Roblox’s physics engine is powerful and expressive, but many developers never move beyond basic Anchored parts. Understanding constraints and joints unlocks a much wider range of game mechanics.
The Basics: WeldConstraint
A WeldConstraint permanently attaches two parts together, moving them as a single unit. This is the simplest constraint and the most commonly used. Insert a WeldConstraint into a part, then set Part0 and Part1 to the two parts you want joined. Unlike the older Weld object, WeldConstraint automatically handles attachment updates when parts move in Studio.
HingeConstraint: Doors and Wheels
HingeConstraint allows rotation around a single axis. A door needs one attachment at the hinge point on both the door and the wall; the HingeConstraint connects them. Set ActuatorType to “Motor” and AngularVelocity to make it spin automatically — perfect for fans, wheels, and spinning obstacles.
SpringConstraint: Bouncy Platforms
SpringConstraint creates an elastic connection between two parts, with configurable stiffness and damping. Use it for suspension systems on vehicles, bouncy platforms, or ragdoll body connections that react physically to impacts.
Motor6D: Character Rigs
Motor6D is the joint used internally by Roblox characters to connect body parts with animated movement. If you’re creating custom character rigs or vehicles that players can sit in with proper animation, you’ll need to work with Motor6D. The AnimationController and Animator objects work in conjunction with Motor6D to drive animations.