Electromagnetic Propulsion of Roller Coasters

By Laura Brownstead

An electromagnetic roller coaster launch is a system that, using electrically induced [1] magnetic fields, propels roller coaster trains forward and slows down the trains, depending on the type of launch. Although these launches are relatively new and are typically used with steel coasters, electromagnets are used in a variety of roller coaster types, including wooden structures! (see Fig. 1)

Figure 1. View of Lightning Rod LSM Launch at Dollywood Amusement Park (CoasterFanatics)

​Two primary electromagnetic launches dominate the roller coaster industry: the linear
synchronous motor (LSM) and linear induction motor (LIM) launches. Of the two types,
LSM systems are more popular among designers due to their superior effectiveness and
dual ability as a launcher and a brake. However, LIM systems are cheaper but require
more power to operate than LSMs (COASTER BOT).

Physics of Electromagnets

Electromagnets are pieces of metal that become magnetic due to an electric current [2] flowing and inducing a magnetic field across the material. Once the field flows through the material, the dipoles inside are aligned (see Fig. 3) and the object becomes magnetized [3]. Typically, electromagnets are made from conductive wire wrapped around metal (see Fig. 2) (Looper). Electromagnets have a variety of uses in modern transportation because the electromagnetic fields exist only when a current induces them, so the magnet can be turned off, turned on, and reversed in direction all with a computer.

Figure 2. Basic Electromagnet Formed From a Battery, Wire, and a Nail (Solenoids)

Figure 3. Dipoles in a Medium in the Absence and Presence of a Magnetic Field (Peshin)

By controlling electromagnets with a computer, the magnetic field can be strengthened or weakened based on the amount of current flowing through the wire, but the strength of the magnetic field induced by the current reaches a maximum once all dipoles [4] are aligned (see Fig. 3).

​Electromagnetic Launch Process

The roller coasters powered by electromagnetic launches are built with metal fins on each piece (track and train) that align, but do not touch, as the train passes over the finned track length (see Fig. 4). Typically, a parallel pair of metal fins with a thin gap between are built on the track (see Fig. 4) while a single fin is located on the underside of the coaster train that passes between the two track fins. The track fins are primarily at points in the ride that require acceleration or deceleration, e.g. to travel up an incline (see Fig. 5).

Figure 4. View of Roller Coaster Train Passing over Electromagnetic Propulsion Fins (The Coaster Guy)

Figure 5. Electromagnetic Propulsion Fins (Stilwell)

When these fins pass through each other as the roller coaster train passes above the track fins, the strong magnetic fields propel the train forward at high and gradually increasing speeds. The specific processes by which magnetic fields are generated between the fins and accelerate the coasters are specific to each type, LSM or LIM, and are described in detail below.

LSM (Linear Synchronous Motor)

Linear synchronous launch systems utilize a permanent magnet [5] fin on the coaster train. The two aligned fins on the coaster track must be adjusted properly for the orientation of the permanent magnet on the train fin.

LSM launches follow these generic steps:

• The coaster train approaches the track fins
• A current is generated (by a power source located near the track) that induces an attractive magnetic field in the track fins and attracts the train (see Fig. 6)
• The train passes through each pair of fins, and the current is reversed by a computerized system, thus reversing the direction of the magnetic field and pushing the coaster train away (see Fig. 7) (COASTER BOT)

Figure 6 Attractive LSM Field (Linear synchronous motor)

Figure 7 Repulsive LSM Field (Linear synchronous motor)

These launch systems require great attention and programmatic commands to coordinate the direction of the magnetic field in the track fin pairs, which is why these systems are more costly than the LIM alternative. However, a strong advantage of this method is the directional control of the magnetic field. This control allows the fins to operate as brakes, in addition to providing acceleration, which provides operators with more consistency in controlling the ride and riders with a more consistently smooth ride from start to finish (COASTER BOT).

LIM (Linear Induction Motor)

In contrast to the LSM system, the coaster train fins are composed of non-directionally
magnetic metal whose dipoles are at random orientations (see Fig. 3 above).

LIM launches follow these generic steps:

• Current is applied to the track fins which generates a magnetic field
• The coaster train fin is attracted by the magnetic field from the track fins and travels forward (see Fig. 6 above)
• As the train passes over the track fins, an Eddy current [6] is generated by the magnetic field within the train fins (according to Lenz’s Law) (see Fig. 8)
  • In Figure 8, initially, a magnetic field is applied to the circle of conductive metal
  • Then, a current is induced in the direction shown by that field (the second circle)
  • Finally, a magnetic field is induced by the current created in the second step whose direction is opposite that of the initial magnetic field
• The Eddy current induces a second magnetic field in opposition to the first that pushes the train forward past the track fins (see Fig. 8) (COASTER BOT)

Figure 8 Diagram Showing Lenz's Law and Eddy Currents (Lenz's Law)

​To generate the amount of current required in the first step of an LIM launch, the coaster requires serious amounts of power, which make it a relatively costly process (though, not more costly than the computerization required for LSMs). However, this method is typically less popular than the LSM because it is less effective in accelerating a roller coaster train, which weighs around 10,000 pounds, and it is not as thoroughly controlled as an LSM launch.

