Billy/Behind the Scenes

Gauge 1 model
Billy's model was built to run on gauge 1 track. Four different facial expressions were worn by Billy on screen. The faces were first sculpted in clay, and from that resin casts were made using a silicone mold. The model was made from brass. The wheels and chassis were custom machined (CNC). The model was track powered, so pickup contacts were attached to the metal wheels, which ran into the motor to power it. The electricity ran from the track to the wheels/pickup contacts and went into the motor to power him. A spare chassis was also constructed.

The eye mechanism had two servos, one for up and down movement and one for left and right movement. The up/down servo was attached to the body. The left/right servo had a rod attached to the arm, which connected to a bracket. The eye balls were coupled to the bracket, and locked in by the face-plate, so whenever the servos were powered, the eye balls would move however the crew member desired.

An unused production made shocked face-mask of Billy is now owned by Twitter user isaackhan29.

Close-up model
A close-up shot of Billy's cab and firebox was required for scenes in Don't be Silly, Billy, where he had to interact with close-up scale figures. It is likely that the model makers reused another engine's interior during production, rather than creating a new model solely for Billy altogether.

CGI model
The eleventh season episode, Don't be Silly, Billy, was planned to be recreated for CGI testing in 2009, therefore, a CGI model of Billy would have be created. In addition, Billy was supposed to appear in the thirteenth season, however, he was dropped in favor of a new character, Charlie. Interestingly, Charlie and Billy share the same basis. It can be theorized that Billy's CGI model may have been reworked to make Charlie.