# Spirograph

To simulate a Sirograph, try applying the following expression to the brush position of the Write-on effect:

```
r1 = 43;
r2 = -14;
o = 53;
v = 15;
s = 2.5;
r = r1 + r2;
x = r*Math.cos(time*v) - (r2 + o)*Math.cos(r*time*v/r2);
y = r*Math.sin(time*v) - (r2 + o)*Math.sin(r*time*v/r2);
[s*x + thisComp.width/2, s*y + thisComp.height/2];
```

Play around with the various parameters:

r1 is the radius of one wheel.

r2 is the radius of the other wheel.

o is the offset.

v is the speed.

s is the scale.

Animating the brush color makes it more interesting.