Rotating Gears - 3D Voxel Animation Tutorial

This guide walks you through how to generate a looping 3D voxel animation of rotating gears using SpatialStudio. The script creates metallic gears that rotate, mesh together, and cast shadows inside a cubic 3D space, then saves the animation to a .splv file.

What this script does

Creates a 3D scene of size 128×128×128
Spawns 3 interlocking gears, each with:
- A detailed cylindrical gear body with teeth
- Metallic gray coloring with highlights
- Realistic rotation mechanics
- Cast shadows for depth
Animates them rotating in sync for 6 seconds at 30 FPS
Outputs the file gear.splv that you can play in your viewer

How it works (simplified)

Voxel volume Each frame is a 3D grid filled with RGBA values (SIZE × SIZE × SIZE × 4).
Gear body Gears are drawn as cylinders with precisely cut teeth around the circumference.
Teeth generation Each gear tooth is calculated using trigonometry to create realistic gear profiles.
Rotation mechanics Gears rotate at different speeds to simulate proper mechanical interlocking.
Metallic shading Gray base colors with white highlights and darker shadows create a metallic appearance.
Animation loop A normalized time variable t cycles from 0 → 2π, ensuring smooth rotation loops.
Encoding Frames are passed into splv.Encoder, which writes them into the .splv video file.

Try it yourself

Install requirements first:

pip install spatialstudio numpy tqdm

Then copy this script into gear.py and run:

python gear.py

Full Script

import numpy as np
from spatialstudio import splv
from tqdm import tqdm

# Scene setup
SIZE, FPS, SECONDS = 128, 30, 6
FRAMES = FPS * SECONDS
CENTER_X = CENTER_Y = CENTER_Z = SIZE // 2
OUT_PATH = "../outputs/gear.splv"

# Gear settings
GEAR_COUNT = 3
GEAR_THICKNESS = 8
TEETH_HEIGHT = 4

def add_voxel(volume, x, y, z, color):
    if 0 <= x < SIZE and 0 <= y < SIZE and 0 <= z < SIZE:
        volume[x, y, z, :3] = color
        volume[x, y, z, 3] = 255

def generate_gear_body(volume, cx, cy, cz, inner_radius, outer_radius, thickness, teeth_count, rotation, color):
    # Generate the main cylindrical body
    for dx in range(-outer_radius-2, outer_radius+3):
        for dz in range(-outer_radius-2, outer_radius+3):
            distance = np.sqrt(dx*dx + dz*dz)
            if distance <= outer_radius:
                for dy in range(-thickness//2, thickness//2+1):
                    # Calculate if this point is part of a tooth
                    angle = np.arctan2(dz, dx) + rotation
                    tooth_angle = (angle % (2*np.pi / teeth_count)) * teeth_count / (2*np.pi)
                    
                    # Create gear teeth
                    is_tooth = (tooth_angle > 0.3 and tooth_angle < 0.7)
                    effective_radius = outer_radius if is_tooth else outer_radius - TEETH_HEIGHT
                    
                    if inner_radius <= distance <= effective_radius:
                        # Add metallic shading
                        shade_factor = 0.8 + 0.4 * np.sin(angle * 3)
                        shaded_color = tuple(int(c * shade_factor) for c in color)
                        add_voxel(volume, cx+dx, cy+dy, cz+dz, shaded_color)

def generate_gear_highlights(volume, cx, cy, cz, inner_radius, outer_radius, thickness, rotation):
    # Add metallic highlights
    highlight_color = (220, 220, 220)
    for dx in range(-outer_radius, outer_radius+1):
        for dz in range(-outer_radius, outer_radius+1):
            distance = np.sqrt(dx*dx + dz*dz)
            if inner_radius+2 <= distance <= outer_radius-1:
                angle = np.arctan2(dz, dx) + rotation
                # Create highlight pattern
                if np.sin(angle * 4) > 0.7:
                    dy = thickness//2
                    add_voxel(volume, cx+dx, cy+dy, cz+dz, highlight_color)

def generate_gear_shadows(volume, cx, cy, cz, inner_radius, outer_radius, thickness):
    # Add shadows below gears
    shadow_color = (40, 40, 40)
    shadow_offset = 3
    for dx in range(-outer_radius, outer_radius+1):
        for dz in range(-outer_radius, outer_radius+1):
            distance = np.sqrt(dx*dx + dz*dz)
            if distance <= outer_radius + 2:
                for dy in range(-thickness//2-shadow_offset, -thickness//2):
                    fade = 1.0 - abs(dy + thickness//2) / shadow_offset
                    if fade > 0:
                        faded_color = tuple(int(c * fade * 0.3) for c in shadow_color)
                        if cx+dx >= 0 and cx+dx < SIZE and cy+dy >= 0 and cy+dy < SIZE and cz+dz >= 0 and cz+dz < SIZE:
                            current = volume[cx+dx, cy+dy, cz+dz]
                            if current[3] == 0:  # Only add shadow to empty space
                                add_voxel(volume, cx+dx, cy+dy, cz+dz, faded_color)

def generate_gear_system(volume, t):
    # Define three interlocking gears with different sizes and positions
    gears = [
        {"pos": (CENTER_X-25, CENTER_Y, CENTER_Z), "inner": 8, "outer": 18, "teeth": 16, "speed": 1.0, "color": (120, 120, 120)},
        {"pos": (CENTER_X+25, CENTER_Y, CENTER_Z-5), "inner": 6, "outer": 14, "teeth": 12, "speed": -1.33, "color": (100, 100, 100)},
        {"pos": (CENTER_X, CENTER_Y+8, CENTER_Z+20), "inner": 10, "outer": 22, "teeth": 20, "speed": 0.8, "color": (140, 140, 140)},
    ]
    
    for gear in gears:
        cx, cy, cz = gear["pos"]
        rotation = t * gear["speed"]
        
        # Generate shadows first (so they appear behind gears)
        generate_gear_shadows(volume, cx, cy, cz, gear["inner"], gear["outer"], GEAR_THICKNESS)
        
        # Generate gear body
        generate_gear_body(volume, cx, cy, cz, gear["inner"], gear["outer"], 
                          GEAR_THICKNESS, gear["teeth"], rotation, gear["color"])
        
        # Add highlights
        generate_gear_highlights(volume, cx, cy, cz, gear["inner"], gear["outer"], 
                               GEAR_THICKNESS, rotation)

def generate_scene(volume, t):
    generate_gear_system(volume, t)

enc = splv.Encoder(SIZE, SIZE, SIZE, framerate=FPS, outputPath=OUT_PATH, motionVectors="off")

for frame in tqdm(range(FRAMES), desc="Generating gears"):
    volume = np.zeros((SIZE, SIZE, SIZE, 4), dtype=np.uint8)
    t = (frame / FRAMES) * 2*np.pi
    generate_scene(volume, t)
    enc.encode(splv.Frame(volume, lrAxis="x", udAxis="y", fbAxis="z"))

enc.finish()
print(f"Created {OUT_PATH}")

Next steps

Adjust GEAR_COUNT and gear definitions to add more gears to the system.
Modify rotation speeds to change how the gears interact.
Experiment with different inner_radius and outer_radius values for varied gear sizes.
Change gear colors to create brass, copper, or steel appearances.
Add a background or mounting structure by drawing additional voxels.

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