Basic Roller Coaster Dynamics
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OK, first
things first. I sometimes take for granted that most people understand the basic dynamics
of how a roller coaster works, but this is not the case. A roller coaster, by traditional
definition is a fairly basic ride. All you really have is a lift chain and a train of cars
which usually has at least 96 wheels that hold it to the steel rails or wooden track.
Other than the braking systems, the train itself and the lift are generally the only
propulsion systems on a roller coaster. Occasionally you will have pusher motors
between the braking fields, but that is not part of this discussion. |
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What you see to the left is the idler wheel on the top of a wood coaster lift hill. It is called an "idler" because it does not turn the chain, but the chain is actually what turs the top and bottom idler wheels. The drive system on most coasters is located directly underneath the bottom of the lift hill, although there are a growing number of new roller coasters being installed with the drive system at the top of the hill. It makes more sense to be at the top of the hill, because it is less wear and tear on the lift chain. I say this because when the drive is at the bottom, the length of chain which is under load is twice as long as when the drive is pulling the load from the top of the hill. It is also nice to have the drive at the top of the hill because it reduces the excessive noise at the ground level. |
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To your left, you see a typical drive system. The motor spins, and transmits this spinning force through a gearbox, (transmission) which uses various sized gears to convert this motion to the proper speed for that particular roller coaster. In order to keep the chain tightly seated onto the gearbox's drive sprocket, so that it does not slip off and create problems, a tensioning pulley is in place. This can be seen next to the white directional arrow just to the left of the center of the photo. That tensioning pulley is mounted at the end of a hinged arm, which has a hydraulic piston mounted to it's underside. The hydraulic piston is set to a certain pressure, which pushes the pulley up into the chain, which then absorbs any slack in the chain. All coasters have some sort of chain tensioning device in one form or another. Some are adjusted manually, whereas this one is automatic. Over time, a lift chain will stretch due to wear between the links, an this is why it must be monitored and properly adjusted. |
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As much as I hate to admit it, yes it is possible for a coaster to stop before completing it's full ride cycle, as you see in the adjacent photo. As much as we depend on gravity, which allows us to have a roller coaster in the first place, it can sometimes be a nuisance. In the beginning of the season after a roller coaster has been rebuilt and now has fresh new grease in all of it's wheel bearings, the outside temperature has an empowering affect on a roller coaster's speed. You, as a pasenger will rarely even notice this. It is when a coaster train is run for the first time each year that the mechanical staff has to take special precautions to make sure they don't have to manually push the train back to the station (wood coasters) or call in a crane (steel coaster). When the bearing grease is new, it creates more friction, thus slowing down the train, and when it is cold outside this makes the new grease even stiffer. A full load is simulated to help propel the coaster to the end of the track when it first runs. Numerous forms of weight can be used in lieu of passengers. Water bags are the simplest, but it takes many of them to simulate a full train. Sand bags are much heavier, but they make a heck of a mess when they tear open inside the cars. The best way that I have seen is using old waterpark inner tubes filled with potatoes and then tie-strapped shut. They are great because they have handles, which makes it a great test weight for suspended coasters, when it is strapped under the shoulder restraints. It sure is a heck of a waste of potatoes though, but it was all that was available after all of the water bags went flying all over the place during the first run. "Duh" |
