A filament extruder is shown on a workbench. On the front is a knob and the display of a PID controller. A black geared spool is mounted on the top of the extruder, and on the right, a clear plastic bottle is positioned over a metal rod.

Turning Waste Plastic Into Spools Of Filament

August 1, 2025 by Aaron Beckendorf 24 Comments

Despite being a readily-available source of useful plastic, massive numbers of disposable bottles go to waste every day. To remedy this problem (or take advantage of this situation, depending on your perspective) [Igor Tylman] created the PETmachine, an extruder to make 3D printer filament from PET plastic bottles.

The design of the extruder is fairly standard for such machines: a knife mounted to the frame slices the bottle into one long strip, which feeds through a heated extruder onto a spool which pulls the plastic strand through the system. This design stands out, though, in its documentation and ease of assembly. The detailed assembly guides, diagrams, and the lack of crimped or soldered connections all make it evident that this was designed to be built in a classroom. The filament produced is of respectable quality: 1.75 mm diameter, usually within a tolerance of 0.05 mm, as long as the extruder’s temperature and the spool’s speed were properly calibrated. However, printing with the filament does require an all-metal hotend capable of 270 ℃, and a dual-drive extruder is recommended.

One issue with the extruder is that each bottle only produces a short strand of filament, which isn’t sufficient for printing larger objects. Thus, [Igor] also created a filament welder and a spooling machine. The welder uses an induction coil to heat up a steel tube, inside of which the ends of the filament sections are pressed together to create a bond. The filament winder, for its part, can wind with adjustable speed and tension, and uses a moving guide to distribute the filament evenly across the spool, avoiding tangles.

If you’re interested in this kind of extruder, we’ve covered a number of similar designs in the past. The variety of filament welders, however, is a bit more limited.

Thanks to [RomanMal] for the tip!

Solar Light? Mains Light? Yes!

July 29, 2025 by Al Williams 21 Comments

So you want a light that runs off solar power. But you don’t want it to go dark if your batteries discharge. The answer? A solar-mains hybrid lamp. You could use solar-charged batteries until they fall below a certain point and then switch to mains, but that’s not nearly cool enough. [Vijay Deshpande] shows how to make a lamp that draws only the power it needs from the mains.

The circuit uses DC operation and does not feed power back into the electric grid. It still works if the mains is down, assuming the solar power supply is still able to power the lamp. In addition, according to [Vijay], it will last up to 15 years with little maintenance.

The circuit was developed in response to an earlier project that utilized solar power to directly drive the light, when possible. If the light was off, the solar power went to waste. Also, if the mains power failed at night, no light.

The answer, of course, is to add a battery to the system and appropriate switching to drive the lights or charge the battery and only draw power from the mains when needed. Since the battery can take up the slack, it becomes easier to load balance. In periods of low sunlight, the battery provides the missing power until it can’t and then the mains supply takes over.

Comparators determine whether there is an under-voltage or over-voltage and use this information to decide whether the battery charges or if the main supply takes over. Some beefy MOSFETs take care of the switching duties. Overall, a good way to save and reuse solar cell output while still drawing from the grid when necessary.

Small solar lights don’t take much, but won’t draw from commercial power. Solar “generators” are all the rage right now, and you could probably adapt this idea for that use, too.

Caltech Scientists Make Producing Plastics From CO2 More Efficient

July 16, 2025 by Maya Posch 26 Comments

For decades there has been this tantalizing idea being pitched of pulling CO₂ out of the air and using the carbon molecules for something more useful, like making plastics. Although this is a fairly simple process, it is also remarkably inefficient. Recently Caltech researchers have managed to boost the efficiency somewhat with a new two-stage process involving electrocatalysis and thermocatalysis that gets a CO₂ utilization of 14%, albeit with pure CO₂ as input.

The experimental setup with the gas diffusion electrode (GDE) and the copolymerization steps. (Credit: Caltech)

The full paper as published in Angewandte Chemie International is sadly paywalled with no preprint available, but we can look at the Supplemental Information for some details. We can see for example the actual gas diffusion cell (GDE) starting on page 107 in which the copper and silver electrodes react with CO₂ in a potassium bicarbonate (KHCO₃) aqueous electrolyte, which produces carbon monoxide (CO) and ethylene (C₂H₄). These then react under influence of a palladium catalyst in the second step to form polyketones, which is already the typical way that these thermoplastics are created on an industrial scale.

The novelty here appears to be that the ethylene and CO are generated in the GDEs, which require only the input of CO₂ and the potassium bicarbonate, with the CO2 recirculated for about an hour to build up high enough concentrations of CO and C₂H₄. Even so, the researchers note a disappointing final quality of the produced polyketones.

Considering that a big commercial outfit like Novomer that attempted something similar just filed for Chapter 11 bankruptcy protection, it seems right to be skeptical about producing plastics on an industrial scale, before even considering using atmospheric CO₂ for this at less than 450 ppm.

