Machine Design

# Blasting Speed Into Amusement – Park Rides

As 200-ft-high roller coasters have become amusement park staples, designers look for new ideas to strike fear into the hearts of park patrons and move rides at higher and higher speeds.

A few years ago some of the trendiest rides at amusement parks were roller coasters with hills exceeding 200 ft and rides that lifted riders to the top of a tower and then dropped them, letting them free fall down a track. But now these rides are becoming commonplace and park owners and ride designers are looking for alternatives to chain-driven coasters and rides that rely on gravity alone for excitement.

Motors, not chains
Conventional roller coasters use chains to hoist cars up an initial hill. Going down that first hill is where the thrills and speeds usually reach their peak. The train coasts as it loses speed during the rest of the ride. Although some manufacturers add tunnels, lights, and fog to jazz up the ride, the only practical way to make coasters faster has been to increase the height of the first hill. It’s impractical to boost the speed of a slowing car on later hills because of the way the chains must engage with the cars. After the first hill the linear speed of a coaster chain would be relatively slow compared to the car’s speed. When chains engage with cars they must be traveling at roughly the same speed. If chains were added to hills after the first one, the cars would have to slow considerably to engage with the chain. This would effectively start the ride over again instead of boost the car’s speed.

Linear motors shine a new light on roller-coaster design. They convert electricity into mechanical motion and can accelerate cars up to 100 mph. The motors mount to the ride tracks anywhere on the ride. They work with cars moving at any speed and can accelerate or decelerate the cars in forward or reverse. Two types of motors, linear induction (LIM) and linear synchronous (LSM) are now being used on rides. Both types are common ac motors typically used to produce rotary torque. Their linear counterparts operate similarly but are laid out flat rather than cylindrically.

Linear motors deliver power quietly without the clanking noises common with chain lifts. Linear motors also have braking advantages. “Coasters sometimes travel faster than designers planned, requiring sensors and brakes on some curves to safely turn the cars,” points out Peter Matilla, director of business development at Magnemotion Inc., Sudbury, Mass., an LSM manufacturer. “Linear motors slow cars more precisely than mechanical brakes. The process works like a generator, sapping power out of the vehicle and slowing it down.” Matilla also notes that the ability to accelerate cars any time during the ride makes coasters with low hills fast. This is appealing for parks with height restrictions, such as those in urban or historic districts.

On roller coasters with linear motors, the train has aluminum fins called reaction plates that act as rotors while the tracks have windings acting as stators. When the train reaches the linear motors, sensors actuate a current running the length of the motor. This current creates a magnetic force that accelerates the fins and the train. Linear motors deliver smooth, quick acceleration on a variety of new coaster-style rides.

Magic Mountain, Valencia, Calif., is one of several Six Flags Theme Parks with linear-motor-powered rides. Superman The Escape uses LSMs to reach top speed in just 7 sec. It is billed as the first amusement-park ride to travel 100 mph and was designed by Intamin, Zurich, Switzerland. There are no turns on the 900-ft-long Superman ride. The track starts off horizontally then climbs 415 ft above the ground. Riders feel 4.5 g when they reach maximum speed just before the steep ascent. At the peak of the 41-story tower, riders experience 6.5 sec of weightlessness as the 6-ton train slows to begin a backward free-fall descent down the track.

Six Flags Great Adventure, Jackson, N.J., has the first ever twin-track LIM coaster, Batman & Robin: The Chiller. It opened this past spring and uses 432 LIMs supplied by Premier Rides, Millersville, Md. Though it may not go quite as fast as the Superman ride — the Chiller maxes out at about 70 mph — the ride has enough twists and turns to make up for any lack of speed. The ride is actually two different coasters that begin and end in the same place. Riders choose either the Batman or Robin track when they go through the line.

