TechyMagThings

Heat pumps are great, because they pump heat around, and we often don’t want heat where it is. Need it somewhere else? Pump it! It’s great. It’s also a bit pricey if you’re buying new, but [Craftsman Chris] over on YouTube realized that the window air conditioning unit he found in a dumpster is, in fact, a heat pump. Normally it’s an air-source heat pump, but with a delightful series of hacks, he gets it automated and hooked into a ground loop in his latest YouTube video.

The heat sink is provided by a bunch of PEX tubing [Chris] buried in his back yard. After experimenting with using the water loop for cooling directly, he realized that pumping heat out of his house into the cold ground would go much better with a heat pump. That’s where the window A/C came in. After cleaning and servicing it, it was time to convert it to dump heat into water rather than outside air. To do that, [Chris] welded up a tank made of scrap metal around the existing heat exchanger. It’s designed for air, sure, but water takes its heat just fine. The nice thing about this is that by keeping the internals of the air conditioner mostly stock, he doesn’t let out any of the tasty, tasty CFCs that may be hiding inside.

Connecting this unit to his thermostat is equally hacky– he takes an old Programmable Logic Controller that looks fit to run a small factory, and hooks it to a single linear actuator to poke the A/C unit’s stock power button. Is it elegant? No. Does it work? Yes. Is it a hack? Indubitably!

We’ve seen window units pressed into whole-house A/C service before, but adding the water loop is a great hack. We saw a window A/C used as a ground-source pump before, too, but that was a Canadian project and so sensibly turned the machine around to provide heating for the maple mansion.

One of the most fun challenges in paleontology is determining characteristics of long-dead species like their behavior and body temperature based on nothing but some fossils and traces that are usually millions of years old. Something that has long vexed the paleontological community for example has been the question whether non-avian dinosaurs like the well-known Tyrannosaurus rex was cold- or warm-blooded, and if the latter, what temperature this was. Cue a recent study by [Randon J. Flores] et al. in Science Advances in which they seek to answer this question.

Although modern-day dinosaurs in the form of birds are all warm-blooded – meaning capable of regulating their body temperature – species like crocodiles, who also lived alongside non-avian dinosaurs, are cold-blooded and have to cycle between sun-basking and a cool dip in a nearby river to maintain their body temperature.

By looking at the temperature-dependent formation of carbonate clumped isotopes in three T. rex teeth from the Late Cretaceous Hell Creek Formation, they were able to deduce that these dinosaurs had a body temperature of 36.3 ± 2.5°C, comparable to modern-day endotherms. This was also much higher than that of contemporary crocodilian teeth found in the same area.

When popular dinosaur movies like Jurassic Park showed T. rex and other non-avian dinosaurs as being active, warm-blooded hunters, this was pretty much based on cutting-edge science at the time. Fortunately for its creators, later paleontological findings have largely confirmed that portrayal, although these days non-avian dinosaurs have often gained more feathers and other details – even outside of feathered theropods that became birds – that were absent in these early 90s reconstructions.

As cool as it would have been to wield lasers that produce a beam of neutrinos, recently two papers were published by MIT researchers that seem to dampen the likelihood of such lasers being at all possible. In a review paper by [Ana Maria Rey] et al. these two papers are investigated in more detail.

Although the concept behind a neutrino laser is rather simple, using the same superradiance effect involving a Bose-Einstein condensate (BEC) that allows for stimulation by photons to result in a synchronized direction of emitted photons, the idea of using a BEC of radioisotopes that naturally emit neutrinos in this fashion has now been effectively shot down.

The problem lies in taking the leap from photons with a BEC and applying this to a BEC of radioisotopes. Whereas photons are relatively slow and low-energy at a mere 1 eV, a neutrino is extremely fast and at 1+ MeV correspondingly has a much greater kinetic effect on the particle that emitted it. Unlike a photon emitted by an atom, this leaves precious little time for the other particles in the BEC to be affected.

This first scenario is covered in the (paywalled) paper by [Yu-Kun Lu] et al. with their calculations showing that superradiance cannot occur with neutrinos in a BEC and thus a laser is impossible. In the (also paywalled) second paper by [Hanzhen Lin] et al. the question is asked whether the assumption that a BEC of a radioisotope will at all enhance radioactive decay, to which the answer is a curt ‘no’.

Although it’s impossible to prove a negative with the scientific method, these two studies have slammed close a couple of doors on the concept of a neutrino laser.

