Quick answer: Niagara mesh particles spinning random directions or facing away from velocity? The Mesh Renderer’s Alignment Mode is set to Custom Alignment with default vector — configure Alignment + Facing properly.
A debris emitter spawns rock meshes, and each rock faces a random direction unrelated to its velocity. The renderer is using Auto Alignment without a velocity input.
Alignment Modes
The Mesh Renderer has Alignment (rotation around facing axis) and Facing (which axis points where). Combos: Velocity Aligned + Camera Facing common for projectiles; Custom Alignment + Custom Facing for fine control.
Velocity Alignment
For motion-aligned debris, set Alignment = Velocity. The mesh’s forward axis follows velocity each frame. Set Facing = Camera to keep the up-direction toward the player.
Sub-Renderer Per Mesh
The Mesh Renderer can pick from a list; each mesh can have its own alignment via per-particle attributes. Useful when different particle types share an emitter.
Pivot Offset
If your mesh isn’t centered, set Pivot Offset on the renderer or shift in the modeling tool. Off-pivot meshes orbit visually even when alignment is correct.
Verifying
Particles point along their motion. Camera-facing axis stays consistent. No random rotations frame-to-frame.
“Alignment + Facing together. Velocity-aligned for moving meshes; camera-facing for stable up.”
For tumbling debris, add rotation rate plus alignment — the alignment provides direction; rotation rate adds tumble.