fotw

17 Articles

Fail Of The Week: Car Starter Motors Aren’t The Best Fit For EBikes

April 14, 2023 by 40 Comments

A lot of what real engineering is all about is designing to the limits of your materials, with a healthy margin for error. On the other hand, seat-of-the-pants engineering often takes the opposite tack — working with the materials you have and finding their limits after the fact. While the former is more rigorous and better suited to anything where life and limb are on the line, there’s something to be said for the flexibility that informal engineering offers.

[Austin Blake]’s latest eBike is a case study in informal engineering. [Austin] started out wondering if a starter motor from a car engine would make a decent electric bike motor. Our first instinct before watching the video below was to answer that question with a resounding “No!” Yes, starter motors seem like a natural for the job, delivering high torque in a compact package. But starting a car engine is the very definition of a low-duty-cycle application, since it should only take a second or two of cranking to get an engine started. Pressing a motor designed for such a task into continuous duty seems like, well, a non-starter.

And to be fair, [Austin] fully acknowledges this from the start. He even retrofits the motor, wisely replacing the shaft bushings with proper bearings in an attempt to get a better duty cycle. And it works, at least for a while — with the motor, a homebrew battery, and an ESC mounted to a bike frame, the bike was actually pretty peppy. But bearings aren’t the only thing limiting a starter motor to intermittent duty operation. The short drive really heated up the motor, and even with a few ventilation holes knocked in the motor housing, it eventually released the Magic Smoke. The video has all the gory details.

As always, we like to stress that “Fail of the Week” is not necessarily a badge of shame. We appreciate it whenever someone shows us the way not to go, as [Austin] did here. And let’s keep in mind that he’s had success with this approach before, albeit with a much, much bigger starter motor.

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World's longest hacksaw

Fail Of The Week: A Bigger Hacksaw Isn’t A Better Hacksaw

February 14, 2022 by 23 Comments

If we’re being honest, the main reason to buy a power tool is to avoid the pain of using one’s muscles. Oh sure, we dress it up with claims that a power tool will make us more productive, or give better results, but more often than not it’s the memory of how your forearm feels after a day of twisting a screwdriver that makes you buy a cordless driver.

It appears that [Artisan Makes] has a high tolerance for pain, seeing how the main prep tool in his metal shop is a plain old hacksaw. So in an effort to speed up his stock prep, he turned not to a bandsaw or cutoff saw, but instead built the world’s silliest hacksaw. It’s the metalworking equivalent of the two-man bucksaws that lumberjacks used to fell trees before chainsaws came along, and at a meter and half in length, it’s about the size of one too. Modifying the frame of his trusty hacksaw was easy — he just popped the end pieces off and attached them to an extra-long piece of tube stock. Finding a 1.5-meter hacksaw blade was the main challenge; not exactly a big-box store item, that. So a section of metal-cutting bandsaw blade was modified to fit the frame, and it was off to the races.

Or not. The video below tells the tale of woe, which starts with the fact that [Artisan]’s shop is too small for the hilariously long hacksaw. Solving the fixturing problems didn’t soo much to help, though — there was no way to tension the blade enough to get it to stop wobbling during cutting. It was also clear that the huge saw wasn’t able to apply enough downforce on the stock to get good cuts. Maybe with a second set of hands, though…

There are plenty of ways to improve hacksawing in the shop, and while this isn’t one of them, we sure appreciate the chuckle we got out of it. And you really should check out [Artisan Makes]’ channel — his more serious stuff is really good.

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Fail Of The Week: This SD Card Won’t Slot

June 29, 2020 by 23 Comments

If you’ve got a few self-designed PCBs under your belt, you probably know the pain of missing some little detail and having to break out the bodge wires to fix it. So we feel for [Arsenio Dev], who placed an SD card slot next to an SoC, only to find that it was the wrong way round. Rather than tossing it in the bin, he decided to employ a particularly crafty set of bodge wires that curve over the board and connect to an SD card adapter on the other side.

Our attention was taken by the board itself, he’s posted little information about it and taken pains to conceal one of the pieces of text on it. Since it has an Octavo Systems BeagleBone-on-chip, a slot for a cellular modem, and a connector marked “CONNECT AERONET HERE” which we are guessing refers to the Aeronet sun photometry network, we’re guessing it might be a controller for remotely-sited nodes for that system. Either way it’s enough to have us intrigued, and we wish him every success with the next spin.

Meanwhile, this certainly isn’t the first PCB CAD fail we’ve brought you.

Fail Of The Week: How Not To Watercool A PC

June 17, 2020 by 50 Comments

To those who choose to overclock their PCs, it’s often a “no expense spared” deal. Fancy heat sinks, complicated liquid cooling setups, and cool clear cases to show off all the expensive guts are all part of the charm. But not everyone’s pockets are deep enough for off-the-shelf parts, so experimentation with cheaper, alternatives, like using an automotive fuel pump to move the cooling liquid, seems like a good idea. In practice — not so much.

The first thing we thought of when we saw the title of [BoltzBrain]’s video was a long-ago warning from a mechanic to never run out of gas in a fuel-injected car. It turns out that the gasoline acts as a coolant and lubricant for the electric pump, and running the tank dry with the power still applied to the pump quickly burns it out. So while [BoltzBrain] expected to see corrosion on the brushes from his use of water as a working fluid, we expected to see seized bearings as the root cause failure. Looks like we were wrong: at about the 6:30 mark, you can see clear signs of corrosion on the copper wires connecting to the brushes. It almost looks like the Dremel tool cut the wire, but that green copper oxide is the giveaway. We suspect the bearings aren’t in great shape, either, but that’s probably secondary to the wires corroding.

