SLVSX Constraint Solver Examples

A collection of examples demonstrating the SLVSX constraint solver for parametric design and mechanical systems.

View Interactive 3D Examples

What is SLVSX?

SLVSX is a command-line interface to the SolveSpace constraint solver. It allows you to define geometric relationships declaratively and have the solver calculate actual positions automatically.

Examples

Mechanical Linkages

Example	Description	Preview
Four-Bar Linkage	Classic planar linkage with parametric crank angle	SVG
Chebyshev Linkage	Approximate straight-line mechanism	SVG
Peaucellier Linkage	First mechanism to convert rotary to exact straight line (1864)	SVG
Theo Jansen Leg	Strandbeest walking mechanism using "holy numbers"	SVG
Crank-Slider	Converts rotary to reciprocating motion (piston/engine)	SVG
Scotch Yoke	Converts rotation to linear motion via sliding yoke	SVG
Whitworth Quick-Return	Asymmetric motion for shaping machines	SVG
Geneva Mechanism	Maltese cross for intermittent motion	SVG
Pantograph	Rhombus linkage for copying/scaling drawings	SVG
Cam Follower	Radial cam with roller follower on vertical guide	SVG
Ferris Wheel	Six-cabin wheel with radial symmetry and support structure	SVG

Gear Systems

Example	Description	Preview
Gear Mechanism	Two meshing gears with proper tooth spacing	SVG

Curves & Paths

Example	Description	Preview
Bezier Path	Cubic Bezier S-curve with perpendicular control handles	SVG
Tangent Arc Chain	Arc-to-line tangent constraint for smooth transitions	SVG

Artistic Patterns

Example	Description	Preview
Islamic Star Pattern	192 points, 88 lines - intricate geometric precision	SVG
Parametric Flower	Organic patterns from geometric constraints	SVG
Spirograph	Mathematical art patterns	SVG
Iris Diaphragm	Camera-style aperture mechanism	SVG

Mechanical Parts

Example	Description	Preview
Symmetric Bracket	Bracket with notch and mounting holes, demonstrating symmetry via parallel constraints	SVG
Parametric Hinge	3D-printable hinge joint with configurable dimensions	SVG

Complex Systems

Example	Description	Preview
Rube Goldberg Machine	Chain-reaction with marble, bucket, lever, dominoes	SVG
Constraint Showcase	Demonstrates many constraint types in one file	SVG

3D Structures

Example	Description	Preview
3D Scissor Lift	3-stage scissor with thick 3D bars (136 entities - largest demo!)	SVG
Tetrahedron	4-faced polyhedron
Octahedron	8-faced polyhedron
Pyramid	Square-based pyramid
3D Truss	Structural truss in 3D

New Constraint Demos (v0.2.8)

Example	Description	Preview
Collinear Demo	Points constrained to a single line using new collinear constraint	SVG
Equal Angles Demo	Radial spokes with equal angular spacing using new equal_angles constraint	SVG

Architecture

Example	Description	Preview
Floor Plan	Room layout with dimensional constraints	SVG
Mandala	Radial symmetry pattern	SVG
Truss Bridge	Structural bridge with triangulated support	SVG

Learning Examples

Example	Description
Basic Shapes	Triangle, square, hexagon, pentagon - for learning constraint basics

Parametric Showcases

Examples showing the same design solved at different parameter values:

Example	Description	Preview
Four-Bar Animation	Same linkage at 6 crank angles (0°, 60°, 120°, 180°, 240°, 300°)	SVG
Prime Stars	Radial patterns with 3, 5, 7, 11, 13 points using equal_angles	SVG

Quick Start

Installation

# Install SLVSX
curl -fsSL https://raw.githubusercontent.com/snoble/slvsx-cli/main/install.sh | bash

# Clone examples
git clone https://github.com/snoble/slvx-examples.git
cd slvx-examples

Try It Out

# Solve a linkage
slvsx solve four_bar_linkage/four_bar_linkage.json

# Export to SVG
slvsx export -f svg four_bar_linkage/four_bar_linkage.json > output.svg
open output.svg

Creating Your Own Examples

Read the Visual Design Guide before creating examples.

Key Principles

1. Build incrementally - Add entities one at a time, test after each
2. Export to SVG - Visually inspect at every step
3. Use parameters - Make key dimensions parametric
4. Provide good initial guesses - Use at fields for points

Example Structure

{
  "schema": "slvs-json/1",
  "units": "mm",
  "parameters": {
    "link_length": 50,
    "angle": 30
  },
  "entities": [
    {"type": "point", "id": "origin", "at": [0, 0, 0]},
    {"type": "line", "id": "link", "p1": "origin", "p2": "end"}
  ],
  "constraints": [
    {"type": "fixed", "entity": "origin"},
    {"type": "distance", "between": ["origin", "end"], "value": "$link_length"}
  ]
}

Key Constraint Types

Constraint	Purpose	Example Use
fixed	Anchor a point	Origin, pivot points
distance	Set distance between points	Lengths, radii
angle	Set angle between lines	Rotations, slopes
perpendicular	Make lines 90 degrees	Right angles
parallel	Make lines parallel	Rails, guides
point_on_line	Point lies on line	Sliders, intersections
equal_length	Make segments equal	Regular polygons
midpoint	Point at midpoint	Centering
point_on_circle	Point lies on circle	Wheels, orbits
diameter	Set circle diameter	Sizing circles
tangent	Make arc/line tangent	Smooth transitions
collinear	3+ points on same line	Rail alignment (v0.2.8+)
equal_angles	Equal angles between lines	Radial patterns (v0.2.8+)

Known Issues (v0.2.8)

See GitHub Issues for current bugs and feature requests.

Fixed in v0.2.8:

• equal_length with >2 entities - FIXED! No longer crashes
• point_on_line fails with 2D entities - FIXED in PR #50

Still Open:

• symmetric_vertical/symmetric_horizontal collapse points (issue #49) - use parallel + fixed as workaround
• Arc and cubic Bezier entities don't render in SVG export (issue #51) - entities solve correctly but SVG output doesn't show curves
• rube_goldberg_machine example fails with "Invalid solver system" (issue #52)
• Circles don't track points - use points for moving parts

Resources

• SLVSX CLI - The constraint solver
• Visual Design Guide - How to create good examples
• SolveSpace - The underlying constraint solver

License

Examples are provided as-is for educational purposes.