Why Electric Trains Sound The Way They Do

October 5, 2024 by Jenny List 20 Comments

If you’re a seasoned international rail traveler you will no doubt have become used to the various sounds of electric locomotives and multiple units as they start up. If you know anything about electronics you’ll probably have made the connection between the sounds and their associated motor control schemes, but unless you’re a railway engineer the chances are you’ll still be in the dark about just what’s going on. To throw light on the matter, [Z&F Railways] have a video explaining the various control schemes and the technologies behind them.

It’s made in Scotland, so the featured trains are largely British or in particular Scottish ones, but since the same systems can be found internationally it’s the sounds which matter rather than the trains themselves. Particularly interesting is the explanation of PWM versus pattern mode, the latter being a series of symmetrical pulses at different frequencies to create the same effect as PWM, but without relying on a single switching frequency as PWM does. This allows the controller to more efficiently match its drive to the AC frequency demanded by the motor at a particular speed, and is responsible for the “gear change” sound of many electric trains. We’re particularly taken by the sound of some German and Austrian locomotives (made by our corporate overlords Siemens, by coincidence) that step through the patterns in a musical scale.

Not for the first time we’re left wondering why electric vehicle manufacturers have considered fake internal combustion noises to make their cars sound sporty, when the sound of true electrical power is right there. The video is below the break.

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Xiaomi M365 Battery Fault? Just Remove A Capacitor

October 1, 2024 by Arya Voronova 11 Comments

Electric scooters have long been a hacker’s friend, Xiaomi ones in particular – starting with M365, the Xiaomi scooter family has expanded a fair bit. They do have a weak spot, like many other devices – the battery, something you expect to wear out.

Let’s say, one day the scooter’s diagnostics app shows one section of the battery going way below 3 volts. Was it a sudden failure of one of the cells that brought the whole stage down? Or perhaps, water damage after a hastily assembled scooter? Now, what if you measure the stages with a multimeter and it turns out they are perfectly fine?

Turns out, it might just be a single capacitor’s fault. In a YouTube video, [darieee] tells us all about debugging a Xiaomi M365 battery with such a fault – a BQ76930 controller being responsible for measuring battery voltages. The BMS (Battery Management System) board has capacitors in parallel with the cells, and it appears that some of these capacitors can go faulty.

Are you experiencing this particular fault? It’s easy to check – measure the battery stages and see if the information checks out with the readings in your scooter monitoring app of choice. Could this be a mechanical failure mode for this poor MLCC? Or maybe, a bad batch of capacitors? One thing is clear, this case is worth learning from, adding this kind of failure to your collection of fun LiIon pack tidbits. This pack seems pretty hacker-friendly – other packs lock up when anything is amiss, like the Ryobi batteries do, overdue for someone to really spill their secrets!

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Inside The F-4 Attitude Indicator

September 30, 2024 by Al Williams 10 Comments

[Ken] recently obtained an attitude indicator—sometimes called an artificial horizon—from an F-4 fighter jet. Unlike some indicators, the F-4’s can rotate to show pitch, roll, and yaw, so it moves in three different directions. [Ken] wondered how that could work, so, like any of us, he took it apart to find out.

With the cover off, the device is a marvel of compact design. Then you realize that some of the circuit is inside the ball, so there’s even more than it appears at a quick glance. As you might have guessed, there are two separate slip rings that allow the ball to turn freely without tangling wires. Of course, even if you don’t tangle wires, getting the ball to reflect the aircraft’s orientation is an exercise in control theory, and [Ken] shows us the servo loop that makes it happen. There’s a gyroscope and synchros—sometimes known by the trade name selsyn—to keep everything in the same position.

You have to be amazed by the designers of things like this. Sophisticated both electrically and mechanically, rugged, compact, and able to handle a lot of stress. Good thing it didn’t have to be cheap.

We’ve seen inside an ADI before. If you want to make any of this look simple, check out the mechanical flight computers from the 1950s.

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Brass Propeller Gets Impressive Hand Trimming

September 22, 2024 by Tom Nardi 4 Comments

Whether you’re a landlubber or an old salt, you’ve got to appreciate the effort that [The Aussie boat guy] puts into cutting an old brass propeller down into a far smaller and sleeker specimen. Especially since he does the entire thing with hand tools, a couple different calipers, and that most valuable of natural resources: experience.

The whole process was made somewhat easier by the fact that [The Aussie boat guy] had a model to work from — his friend had a small propeller that was already known to perform well, it was just a matter of cutting the larger prop down to match its dimensions. Using what appears to be pieces of leather (presumably for its flexibility), a template was made to accurately map out the front face of the blade.

As Bob Ross would say — “Here comes your bravery test”

By measuring out from the hub of the prop with his calipers, [The Aussie boat guy] was able to make sure the template was properly positioned before scribing its shape into the larger prop. An angle grinder was used to cut the shape out of each blade, followed by a smoothing off with a flap wheel.

