fix: Torsion joint directrix

nhf/parts/joints.py

@@ -265,7 +265,7 @@ class TorsionJoint:
     spring_thickness: float = 2
     spring_height: float = 15
 
-    spring_tail_length: float = 40
+    spring_tail_length: float = 35
 
     groove_radius_outer: float = 35
     groove_radius_inner: float = 20
@@ -314,15 +314,11 @@ class TorsionJoint:
         l = self.spring_tail_length
         if self.right_handed:
             r2 = -r2
+        # This is (0, r2) and (l, r2) transformed by right handed rotation
+        # matrix `[[c, -s], [s, c]]`
         return [
-            (0, 0, height),
-            (c, s, height)
-        ]
-        # This is (0, r2) and (l, r2) transformed by rotation matrix
-        # [[c, s], [-s, c]]
-        return [
-            (s * r2,         -s * l + c * r2, height),
-            (c * l + s * r2, -s * l + c * r2, height),
+            (-s * r2,         c * r2, height),
+            (c * l - s * r2, s * l + c * r2, height),
         ]
 
 

nhf/parts/test.py

@@ -27,6 +27,8 @@ class TestJoints(unittest.TestCase):
         assembly = joint.rider_track_assembly(slot)
         bbox = assembly.toCompound().BoundingBox()
         self.assertAlmostEqual(bbox.zlen, joint.total_height)
+        self.assertAlmostEqual(bbox.xlen, joint.radius * 2)
+        self.assertAlmostEqual(bbox.ylen, joint.radius * 2)
         self.assertEqual(pairwise_intersection(assembly), [])
 
     def test_torsion_joint(self):