resin printed pulsejet engine in operation

A Detonation Engine Prototyped Using Resin Printing

August 29, 2022 by Dave Rowntree 5 Comments

Over the years [Integza] has blown up or melted many types of jet engine, including the humble pulsejet. Earlier improvements revolved around pumping in more fuel, or forced air intakes, but now it’s time for a bit more refinement of the idea, and he takes a sidestep towards the more controllable detonation engine. His latest experiment (video, embedded below) attempts to dial-in the concept a little more. First he built a prototype from a set of resin printed parts, with associated tubing and gas control valves, and a long acrylic tube to send the exhaust down. Control of the butane and air injection, as well as triggering of the spark-ignition, are handled by an Arduino — although he could have just used a 555 timer — driving a few solid state relays. This provided some repeatable control of the pulse rate. This is a journey towards a very interesting engine design, known as the rotating detonation engine. This will be very interesting to see, if he can get it to work.

supersonic exhaust plume from a pulsejet engine — Supersonic exhaust plume with the characteristic ‘mushroom’ shape

Detonation engines operate due to the pressure part of the general thrust equation, where the action is in the detonative combustion. Detonative combustion takes place at constant pressure, which theoretically should lead to a greater efficiency than boring old deflagration, but the risks are somewhat higher. Apparently this is tricky to achieve with a fuel/air mix, as there just isn’t enough oomph in the mixture. [Integza] did try adding a Shchelkin spiral (we call them springs around here) which acts to slow down the combustion and shorten the time taken for it to transition from deflagration to detonation.

It sort of worked, but not well enough, so running with butane and pure oxygen was the way forward. This proved the basic idea worked, and the final step was to rebuild the whole thing in metal, with CNC machined end plates and some box section clamped with a few bolts. This appeared to work reasonably well at around 10 pulses/sec with some measurable thrust, but not a lot. More work to be done we think.

We hinted at earlier work on forced-air pulsejets, so here that is. Of course, whilst we’re on the subject of pulsejets, we can’t not mention [Colinfurze] and his pulsejet go kart.

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Small Combat Robots Pack A Punch In Antweight Division

August 22, 2022 by Donald Papp 6 Comments

Two robots enter, one robot leaves! Combat robotics are a fantastic showcase of design and skill, but the mechanical contenders don’t have to be big, heavy, and expensive. There is an Antweight division for combat robots in which most contenders weigh a mere 150 grams, and [Harry Makes Things] shows off four participants for Antweight World Series (AWS) 64.

Clockwise: ReLoader, Shakma, Sad Ken, and HobGoblet antweight combat robots.

Each of them have very different designs, and there are plenty of photos as well as insightful details about what was done and how well it worked. That’s exactly the kind of detail we love to read about, so huge thanks to [Harry] for sharing!

In combat robotics, contenders generally maneuver their remote-controlled machines to pin or immobilize their opponent. This can happen as a result of damaging them to the point that they stop functioning, but it can also happen by rending them helpless by working some kind of mechanical advantage. Continue reading “Small Combat Robots Pack A Punch In Antweight Division” →

Livestreaming Backpack Takes Streaming On-The-Go

August 19, 2022 by Bryan Cockfield 17 Comments

Anyone who’s anyone on the internet these days occasionally streams content online. Whether that’s the occasional livestream on YouTube or an every day video game session on Twitch, it’s definitely a trend that’s here to stay. If you want to take your streaming session on the go, though, you’ll need some specialized hardware like [Melissa] built into this livestreaming backpack.

[Melissa] isn’t actually much of a streamer but built this project just to see if it could be done. The backpack hosts a GoPro camera with a USB interface, mounted on one of the straps of the pack with some 3D printed parts, allowing it to act as a webcam. It is plugged into a Raspberry Pi which is set up inside the backpack, and includes a large heat sink to prevent it from overheating in its low-ventilation environment. There’s also a 4G modem included along with a USB battery pack to keep everything powered up.

The build doesn’t stop at compiling hardware inside a backpack, though. [Melissa] goes into detail on the project’s page about how to get all of the hardware to talk amongst themselves and where the livestream is setup as well. If you’d like a more permanently-located streaming setup with less expensive hardware, we have seen plenty of builds like this which will get the job done as well.

