This is the USA Trains R22-115 G Scale motor block. It contains a horizontal DC can motor with a shaft out each end, gear drive to each axle.
Both the top and the bottom of the motor have easily removed cover plates to gain access. Also, the screws that hold the covers on can be used to mount the motor to a truck or frame, or attach the roller pickups to the bottom, the way I did on the Marklin.
I remove the center sliding pickups, don't need them for 3-rail. I also remove the contact pins that you see on one end, replacing them with wire leads. Two are for the two motor leads, and the other two are track contact through the wheels, they can be combined for track ground. Since the housing is plastic, you will not ground through the motor housing. The motor has internal "swipes", thin springs that rub along the axles to create a ground; two of the end pins come connected to these swipes, and you can use that as your ground.
Notice that there is extra length on the axles: Perfect for widening to Standard Gauge, either using the same wheels or substituting larger ones. I usually end up using larger ones to give it a little more ground clearance.
Then all you need is a center third rail pickup, and a bridge rectifier between that and the motor leads. If what you are building has a second (idler) truck - like the front truck on my rail bus for example - it is easier to put the pickup roller assembly in that other truck and wire it back to the motor through the cab. If the motor block is your only truck, you have to get creative.
To accomodate the DC motor, a simple bridge rectifier is one solution: but I often use a Williams reversing board, a small circuit board that sells for around $35, to give me smooth sequential forward-neutral-reverse-neutral. The board also contains a bridge rectifier, so it serves that function as well.
This motor is about 4" long. It is quite powerful and runs very strong, it is designed to pull some big G Scale trains.
There is also a slightly smaller version, the USA Trains R22-12:
Although the 12 has a smaller motor, it has one advantage over the 115: the can motor does not rise above the black housing on top, so the block can be more easily attached to the bottom of whatever it is that you are building.
These motors can usually be found on eBay in the G Scale section, I search for "motors". I get the Williams reversing boards from Train World, I am sure they are available elsewhere.
david
