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Comment by hwillis | Hacker News Reader

>When you ride on BART, that's what you're hearing from the motors.

https://www.youtube.com/watch?v=vdNCrj14cK0

That's brilliant!

There are some trains on the London Underground that use gate turn-off thyristors, which make a sort of Star Trek klaxon sound when they start up:

https://www.youtube.com/watch?v=pagB58tGpRY

My favorite bit of electric locomotive technology: https://www.youtube.com/watch?v=yjMZ5qtyCUc

Closely followed by dynamic braking, or as it is more accurately and much more awesomely called in the UK, rheostatic braking.

Someone posted one of these on /r/electricians the other day running an elevator in New Zealand; very cool piece of tech.

https://www.reddit.com/r/electricians/comments/6vpg8n/the_me...

That sounds similar to this, but with much less time spent on the intermediate frequencies: https://www.youtube.com/watch?v=NWEexwZSXF8

This melody is unique (on London Underground) to the Jubilee line.

Although the Northern line trains have an almost identical body design, they use a more modern IGBT traction system which, although presumably more efficient, has a little less character!

Yes, the 3-phase synchronous AC locomotives driven with IGBTs seem to be quieter.[1] But the real advantage is precise wheel control. Here's the biggest steam locomotive ever built being towed out of the Pomona Fairgrounds for restoration. They're towing it through a very tight turn on temporary track to get it out.

The locomotive doing the towing is a 2006-model Electro-Motive Diesel-electric locomotive. It's towing the old steam locomotive at a very slow speed, smoothly, with no wheel slip. Nothing special about it; Union Pacific has hundreds of them. Six axles, each powered by its own motor. AC synchronous, IGBT power control. The motors are run as servomotors, all locked together. No wheel can slip relative to the others. This is a huge win when you need to get a few thousand tons moving.

This boring but useful modern locomotive, although much smaller, has more drawbar pull than the Big Boy. Multiple locomotives can be ganged together with wheels locked in sync, if you need more pulling power. Here's Union Pacific overdoing that.[2] They put together a train 3.5 miles long, with 9 locomotives spaced throughout the train, and ran it from Long Beach to Denver. This was just a test; they don't normally run trains that long.

All this is made possible by modern electronic motor controls.

[1] https://youtu.be/JRoIrFgcIjc?t=894 [2] https://www.youtube.com/watch?v=jdIzRFOaTCY

Oh, that's cute. Siemens makes a locomotive that uses switching frequencies spaced one note apart and steps through them during acceleration. That has to be on purpose.

Likely due to some exponential thing with the switching frequency following the soft acceleration, as the speed as far as I know increases according to a cubic function until about half of full acceleration is reached, and from there on it goes over to quadratic until the train hits about 80 km/h, as they lack power at around that speed to keep the acceleration at the usual 0.9-1.1 m/s^2. And the harmonics are exponential, with log_2(#of_notes/12) giving you the relative frequency difference for a given number of notes spacing.

Yes, this was done on purpose :)

And then there's "Somewhere" in NY:

http://www.nytimes.com/2009/02/21/nyregion/21about.html https://www.youtube.com/watch?v=WL436Qddigw

I always wondered what this sound was about.

https://youtu.be/TM0bOpwxxO8

Sounds like there is a steam engine inside (but the 451s are electrical)

Those are relay contacts selecting which field windings are getting power. As the locomotive accelerates, the number of enegerqzed coils is reduced in order to reduce back EMF (electro motive force)

I thought it was a PA jingle .. crazy.

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