Hi!

I've been working on a hobby project for a while and finally have something worth sharing: **MechSim** — a 2D planar linkage simulator that runs entirely in your browser.

**What it does:** You place pins, connect them with links, ground some joints, and set a crank spinning — then watch the mechanism move in real time. It supports revolute joints, rail sliders, arc sliders, and circle sliders. You can also trace pin paths, record position/velocity/acceleration data, and export it as CSV.

**The interesting technical bits:**

* Constraint solver built from scratch using Newton-Raphson with Levenberg-Marquardt damping — no physics engine, no libraries
* Handles overconstrained and degenerate configurations gracefully
* Save/load projects as JSON
* Fully keyboard-shortcut driven for fast workflow

**Why I built it:** I needed a quick way to sketch and validate simple linkage mechanisms without spinning up a full CAD tool. Couldn't find anything lightweight and browser-based that wasn't either abandoned or paywalled, so I built it.

**Stack:** Single-file HTML + vanilla JS + Canvas. Zero dependencies.

Still in early days — the tutorial page walks through the basics if you want to try it.

[**mechsim.app**](http://mechsim.app)

Happy to answer questions about the solver implementation or any of the design decisions. Would love feedback from anyone who pokes at it!²

I built a browser-based 2D kinematic mechanism simulator — no install, no libraries, pure JS