During coordinated operation of multiple different modular traction power units (MPUs), a desired change in relative tractive effort contributed by each of the MPUs is identified. Relative distances between a connection point for each MPU and an implement hitch point is determined, in order to identify a hitch bar target position that will achieve the identified relative tractive effort contribution. The hitch bar is adjusted to make distance adjustments, based on the target position, to achieve the identified relative tractive effort for the MPUs.

During coordinated operation of multiple different modular traction power units (MPUs), a desired change in relative tractive effort contributed by each of the MPUs is identified. Relative distances between a connection point for each MPU and an implement hitch point is determined, in order to identify a hitch bar target position that will achieve the identified relative tractive effort contribution. The hitch bar is adjusted to make distance adjustments, based on the target position, to achieve the identified relative tractive effort for the MPUs.

Systems and methods for automated maintenance of the top and bottom surfaces or skins of an integrally stiffened hollow structure (e.g., a horizontal stabilizer) using surface crawling vehicles. Each system uses dynamically controlled magnetic coupling to couple an external drive tractor to a pair of passive trailers disposed in the interior of the hollow structure on opposite sides of a vertical structural element. The external drive tractor is also coupled to an external maintenance tool, which the tractor pushes or pulls across the surface skin to perform a maintenance function. The systems allow maintenance operations to be performed on both surface skins without turning the hollow structure over. Each system is modular and can be transported to and easily set up in a building or factory.

A top link for a tractor front counterweight support linkage. The link is a fixed length elongate body having at a first end a pivoting connection with a chassis of the tractor and at a second end a slot to slidably receive an attachment bolt connectable to a tractor front counterweight. The link further includes a mechanism to selectively permit or prevent sliding movement of an attachment bolt received in the slot.