Once you arrive at your destination via plane, it can be a drag waiting for a rental car. Why not bring your own with a replica of the Mazda suitcase car?

The heady days of the 90s brought us many wild vehicles from Japan, and in 1991, Mazda built three prototype go carts built inside Samsonite suitcases as a potential rival to the Honda Motocompo. After some appearances on the talk show circuit, two of the prototypes were destroyed, and the world moved on. [Bucket] felt wistful about the vehicle and decided it was time to build his own since the only remaining example is in collector hands, although they were able to reach out to the owner for more information on how the original prototypes functioned.

Using a very small gas motor from a pocket rocket and a welded aluminum frame inside the suitcase, the builders managed to beat the stated top speed of the original, hitting 33 kph (20 mph) before the driver decided things were getting too frightening. The final build tips the scales at 56.8 lbs, so some further refinement might even get it under the 50 lb airline limit.

Surprisingly, this isn’t the first suitcase-sized go cart we’ve seen. We wonder if a ride-able suitcase hovercraft is next?

Even if the world has already settled on plain old propellers as the way to make quadcopter drones fly, this doesn’t mean that you cannot give other designs a shake to see what kind of flying performance they result in. For example impeller designs that depart radically from standard propellers – themselves a sub-category of axial impellers – and go radically radial instead as in this design by [quadmovr] with accompanying demonstration video.

This is itself a remix of a design by [Baba] to make it fit the target 1750KV T-mount motor. As for whether this is a design that you want to slap on your own quadcopter, the obvious disadvantage is that it’s much heavier than regular propellers.

Weighing [quadmovr]’s drone without battery pack and with these 3D-printed PETG impellers shows them to weigh 189 grams. This compares to 141 grams with the standard three-bladed propellers, or a hefty 12.8 gram weight penalty per impeller. Naturally this translates into less flying time, so what are the advantages?

The noise profile of the impeller design is definitely more pleasant, and much like novice quadcopters with the protective ring around the propellers these impellers should be more robust. On the other hand increased mass adds to inertia, and there is a lot more surface area with the air to add drag, so despite the absolutely sick moves that [quadmovr] pulls off with both impeller configurations in the video one has to admit that regular three-blade propellers do have the edge here.

In the US, among other places, housing costs are skyrocketing. It can sometimes be difficult to get a feel for the scale of the issue and how it hits neighborhoods differently. [Justin Blinder] has designed a device to help people get a more visceral understanding of the problem.

In New York City, Citi Bikes are everywhere in the city’s transportation landscape. [Blinder] used a GPS module plugged into an ESP32S3 to vary the amount of resistance on one of these bikes by actuating the front brake with a servo. As a rider takes the bike through different neighborhoods, the resistance varies in proportion to the rent burden experienced there.

[Blinder] explains, “One of the main technical challenges was calibrating this relationship so that the changes were physically noticeable without feeling abrupt or unsafe.” As rent burden is merely the percentage of income taken up by rent in an area (by the block in this dataset), it is only one indicator of the additional friction a family might feel in an area, but a useful one to at least begin to convey the disparities in the urban environment. We really like how this connects abstract statistics to something more experiential.

If you’re looking for some other bike hacks, how about wireless brakes or a sleeper e-bike with a solenoid display?

via Next City

Photodetectors come in a wide variety of constructions and materials, with the Cu₂O-based photodetector that [Mad Scientist Creations] demonstrates in a recent video being a good example of a photodetector that can be created at home using nothing but some copper and a heat source.

Of the two copper elements in a salt water cell, one element is heated to the point where a copper oxide layer forms, specifically Cu₂O, which acts as a semiconductor and provides the photosensitive layer. Even a fairly crude sensor created with a regular gas stove produces enough of a current that it can be used in a simple light detection circuit.

Although copper-oxide photodetectors may seem quaint, they are getting a lot of interest as they feature a very narrow bandgap at 1.2 eV. In a 2019 study by [Hyeon-Joo Song] et al. as published in Scientific Reports such a sensor is enhanced with an optimized grain structure that improves its performance, with much higher sensitivity and faster response times.

As demonstrated by [Andrzej Kwiatkowski] et al. in a 2024 paper in Solar Energy Materials and Solar Cells these copper-oxide sensors can also be used for gas detectors, though they used advanced gas deposition to produce the thin films instead of sticking a bit of copper tape into a natural gas flame.

Even if DIY copper-oxide sensors aren’t quite as exciting as what one can do with access to a well-equipped (semiconductor) lab, it’s still a pretty accessible material that lends itself for easy experimentation.