mec2 Main Page

mec2 #

mec2 is a javascript library for simulating and analysing planar mechanisms or linkages. The concept is based on nodes constrained by one of four different vectors. Solving the kinematic equations is done by using Erin Catto's principle of sequential impulses, often used by gaming physics engines.

Its API is minimal and easy to understand. The library is tiny and fast. Mechanisms are described using an easy to read JSON format.

Example #

first

JSON #

{
    "id":"4bar",
    "nodes": [
        { "id":"A0","x":100,"y":100,"base":true },
        { "id":"A", "x":100,"y":150 },
        { "id":"B", "x":350,"y":220 },
        { "id":"B0","x":300,"y":100,"base":true }
    ],
    "constraints": [
        { "id":"a","p1":"A0","p2":"A","len":{ "type":"const" } },
        { "id":"b","p1":"A", "p2":"B","len":{ "type":"const" } },
        { "id":"c","p1":"B0","p2":"B","len":{ "type":"const" } }
    ]
}

How do I use it? #

You can build an environment yourself.

Here's a minimal example:

<html>
<head>
    <title>minimal mec2 example</title>
    <meta charset='utf-8'>
</head>
<body>
    <canvas id="c" width="601" height="401"></canvas>

    <script src="https://gitcdn.xyz/repo/goessner/g2/master/src/g2.js"></script>
    <script src="https://gitcdn.xyz/repo/goessner/mec2/master/mec2.min.js"></script>

    <script>
        const ctx = document.getElementById('c').getContext('2d');  // the canvas-context
        let   g = g2().clr().view({cartesian:true}).grid(),         // a g2 graphics-object
              model = {                                             // your model
                id: 'pendulum',
                gravity:true,
                nodes: [
                    {id:'A0',x:300,y:240,base:true},
                    {id:'A1',x:380,y:300}
                ],
                constraints: [
                    { id:'a',p1:'A0',p2:'A1',len:{type:'const'} }
                ]
              };

        // simulation
        const simulate = () => {
                  model.tick(1/60);                 // solve model with fixed stepping
                  g.exe(ctx);                       // render its pose on the canvas
                  requestAnimationFrame(simulate);  // keep calling back
              };

        mec.model.extend(model);                    // extend the model
        model.init();                               // initialize it
        model.draw(g);                              // append model-graphics to graphics-obj

        simulate();                                 // kick-off the simulation
    </script>
</body>
</html>

If you don't want to do that, check out the project mecEdit. mecEdit is a standalone, installable editor for planar mechanisms, that uses mec2 as a physics engine and focuses on user experience. It's hosted here.

License #

mec2 is licensed under the terms of the MIT License.