Orb of Sigma

The Orb of Sigma was part of a system required to locate and activate Fortress Maximus. To find and activate the Orb requires the use of seven O-Parts. The Orb itself indicates the location of Cerebros, who is able to power-up Fortress Maximus. It is a sphere, roughly a metre in diametre, with a map of Earth inscribed on it.

2001 Robots in Disguise cartoon
The Orb of Sigma was hidden at the top of a pyramid in a cavern deep beneath the Sahara Desert. Optimus Prime, Prowl, and X-Brawn entered the pyramid by using a glowing orb formed from the O-Parts, within which was trapped T-AI. Once they reached the Orb of Sigma, the glowing orb merged with it, cutting off their ability to communicate with T-AI.

Megatron and his Decepticons soon arrived and fought the Autobots, but when Megatron attempted to take the Orb, he triggered a booby trap which paralysed and shocked him. The Orb was snatched from Megatron's hand by Side Burn who escaped from the cavern while under heavy fire from the Decepticons. The cavern itself collapsed, but there was still enough power stored in the pyramid to rebuild Megatron as Galvatron.

The Orb was returned to the Autobot base, where they managed to extract T-AI, who reported that the Orb pointed to the location of Cerebros.