How does an S&S Screamin' Swing work?

[CrashCoaster]

So I rode Rush at Thorpe Park, and got fascinated by how it worked. I know it uses kneumatics, however I haven't quite worked out how the compressed air works to make the ride vehicles swing. There is a cable that attaches to the swings that moves them back and forth, but how do the cables get powered? Can anyone please answer?

 

[Hixee]

Crude sketch incoming.

Blue = seats and support arm
Green = cable drum
Red = cylinder with piston inside
Orange = cables
Black = connections to pneumatic system

The ride "at rest" has no pressure applied to the cylinder (and presumably there are some locking pins or brakes or something so the guests can board etc).

Air (under pressure from a series of compressors and storage tanks) is pushed in to the top of the cylinder, forcing the piston down. This in turn pulls a cable that is looped over part of the drum. This causes the ride vehicle to move. The pressure is then reversed, and air now pushed into the bottom of the cylinder, causing the piston to move up and pulling the cable (and rotating the drum) in the other direction. Repeat until your cycle is done.

What I'm not entirely sure on, and either is possible, is what all the hissing is. Either the air from the cylinder is vented during the compression stroke, and not pushed back into the accumulators (simple, but wasteful of energy), or it's a result of the compressors working. I've not shown those, but they're basically just special pumps that can compress air. The former is more likely, but I couldn't confidently rule out the latter.

That's pretty much the gist of it, anyway. Not sure if that makes sense? Happy to try again if I've not helped!

 

[CrashCoaster]

@Hixee Thanks a lot!

 

[Dar]

I always assumed the hissing was the cylinders exhausting, to create a bit of a vacuum to make the other stroke easier?

 

[Hixee]

I always assumed the hissing was the cylinders exhausting, to create a bit of a vacuum to make the other stroke easier?

Probably just venting, as it's the simplest way of doing it. I only mentioned the other options as there are systems that will recover the air from the piston - I think the theory is that it saves some of the compressor energy. At least, that's how I've had it described to me, I'm not really a pneumatic expert.

 

[Peet]

Nah you need to vent the used air at as low a pressure as possible since it will be working against the high pressure air on the other side of the piston. You want the biggest possible pressure difference.
One of the biggest innovations in steam technology was the condenser which actually creates a partial vacuum to suck the piston on one side while the high pressure steam pushes it on the other.
Obviously you can't really condense air without going to about -196 degC so venting to atmosphere is the best you can do.

 

[Hixee]

Quite right, I'm getting my technologies muddled up! Thanks for clarifying.

 

[Hyde]

Oh man @Hixee, just when we thought magnetic launches were too difficult to explain for Table of Elements.

 

[CrashCoaster]

Sorry to bump a 3-year dead thread but I have come about a fascination for Screamin' Swings once again and I can't help but wonder what advantages does a pneumatic system have over an electric motor for this style of ride? I mean literally every other pendulum ride in existence uses a motor afaik, so are there any actual benefits to using the pneumatic system or is it just a gimmick/extra faff? Not to mention the ride cycle is limited by the size of the air tanks and they have to re-fill between cycles.

 

[oriolat2]

Sorry to bump a 3-year dead thread but I have come about a fascination for Screamin' Swings once again and I can't help but wonder what advantages does a pneumatic system have over an electric motor for this style of ride? I mean literally every other pendulum ride in existence uses a motor afaik, so are there any actual benefits to using the pneumatic system or is it just a gimmick/extra faff? Not to mention the ride cycle is limited by the size of the air tanks and they have to re-fill between cycles.

I believe S&S is the leading company when it comes to pneumatic technology. All their rides use compressed air to propel their rides, so that might explain why they feel more comfortable working with something they are familiar with rather than coming up with an electrical motor and a whole new system not based on air compression.

 

[The Undead Creature]

Sorry to bump a 3-year dead thread but I have come about a fascination for Screamin' Swings once again and I can't help but wonder what advantages does a pneumatic system have over an electric motor for this style of ride? I mean literally every other pendulum ride in existence uses a motor afaik, so are there any actual benefits to using the pneumatic system or is it just a gimmick/extra faff? Not to mention the ride cycle is limited by the size of the air tanks and they have to re-fill between cycles

S&S use compressed air because the system as a whole is a lot simpler as it only requires power for the control valves.
Not only that but to generate enough torque to make Rush move like it does, you would need a stupidly large electric motor. Everything Rush needs to move is contained neatly inside the towers.

Hixee's drawing is spot on in terms of the basic concept, if I remember rightly, the piston is about 20 inches in diameter so it only needs about 40psi to do its thing. The hissing is the air doing work on the piston to drive the ride, the louder huffing is that air being exhausted to atmosphere at the end of the stroke.
As for trying to return the air back to the reciever, it would be pointless as there is an unlimited supply of air all around and the compressor would still have to compress it again back up to the storage pressure.

When it comes to running out of compressed air, the ride has a pneumatic requirement just like an electric requirement. This is provided by S&S and so long as your air compressor meets this requirement, you can run the ride as long as you want. The compressor shouldn't have any trouble keeping up. In fact, the compressor used for Rush exceeds the specification by so much, it is also used to provide compressed air for Colossus and is in fact housed in the shed at the end of Colossus' workshop.

The air compressor itself is nothing special or fancy. It's just a rotary screw system exactly like what you would find in a supercharger, just in a much bigger box. I think it's an Atlas-Copco compressor, so not exactly unique to the theme park industry.

