SLC train storage & anti-rollback questions

Sunday, June 27, 2004 8:30 PM
At SFMW, the SLC spends the night with one train on the lift hill. Is this standard practice or are they doing something special?

I also can't figure out, for the life of me, where the anti-rollback ratchets are on an SLC lift hill. All I see is a fin that run the length of the lift hill.

Monday, June 28, 2004 12:51 AM
They do that so that the trains don't roll around during the night.;) It's actually faster and easier than using the transfer.
Monday, June 28, 2004 1:22 AM
And for your other question...

On the SLC lift hill, there is a metal fin that runs alongside the chain lift. See it up there? Good. :) On the top of the train, on each axle, I believe, there are pairs of spring-loaded cams which squeeze against that fin. When the train is moving forward, the fin pushes the cams open. When the train attempts to move backward, friction between the cams and the fin actually pulls the teeth on the cams backward, such that the harder the train tries to pull back, the harder the teeth on the cams will 'bite' into the fin to keep the train from moving.

I think I have a photo of those things around here somewhere.....

--Dave Althoff, Jr.

Monday, June 28, 2004 9:21 AM
They can't just leave the train on the final brake run or the transfer brake?

What is a cam?

Monday, June 28, 2004 3:51 PM
Same thing I was wondering too. One in the station and one in the final brake.

Just how reliable is that brake friction when the fin is wet? Sounds a little scary to me. There must be something I am missing.

Monday, June 28, 2004 4:54 PM
I know Richie should recognize this...

You know those old Hampton kiddie rides with the umbrella on top and the little cars and the buzzers that go "erk erk erk erk erk erk erk"? Remember how those things used to (presumably some still do...) secure kids in place with a little piece of clothesline pulled through a little spring-loaded plastic cleat?

The cleat consists of two little round plastic jaws with teeth. When you put the line through them, if you pull the line through, the friction pulls the teeth open, but if you try to pull the line the other way, the teeth dig into the line and the kid stays secure. At least that's the idea.

Well, make the springs a bit stronger, make the jaws out of hardened steel (harder than the fin on the lift) and fit them a little closer together, and you have an SLC anti-rollback device. Friction isn't really an issue, as if the train tries to roll back, the teeth will actually 'bite' into the steel fin.

Arrow used the same anti-rollback device on the Big Bad Wolf, putting the cams on the lift hill and having them clamp against the brake fin. Busch Gardens replaced that system with a more conventional anti-rollback system a few years ago.

--Dave Althoff, Jr.

Monday, June 28, 2004 5:27 PM
Thanks Dave. Let me know if you come across a photo.

I never thought I would have this much interest in a SLC. :)

Monday, June 28, 2004 10:52 PM
SFMW's Kong, was as most of us know at one time known as Hangman, and was located at Opryland in Nashville. In 1997 while at Opryland, something serious happened to those fins while a train was on the lift hill. It took NFD about five hours to unload the people from the train.

Just a little story.

Tuesday, June 29, 2004 12:17 AM
As Dave suggested, it's not so much friction as it is insane forces that will clamp into place if the train tries to move. Water would be no issue, because these things will snap before they ever slip.

Rock climbers use what's known as active protection for trad climbing. Pull back the lever, stick it into a crack and you're set. They're spring-loaded to stay in place, and any further force on them will make them want to get real big, real fast. There's only two ways you'll ever have one of these fail - bad placement or rock breaking (which goes back to bad placement). The same as those on an SLC, they push outwards onto the rock rather than inwards onto a metal fin as with the SLC.

Most elevators use a similar system to stop them from plummeting into the ground. Because they've got to be able to travel both up and down, instead of being one-way like those on an SLC, they're triggered by reaching a specified speed, and all purely mechanical.

When you're on an SLC you can very clearly hear them. Instead of the sound of the anti-rollbacks, you have a distinct sound that believe it or not sounds like sliding something metal on another metal object.

Tuesday, June 29, 2004 1:27 AM
You know, you should probably get a property release from the companies that own the rides you're selling pictures of if you don't want to get sued.

All of these anti-rollback systems have some degree of ware potential, and I guess you just need to decide what's acceptable. Many wood coasters go flying over anti-rollback teeth and undoubtedly require that the dogs be replaced frequently. Many of the Intamin rides rarely make contact save for morning block checks, so they probably last. I've not seen the SLC device, but it sure sounds kind of destructive, and the lifts aren't exactly the most maintenance-friendly or accessible things on the ride.

Tuesday, June 29, 2004 3:08 AM
Just quickly regarding the pictures, in about seven days it'll be no more. I had a go of CafePress' premium shop thing, just to see if it would work. No bites in 1+ months, so I see no reason to keep paying. :)

Anyway, there would be wear, that's a granted whenever there's anything remotely mechanical. I don't know the nitty-gritty about it, but I'd be surprised if they're replacing more than a handful a season on even the most ratchety coaster out there.

The SLC uses a fin on the track and the cam components, which are the only part you'd be worried at all about, are on the car. Common sense would dictate that you use a softer alloy for the teeth and a harder one for the fin so as to direct the wear on the easily checked and replaced part of the ride. Same goes with friction brakes, Arrow's upstop pads and all of that, and the most simple solution is to concentrate the wear on the easily inspected and maintained part of the ride. They'd need to check the anti-rollback fin no more than they ever check the track of a steel coaster, which is to say not very often.

Tuesday, June 29, 2004 9:27 AM
Actually, the traditional way to do the safety device on an elevator is to attach the hoisting rope to a scissor mechanism that holds the teeth on the safety device open so long as it is under tension. When the elevator is going up, the tension on the hoisting rope holds the safety device open. When the elevator is going down, it's going slower than free-fall so it is still under tension. But if the hoisting rope fails, the tension goes away and the safety device closes, stopping the elevator from falling in a very big hurry.

--Dave Althoff, Jr.

Tuesday, June 29, 2004 10:28 AM
OK, scrap that. A little research into standard elevators has confirmed what you said. Change what I said to mine shaft elevators (we're talking the big things used to take those colossal trucks down, not some industrial revolution or goldrush deathtrap). I can say from experience that they use centrifugal cams as I mentioned above (well, the handful of mines I've toured did). I remember some terrible action movie a few years back (Mission: Impossible or something?) which had the cams on the rails sparking and doing all sorts of crazy thing - I guess that's where that quantum leap came from.

Go back to my rock climbing example. That ties in nicely with another one of my passions. Throw in the cleats you have on yachts (same thing as what you mentioned with the umbrella rides earlier) and the SLCs can be explained without getting too boring. ;)

Wednesday, July 7, 2004 11:55 PM
I didn't find the pictures I was looking for, but I was in the presence of an SLC on Monday, so I shot some new ones.

There is now a page on my website that shows the SLC anti-rollback system. For now, that's a blind link; I'll add links to the tech and main pages when I get a chance...

--Dave Althoff, Jr.

Sunday, July 11, 2004 12:46 AM
Hate to bring back the SLC topic ;) but I just wanted to say that it appears Jester uses this same type of anti-rollback. Do other vekoma sit down loopers use this as well?

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