From 96418523ec411a10a9379ca8a7f74b7dfe0570c3 Mon Sep 17 00:00:00 2001
From: Jan Huwald <jh@sotun.de>
Date: Sat, 31 Jan 2015 11:53:52 +0100
Subject: reshape top to allow free rotation of payload


diff --git a/gimbal.scad b/gimbal.scad
index f85a4fa..e4a54f0 100644
--- a/gimbal.scad
+++ b/gimbal.scad
@@ -89,6 +89,16 @@ module shell() {
 	// hollow out the sphere
 	sphere(d/2);
 
+	// reduce top to a cone, so that an attached surface can
+	// rotate freely
+	assign(a=2 * (45 - acos((d - 2*cutoff) / d)))
+	assign(h=d * tan(a))
+	translate([0, 0, d/2 - h - cutoff*cos(a/2)])
+	difference() {
+	    cylinder(r=d, h=d);
+	    cylinder(r1=d, r2=0, h=h);
+	}
+	
 	// add intro region
 	translate([0, 0, d])
 	cube([d-2*cutoff, d*2, 2*d], center=true);
-- 
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