The robot transporter is a large machine about the size of Dr. Eggman in his Egg Mobile. It is mostly black with both ends of its 'shell' parts being silver. These 'shells' also appear to have yellow, black and red stripes, and are divided by three columns of electricity.
There is a dilapidated version of the machine placed in the present of the Rounds. It looks similar to the regular one, but all the colors are replaced by shades of blue and there's no electricity going through it.
Sonic the Hedgehog CD
Although its story purpose is debatable, the robot transporter provides a very definite purpose in Sonic the Hedgehog CD. In gameplay, it is placed in the past of every first and second Round. Robot transporters exist in other time frames as well, but are inactive, merely giving a clue for where they were placed. Destroying the robot transporters in one Zone will grant a good future for that Zone and destroy all Badniks there. Destroying all the robot transporters in the game, along with the Metal Sonic holograms, will earn the player the good ending for Sonic the Hedgehog CD. Alternatively, the player can collect all the Time Stones to achieve the good ending.
↑Christian Whitehead (December 14, 2011). Sonic the Hedgehog CD(2011). IOS. Sega. Instruction Manual: "To ensure a good future for a Zone, you must either collect all the Time Stones, or destroy Eggman’s robot transporter contained within the Past."
↑Christian Whitehead (December 14, 2011). Sonic the Hedgehog CD (2011). PSN. Sega. "Savior of the Planet Achievement: Destroy all the robot teleporters and Metal Sonic holograms in the past."