Hacked Car Axle Yields Custom 90° Gearbox

Need a sturdy angle gearbox to handle power transmission for your next big project? Why not harvest a rear axle from a car and make one yourself?

When you think about it, the axle of a rear-wheel drive vehicle is really just a couple of 90° gearboxes linked together internally, and a pretty sturdy assembly that’s readily available for free or on the cheap. [Donn DIY]’s need for a gearbox to run a mower lead him to a boneyard for the raw material. The video below shows some truly impressive work with that indispensable tool of hardware hackers, the angle grinder. Not only does he amputate one of the half axles with it, he actually creates almost perfect splines on the remaining shortened shaft. Such work is usually done on a milling machine with a dividing head and an end mill, but [DonnDIY]’s junkyard approach worked great. Just goes to show how much you can accomplish with what you’ve got when you have no choice.

We’re surprised to not see any of [DonnDIY]’s projects featured here before, as he seems to have quite a body of hacks built up. We hope to feature some more of his stuff soon, but in the meantime, you can always check out some of the perils and pitfalls of automotive differentials.

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Different Differentials & The Pitfalls of the Easy Swap

I dig cars, and I do car stuff. I started fairly late in life, though, and I’m only just starting to get into the whole modification thing. Now, as far as automobiles go, you can pretty much do anything you set your mind to – engine swaps, drivetrain conversions, you name it – it’s been done. But such jobs require a high level of fabrication skill, automotive knowledge, and often a fully stocked machine shop to match. Those of us new to the scene tend to start a little bit smaller.

So where does one begin? Well, there’s a huge realm of mods that can be done that are generally referred to as “bolt-ons”. This centers around the idea that the install process of the modification is as simple as following a basic set of instructions to unbolt the old hardware and bolt in the upgraded parts. Those that have tread this ground before me will be chuckling at this point – so rarely is a bolt-on ever just a bolt-on. As follows, the journey of my Mazda’s differential upgrade will bear this out.

The car in question, currently known as the “Junkbox MX-5” until it starts running well enough to earn a real name. It somehow looks passable here, but in person I promise you, it looks awful.

It all started when I bought the car, back in December 2016. I’d just started writing for Hackaday and my humble Daihatsu had, unbeknownst to me, just breathed its last. I’d recently come to the realisation that I wasn’t getting any younger, and despite being obsessed with cars, I’d never actually owned a sports car or driven one in anger. It was time to change. Continue reading “Different Differentials & The Pitfalls of the Easy Swap”

DIY Active Sub-GHz Differential Scope Probe

Fancy measurement gear is often expensive to buy, but some bits of kit are entirely DIY’able if you’re willing to put a little work into the project. [Christer Weinigel] needed to get some measurements of a differential clock signal that was ticking away around 500 MHz. El-cheapo probes aren’t going to cut it here. They won’t have the bandwidth and most off-the-rack probes are single-ended, that is they’re referenced to ground. [Christer] needed the difference between two balanced signals, neither of which is grounded. In short, [Christer] needed a high-frequency active differential oscilloscope probe, and they’re not cheap. So he built one himself.

simulation-schematicThe circuit in the probe is really just an instrumentation amplifier design with a modified input stage and a 50 ohm output impedance. (See this article on in-amps if you need to brush up.) With higher frequencies like this, it’s going to be demanding on the op-amp, so [Christer] spent some time simulating the circuit to make sure it would work with his chosen part. Then he made up a bunch of PCB designs and had them made. Actual results matched fairly well with the simulation.

With some minor tweaking on the input damping resistors, he got a tool that’s dead flat up to 300 MHz, and totally usable up to 850 MHz. If you tried to buy one of these, it’d set you back the cost of a few hundred lattes, but this one can be made for the price of one or two if you get the PCBs done cheaply. Of course, the design files are available for your own use. Kudos [Christer].

Edit: By total coincidence, Bil Herd just posted a video intro to differential signals. Go check it out.

And thanks to [nebk] for the tip!

Sit ‘n Spin for Big Kids

Humans seem to have a strange love affair with testing their limits, especially when it comes to spinning. Perhaps they ride the Gravitron while dreaming they’re in NASA’s 20 g test centrifuge. When carnival rides aren’t enough though, a few intrepid hackers bust out the welders and take matters into their own hands. This is a hack that goes by many names, though  “The Redneck Spin Chair” will bring up plenty of hits on YouTube.

