next, followed by more bench tests. On the test flight, it turned out the aircraft was now underpowered and struggled to gain altitude thanks to the added weight of the solar system. With sluggish control responses,[James] eventually lost sight of it behind some trees, which led to a flat spin and unplanned landing.

Fortunately, the aircraft didn’t sustain any damage, but [James] plans to redesign it anyway to reduce the weight and make it work with the existing power system.

We’ve seen several solar planes from [rctestflight] and meticulously engineered versions from [Bearospace Industrues]. If long flight times is primarily what you are after, you can always ditch the panels and  use a big battery for 10+ hour flights.

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Remembering John Wheeler: You’ve Definitely Heard Of His Work

October 12, 2024 by 9 Comments

Physicist John Archibald Wheeler made groundbreaking contributions to physics, and [Amanda Gefter] has a fantastic writeup about the man. He was undeniably brilliant, and if you haven’t heard of him, you have certainly heard of some of his students, not to mention his work.

Ever heard of wormholes? Black holes? How about the phrase “It from Bit”? Then you’ve heard of his work. All of those terms were coined by Wheeler; a knack for naming things being one of his talents. His students included Richard Feynman and Kip Thorne (if you enjoyed The Martian, you at least indirectly know of Kip Thorne) and more. He never won a Nobel prize, but his contributions were lifelong and varied.

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Cockroaches In Space: Waste Processing And A Healthy Protein Source Combined

October 12, 2024 by 51 Comments

As the current frontier of humanity in space, the International Space Station is heavily reliant on Earth not only for fresh supplies but also as a garbage disposal service for the various types of waste produced on the ISS by its human occupants. As future manned missions take humans further away from Earth, finding ways to reprocess this waste rather than chucking it out of the nearest airlock becomes a priority. One suggested solution comes from a Polish company, Astronika, with their insect bioreactor that can process organic material into useful biomass.

Interestingly, the cockroach species picked was the Madagascar hissing cockroach, one of the largest (5 – 7.5 cm) species. This is also a cockroach species which is often kept as a pet. In this closed-loop bioreactor that Astronika has developed, these cockroaches would chew their way through up to 3.6 kg of waste per week in the large version, with the adult cockroaches presumably getting turned into fresh chow and various materials at some point. Beyond the irrational ‘yuck’ factor that comes with eating insect protein, one of the biggest issues we can see with this system is that the long-duration mission crew may get attached to the cockroaches, as they are rather cute.

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Approximating An ADC With Successive Approximation

October 12, 2024 by 17 Comments

[Igor] made a VU meter with LEDs using 8 LEDs and 8 comparators. This is a fast way to get one of 8 bits to indicate an input voltage, but that’s only the equivalent of a 3-bit analog to digital converter (ADC). To get more bits, you have to use a smarter technique, such as successive approximation. He shows a chip that uses that technique internally and then shows how you can make one without using the chip.

The idea is simple. You essentially build a specialized counter and use it to generate a voltage that will perform a binary search on an unknown input signal. For example, assuming a 5 V reference, you will guess 2.5 V first. If the voltage is lower, your next guess will be 1.25 V. If 2.5 was the low voltage, your next guess will be 3.75 V.

The process repeats until you get all the bits. You can do this with a microcontroller or, as [Igor] shows, with a shift register quite simply. Of course, you can also buy the whole function on a chip like the one he shows at the start of the video. The downside, of course, is the converter is relatively slow, requiring some amount of time for each bit. The input voltage also needs to stay stable over the conversion period. That’s not always a problem, of course.

If that explanation didn’t make sense, watch the video. An oscilloscope trace is often worth at least 1,000 words.

There are, of course, many ways to do such a conversion. Of course, when you start trying to really figure out how many bits of resolution you have or need, it gets tricky pretty fast.

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