If you use a train as your crusher, then you dont need to use a morter field. I know how you could make this but just thinking about it is hurting my head. This will be pretty compilated:
It could be done with a couple levers, a bunch of path_corners, a button, a lot of multimanagers, and a shitload of trigger_changetarget.
Make 2 grids of path_corners, 1 in the air, 1 on the floor.
Make your crusher target one of the path corners in the air.
Have 2 levers, when you use the first one, it activates a multimanager which activates a changetarget that changes the trains target to the corner directly to the west of it. Then it would activate the train itself.
The other lever would activate a different multimanager which activates a different changetarget that changes the trains target to the corner north of it. Then it would activate the train itself.
When the train reaches a corner, it would need to change the targets of the levers to different multimanagers. Those multimanagers would do the same thing the ones with the levers did, but in different places.
Once you reach an edge of your grid, the changetarget needs to target a new layer of multimanagers which go in the opposite directions so that you can get to any place on the grid.
For your crusher to work, make a button. All of the multimanagers need to have a change target that will target the button and change it to target a multimanager, that will target a changetarget that targets the train, then targets the train itself. Then it should target a changetarget which makes the trains target the corner above it, then targets the train again so it goes back up and you can use the train multiple times.
I think thats pretty much it, theres probably a lot of errors, but it makes sense in my head.
God that took a lot of thinking!!!