From Sonic Retro
Special Generators have the appearance of floating rainbow-coloured devices emblazoned with a star on the front with two handles to hang on to. They can be found in many different locations throughout the Zones of Sonic Rush when playing as Sonic the Hedgehog, and he can grab hold of one by jumping at one of the handles. At this point, the player can either jump off with / to ignore it, or hold / to use the Super Boost and make Sonic swing around it at high speed and create a dimensional distortion above. The player must keep boosting for a while until Sonic automatically lets go and enters the distortion to warp to the Special Stage. If the player jumps off the handle or stops boosting (either by letting go of / or running out of energy in the Tension Gauge), they will fail to enter the Special Stage. At least 105% of the Tension Gauge is needed to successfully enter the Special Stage.
The Special Generator will still be there when Sonic returns from the Special Stage regardless of whether he has completed it or failed it. In the case of the latter, the player can grab its handles and try again so long as there is enough energy in the Tension Gauge to do so, or locate another Special Generator elsewhere.