Moving an object along a path with physics..

[r0binhood]

Hi,

I need to let an object, say some sort of vehicle, move along a path, like a train on a railroad. The railroad can have any trajectory into the 3d space and the train is subject to gravity. In other words, let's say that I have to keep the vehicle anchored to the track even if it has the top side down.

To make it simple, I tried to make a simple ring object move along a simple path. Here is a screenshot:

http://r0binhood.50megs.com/screenshot_1.html

I tried with OgreOde, OgreTokamak and OgreNewt but I can't make it work. The best result I got is shown in the picture, with a ring around the path, done with OgreOde. The problem is that the ring goes inside the other mesh! How to disable mesh inter-penetrations at all? (I set zero friction and zero softness, I think.. but nothing)

<<Any suggestions are welcomed>>

Maybe there are other tricks to do that? Like some kind of contact joint or some strange vehicle with many wheels and no steering..