(Re)designing The LumenPnP Tape Feeder

August 15, 2022 by Dave Rowntree 9 Comments

Many of the hardware orientated hackers among us will likely have been following along with the story of [Stephen Hawes] and the Lumen pick-and-place project but kind of waiting a bit for the project to mature some more before maybe taking the plunge and ordering a kit. One reason for this might be that whilst the basic machine design is there and working, the tape feeders did need a fair bit of work, and a lack of usable feeders does not make a great PnP machine. [Stephen] has been working on a newer design that addresses some of the identified shortcomings, and has started documenting his progress (video, embedded below) along the way.

Gone is the PCB-based ‘case’, reverting back to a 3D printable affair and a much smaller PCB. After flip-flopping a bit between different geared DC motors, [Stephen] settled back on the original, smaller unit, which after a wee spot of hacking, was convinced to accept an optical encoder stripped from another unit, and this proved that it was indeed more than up to the tape-advancement duty. The reason for this change was physical size — the original motor resulted in an assembly 38mm wide — this limited the number for feeders on the front rail to barely eleven units. This is not really enough, but with the narrower assembly, the width is reduced to 15.5mm allowing 27 feeders to snuggle together on the rail, and that should make the machine much more usable.

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3D Printed Braiding Machine Brings Back Some History

August 4, 2022 by Danie Conradie 19 Comments

Mechanizing the production of textiles was a major part of the industrial revolution, and with the convenience of many people are recreating the classic machines. A perfect example of this is [Fraens]’ 3D printed braiding machine, which was reverse engineered from old photos of the early machines.

The trick behind braiding is the mesmerizing path the six bobbins need to weave around each other while maintaining the correct tension on the strands. To achieve this, they slide along a path in a guide plate while being passed between a series of guide gears for each section of the track. [Fraens] cut the guide plate components and the base plate below it from acrylic and mounted them together with standoffs to allow space for the guide gears.

Each of the six bobbins contains multiple parts to maintain the correct tension. The strands are fed through a single guide ring, where the braid is formed, and through pair of traction gears. All the moving parts are driven by a single 24 V motor and can produce about 42 cm of a braided cord per minute, and you can even set up the machine to braid around an inner core.

This braiding machine is just one in a series of early industrial machines recreated by [Fraens] using 3D printing. The others include a sewing machine, and a power loom, and a generator.

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Upgraded Film Scanner Handles Bigger Formats At No Cost

July 30, 2022 by Donald Papp 2 Comments

Film scanners are a useful tool for digitizing slides and negatives, and the Plustek 8100 that [Christian Chapman] had was capable, but limited to small format film only. Rather than pay for a much more expensive medium format scanner that could handle 120 film, he modified his 8100 to accomplish the same thing with a combination of good old software and hardware tampering.

On the software side, [Christian] modified a driver for the Plustek 8100 so that it sweeps the scan head further than usual. At the application level, to scan medium format frames, it does a total of four scans: one for each quadrant. The results get stitched together in software with a thoughtfully-designed shell script that provides previews and handles failures and restarts gracefully.

Hardware-wise, the scanning carriage needs modification to ensure nothing interferes with the scan head as it moves further than originally designed. Some CAD and 3D printing made short work of this. Incidentally, this hardware mod is an excellent demonstration of one of the core strengths of 3D printing: the ability to make geometrically-straightforward objects that would nevertheless be troublesome or impractical to construct in any other way.

Adding A Battery To Extend Speaker Life

July 23, 2022 by Bryan Cockfield 14 Comments

Perhaps the weakest point in modern electronics when it comes to user servicability is the lifecycle of the batteries included from the manufacturer. Without easily replaceable batteries, many consumer goods end up in the landfill when they’re otherwise working perfectly. If you’d like to get more out of your devices than the manufacturer intends, you might have to go to great lengths like [Théo] did with his JBL speaker.

This was a Bluetooth device produced by JBL nearly a decade ago, and while the original device boasted several hours of battery life, after so many years of service, it was lucky to get a half hour before the battery died. To replace it, [Théo] removed the original battery and extended the case to be able to hold a larger cell phone battery. He also decided to use the original battery management circuit from the speaker with the new battery after verifying the voltage and chemistry were close enough to the original.

Since the phone battery is a proprietary Samsung device, [Théo] also decided to build a version that uses standard 18650 cells instead, although he prefers the slimmer design with the phone battery for his use case. Straightforward as this build may be, it does go a long way to demonstrate the principle that if you can’t fix your devices, you don’t really own them.