Why You Probably Shouldn’t DIY A Car Airbag

May 10, 2026 by Maya Posch 13 Comments

Car airbags are both a very simple concept and a marvel of engineering, replacing the bone-shattering impact of unforgiving plastic and steel with a relatively soft landing in a funky-smelling air cushion. This deceptively simple concept requires that the gas generator activates only when there is a crash and finishes filling the airbag in the milliseconds before the squishy human’s cranium with its soft filling attempts to occupy the same space as said airbag. This makes mad Aussie bloke [Turnah81]’s attempt at DIY-ing a car airbag a most daring proposition.

Rather than messing about with an IMU and microprocessors, he went low-tech with an inertial fuel cut-off switch. These are mechanical switches that hold a steel ball in place with a magnet until a sufficiently large force — like a crash — dislodges the ball and triggers an event. Usually, a switch like this cuts off the fuel pump.

After a bit of fun with a crash-test rig and the airbag of a salvaged steering wheel, a DIY airbag was assembled using a compressed-gas cylinder instead of the fancy gas generator, along with an electrically triggered valve. Here, you can already see why modern airbags use a gas generator, as it is simply far more compact.

For the bag itself, a pillow case was adapted, with the subsequent crash test — as pictured above — going about as well as you can imagine. After this, he tried a few improvements, like using a bin liner and detonating some fuel, but it seems that the gas generator is very hard to beat for producing a large amount of gas in very little time.

Meanwhile, the inertial cut-off switch turned out to be more than sufficient for this purpose, and it was also used to trigger the original airbag. Of course, with how cheap those off-the-shelf airbag units are and are tested to be fit for purpose, you’d never DIY them for actual use in a car unless you were stark raving mad.

Airbags have a checkered history. There are some places you shouldn’t try to save costs.

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Challenging The Way We Pedal

May 9, 2026 by Jenny List 59 Comments

The bicycle is an invention that has not changed in its fundamentals since the first recognisably modern machines appeared in the closing years of the 19th century. Its frame uses a structure of two triangles, its wheels are equal in size, and it’s propelled by a pedal crank and (in most cases) a chain. Bicycles have improved vastly in materials and performance, but if you were to wheel a 2026 tourer into an 1886 bike shop, the Victorian proprietor would recognise it. Only a very brave engineer would try to fundamentally change such a formula, but here’s [Not programming] with a crankless bicycle.

The idea is to replace the crank’s circular motion with a linear one, thus providing a more constant propulsion. The build was inspired by another that used a sinusoidal track in a rotating cylinder to achieve the necessary conversion. This design takes a different tack, using an arrangement of gears and freewheels he describes as a mechanical rectifier to convert the back-and-forth motion of pedaling into rotation. The pedals themselves are stirrups mounted at each end of a V-belt.

This build is an exercise in pushing the limits of 3D print strength, as prototype after prototype shears under load. He does finally get the thing to work, though, and we admire his persistence. Oddly, this isn’t the first 3D-printed bicycle geartrain we’ve seen.

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Why Opposed Piston Internal Combustion Engines Are Great

May 6, 2026 by Maya Posch 76 Comments

Converting the ignition of a fuel-air mixture into usable mechanical energy lies at the core of a dizzying number of internal combustion engines developed over the course of more than century. Although typical piston engines with a cylinder head and valve-train are the most common by far, and even rotary engines are quite well-known, the opposed-piston engine design is significantly more obscure. In a recent video by [driving 4 answers], this type of engine is covered and why it’s actually a pretty nifty ICE design with many benefits.

Achates opposed-piston design. (Source: driving 4 answers, YouTube)

Above all, the design is mechanically far more simple, as it omits all the valves and timing-related hardware of the typical four-stroke ICE. Each ignition event pushes against two pistons at the same time, allowing for more of the kinetic energy to be converted into usable power, as well as enabling largely vibration-free operation in a more compact package, especially in the case of the Asender design that eliminates the second crankshaft of the Achates design. This makes the Asender rather similar to the 1914 Simpson’s design.

Despite these many advantages, opposed-piston engines have mostly led a quiet life in industrial and military applications, including tanks, submarines and airplanes. This is where the video also sees their continued use, but as a 2021 article in Autoweek suggests, we might be seeing more of these engines in everywhere from trucks to cars as well. Even if it’s only in hybrid cars where it would be in a generator role, there are many reasons why this ICE design would fit right into certain roles.

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A Tractor From A Small Town Might Just Be The Catalyst For Ousting Machinery DRM

April 30, 2026 by Jenny List 82 Comments

Odd things sometimes pop up in the feed of a Hackaday scribe, not hacks as such, but stories with a meaning in our community. One such that’s come our way from a variety of sources over the last week features Ursa Ag, a small machinery manufacturer based in Alberta, Canada. The reason they’re in the news is because they have gained bulging order books by taking on the likes of John Deere with a tractor more like the one their customers’ parents bought back in the ’80s or ’90s. It’s a basic machine without much in the way of electronics, and certainly without all the DRM lockdown that has made those big manufacturers so unpopular.

