Here is an explanation of how the Make Tracks roller coaster simulator works - virtually, of course.

The 3D world is built to real world specifications as far as it is possible. It uses Havok physics (a software package) which provides close to real world physics. For example gravity is 9.8 m.s^-2. However as with a lot of physics theory the roller coaster’s world is assumed to be frictionless.

The physical situation being modeled is not of a car rolling down track but rather a box sliding through a (frictionless) square section tube. This was done to stop the ‘car’ from flying off the rails when it went over a hump, and to avoid modeling real roller coaster x, y and z-axis style wheels running on tubular rails.

Velocity is calculated using √[(a²)+(b²)+(c²)] where a is the x-axis velocity (m.s^-1), b is the y-axis velocity (m.s^-1) and c is the z-axis velocity (m.s^-1). Velocity is calculated every 30th of a second.

G-force is calculated using |(V_old - V_now)| where V_old is the previous velocity reading and V_now is the current velocity reading and then converting it (using gravity (9.8 m.s^-2) as 1 G). Again this is calculated every 30th of a second. Positive and negative G’s are not distinguished as some of the G-force on the roller coaster also comes from corners so therefore the force is calculated using the absolute value of the total of all 3 vectors.

The scrapes on the side are triggered if the impact or collision occurs at greater than 11.11 m.s^-1 (40 km/h) which is calculated by adding the velocity of the car + the velocity of the track (which is always zero).

The screams are triggered when the velocity is greater than 16.67 m.s^-1 (60 km/h).

The track noise is a looped sound file with regular beats or clicks and it is effected by the velocity of the car. The faster the car the higher the ‘rateshift’ of the sound file. Basically it is shortening the sound and increasing the pitch the higher the velocity - it is not perfect but it gives the right effect!

With thanks to Make Tracks’ Director MX programmer Paul Burnett of Multimedia Art Design (MAD), Canberra.