delta_calibrate: Initial support for enhanced delta calibration

Add support for an enhanced delta calibration routine that performs XY
dimension calibration.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

docs/prints/calibrate_size.scad

@@ -0,0 +1,77 @@
+// Calibration object for delta sizing
+//
+// Generate STL using OpenSCAD:
+//   openscad calibrate_size.scad -o calibrate_size.stl
+
+base_radius = 70;
+base_height = 1.5;
+base_width = 8;
+cylinder_height = 5;
+cylinder_radius = 5;
+cylinder_outer_dist = 65;
+ridge_cut_radius = .5;
+text_height = 1;
+text_size = 5;
+spoke_angles = [0, 60, 120, 180, 240, 300];
+CUT=0.01;
+
+// Circular ring around entire object (to help reduce warping)
+module base_ring() {
+    difference() {
+        cylinder(h=base_height, r=base_radius);
+        translate([0, 0, -CUT])
+            cylinder(h=base_height + 2*CUT, r=base_radius-base_width);
+    }
+}
+
+// The base ring plus the base spokes
+module base() {
+    base_ring();
+    // Spokes
+    for (angle=spoke_angles)
+        rotate([0, 0, angle])
+            translate([-base_width/2, -CUT, 0])
+                cube([base_width, base_radius-base_width+2*CUT, base_height]);
+}
+
+// Cylinder that measurement ridges are cut out of
+module measuring_cylinder() {
+    cut_width = cylinder_radius;
+    difference() {
+        cylinder(h=cylinder_height+CUT, r=cylinder_radius, $fn=60);
+        for (angle=spoke_angles)
+            rotate([0, 0, angle])
+                translate([-cut_width, cylinder_radius - ridge_cut_radius, -CUT])
+                    cube([2*cut_width, cut_width, cylinder_height+3*CUT]);
+    }
+}
+
+// All the measuring cylinders around the ring
+module measuring_cylinders() {
+    measuring_cylinder();
+    for (angle=spoke_angles)
+        rotate([0, 0, angle])
+            translate([0, cylinder_outer_dist, 0])
+                measuring_cylinder();
+}
+
+// Text writing
+module write_text(angle, dist, msg) {
+    text_offset = dist + 1 - text_size/2;
+    rotate([0, 0, angle])
+        translate([0, text_offset, base_height - CUT])
+            linear_extrude(height=text_height + CUT)
+                text(msg, size=text_size, halign="center");
+}
+
+// Final object with text descriptions
+module calibration_object() {
+    base();
+    translate([0, 0, base_height-CUT])
+        measuring_cylinders();
+    write_text(120, cylinder_outer_dist - 20, "A");
+    write_text(240, cylinder_outer_dist - 20, "B");
+    write_text(0, cylinder_outer_dist - 20, "C");
+}
+
+calibration_object();