The tractor beam generators are large devices in their own right. Their junction boxes look like isosceles trapezoid cubes, with a one-eyed skull on the front and two antennas on the top, which have purple energy between them. They can be found on the top of much larger platforms with an antenna shaped likespheres stacked on top of one another.
Much further away from the junction boxes are large domes that generate the generators' tractor beams, which are shaped liked chains. These domes shoot the tractor beams from their centers into the sky and connect to the "bottom" of the Tropical Resort, effectively keeping the planet the generate is on permanently close to Eggman's operations.
Each generator is guarded by one of Dr. Eggman's more powerful robots (Captain Jelly on Sweet Mountain, Frigate Orcan on Starlight Carnival, Refreshinator/Drillinator on Planet Wisp, Admiral Jelly on Aquarium Park and Frigate Skullian on Asteroid Coaster). These robots are critical components in their respective generators' operations; should they be destroyed, their generator will shut down and their tractor beam will be weakened, though not dispersing. It is only when all five generators are shut down that the tractor beams will cease functioning.
When Sonic and Tails investigated the amusement park, Sonic disabled two of the generators without knowing. At that point, the duo were filled in on the generators' role by Yacker. Understanding that shutting down all the generators and freeing the planets would cut Eggman off from his Hyper-go-on, Sonic headed out and destroyed the remaining three, thus freeing all the planets.
↑Sonic Team (November 16, 2010). Sonic Colors. Nintendo Wii. Sega. Area/Level: Sweet Mountain. "Tails: So basically, Eggman is using five tractor beam generators to hold their planet in orbit while he scoops the aliens all up."