Modern Legacy

Electromagnetically launched roller coasters have become a modern standard due to their reliability, smooth accelerations, and effectiveness. The LSM launch method has surpassed the LIM method in popularity because LSMs more effectively launch the trains and because of their dual capabilities to accelerate and slow the trains.

Figure 9 Maverick at Cedar Point (LSM Launched Coasters)

Figure 10 (Rock 'n' Roller Coaster Starring Aerosmith)

The primary disadvantages to these systems are the requirement of space (to place straight metal fins that propel the coaster) and higher costs (to power and operate the rides), but each have proven their worth in a number of popular roller coasters around the world.

As engineers in a variety of fields begin to develop new technologies and improve existing forms, so will these technological advancements influence industries like theme parks and roller coasters in the same manner as electromagnetic launches have changed the experience of a roller coaster.

Figure 11 Cheetah Hunt at Busch Gardens (Cheetah Hunt)

Footnotes

[1] Induced - brought about by some other event (in this case, current induces magnetic fields and magnetic fields induce a current)
[2] Electric current - the flow of electrons through a conductive medium
[3] Magnetized - a state in which the dipoles inside a material align with their ends positive-to negative (attracting ends of the dipole join and the positive-negative arrows of each dipole are parallel)
[4] Dipoles - a collection of relatively equal, opposite charges; or, a set of charges containing a net dipole moment
[5] Permanent magnet - a magnet whose poles (North and South) cannot be changed
[6] Eddy current - a looped electrical current induced by a directional magnetic field

References

"Cheetah Hunt." 24 March 2019. Wikipedia. Image. 5 June 2019. <https://en.wikipedia.org/wiki/Cheetah_Hunt>.

COASTER BOT. Roller Coaster Launches: Explained. 30 October 2016. Video. 5 June
2019. <https://www.youtube.com/watch?v=rPTL_PXo0oY&t=150s>.

CoasterFanatics. Lightning Rod HD Front Seat On Ride POV & Review RMC Wood
Launch Coaster At Dollywood. 4 June 2016. Video. 5 June 2019.

<https://www.youtube.com/watch?v=5pxbZWPNRsY>.
"Lenz's Law." n.d. Brilliant.org. Image. 5 June 2019.

"Linear synchronous motor." 2019. Encyclopædia Britannica. Video. 5 June 2019.
<https://www.britannica.com/technology/linear-synchronous-motor>.

Looper, Marshall Brain and Lance. How Electromagnets Work. 1 April 2000. Webpage.
5 June 2019. <https://science.howstuffworks.com/electromagnet.htm>.

"LSM Launched Coasters." n.d. Coasterforce. Image. 5 June 2019.
<https://coasterforce.com/lsm/>.

Peshin, Akash. "Why Are Some Materials Magnetic? Is Aluminum Magnetic? ." 6
November 2017. Science ABC. Image. 5 June 2019. <https://www.scienceabc.com/eyeopeners/why-are-some-materials-magnetic-and-is-aluminum-magnetic.html>.

"Rock 'n' Roller Coaster Starring Aerosmith." n.d. Walt Disney World. Image. 5 June 2019. <https://disneyworld.disney.go.com/attractions/hollywood-studios/rock-and-roller-coaster-starring-aerosmith/>.

"Solenoids." 2019. DK Find Out. Image. 5 June 2019. <https://www.dkfindout.com/us/science/magnets/solenoids/>.

Stilwell, Andrew. "DOUBLE THE LAUNCH, DOUBLE THE FUN!" 1 March 2019.
Carowinds. Image. 5 June 2019. <https://www.carowinds.com/blog/2019/copperhead-strike-double-launch-coaster>.

The Coaster Guy. "Ride Profile: Full Throttle." 19 January 2016. The Coaster Guy. Image. 5 June 2019. <http://www.thecoasterguy.com/2016/01/19/ride-profile-full-throttle/>.

Weisenberger, Nick. Coasters-101: Launch Systems. 8 October 2013. Webpage. 5 June 2019. <https://www.coaster101.com/2013/10/08/coasters-101-launch-
systems/>.