Both tracks have LIMs to accelerate the trains up to 70 mph in under 4 sec. On Batman, riders go through their first inversion, known as a top-hat maneuver, at a height of 139 ft. At the same time cars on Robin are coiling through a twisted loop called a cobra roll that reaches 105 ft. The cars then follow side-by-side tracks through “heartline” inversions while climbing a 45° hill. A second set of LIMs then boosts the cars to the peak of a 200-ft-high incline where they momentarily come to rest. As the cars begin to roll backward, the LIMs send them speeding through the entire ride in reverse.

What a blast
The 300-ft-high Power Tower is another new ride that goes beyond chain drives and gravity to give parkgoers a choice in how they get their kicks. Pressurized air shoots riders up or down on this new thrill ride at Cedar Point, Sandusky, Ohio. The ride has four separate towers. Two towers, called Space Shots, blast up to the top while the other two, called Turbo Drops, slowly lift to the top and then blast down to the bottom. The 45-sec ride hits 50 mph in just 3 sec, making riders feel 4 g of force going up and –1 g of force going down.

The Power Tower, designed by S & S Sports Power, Logan, Utah, is considered two separate rides — the Space Shot and the Turbo Blast. Each tower has a 250-hp air compressor for pressurizing the air that moves the carts and a 900-cu-ft pressure vessel for storing air. A 12-seat cart connects to a piston inside an air cylinder. Riders sit in open-air chairs with over-the-shoulder safety bars and seat belts. After passengers strap in, the compressor fills a small reservoir that S & S calls the shot tank. Pressurized air initially lifts the cart and riders about 6 in. while their total weight is measured based on the pressure they exert on the air. The compressor precisely fills the 160-cu-ft shot tank according to the measured weight. Riders are blasted up or lifted slowly depending on their choice as they went through the line.

On Space Shot, a valve opens and quickly releases all the air, sending riders shooting up 240 ft. After reaching the top, the car free falls down and bounces on the same air. After two bounces, a valve at the top of the cylinder slowly releases the air and lowers the cart to the launch pad.

On Turbo Drop, the valve in the shot tank opens enough to slowly lift the cart to the top of the tower where a brake holds them momentarily while a second shot tank fills. The brake then releases when the second shot tank opens. That puts air above the piston and accelerates riders toward the ground faster than gravity. Like the Space Shot, the cart bounces twice before lowering to the ground.

A new twist for motion platforms
Virtual-reality rides are a great alternative for those who shy away from real-life thrill rides. VR rides stimulate the senses using soundtracks synchronized with computer images and motion. For example a VR motorcycle might have riders sit on a mock cycle mounted to a motion platform. A headset plays sounds of the motorcycle and other traffic while a video depicting a road and passing cars is shown on a wraparound screen. When the motorcycle rounds “virtual” turns, the platform tilts. The platform might also jolt forward or up and down to give the feeling of a bumpy road. The same principle is used to simulate car races, aerial combats, and space ships. The rides are found anywhere from shopping malls to amusement parks.

The motion platform is the key element in making simulated experiences feel realistic. Doing this requires platforms with up to six degrees of freedom providing motion classified as heave, surge, sway, roll, pitch, and yaw. Some platforms use six hydraulic cylinders to provide this motion. But when an amusement ride manufacturer recently needed a moving platform for a new ride, its engineers looked for alternatives to conventional hydraulic systems. They wanted to avoid common hydraulics problems like separate pump rooms, excessive plumbing, noise, and environmental concerns. They eventually chose electromechanical actuation.

The actuators, from Thomson Saginaw Ball Screw Co., Saginaw, Mich., consist of ball screws, motors, and belt drives enclosed in a telescoping housing. An electric motor turns a ball screw, which extends and retracts. The actuators mount to a platform holding a simulated spaceship made up of little more than an enclosed cockpit.

Each actuator has a peak load capacity of 2,400 lb, a top speed of 24 ips at 56% duty cycle, and extensions from 1 to 40 in. The self-contained, control-by-wire units are clean and quiet and are simpler to install than hydraulics.

TAGS: Recreation