Use this skill when building physics-driven gameplay: vehicles, ragdolls, projectiles, mechanical contraptions, elevators, swinging platforms, or anything using constraints and forces.

Quick Reference

Constraint Types

Mechanical: HingeConstraint, PrismaticConstraint, CylindricalConstraint, BallSocketConstraint, UniversalConstraint, WeldConstraint/RigidConstraint Motion: AlignPosition, AlignOrientation, LinearVelocity, AngularVelocity, VectorForce, Torque Spring/Rope: SpringConstraint, RopeConstraint, RodConstraint

Attachment Pattern

Constraints connect via Attachment objects. Create one on each part, set Attachment0/Attachment1, and parent the constraint to part0. Actuator types include None, Motor, and Servo.

Vehicles

Vehicles: use motorized HingeConstraint wheels, SpringConstraint suspension, servo steering, and CustomPhysicalProperties for friction tuning.

Ragdoll

Replace Motor6Ds with BallSocketConstraint: create Attachments from motor.C0/C1, set LimitsEnabled=true, UpperAngle=45. Keep Root Motor6D for HRP. Set humanoid state to Physics. On recovery, destroy only the instances ragdoll created and restore only the motors it disabled (track both at enable time).

Authority and Network Ownership

Classic projects: automatic ownership can give an unanchored assembly to a nearby player. SetNetworkOwner(nil) keeps it server-owned; SetNetworkOwner(player) gives a player simulation ownership. Treat player-owned physics as untrusted and validate gameplay outcomes.

Server Authority: set Workspace.AuthorityMode = Server with its required settings. Core objects can remain server-owned while prediction keeps controls responsive, so the classic secure-but-laggy trade-off does not apply. SetNetworkOwner() is not a substitute.

Rule: choose the model first. Keep NPC and gameplay-critical objects authoritative; give client ownership to non-critical physics only when the resulting behavior is acceptable and tested.

Common Gotchas

Constraints do nothing on Anchored parts
Both Attachment0 AND Attachment1 required (missing one = silent fail)
Over-constraining = jitter. Tune mass with CustomPhysicalProperties
Use Raycast for hitscan, Touched only for slow physics projectiles
Always set lifetime on physics projectiles (forgotten ones kill perf)

Need more detail? Load references/full.md for the complete reference with code examples, API tables, and edge cases.

npx skills add tabooharmony/roblox-brain --skill roblox-physics