Fully rigged and ready to go; all materials and textures included (lighting is mental ray sun & sky, materials are Arch & Design). For path motion your only variable will be the length/shape of a path taken. The point highest in the linked hierarchy is currently assigned a path constraint; simply remove that path and add a different one.
For the track animation previews, a path constraint was used for the body, and expression controllers related to the length of that path control the tracks (both of which can be made to operate independently). For straight path animation segments, adjust the left/right track sliders (equally) to match the path length. For curved paths, the values of the left/right sliders can be adjusted, allowing for the tracks to change speed (i.e., the track towards the inside moves slower). The motion of the track bones (50 on each) is controlled by points (50 on each) which are controlled by the value of the slider, making short work of adjusting the track motion (the points use an expression controller with two variables: overall path length, and the percent along path of the body. These variables are assigned to the sliders).
The tracks are boned and skinned, and linked to helpers constrained to the track shape, (motion of which are described in track_animation.jpg). Arrays of bone objects also control the motion of the flexible hoses through IK (with appropriate skin modifiers). Every piece of geometry that can or should move (arm, bucket, cab door, joysticks, etc.) is controlled by viewport sliders.
Wireframe views located at right.
All paths are stripped & the file is ready for rendering right out of the box. Other than mental ray, no other special plugins are needed. If you do need to use another renderer, all objects are logically and carefully named to do so easily. Optionally you can download the (rather large) texture map used for the ground plane in the previews (tan_dirt_map.ZIP).