Solid wheels and spring set for main drive axle

Previously the front-back wheel has been remixed solid.
Here are the other two types of driving wheels remixed solid for easier print and sturdiness.
The main drive wheel has also been remixed to have a flat back

The spring sets has been modified for the Main drive axle, which has a larger diameter and does not fit together with the normal spring sets.

All parts has been tested on my own print of the Big Boy