// a chain around two gears of given radii (r1, r2) and distance;
// coord origin is at the gear with r1
module chain(r1, r2, dist, chain_width, chain_height) {
//    rotate([90, 0, 0])
    difference() {
	 chain_template(r1 + chain_height, r2 + chain_height, dist, chain_width);
	 chain_template(r1, r2, dist, chain_width + 1);
    }
}

module chain_template(r1, r2, dist, chain_width)
    hull () {
	cylinder(r=r1, h=chain_width, center=true);

	translate([dist, 0, 0])
	cylinder(r=r2, h=chain_width, center=true);
    }

chain(20, 30, 100, 10, 5);