Chaos Pendulum

Mike — Sat, 07 Nov 2009 13:51:58 +0000

We saw a program that had a double pendulum called the chaos pendulum and my girlfriend said I should try and make it, so I had a quick play in quickbox2d. It was being used as an example of chaotic looking movement that wasn’t random. Here’s a real one.

and here’s the flash on, it’s not as good but box2d does an interesting job.

let’s test putting some code on here.. then you need to get quickbox2d…

import com.actionsnippet.qbox.*;
stage.frameRate = 60;

var sim:QuickBox2D = new QuickBox2D(this);

var $x:Number = 9
var $y:int = 4
var $length:int = 5
var $radius:Number = 0.5

var pin_to:QuickObject = sim.addBox({x:$x, y:$y, width:0.5, height:0.25,density:0, maskBits:0x0008 } );
var top_pendulum:QuickObject = sim.addBox({x:$x, y:$y+($length * 0.5), height:$length,width:1.5,friction:0,restitution:0 } );
var bottom_pendulum:QuickObject = sim.addBox({x:$x, y:$y + ( $length * 1.3 ), height:$length,width:0.75,friction:0,restitution:0 } );

//SET UP JOINTS
sim.addJoint( {type:"revolute",a:pin_to.body,b:top_pendulum.body,collideConnected:false, x1:$x, y1:$y, x2:$x, y2:$y } );
sim.addJoint( {type:"revolute",a:top_pendulum.body,b:bottom_pendulum.body,collideConnected:false, x1:$x, y1:$y+( $length * 0.9 ), x2:$x, y2:$y+$length-0.25 } );

sim.start();
sim.mouseDrag();

//ADD RANDOM ANGULAR VELOCITY ON CLICK
//JUST SETTING THE bottom_pendulum SEEMS TO WORK
stage.addEventListener( MouseEvent.CLICK, clicked );

function clicked( e:MouseEvent ):void
{
bottom_pendulum.body.SetAngularVelocity( 10000-Math.random() * 20000 )
}

Quickbox2d string and balls

Mike — Fri, 06 Nov 2009 00:15:43 +0000

Right my first geeky quick flash experiment…… Skip past the text and take a look at the fun.

A few games I’ve been working on at the mo have required some 2d physics so I’ve been looking at box2d again. The last thing I did with it was “banana cannon” balancing game for Gorillaz Bananaz. Since then actionsnippet.org has packaged up box2d into quickbox2d making it “quick”. It’s worth a look.

Anyway one of the things needed was a nice looking rope/wire effect connecting 2 objects that would allow them to move freely when the rope wasn’t tort. I couldn’t find a single joint that didn’t affect the rotation of the other object while moving around. I’m sure there’s probably a better way, but I managed to achieve the effect by creating a an extra hidden object like a knee inbetween the 2 and applying a distance joint from the knee to each object. Then to cheat a nice bendy/rubbery rope look I drew a line using curveTo going from one object to the other bending towards the knee. Take a look below.

And behind the scenes

UPDATE:
I’ve added a post about calculating a point to make curveTo curveThrough a point. It’s how the string curves towards the knee.
graphics-curveto-through-point

Mike R :: R ekim » experiments

Chaos Pendulum

Quickbox2d string and balls