The design is dead simple. Take a rear differential and axle assembly out of an old car or truck. Rotate it 90 degrees, so the diff is now pointing up. Weld a chair on. Finally, weld on a couple of tow bars. Pulling the whole mess will cause the wheels to spin, which transmits power through the differential and rotates the chair. The ride doesn’t have be pulled very fast, as automotive differentials generally have reduction between 3:1 and 5:1. We’re running things in reverse, so that reduction becomes a multiplier. The result, which can be seen in the video below is a very dizzy rider.

The earliest incarnation of this ride we could find was created at Eagle Mountain in Burtrum, Minnesota. We’re betting this particular hack has been around for decades longer though. The closest in our recent memory is North Street Labs’ Centrifury. Do you know of an earlier incarnation? Let us know in the comments!

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Retrotechtacular: Fire Control Computers in Navy Ships

Here is a two-part Navy training film from 1953 that describes the inner workings of mechanical fire control computers. It covers seven mechanisms: shafts, gears, cams, differentials, component solvers, integrators, and multipliers, and does so in the well-executed fashion typical of the era.

Fire control systems depend on many factors that occur simultaneously, not the least of which are own ship’s speed and course, distance to a target, bearing, the target’s speed and course if not stationary, initial shell velocity, and wind speed and direction.

The mechanisms are introduced with a rack and pinion demonstration in two dimensions. Principally speaking, a shaft carries a value based on revolutions. From this, a system can be geared at different ratios.

Cams take this idea further, transferring a regular motion such as rotation to an irregular motion. They do so using a working surface as input and a follower as output. We are shown how cams change rotary motion to linear motion. While the simplest example is limited to a single revolution, additional revolutions can be obtained by extending the working surface. This is usually done with a ball in a groove.

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Hackaday Links: September 28, 2014

hackaday-links-chain

Kyocera is vastly expanding their product lineup with the Shop Sink 3530. The perfect addition to your copiers, fax machines, and laser printers.

About a year and a half ago and with objections from the editorial staff, we did a Top 10 hacking fails in movies and TV post. The number one fail is, “Stupid crime shows like NCIS, CSI, and Bones.” A new show on CBS just topped this list. It’s named Scorpion, and wow. Dropping a Cat5 cable from an airplane doing an almost-touch-and-go because something is wrong with the computers in the tower. Four million adults age 18-49 watched this.

thing[Derek] found something that really looks like the Hackaday logo in a spacer of some kind. It’s been sitting on his shelf for a few months, and is only now sending it in. He picked it up in a pile of scrap metal, and he (and we) really have no idea what this thing is. Any guesses?

[Sheldon] has a teardown of a vintage voltage and current standard. Just look at those hand drawn traces on a single sided board. Beautiful.

[Art] has another, ‘what is this thing’. He has two of them, and he’s pretty sure it’s some sort of differential, but other than that he’s got nothing. The only real clue is that [Art] lives near a harbor on the N. Cali coast. Maybe from a navigation system, or a governor from a weird diesel?

So you have a Kinect sitting on a shelf somewhere. That’s fine, we completely understand that. Here’s something: freeze yourself in carbonite. Yeah, it turns out having a depth sensor is exactly what you need to make a carbonite copy of yourself.

Retrotechtacular: The differential

retrotechtacular-how-a-differential-works

Any video that starts off with two minutes of motorcycle formation riding has got to be good. If the grainy black and white video didn’t tip you off that this was made in a different time the helmetless riders standing on the seats of moving motorcycles certainly would have. But there is a purpose to this exposition. A single line of motorcycles riding shoulder to shoulder as they go around a curve illustrates why a differential is necessary and soon after you’ll find out how one works.

Two wheels mounted on one axle need to turn at different speeds as a vehicle goes around a corner or one of the wheels must slip to accommodate the speed difference. The differential is necessary to allow for these different turning rates while still letting both wheels connect to the power train. We were surprised to learn from the video after the break that early automobiles got around this issues by powering only one of the four wheels.

This instructional video is a prefect compliment to the fluid coupling video we saw in the last installment of Retrotechtacular.

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