It’s clear that Hackaday isn’t in the business of shilling Canadian tractors, but it should be of interest to readers because it represents an alternative route to challenge the DRM lockdowns than the legal and consumer routes we’ve previously reported on. The Ursa Ag tractor may be as niche Albertan as a Corb Lund CD, but it’s not the tractor itself but the idea which matters. We doubt much sweat will be shed by John Deere execs over a tiny company out on the prairies making a basic spec tractor, but given that Ursa Ag customers are reported as buying them because they have no DRM, the prospect of larger upstart competitors taking note and offering machines without it may cause them some sleep loss. The free market is held up to outsiders as perhaps the most American of ideals, and for it to eventually prove to be the means by which something intended to limit it might be defeated, is sweet justice indeed.

We’ve reported extensively on the Deere tractor saga over the years, but perhaps the best illustration of the self-inflicted damage the brand has suffered through DRM comes in their older products being worth considerably more than their newer ones.

A Sail And Oar Skiff Built From Common Lumber

April 26, 2026 by Bryan Cockfield 13 Comments

For those first venturing into sailing, it can be overwhelming since the experience is thick with jargon and skills that don’t often show up in life ashore. With endless choices, including monohulls versus catamarans, fiberglass versus wood, fractional versus masthead rigs, and sloops versus ketches, a new sailor risks doing something like single-handing a staysail schooner when they should have started on a Bermuda-rigged dinghy without a spinnaker. Luckily, there are some shortcuts to picking up the hobby, like the venerable Sunfish or Hobie ships. It’s also possible to build a simple sailing vessel completely out of materials from a local hardware store, as [Cumberland Rover] has been demonstrating.

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Quirky Electric Car Rides The Rails

April 19, 2026 by Bryan Cockfield 22 Comments

We wouldn’t be surprised if you’d never seen the Spira before. The lightweight three-wheel vehicle is closer to a go-kart than a traditional car, and that’s before you even get to the foam body panels. But even the most niche of products enjoys a certain fandom, and [Matt Spears] certainly seems to love working on his Spira. His latest video documents the new modifications he’s made to the car in an effort to ride it on abandoned railroad tracks in the western United States.

His first attempt at riding the rails worked pretty well but he hit an obstruction at high speed which destroyed his front axle and damaged a few other parts on the vehicle, which gave him a perfect excuse to make some upgrades. He swapped the old rear axle out with one from a go-kart, complete with custom wheels and a new braking system. The drivetrain received an upgrade with a 5 kW electric motor, and although [Matt] planned on casting new wheels for the higher speeds, the chemicals he needed didn’t arrive in time. So, to test the new vehicle he repurposed some old wheels just to get the Spria back out on the tracks.

The test run went so well that [Matt] ended up pushing the vehicle farther than he had ever been on this abandoned rail, including over a questionable trestle and far out into the wilderness. Hopefully we’ll see more videos of [Matt] taking this car to explore even more remote places. In the meantime, take a look at some simpler, non-electric vehicles that are often used to explore abandoned rail lines in California.

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A Better Jogging Stroller

April 1, 2026 by Bryan Cockfield 13 Comments

Although the jogging stroller is a fixture of suburban life, allowing parents the opportunity to get some exercise while letting their young children a chance for some fresh air, it would seem like the designers of these strollers have never actually gone for a jog. Requiring a runner to hold their hands at fixed positions can be incredibly uncomfortable and disrupts most people’s strides and cadence — so [John] attempted to solve the problem after finding one of these strollers on the secondhand market.

While there are some purpose-built strollers that attempt to address these issues, they can be pricey. Rather than shell out for a top-dollar model, [John] got to work with his 3D printer and created a prototype device that allows him to attach the stroller at his waist while leaving his hands free. There were a few problems to overcome here, the first of which would cause the device to buckle under certain loading situations. This was solved with some small pieces of rope which act as flexible bump stops, keeping the hinge mechanism from binding up. Another needed to be solved with practice, which was that it took some time to be able to steer the stroller without using one’s hands.

As an added bonus, [John] also included a system that tracks the distance the stroller has traveled. Using a hall effect sensor and a magnet attached to the wheel, a small microcontroller is able to quickly calculate distance and display it on a tiny screen mounted near the handlebars. Although smartphones are handy, their GPS systems can be surprisingly inaccurate, so a system like this can be a better indicator since it’s being directly measured. All in all, not a bad few upgrades to a secondhand stroller.

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