A roller coaster seat is mounted inside a hoop of pipe that serves as handgrip and seat roller track. The hoop is at right angles to the direction of travel, and is located where it can be grasped by the rider, his hands raised in the common "no hands" position. The rider can roll the seat sideways using
his arms, with no limits to rotation. He can add to the thrill of the ride as he chooses. (Sissies can leave the seat locked upright.)
The bottom of the seat rides on rollers on the hoop, just like a coaster car rides on the steel track. The back of the seat attaches to a separate bearing. (I'm leaving out details, for brevity, but it can easily be built and safely be used.) Straps are strong enough to hold the rider in while upside down, but allow free arm movement. The feet and legs are also free to be used for balance.
Disadvantages of the design include riders at any angle at any time, which limits G-forces allowed. The width of each seat with its hoop is greater than a non-rolling seat, which reduces the number of seats across a car.
This idea was not inspired by SpinBallCoaster (see link) and is limited to only one axis of rotation, the one parallel to the track. The originality of this idea is in the use of the hoop for both the handgrip and the seat roller track, and allowing the rider to roll at his pleasure.