Question – I’m 13 years old and I’ve got a science project to do that involves the LIM. I’m thinking of applying the LIM to things other than roller coasters, like maybe subways or even elevators but I don’t know too much about the LIM. Can you help?
Thank you for your inquiry about LIM (Linear Induction Motors). Birket Engineering does not design LIM motors. We do design control systems for LIM motors. We do not have any diagrams of the actual motors or any written information about LIM motors to send to you. We work with a company in England called Force Engineering. They designs the LIM motors that we work with on roller coasters.
Since you are interested in applying LIM motors to new applications such as subways and elevators, I can give you a some thoughts about the characteristics of LIM Motors as we have come to understand . LIM Motors have some unique and desirable characteristics, but like with most things, the advantages are usually accompanied by some disadvantages.
LIM motors are similar to regular motors in many ways. The motors can move a vehicle in both directions in can by used to stop the vehicle without the use of mechanical breaks. (Run them backwards and turn them off before the vehicle starts going the wrong way.) A major advantage of LIM Motors is of course that there is no wear due to friction because there are no bearings or rotating parts.
Disadvantages and other considerations when using LIM Motors:
1. The motor cannot be left on when the vehicle is not there to push against. This causes the motor to overheat and possibly burn up. A regular motor can just sit there and spin with out a load on it. Not so with LIMs. Therefore the control of the LIM becomes critical, to make sure it is turned off almost instantly after the vehicle passes and is not turned on again until just before the next vehicle arrives.
2. Each motor must be designed to propel the vehicle within a certain range of speeds. In other words as the vehicle goes faster the motor that started the vehicle from a stop is no longer effective. Likewise the motor that is effective for keeping the vehicles moving at higher speeds is fairly useless for starting the vehicle. To go from a stop to about 50 MPH in a few seconds requires that the vehicle pass over a succession of at least four different types of motors, each built to operate at a different speed.
3. In addition to generating a strong force to move in the forward and reversed directions, LIM motors develops a strong force pulling the vehicle toward the motor. This must be counteracted by a strong suspension system on board the vehicle to maintain the separation between the motor vehicle. One solution to this problem is to place two motors together, facing each other with a gap in between them. Then a fin on the bottom of the vehicle is run between the two motors. Now the motors will propel the vehicle along the track without pulling it down. Even this leads to another kind of problem. The motors now pull toward each other with such force that they can collapse their own housings. Therefore the motor housing must be built of very strong materials.
I am aware of two subways that use LIM motors. The first is the “people mover” at the airport in Houston, Texas. It was designed by Walt Disney Imagineering in cooperation with Turner Construction. The project was finished in about 1981 and is still operating successfully.
The second installation is the subway that transports U.S. senators from their offices to the Capitol building in Washington D.C. The system is similar to the Houston project. Both designs are based upon the original work done by Disney for the Disney World “WEDWAY” attraction at Tomorrowland in the Magic Kingdom.
It may indeed be possible to use LIM Motors in an elevator application. I don’t know if this is been considered before. I would want to talk with someone who is more of an expert with these motors than I am, before I tried it. I have heard in the news that LIM Motors have been considered as a part of an accelerator to launch (or to assist with the launch) of vehicles into space. This would be a very elaborate system requiring a tremendous amount of power. I think it will be many years before we see anything like that.