Retrotechtacular: The Power To Stop

In everyday life, the largest moving object most people are likely to encounter is probably a train. Watching a train rolling along a track, it’s hard not to be impressed with the vast amount of power needed to put what might be a mile-long string of hopper cars carrying megatons of freight into motion.

But it’s the other side of that coin — the engineering needed to keep that train under control and eventually get it to stop — that’s the subject of this gem from British Transport Films on “The Power to Stop.” On the face of it, stopping a train isn’t exactly high-technology; the technique of pressing cast-iron brake shoes against the wheels was largely unchanged in the 100 years prior to the making of this 1979 film. The interesting thing here is the discovery that the metallurgy of the iron used for brakes has a huge impact on braking efficiency and safety. And given that British Railways was going through about 3.5 million brake shoes a year at the time, anything that could make them last even a little longer could result in significant savings.

It was the safety of railway brakes, though, that led to research into how they can be improved. Noting that cast iron is brittle, prone to rapid wear, and liable to create showers of dangerous sparks, the research arm of British Railways undertook a study of the phosphorus content of the cast iron, to find the best mix for the job. They turned to an impressively energetic brake dynamometer for their tests, where it turned out that increasing the amount of the trace element greatly reduced wear and sparking while reducing braking times.

Although we’re all for safety, we have to admit that some of the rooster-tails of sparks thrown off by the low-phosphorus shoes were pretty spectacular. Still, it’s interesting to see just how much thought and effort went into optimizing something so seemingly simple. Think about that the next time you watch a train go by.

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Cheap Electric Scooter Gets A Big Brake Upgrade; Unlocks Proper Drift Mode

The last few years have seen a huge rise in the prominence of electric scooters. Brushless motors, lithium batteries, and scooter sharing companies have brought them to the mainstream. However, electric scooters of a variety of designs have been around for a long time, spawning a dedicated subculture of hackers intent on getting the best out of them.

One such hacker is yours truly, having started by modifying basic kick scooters with a variety of propulsion systems way back in 2009. After growing frustrated with the limitations of creating high-speed rotating assemblies without machine tools, I turned my eye to what was commercially available. With my first engineering paycheck under my belt, I bought myself a Razor E300, and was promptly disappointed by the performance. Naturally, hacking ensued as the lead-acid batteries were jettisoned for lithium replacements.

Over the years, batteries, controllers and even the big old heavy brushed motor were replaced. The basic mechanical layout was sound, making it easy to make changes with simple hand tools. As acceleration became violent and top speeds inched closer to 40 km/h, I began to grow increasingly frustrated with the scooter’s one glaring major flaw. It was time to fix the brakes.

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Anti-Lock Brakes For Bike Might Make Rides A Little Safer

Crashing one’s bike is a childhood rite of passage, one that can teach valuable lessons in applied physics. Assuming the kid is properly protected and the crash is fairly tame, scrapes and bruises are exchanged for the wisdom to avoid sand and gravel patches, and how to avoid a ballistic dismount by not applying the front brakes harder than or before the rear brakes.

But for many of us, those lessons were learned long ago using a body far more flexible than the version we’re currently in, and the stakes are higher for a bike ride that includes braking mistakes. To help with that, [Tom Stanton] has been working on anti-lock brakes for bicycles, and in the process he’s learned a lot about the physics and engineering of controlled deceleration.

It seems a simple concept – use a sensor to detect when a wheel is slipping due to decreased friction between the tire and the roadway, and release braking force repeatedly through an actuator to allow the driver or rider to maintain control while stopping. But that abstracts away a ton of detail, which [Tom] quickly got bogged down in. With a photosensor on the front wheel and a stepper motor to override brake lever inputs, he was able to modulate the braking force, but not with the responsiveness needed to maintain control. Several iterations later, [Tom] hit on the right combination of sensors, actuators, and algorithms to make a decent bike ABS system. The video below has all the details of the build and testing.

[Tom] admits bike ABS isn’t much of an innovation. We even covered an Arduino-instrumented bike that was to be an ABS testbed a few years back. But it’s still cool to see how much goes into anti-lock systems.

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