This is the motor unit that drives all of the 9V Trains. The pack includes the chassis/suspension components that attach each side of the motor unit and make the wheels look very much like the plastic wheelsets used everywhere else. All four wheels are driven by the motor which uses exactly the same part inside as the Technic 9V motor. Four of the studs at one end are conducting, allowing a wire or conducting plate to be attached so that you can have working headlights. The voltage supplied is the same as the motor is getting so the lights are dim when the motor is going slowly.
The wheels are plastic and have rubber rims for improved traction. The flanges are separate metal pieces and are spring loaded so that they push against the inside of the rails. This ensures a good electrical connection. All four wheels pick up electricity so even when one wheel is over an insulated part of a point the motor will still start.
The top of the motor is smooth with a Technic style connector sticking out of the centre. This allows it to swivel underneath one of the several wagon floor pieces. Alternatively, the motor unit can be fixed permanently to a locomotive using the studs each end. Also, there are clips at the bottom each end that accept the side of a brick or inverted slope.