Why does my Unreal ragdoll flail like jelly?

Constraint Swing/Twist limits are too loose or absent. Open the Physics Asset, click each constraint, and configure Limited swing 1/2 angles (e.g., 30 deg) and Twist (15 deg) to keep joints anatomically reasonable.

What is a Constraint Profile in Physics Asset?

Named sets of constraint parameters. Use Profiles for different states: 'Loose' for ragdoll, 'Stiff' for partial physics. Switch via SetConstraintProfileForAll at runtime.

Why does my ragdoll feel weightless?

Per-bone masses sum to a tiny total. In the Physics Asset, set total mass to a realistic value (50-90 kg for human) via Mass Override, distributed across bodies. Otherwise gravity has nothing to push.

Fix: Unreal Physics Asset Bone Constraint Broken

Quick answer: Set Swing 1/Swing 2/Twist limits per constraint to anatomically reasonable angles. Use Constraint Profiles for state switching. Set total mass on the Physics Asset realistic for the character.

Here is how to fix Unreal Physics Asset ragdolls that flail like jelly or stick stiffly. Per-bone constraint limits and mass distribution determine the feel.

The Symptom

Activate ragdoll on a humanoid; arms and legs flail in impossible angles. Or, conversely, the ragdoll is rigid and slides as a single block.

What Causes This

Loose constraints. Default Free swing on each constraint produces no anatomical limit.

Tight constraints. All locked or 0 swing produces rigid body.

Tiny mass. Each per-bone body at 1kg sums to maybe 20kg total; gravity barely affects.

The Fix

Step 1: Configure constraint limits per joint.

Shoulder:    Swing1 90, Swing2 90, Twist 45
Elbow:       Swing1 130, Swing2 5,  Twist 5
Knee:        Swing1 130, Swing2 5,  Twist 5
Ankle:       Swing1 30,  Swing2 15, Twist 15
Spine:       Swing1 25,  Swing2 15, Twist 15

Match anatomical ranges. Stiffer for elbows/knees that bend in one axis only.

Step 2: Set total mass. In Physics Asset details, set Mass Override (Total) to 70–90 kg for a human. Engine distributes across bodies by volume.

Step 3: Use Constraint Profiles for state.

// Profile names
Default:  loose ragdoll (jelly-ish for impact)
Combat:   stiff (partial ragdoll, controlled animation)

// Switch at runtime
Mesh->SetConstraintProfileForAll(FName("Combat"));

Step 4: Iterate in PhAT. Open the Physics Asset editor, click Simulate. Tweak limits live. Stop when the simulation looks anatomical.

Step 5: Add Drives for animation blending. Constraint Drives apply target torques to drive bones toward an animation pose; useful for partial ragdoll where you want some limbs to follow animation while others react to physics.

“Limits per joint, total mass realistic, Profiles for state switching. Ragdolls feel right.”

Related Issues

For physics constraint after load, see Constraint After Load. For cloth LOD, see Cloth LOD.

Anatomical limits. Total mass. Profiles. Ragdoll feels right.