Launch LSM/LIM Sounds

[Dave]

Watching videos on the CF Youtube, watched Anubis and Taron and noticed they had different sounds when launching, despite both being rolling launches.

Question is what makes that sound on LIM/LSM launches? As I know with rides like Stealth, old Schwarzkopf's it's the sound of the flywheel and catch car moving at speed.

Usual with this sort of question it is probably quite simple!

 

[Hixee]

It's essentially just the magnetic fins and static fins (stators) vibrating as the magnetic fields interact.

How they work on each is different, but the basic principle is fundamentally the same - you generate an alternating magnetic field, and by controlling the field carefully you can accelerate the train. In both instances, it's AC current that is used (this generates magnetic fields in wound copper elements), which switches direction many times a second. In doing this, slight imperfections in the spacing of all of the components mean that the forces on the fins aren't quite balanced, and therefore the fins vibrate - generating that "whoosh" that you hear from the launches.

 

[Mack]

The launch engines (CMIIW) are kind of like electric car engines except they produce, as the name suggests, linear force rather than rotary as would be found in an electric car. You can hear a similar whoosh on a Tesla or a Prius in "stealth mode."

 

[Hixee]

Actually, yeah, just to expand on Mack's and my own comment.

There is also a hum from the electrical components themselves (that is, if you ran the launch without a train, you'd still hear some of the noise - albeit likely a lot quieter). Again, this is vibrations caused by the magnetic fields interacting harmonically with the materials within the device. Electric motors with laminated cores will be excited at some natural frequency depending on the pattern of the electricity being supplied to them (hence why the pitch changes as the speed or torque changes). You can often hear a constant "hum" from those big electrical substations dotted around cities - this is the effect of these natural resonances occurring at a constant frequency (50 or 60 Hz depending on your country). It's the same effect within electric motors (linear or rotational).

Should note that the pitch of the noises is often due to frequency of the electrical supply, meaning you excite different modes (stable vibration patterns) and therefore causing different pitches.

On an LIM/LSM, it's this effect of the electrical components, plus the actual vibration of the fins themselves, that cause the 'whoosh' noise.

Equally, on magnetic brake runs (which have no power supply), you're hearing both the vibration of the fins and some natural frequencies of the components due to the electric currents generated by the fins moving past each other. Again, why you hear the noise (although generally quieter) on some brake runs.

 

[Mack]

This makes me curious as to whether there is a perceptible difference in the LIM/LSM shriek between North America and Europe due to the differing AC frequency.

 

[Hixee]

Difference? Yes. Perceivable? I doubt it.

Don't forget we're talking about extremely complex vibrations between many different materials and components, each with different individual natural frequencies, all interacting together. I would image the difference in noise would possibly be measurable, but I doubt you'd be able to actually identify it by ear. It's not as simple as the difference between a 50 Hz and 60 Hz sound signal.

That said, we're pushing my [self-professed] reasonable understanding of structural harmonics and modes of vibration at this point, so this is mostly (again) just engineering judgement.

 

[Ireeb]

Why would the frequency of the electric network have an impact on the sound? The frequency of a LSM changes with the speed of the train. It has to accelerate with the speed of the train, otherwise the train wouldn't accelerate but just move with a set speed.

 

[Mack]

The frequency of a LSM changes with the speed of the train

The LSM is applying the same force throughout the launch, correct me if I'm mistaken. You can notably hear this on Superman: Escape from Krypton as the most dramatic "whoop" happens immediately at the beginning of the launch as the LSMs are energized and on impulse coasters you can hear that the whoosh/shriek from the LIMs is a constant pitch each time the train passes them in the "active" state. F=ma, so application of a constant force means a constant acceleration, thus an increasing speed.

@Hixee was quite detailed in explaining why alternating current results in this phenomenon. The roller coaster gets its electricity from the electricity grid. I'm not sure how else to clarify.

 

[Ireeb]

The LSM is applying the same force throughout the launch, correct me if I'm mistaken. You can notably hear this on Superman: Escape from Krypton as the most dramatic "whoop" happens immediately at the beginning of the launch as the LSMs are energized and on impulse coasters you can hear that the whoosh/shriek from the LIMs is a constant pitch each time the train passes them in the "active" state. F=ma, so application of a constant force means a constant acceleration, thus an increasing speed.

