RideMan will probably elaborate for me, but it's USUALLY the bottom gear that drives the chain. However, I'm pretty sure I've seen kiddie coasters, at least, with the lift motor at the TOP of the hill.
----------------- --Greg "The questions ticket agents ask at airports are useless, but give an illusion of security to the GP. Much like seatbelts on roller coasters... My page
makes a heck of a lot more sense to have the "drive motor" at the bottom, where mechanics could work on it if need be... ----------------- PoTP acolyte - remove fear to reply Son of Drop Zone - PKI CoasterCamp I Champions!!!
I've seen it set up both ways. Technically, neither of the chain wheels on the lift hill is usually doing the driving...the most common arrangement seems to be to put the drive wheel under the lift hill, have that pull the chain over the top, up the lift, around the bottom sprocket, through a chain tensioner, and back to the drive wheel.
In any case, the tension has to come from the top, so if there is any slack in the chain, that will be on the return side of the drive sprocket.
Isn't MAgnum's at the top? I thought I saw a picture of the profile and it looked as there was a bunch of stuff up there. And Rideman, thanks for being our great and powerful library of roller coaster and amusement related things. ;)
Other than kiddie coasters, every coaster I can think of has the chain drive on the return at the bottom of the hill along with the tensioner.
Actually there shouldn't be any real slack in the chain unless the tensioner isn't working. And if it isn't working, you are in big trouble. Note that no chain ever is perfectly straight no matter how high the tension unless it is a physics professors masssless chain or it is running vertically.
MFRULES - Nope, Magnum's motor is definately at the bottom. What looks to be alot of mechanical stuff is actually just alot of grease and the large chain wheel which is located on 15feet under the crest of the lifthill. ----------------- Corey "Have you ever tried backing out of a drive-through bank?" - George Carlin
Ninja's chain, at SFOG, has a motor at the top I believe... it's 120 feet tall and over water, don't ask me why Vekoma put it there... It doesn't mater if it's at the top or the bottom--it still has to exert the same work to lift the train regardless. Usually, the motors run much faster than the chain does. The motor drive is attached to chains through a reduction gear(s). This gives the motor much more torque to pull the train uphill, and it means you can use a smaller motor to do the same job as a larger, more power-consuming one. The trade-off os the speed at which it can move the chain (train).
*** This post was edited by MisterX on 1/30/2002. ***
Here's one for you. Dragon Mountain at Marineland, the lift drive is in the middle of the lift. There are two chains, due to the length of the lift hill, but they are driven by the same motor and gearbox.
*** This post was edited by Dutchman on 1/31/2002. ***
If you have to work on Ninja's drive you will appreciate that there is a difference between having it on the ground and having it 120' up over water. It will take more time and cost more to do anything on it.
If you are going to have 2 chains the one drive in the middle makes a lot of sense. I looked at photos of SD2K and it has a drive 1/2 way up the lift hill. I couldn't tell though if the drive operates both chains or if there is another drive at ground level for the lower chain.
It is more logical to put the motor at the bottom of the lift hill do to the fact that if it breaks down and its a tall coaster, you will not have to go to the top and very carefully work on the engine. I think there would be alot more worker related accidents due to parts falling 200+ feet and hitting someone that is walking below. I could see the motors being at the top of small coasters, but tall ones, i just dont see that.
It is definitely smarter to put the lifts at the bottom of hills rather than the top. If Ninja's motor had to be replaced, a huge crane would be needed to pluck the motor off the top and drop a new one in. If the motor was at the lift base, then a smaller, more practical crane could be used to do the job.
Then again, different coasters call for different setups.
You may be overlooking something with Ninja. Ninja is a Vekoma coaster, and while I don't know for certain about that ride, many Vekoma coasters have hydraulic lift motors. Which means you can connect the relatively small hydraulic motor directly to the upper chain sprocket and put the big electric motor, pump, reservoir, oil cooler, and such-like wherever it is convenient.
As for gear boxes...these days, most coasters (except those with hydraulic lifts) have reducing gearboxes as someone described above. Partly because of the torque issue, partly because electric motors have a nasty habit of running at 3,600 RPM. Many older coasters, instead of using a gearbox, get speed reduction by using a small motor pinion and a large belt to drive a very large wheel attached to the chain drive. See it in action on the Knoebel's Phoenix.
I think that most drive sprockets operate in the range of 100-200 RPM. Motors below 1150 RPM are fairly rare, and it is usually the most economical to use a 1750 or 3500 RPM motor as lower RPM motors cost more and weigh more per horsepower. Hence, you need to do a speed reduction. As Dave said this used to be done with belts and open gears. Now you just buy a nice little packeged gear reducer.
The rotation speed of an AC motor is based on power line frequency, hence in a 60-Hz country such as the USA, you're looking at 3,600 RPM for a single-pole motor or 1,800 RPM for a two-pole motor...this is also why it used to be a big problem with European rides (designed for 50 Hz power) running 20% too fast in the USA (under 60 Hz power).
So why do your numbers (which come from your apparent industrial experience) disagree with my numbers (which come from book-learnin') by about 3%? Does that account for the lag found in an induction motor core?
(FWIW, I'm guessing Jim knows better than I do about such things, for the reason described above...!)
Unlike an synchronous motor, an induction motor has to have some slippage in order to generate torque. If it is perfectly in phase the magnetic fields would match and no force would be produced. In theory it can turn at 3600, 1800, etc., but only if it does no work. In practice internal friction, etc. mean it can never reach its phase speed.
The speeds of the motors are really nominal speeds, not exact. Induction motor speeds actually vary slightly depending on how hard they are working. Under a light load they turn a little faster than under a heavy load. Each motor is stamped with its actual operating speed under design conditions, usually to the nearest 5 RPM. Look at the nameplates on these motors, and you will see speeds like 1765 RPM stamped on them.
I'm not sure that I explained the theory too well, the practice is of most interest too me since I'm a mechanical engineer. Now if you want to talk about permanent magnet DC motors, I used to be a slot car racer and can talk about them for hours.