 

[Hixee]

Couple of advantages/thoughts from my perspective:

You keep all of the really heavy stuff at ground level. Clearly not actually a problem as, like you rightly point out, most other manufacturers put the motors up top, but there would technically be a benefit. The S&S Screaming Swings have much shorter structures (in other words, the legs aren't sticking out at 45° or so), which probably wouldn't be possible with the strange structural dynamics that would happen with the weight of a motor on top. Maybe this is part of the ride experience they're going for - a much thinner structure probably amplifies the effect of the speed/exposure of the swing.

I've never actually seen pictures inside the compressor rooms for these rides (if anyone knows where some are, I'd love to see a link), but it's possible they continue to run the air compressors while the ride is operational. I've worked on compressed air systems which can operate continuously, it's no biggie.

EDIT: @The Undead Creature got there just before me with his usual hands-on wisdom!

 

[CrashCoaster]

Wait so the compressor runs when the ride is in motion? I thought it only ran to re-fill the tanks at the end of the ride after they ran out of air. Why do they all have really short cycles then if they can technically run for longer?

In response to @Hixee's post, surely you could hook up a motor near the ground and use the same cable system the ride currently uses to make the swing move?

And another question I have is; when they are running both swings, how do they make sure that the swings always swing opposite one another throughout the whole ride cycle and don't start getting out of sync if there are weight differences and such?

 

[Hixee]

Wait so the compressor runs when the ride is in motion? I thought it only ran to re-fill the tanks at the end of the ride after they ran out of air. Why do they all have really short cycles then if they can technically run for longer?

Might let @The Undead Creature take the detail, but yes you could. I assume they don't run long cycles for the same reason that some Zamperla ones don't have long ride cycles - it's the trade off between throughput and ride experience.

In response to @Hixee's post, surely you could hook up a motor near the ground and use the same cable system the ride currently uses to make the swing move?

Yup - you could. See @oriolat2's post above.

 

[The Undead Creature]

Wait so the compressor runs when the ride is in motion? I thought it only ran to re-fill the tanks at the end of the ride after they ran out of air. Why do they all have really short cycles then if they can technically run for longer?

The only one who could answer that is whoever wrote the program for it back in the US, but it isn't an air supply limitation.

The compressor runs all day long without stopping, the only thing that changes is the load state. If the supply pressure is below the setpoint, the bypass valve closes and sends air into the system. Once the pressure reaches the setpoint, the valve opens allowing air to pass through the compressor stage and back to atmosphere without being compressed. This means you can keep the motor spinning even though you don't need more air as stopping and starting a 200Kw motor every few minutes or so would earn you a strongly worded letter from your power supplier.

To give you an idea of just how quicly the air compressor works, the 2 large air tanks either side of the tower holds enough air for about 2 swings before a low pressure alarm is triggered.

 

[Pokemaniac]

Why do they all have really short cycles then if they can technically run for longer?

Possibly for capacity, possibly to reduce the risk of, er, "protein spill" from the guests.

 

[Hyde]

Possibly for capacity, possibly to reduce the risk of, er, "protein spill" from the guests.

Bingo, it’s to move capacity, and partly due to tank size for larger Screamin’ Swings is the same as smaller, making sense that a shorter cycle is needed due to capacity limit.

The only one who could answer that is whoever wrote the program for it back in the US, but it isn't an air supply limitation.

The compressor runs all day long without stopping, the only thing that changes is the load state. If the supply pressure is below the setpoint, the bypass valve closes and sends air into the system. Once the pressure reaches the setpoint, the valve opens allowing air to pass through the compressor stage and back to atmosphere without being compressed. This means you can keep the motor spinning even though you don't need more air as stopping and starting a 200Kw motor every few minutes or so would earn you a strongly worded letter from your power supplier.

To give you an idea of just how quicly the air compressor works, the 2 large air tanks either side of the tower holds enough air for about 2 swings before a low pressure alarm is triggered.

I do know for Cedar Point’s model the compressor does turn on and off between cycles. I used to do A LOT of work with compressors through Compressed Natural Gas work as a transportation fuel - it can be common affair to have the compressor turn off if you’re not using a tank series, where you can direct compression to alternating tanks. 200 kW isn’t that big of a power hit, relative to magnetic launches, ride cycles, or other load demand built into a daily amusement park operation.

 

[The Undead Creature]

You are correct, 200 kW isn't a big load at all. But starting that motor from a standstill uses around 20 minutes worth of full load running energy. This causes all the lights that happen to be on the same transformer to dim by quite a lot whenever the compressor is fired up. So it is only ever started up once and that is first thing in the morning. This is also why the vast majority of lift hill drives are kept running between trains, to significantly reduce the startup current.

Most rotary compressors will stop the motor if they have been running off load for more than about 10 minutes depending on the brand and model. If you find that your screw is stopping a lot then you likely have an over spec compressor.

That said, Cedar Point may have gone with a machine that just meets the spec for the one ride and are happy with a stop-start setup. But Thorpe have a right monster that not only runs Rush, but also Colossus, Walking Dead and all their associated workshops.

 

[Dan?]

And another question I have is; when they are running both swings, how do they make sure that the swings always swing opposite one another throughout the whole ride cycle and don't start getting out of sync if there are weight differences and such?

As Rush staff, I can tell you now that there is no mechanical means of sync correction on Screamin' Swings - at least, not on ours. We correct for weight by shuffling guests around, which is why - when all seats are available - we fill systematically, rather than letting groups pick for themselves.

 

[The Undead Creature]

As Rush staff, I can tell you now that there is no mechanical means of sync correction on Screamin' Swings - at least, not on ours. We correct for weight by shuffling guests around, which is why - when all seats are available - we fill systematically, rather than letting groups pick for themselves.

This is correct, the 2 swings are essentialy 2 completely seperate machines and can be operated individually.
The only synchronisation they have is that they both operate the same program from a single button press. If they get too far out of sync, an alarm is triggered.