Miller Trucks

The Miller Truck was an ingenious invention that was basically two DC  motors with a shaft on each side and wheels mounted on those shafts.  In this truck, the wheel rims were segmented and served as the commutator contact points with the rails serving as "brushes."  This enabled the entire motor and drive mechanism to be mounted below the car body.  This enabled the truck to be used to motorize units not originally designed to be powered and allowed for interior details.  A.C. Gilbert used these on wooden preproduction models such as the GP7.