For an overview on creating, visualizing, and simulating mechanical constraints, including HingeConstraint, see Mechanical Constraints. Also see Roblox Units to understand how Roblox units compare to metric units.
A HingeConstraint allows its two attachments to rotate about one axis, forcing them into the same position and X axis alignment. This constraint can also be powered to behave like a motor or servo, and you can set limits to restrict the hinge's rotational range.
Orientation of a hinge's attachments affects how it rotates. To ensure rotation occurs around the desired axis, each attachment's Axis, visualized by the yellow arrow, should point in the same direction.
Angular Power
If a hinge's ActuatorType is set to Motor, it attempts to rotate the attachments with the goal of reaching its AngularVelocity. You can further control this rotation through both MotorMaxAcceleration and MotorMaxTorque.
If a hinge's ActuatorType is set to Servo, it attempts to rotate to an angle specified by TargetAngle. This rotation is controlled by both AngularSpeed and ServoMaxTorque.
Limits
You can set limits to restrict the rotation of a hinge, useful for mechanisms like doors which should only swing open or closed within a set range. Enabling the LimitsEnabled property exposes the LowerAngle and UpperAngle limits, as well as Restitution which defines the elasticity of the attachments when they reach either limit.