TwinSpin: A Virtual Ball in a VR Controller Enabling In-Hand 3DoF Rotation

In-hand rotation is a natural motor skill of humans, yet current VR controllers mainly rely on arm and wrist movements to rotate virtual objects, leading to significant arm motion and fatigue. To address this, we propose TwinSpin, a VR controller employing two embedded mini-trackballs manipulated by the thumb and index finger. Its design is based on the intuitive metaphor of rolling a virtual ball in-hand to achieve three degrees-of-freedom (3DoF) rotation, leveraging finger dexterity to reduce arm movement and improve task efficiency in VR object manipulation tasks. Through docking tasks in both direct and distant object manipulations, our evaluation showed that TwinSpin significantly reduced arm travel distance, arm rotation, and task completion time compared to conventional arm-based rotation techniques. In line with the objective metrics, participants reported lower perceived physical demand, effort, and less perceived fatigue in the wrist, arm, and shoulder. We also share deeper analyses of the parallel control of translation and rotation, as well as optimal rotation trajectories, to gain further insights into user behavior with TwinSpin. To the best of our knowledge, this is the first attempt to enable full in-hand 3DoF rotation in a power-grip style VR controller.