Arduino Saves Heat Pump

July 16, 2025 by Bryan Cockfield 28 Comments

For home HVAC systems, heat pumps seem to be the way of the future. When compared to electric heating they can be three to four times more efficient, and they don’t directly burn fossil fuels. They also have a leg up over standard air conditioning systems since they can provide both cooling and heating, and they can even be used on water heating systems. Their versatility seems unmatched, but it does come at a slight cost of complexity as [Janne] learned while trying to bring one back to life.

The heat pump here is a Samsung with some physical damage, as well as missing the indoor half of the system. Once the damage to the unit was repaired and refilled with refrigerant, [Janne] used an Optidrive E3 inverter controlled by an Arduino Mega to get the system functional since the original setup wouldn’t run the compressor without the indoor unit attached. The Arduino manages everything else on the system as well including all of the temperature sensors and fan motor control.

With everything up and running [Janne] connected the system to a swimming pool, which was able to heat the pool in about three hours using 60 kWh of energy. The system is surprisingly efficient especially compared to more traditional means of heating water, and repairing an old or damaged unit rather than buying a new one likely saves a significant amount of money as well. Heat pump projects are getting more common around here as well, and if you have one in your home take a look at this project which adds better climate control capabilities. to a wall mount unit.

3 yellow modules are connected with bees filling 2 out of 3

View A Beehive Up Close With This 3D Printed Hive

July 8, 2025 by Ian Bos 24 Comments

Bees are incredible insects that live and die for their hive, producing rich honey in complicated hive structures. The problem is as the average beekeeper, you wouldn’t see much of these intricate structures without disturbing the hive. So why not 3D print an observation hive? With [Teddy Hatcher]’s 3D printing creativity, that is exactly what he did.

Hexagonal sections allow for viewing of entire panels of hexagonal cells, growing new workers, and storing the rich syrup we all enjoy. Each module has two cell panels, giving depth to the hive for heat/humidity gradients. The rear of a module has a plywood backing and an acrylic front for ample viewing. [Teddy] uses three modules plus a Flow Hive for a single colony, enough room for more bees than we here at Hackaday would ever consider letting in the front door.

As with many 3D printed projects involving food or animals, the question remains about health down the line. Plastic can bio-accumulate in hives, which is a valid concern for anyone wanting to add the honey to their morning coffee. On the other hand, the printed plastic is not what honey is added to, nor what the actual cell panels are made from. When considering the collected honey, this is collected from the connected Flow Hive rather than anything directly in contact with 3D printed plastic.

Beehives might not always need a fancy 3D printed enclosure; the standard wooden crates seem to work just fine for most, but there’s a time and place for some bio-ingenuity. Conditions in a hive might vary creating problems for your honey production, so you better check out this monitoring system dedicated to just that!

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Making Corrugated Cardboard Stronger And Waterproof

June 15, 2025 by Maya Posch 45 Comments

As useful as corrugated cardboard is, we generally don’t consider it to be a very sturdy material. The moment it’s exposed to moisture, it begins to fall apart, and it’s easily damaged even when kept dry. That said, there are ways to make corrugated cardboard a lot more durable, as demonstrated by the [NightHawkInLight]. Gluing multiple panels together so that the corrugation alternates by 90 degrees every other panel makes them more sturdy, with wheat paste (1:5 mixture of flour and water) recommended as adhesive.

Other tricks are folding over edges help to protect against damage, and integrating wood supports. Normal woodworking tools like saws can cut these glued-together panels. Adding the wheat paste to external surfaces can also protect against damage. By applying kindergarten papier-mâché skills, a custom outside layer can be made that can be sanded and painted for making furniture, etc.

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Scratch-built Electric Boat Shows Off Surprising Speed

June 7, 2025 by Bryan Cockfield 10 Comments

Electric cars are everywhere these days, but what about boats? Looking to go green on the water, [NASAT] put together this impressively nimble boat propelled by a pair of brushless motors.

The boat itself has a completely custom-built hull, using plywood as a mold for the ultimate fiberglass body. It’s a catamaran-like shape that seems to allow it to get on plane fairly easily, increasing its ultimate speed compared to a displacement hull. It gets up to that speed with two electric motors totaling 4 kW, mated to a belt-driven drivetrain spinning a fairly standard prop. Power is provided by a large battery, and the solar panel at the top can provide not only shade for the operator, but 300 W to charge the battery when the motors are not being used.

With the finishing touches put on, the small single-seat boat effortlessly powers around the water with many of the same benefits of an electric car: low noise, low pollution, a quiet ride, and a surprisingly quick feel. Electrification has come for other boats as well, like this sailing catamaran converted to electric-only. Even some commercial boats have begun to take the plunge.

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