I wasn't sure about making a thread here, but not everyone on the forums follows the Github repository, so I figured it'd be about time to give the official lowdown on the new system.
Here it is, in four easy steps:
- Every square must start with a frame. (Spikes/blades can also be put in empty squares, but no other parts can go in those squares if you do)
- Each part now has a 'location', such as "wheel" or "engine" or "on_roof". You can only have at most one part in each location. Some parts are so small (headlights, for instance) that they have no location.
- You can't have more than one identical part in a square, even if the part has no location. So you can't have 5 headlights in a single square, for instance.
- Any setup of parts not prohibited by the above rules is allowed
Additionally, the various types of plating were changed so they now take up a square and block movement through it (because they're big sheets of plating, and won't do you much good if zombies can just walk past them). Think of them as being like transparent boards, but tougher.
(EDIT: Armor has since been changed; it has its own location and does not block movement, and can be placed on any square that doesn't already have armor. Quarterpanels have been added to fill the 'transparent board' niche.)
It's worth noting that all of the old standard vehicle configurations are allowed under the new system if extra frames are added to squares that didn't have them before. If you load a save from before the change into the new system, the game will automatically add extra frames for you.
All you have to worry about now is that you must remember to start each square with a frame. Many more combinations of parts have been permitted by this, for instance, having a board over a wheel. Feel free to experiment!