NEW VERSION FOR 2.5:
TrackEx25.blend (199 KB)
Putting this feature in your own game is easy, just append the 4 objects with actual names and vertex parent a platform to the center-front verticie in the wheel, then adjust the track all you want as long as the width and depth stays the same, or make a new one or multiple ones because there’s no rigid body joints and IPO’s to mess with.
Use the invisible plane objects to help the wheel go all the way around the track, attach a platform to the wheel using vertex parent, or maybe you want the end of the track open so the wheel falls off the end in which case you add another plane which disables the motion actuator on collision with the wheel.
NOTE: I originally intended for this to be a python-free example for beginners but I changed it to use a script as it’s important to get beginners knowing basic python as soon as possible.
NOTE2: Made in 2.5, but should work in 2.49 too as it doesn’t use 2.5-only features.
EDIT1: Version 2.0 for 2.5 is up
-Shiny new materials for the wheel and track
-Adjusted friction and wheel-size for good stability
-New code in the script that allows for curves with the help of an additional object
-Turn property toggle objects that lock the wheel to a certain rotation outside of the curve (for more stability)
-2 ends where the wheel goes back and forth between, it turns back when it reaches the objects at the ends.
-More use of object properties to make the speed more adjustable
Note if you have the friction too high or something and the wheel gets practically stuck in the turn there’s a glitch where it will do a 180 then, but at the current friction settings that pretty much never happens.