For an overview on creating, visualizing, and simulating mechanical constraints, including TorsionSpringConstraint, see Mechanical Constraints. Also see Roblox Units to understand how Roblox units compare to metric units.
A TorsionSpringConstraint applies torque based on a relative angle and relative angular velocity. It attempts to bring two axes from two parts together and is useful for hinged swinging doors with a spring-back effect.
Correct orientation of a torsion spring's attachments is important. The constraint will attempt to bring the SecondaryAxis of each attachment, visualized by the orange arrows, into alignment. When building mechanisms like swinging doors, ensure that the secondary axes are perpendicular to the intended axis of rotation.
Damping
The Damping value controls how fast the spring's oscillation dies down. A value of 0 allows the spring to oscillate endlessly, while higher values bring the spring to a rest more quickly.
Stiffness
Stiffness sets the torsional strength of the spring. Higher values create a spring that responds with more force.
Limits
Enabling the LimitsEnabled property exposes the MaxAngle value to restrict the spring's range within a cone; it also exposes the Restitution value which defines the elasticity of the attachments when they reach their limit.