Two full Stargate props were originally built for the "SG-1" pilot "Children of the Gods", the second of which was reconstructed from the prop used in the film. They are made of steel and fiberglass, and are in diameter. The second prop is less detailed, and is used for exterior scenes; in the pilot it was used solely on the planet Chulak. The primary one is fully automated and capable of rotating and emitting light. This is achieved by the use of a specially designed circular gear, which turns the inner ring on a precise pinion drive wheel, using an eight horsepower electric motor. The top seven chevrons emit laser pulses that are read by a sensor fed into a computer responsible for the gate's movement, which is consequently able to start and stop the rotation very quickly. This main prop is kept almost immovably at the permanent set of the SGC, at Bridge Studios, Vancouver.