AkuSSPOD requested a book called 'Rust' - there's a few of 'em, so I hope this is the one you were looking for...
'Rust - Visitor In The Field' Part One
Archaia Entertainment, 2011, 109 pages
Written and Illustrated by Royden Lepp
Rust is a high-octane adventure set in the prairie lands of an unknown time. Life on the Taylor family farm was difficult enough before Jet Jones crashes into the barn, chased by a giant decommissioned war robot! Oldest son Roman Taylor struggles to keep his family's small farm afloat as the area heals from a devastating world war. While the rest of his family may not trust the mysterious boy with the jetpack, Roman believes the secrets of Jet's past may be the key to their survival.