Whatever the root cause, it’s an interesting tour inside a common part, and the level of engineering needed to build a brushed motor that runs bathed in a highly flammable fluid is pretty impressive. We liked the axial arrangement of the brushes and commutator especially. We wonder if fuel pumps could still serve as a PC cooler — perhaps changing to a dielectric fluid would do the trick.

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Fail Of The Week: Bright Idea For LED Signs Goes Bad

May 8, 2020 by 43 Comments

Typically when we select a project for “Fail to the Week” honors, it’s because something went wrong with the technology of the project. But the tech of [Leo Fernekes]’ innovative LED sign system was never the problem; it was the realities of scaling up to production as well as the broken patent process that put a nail in this promising project’s coffin, which [Leo] sums up succinctly as “The Inventor’s Paradox” in the video below.

The idea [Leo] had a few years back was pretty smart. He noticed that there was no middle ground between cheap, pre-made LED signs and expensive programmable signboards, so he sought to fill the gap. The result was an ingenious “LED pin”, a tiny module with an RGB LED and a microcontroller along with a small number of support components. The big idea is that each pin would store its own part of a display-wide animation in flash memory. Each pin has two terminals that connect to metal cladding on either side of the board they attach to. These two conductors supply not only power but synchronization for all the pins with a low-frequency square wave. [Leo]’s method for programming the animations — using a light sensor on each pin to receive signals from a video projector — is perhaps even more ingenious than the pins themselves.

[Leo]’s idea seemed destined for greatness, but alas, the cruel realities of scaling up struck hard. Each prototype pin had a low part count, but to be manufactured economically, the entire BOM would have to be reduced to almost nothing. That means an ASIC, but the time and expense involved in tooling up for that were too much to bear. [Leo] has nothing good to say about the patent game, either, which his business partners in this venture insisted on playing. There’s plenty of detail in the video, but he sums it up with a pithy proclamation: “Patents suck.”

Watching this video, it’s hard not to feel sorry for [Leo] for all the time he spent getting the tech right only to have no feasible way to get a return on that investment. It’s a sobering tale for those of us who fancy ourselves to be inventors, and a cautionary tale about the perils of participating in a patent system that clearly operates for the benefit of the corporations rather than the solo inventor. It’s not impossible to win at this game, as our own [Bob Baddeley] shows us, but it is easy to fail.

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Fail Of The Week: How Not To Die Of Boredom During Isolation

April 1, 2020 by 26 Comments

They say you can’t actually die from boredom, but put a billion or so people into self-isolation, and someone is bound to say, “Hold my beer and watch this.” [Daniel Reardon]’s brush with failure, in the form of getting magnets stuck up his nose while trying to invent a facial touch reminder, probably wasn’t directly life-threatening, but it does underscore the need to be especially careful these days.

The story begins with good intentions and a small stack of neodymium magnets. [Daniel]’s idea for a sensor to warn one of impending face touches was solid: a necklace with magnetic sensors and wristbands studded with magnets. Sounds reasonable enough; one can easily see a compact system that sounds an alarm when a hand subconsciously crosses into the Danger Zone while going in for a scratch. Lacking any experience in circuits, though, [Daniel] was unable to get the thing working, so he started playing with the magnets instead. One thing led to another, and magnets were soon adorning his earlobes, and then his nostrils. Unfortunately, two magnets became locked on either side of his septum, as did two others meant to neutralize the pull of the first pair. So off [Daniel] went to the emergency department for a magnetectomy.

Of course it’s easy to laugh at someone’s misfortune, especially when self-inflicted. And the now-degaussed [Daniel] seems to be a good sport about the whole thing. But the important thing here is that we all do dumb things, and hackers need to be especially careful these days. We often work with sharp, pointy, sparky, toxic, or flammable things, and if we don’t keep our wits about us, we could easily end up in an ER somewhere. Not only does that risk unnecessary exposure to COVID-19, but it also takes medical resources away from people who need it more than you do.

By all means, we should be hacking away these idle hours. Even if it’s not in support of COVID-19 solutions, continuing to do what we do is key to our mental health and well-being. But we also need to be careful, to not stretch dangerously beyond our abilities, and to remember that the safety net that’s normally there to catch us is full of holes now.

Thanks to [gir.st] for the tip — you actually were the only one to send this in.

Fail Of The Week: Padlock Purports To Provide Protection, Proves Pathetic

January 21, 2020 by 49 Comments

Anyone in the know about IoT security is likely to steer clear of a physical security product that’s got some sort of wireless control. The list of exploits for such devices is a long, sad statement on security as an afterthought, if at all. So it’s understandable if you think a Bluetooth-enabled lock is best attacked via its wireless stack.

As it turns out, the Master 5440D Bluetooth Key Safe can be defeated in a few minutes with just a screwdriver. The key safe is the type a realtor or AirBnB host would use to allow access to a property’s keys. [Bosnianbill] embarked on an inspection of the $120 unit, looking for weaknesses. When physical attacks with a hammer and spoofing the solenoids with a magnet didn’t pay off, he decided to strip off the resilient skin that Master so thoughtfully provided to prevent the box from marring the finish of a door or gate. The denuded device thus revealed its awful secret: two Phillips screws, each securing a locking shackle to the cover. Once those are loose, a little prying with a screwdriver is all that’s need to get the keys to the kingdom.

In a follow-up video posted later, [Bill] took a closer look at another key safe and found that Master had made an anemic effort to fix this vulnerability with a squirt of epoxy in each screw head. It’s weak, at best, since a tap with a hammer compresses the gunk enough to get a grip on the screw.

We really thought [Bosnianbill]’s attack would be electronic, like that time [Dave Jones] cracked a safe with an oscilloscope. Who’d have thought a screwdriver would be the best way past the wireless stack?

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