The Transmetal driver is a small spherical device that Megatron presumably found at one of the Vok sites on prehistoric Earth. Its original function is unknown, and according to an analysis by the Maximals' computer it was altered by Megatron. The driver was a necessary part of a transformation into a Transmetal 2.
Megatron initially used the driver as part of the Machine that gave Dinobot 2 life. The transmetal driver seems to give off the same type of energy/radiation as the quantum surge, perhaps in a stronger dose.
Cheetor and Depth Charge destroyed Megatron's machine, but not before Cheetor got a full dose of the driver's energy turning him into a Transmetal 2. Depth Charge recovered the driver and threw it into the lava around the Ark. However, Blackarachnia saved the device and tried to use it on herself. The driver caused her systems to crash, but mysteriously changed her into a Transmetal 2.