Linear-induction motors slingshot thrill seekers out the launch bay at the Sahara Hotel and Casino and over the first hill. A steep drop follows as passengers travel 25 ft below the surface of the Las Vegas Strip through an underground tunnel before being propelled back up and through a breathtaking 360° loop. A second set of LIMs then push the coaster from 35 to 70 mph in 2 sec, threading it through the Sahara's 192-ft-tall marquee and finally up a 90° incline. The cars finally run out of momentum 224 ft in the air. Riders then retrace the path in reverse, ending up where they started some 45 sec earlier.
The Sahara coaster, called Speed — The Ride, is the latest in a new generation of attractions to employ LIMs for motive power. "There are a lot of challenges to designing a ride with a linear motor system," says Mike Reitz, a project engineer for Premier Rides Inc. of Millersville, Md., designers of Speed. Aluminum fins attached to either side of the car bottom form the motor stator. These pass through a mere 18-mm gap between top and bottom motor windings affixed along two sections of the track. "There's perhaps a quarter-inch of tolerance up or down for the fin," says Reitz. "There are lots of systems that must work within that tolerance."
For example, the track on which the cars ride must be kept super straight, welds and all. Premier also had to devise a special attachment scheme for the linear motor housings. "We came up with a system of mounting-beams that permit adjustments to each corner of the motor housing," explains Reitz. "This lets us level these components without resorting to shim packs."
Premier's design also takes wear into consideration. "As the coaster wheels abrade over time, the vehicle elevation drops slightly. The aluminum fins also have a small tendency to sag because they are basically cantilevers," says Reitz. "All this has to be factored into the tolerances."
An Allen-Bradley SLC-500 PLC handles the control of the 88 linear motor coils positioned on the track, which are units from Force Engineering Ltd. in Leicester, England. Magnetic proximity sensors positioned throughout the ride monitor vehicle location. The PLC uses this information to sequence the motors and turn them off when the six-car train reaches the right launch speed.
The highly inductive linear motors also put severe demands on the electrical system. Momentary inrush current can reach 6 kA. To compensate, a PLC-controlled capacitor bank from ABB USA reacts within 1.5 cycles of the ac line to adjust the power factor.