But there was still a problem — the blades were the right shape, but they were far too thick. So he took the angle grinder to the back of each one to start removing material, using another set of calipers to occasionally spot-check them to make sure they were thinning out at roughly the same rate.

This thinning out process continued until the prop was brought into balance. How do you check that, you might be wondering? Well, if you’re a madman like [The Aussie boat guy], you chuck the thing into a power drill and spin er’ up to see how badly it shakes. But this only gives you a rough idea, so he has to move over to a somewhat more scientific apparatus that uses a set of parallel bars to help determine which blade is heavier than its peers.

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COBB Tuning Hit With $2.9 Million Fine Over Emissions Defeat Devices

September 20, 2024 by Maya Posch 110 Comments

Recently, the EPA and COBB Tuning have settled after the latter was sued for providing emissions control defeating equipment. As per the EPA’s settlement details document, COBB Tuning have since 2015 provided customers with the means to disable certain emission controls in cars, in addition to selling aftermarket exhaust pipes with insufficient catalytic systems. As part of the settlement, COBB Tuning will have to destroy any remaining device, delete any such features from its custom tuning software and otherwise take measures to fully comply with the Clean Air Act, in addition to paying a $2,914,000 civil fine.

The tuning of cars has come a long way from the 1960s when tweaking the carburetor air-fuel ratios was the way to get more power. These days cars not only have multiple layers of computers and sensor systems that constantly monitor and tweak the car’s systems, they also have a myriad of emission controls, ranging from permissible air-fuel ratios to catalytic converters. It’s little surprise that these systems can significantly impact the raw performance one might extract from a car’s engine, but if the exhaust of nitrogen-oxides and other pollutants is to be kept within legal limits, simply deleting these limits is not a permissible option.

COBB Tuning proclaimed that they weren’t aware of these issues, and that they never marketed these features as ’emission controls defeating’. They were however aware of issues regarding their products, which is why they announced ‘Project Green Speed’ in 2022, which supposedly would have brought COBB into compliance. Now it would seem that the EPA did find fault despite this, and COBB was forced to making adjustments.

Although perhaps not as egregious as modifying diesel trucks to ‘roll coal’, federal law has made it abundantly clear that if you really want to have fun tweaking and tuning your car without pesky environmental laws getting in the way, you could consider switching to electric drivetrains, even if they’re mind-numbingly easy to make performant compared to internal combustion engines.

Airline Seats Are For Dummies

September 18, 2024 by Al Williams 9 Comments

You normally don’t think a lot would go into the construction of a chair. However, when that chair is attached to a commercial jet plane, there’s a lot of technology that goes into making sure they are safe. According to a recent BBC article, testing involves crash dummies and robot arms.

Admittedly, these are first-class and business-class seats. Robots do repetitive mundane tasks like opening and closing the tray table many, many times. They also shoot the seats with crash dummies aboard at up to 16 Gs of acceleration. Just to put that into perspective, a jet pilot ejecting gets about the same amount of force. A MiG-35 pilot might experience 10 G.

We didn’t realize how big the airline seat industry is in Northern Ireland. Thompson, the company that has the lab in question, is only one of the companies in the country that builds seats. Apparently, the industry suffered from the global travel slowdown during the pandemic but is now bouncing back.

While people worry about robots taking jobs, we can’t imagine anyone wanting to spend all day returning their tray table to the upright and locked position repeatedly. We certainly don’t want to be 16 G crash dummies, either.

Crash dummies have a long history, of course. Be glad airliners don’t feature ejector seats.

Thermal Runaway: Solving The Bane Of Electric Vehicles

September 17, 2024 by Maya Posch 86 Comments

Although battery fires in electric cars and two-wheeled vehicles are not a common phenomenon, they are notoriously hard to put out, requiring special training and equipment by firefighters. Although the full scope of the issue is part of a contentious debate, [Aarian Marshall] over at Wired recently wrote an article about how the electric car industry has a plan to make a purportedly minor issue even less of an issue. Here the questions seem to be mostly about what the true statistics are for battery fires and what can be done about the primary issue with batteries: thermal runaway.

While the Wired article references a study by a car insurance company about the incidence of car fires by fuel type (gas, hybrid, electric), its cited sources are dubious as the NTSB nor NHTSA collect statistics on these fires. The NFPA does, but this only gets you up to 2018, and they note that the data gathering here is spotty. Better data is found from European sources, which makes clear that battery electric vehicles (BEVs) catch fire less often than gasoline cars at 25 per 100,000 cars sold vs 1529/100k for ICE cars, but when BEVs do burn it’s most often (60%) from thermal runaway, which can be due to factors like a short circuit in a cell, overcharging and high ambient temperatures (including from arson or after-effects of a car crash). Continue reading “Thermal Runaway: Solving The Bane Of Electric Vehicles” →