topeak-mtx-tortec-expeditionrack-adapter: fix elevations etc.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/topeak-mtx-tortec-expeditionrack-adapter.scad b/topeak-mtx-tortec-expeditionrack-adapter.scad
index 705a3f9a0122f111f11abba2056c8966d0c982cf..423815796c8b868fc4f22d51269a04cf0fa5fabc 100644 (file)
--- a/topeak-mtx-tortec-expeditionrack-adapter.scad
+++ b/topeak-mtx-tortec-expeditionrack-adapter.scad
@@ -95,7 +95,8 @@ block_y_min = adapt_main_top_y - main_sz_y;
 
 strap_barrel_x = rack_width_inner/2 + strap_barrel_dia/2;
 
-rack_shear_ratio = -rear_elevation_nominal / rear_to_front_distance;
+rack_shear_ratio = -(rear_elevation_nominal - front_elevation_nominal)
+  / rear_to_front_distance;
 
 front_to_cross_rail =
   cross_rail_distance * sqrt(1 - rack_shear_ratio * rack_shear_ratio)
@@ -391,7 +392,10 @@ module ForRackForDemo(){
   elevation = elevation_of_bolt_for(rear_to_cross_rail);
   rack_rail_y = rack_rail_y_of_elevation(elevation);
 
-  rotate([-atan(rack_shear_ratio), 0,0])
+  rotate([atan(
+               (rear_elevation_nominal - front_elevation_nominal) /
+               cross_rail_distance
+               ), 0,0])
     translate([0, rack_rail_y, brk_block_z/2 + rack_rail_y*rack_shear_ratio])
     children();
 }