Dynamics wheels rolling problem

Hi,

I am trying to make one wheel roll inside of another using dynamics.

At the moment all the wheels seem to do is repel one another rather than staying together.

I have experimented using Force>follow position which seems to keep them together but it acts erratically.

If anyone can shed any light on how to achieve this that would be great.

Here is the link to the project file:

4468_rollingwheels.zip

Many thanks,

Rich