That's not how LSMs work. I don't know about LIMs, but LSMs are way more complex than "give them power and they accelerate a train."
For an LSM launch, you need a permanent magnet on the bottom of the train (of course there are more than one, but we just pretend a single one would be enough). In the track, we have spools, which are supplied alternating current, and every single spool has a slight offset to the spools next to it. This means that if you supply them with alternating currents, you will get "waves" of south and north poles, because of the offsets, those waves travel in the direction in which the trains will be launched. Now since our train has a magnet on the bottom, these waves will carry the magnet with them. But if the waves remain at the same speed, the train will as well. In order to accelerate, the waves have to get faster, which means the spools have to change their magnetic fields with a higher frequency, which means you have to turn up the frequency of the AC.

 

[Hixee]

Yes, quite right Ireeb. A much better answer to the question. My answer would be more appropriate for a substations feeding the park/ride than the launches themselves.

 

[Ireeb]

If you listen closely, you can actually hear the frequency increasing e.g. on Taron

Like a gasoline engine that is speeding up.

 

[Hixee]

Taron's acoustics in that trench are to die for. <3

 

[CrashCoaster]

You can here the launch sounds even better on this one:-

Another question, why do Intamin's LSM's look and sound different to ones on Mack Launch Coasters and other kinds? Apparently Intamin's LSM's are manufactured by Indrivetc. And why do Mack's LSM's have 2 sets of fins?

 

[Ireeb]

You can here the launch sounds even better on this one:-

Another question, why do Intamin's LSM's look and sound different to ones on Mack Launch Coasters and other kinds? Apparently Intamin's LSM's are manufactured by Indrivetc. And why do Mack's LSM's have 2 sets of fins?

Good video.
Mack (and Gerstlauer, too, I think) get their LSMs from Intrasys. I don't know why they use 2 fins though. According to Intrasys that makes it twice as powerful and causes less horizontal forces because it is symmetrical. If I recall correctly, the Intrasys LSMs are not as loud as the Indrivetec ones. Perhaps the symmetrical LSMs cause less vibration in the fins/track.

 

[Hixee]

Mack (and Gerstlauer, too, I think) get their LSMs from Intrasys. I don't know why they use 2 fins though. According to Intrasys that makes it twice as powerful and causes less horizontal forces because it is symmetrical. If I recall correctly, the Intrasys LSM are not as loud as the Indrivetec ones.

I didn't know about the manufacturers - good to know.

The two fins vs one fin is likely just a manufacturing process. It's fairly common to see that sort of thing (for example, in my line of work it's common for some manufactures to use single scroll compressors, while others use dual scroll - they each argue their relative merits, but at the end of the day they're doing the same thing in essentially the same way, it's just a company decision). That said, I can see the arguments for less power in each individual fin, and possibly a more balanced arrangement. That said, I don't know if the Intamin trains have two stator fins underneath - possibly helping stability? Haven't really researched that though.

 

[Ireeb]

I didn't know about the manufacturers - good to know.

The two fins vs one fin is likely just a manufacturing process. It's fairly common to see that sort of thing (for example, in my line of work it's common for some manufactures to use single scroll compressors, while others use dual scroll - they each argue their relative merits, but at the end of the day they're doing the same thing in essentially the same way, it's just a company decision). That said, I can see the arguments for less power in each individual fin, and possibly a more balanced arrangement. That said, I don't know if the Intamin trains have two stator fins underneath - possibly helping stability? Haven't really researched that though.

Usually for an LSM you don't just have a thin fin like you need for a LIM, they have rather big magnets down there. That's why I think the 2 fins on the track are more silent, because the fins on the track are more likely to vibrate than the magnets on the train. If the power is split between the two fins, I guess that both only vibrate half as much.
That's how the Magnets on Karacho (Intrasys LSM) look like:
(It's a photo posted by StifflersMum at forum.airtimers.com)

 

[CrashCoaster]

^Can you send me a link to Intrasys' website because there are lots of sites named that.

 

[Ireeb]

^Can you send me a link to Intrasys' website because there are lots of sites named that.

http://intrasys-gmbh.com/
(You can switch to English in the top right corner)

 

[Hixee]

Seems like a good resource there @Ireeb. A good place to read some more technical information on the systems. @ATI, if you've got any more questions - fire away! I'm sure between us (the members on here) we can muddle our way to an answer to most things.

 

[Ireeb]

Seems like a good resource there @Ireeb. A good place to read some more technical information on the systems. @ATI, if you've got any more questions - fire away! I'm sure between us (the members on here) we can muddle our way to an answer to most things.

Thanks
I had a presentation in physics class on LSMs and Eddy Current brakes in the year before my A-Levels, that's why I am rather fit on that topic. Obviously, I opened the presentation with a Blue Fire POV. Launch coasters are my favorite anyway (because I find lifthills boring )