feat: Tension fibre

nhf/parts/fibre.py

@@ -0,0 +1,58 @@
+"""
+A fibre, for bearing tension
+"""
+import cadquery as Cq
+from dataclasses import dataclass
+import nhf.utils
+
+def tension_fibre(
+        length: float,
+        hole_diam: float,
+        hole_twist: float=0,
+        thickness: float=0.5) -> Cq.Workplane:
+    """
+    A fibre which holds tension, with an eyes on each end.
+
+    """
+    eye_female = Cq.Solid.makeTorus(
+        radius1=hole_diam/2 + thickness/2,
+        radius2=thickness/2,
+        dir=(1,0,0),
+    )
+    hole_length_male = hole_diam * 2.5
+    hole_height_male = hole_diam * 1.2
+    eye_male = Cq.Solid.makeBox(
+        length=hole_length_male + thickness * 2,
+        width=thickness,
+        height=hole_height_male + thickness * 2,
+    ).located(
+        Cq.Location((-hole_length_male/2-thickness, -thickness/2, -hole_height_male/2-thickness))
+    ).cut(Cq.Solid.makeBox(
+        length=hole_length_male,
+        width=thickness,
+        height=hole_height_male,
+    ).located(Cq.Location((-hole_length_male/2, -thickness/2, -hole_height_male/2))))
+    height = length - hole_diam - thickness
+    assert height > 0, "String is too short to support the given hole sizes"
+    h1 = length/2 - hole_diam/2 - thickness/2
+    h2 = length/2 - hole_height_male - thickness/2
+    result = (
+        Cq.Workplane('XY')
+        .cylinder(
+            radius=thickness/2,
+            height=h1,
+            centered=(True, True, False),
+        )
+        .copyWorkplane(Cq.Workplane('YX'))
+        .cylinder(
+            radius=thickness/2,
+            height=h2,
+            centered=(True, True, False),
+        )
+        .union(eye_female.located(Cq.Location((0, 0,length/2))))
+        .union(eye_male.located(Cq.Location((0, 0,-length/2+hole_height_male/2+thickness/2), (0,0,1), hole_twist)))
+    )
+    result.copyWorkplane(Cq.Workplane(Cq.Plane(origin=(0,0,length/2), normal=(1,0,0)))).tagPlane("female")
+    conn1_normal, _ = (Cq.Location((0,0,0),(0,0,1),hole_twist) * Cq.Location((1,0,0))).toTuple()
+    result.copyWorkplane(Cq.Workplane(Cq.Plane(origin=(0,0,-length/2), normal=conn1_normal))).tagPlane("male")
+    return result

nhf/touhou/houjuu_nue/electronics.py

@@ -8,6 +8,7 @@ import cadquery as Cq
 from nhf.build import Model, TargetKind, target, assembly, submodel
 from nhf.materials import Role, Material
 from nhf.parts.box import MountingBox, Hole
+from nhf.parts.fibre import tension_fibre
 from nhf.parts.item import Item
 from nhf.parts.fasteners import FlatHeadBolt, HexNut
 from nhf.touhou.houjuu_nue.common import NUT_COMMON, BOLT_COMMON
@@ -333,7 +334,7 @@ LINEAR_ACTUATOR_BRACKET = MountingBracket()
 
 BATTERY_BOX = BatteryBox18650()
 
-@dataclass
+@dataclass(kw_only=True)
 class Flexor:
     """
     Actuator assembly which flexes, similar to biceps
@@ -346,17 +347,30 @@ class Flexor:
     nut: HexNut = LINEAR_ACTUATOR_HEX_NUT
     bolt: FlatHeadBolt = LINEAR_ACTUATOR_BOLT
     bracket: MountingBracket = LINEAR_ACTUATOR_BRACKET
+    # Length of line attached to the flexor
+    line_length: float = 0.0
+    line_thickness: float = 0.5
+    # By how much is the line permitted to slack. This reduces the effective stroke length
+    line_slack: float = 0.0
 
-    # FIXME: Add a compression spring so the serviceable distances are not as fixed
+    def __post_init__(self):
+        assert self.line_slack <= self.line_length < self.actuator.stroke_length
 
     @property
     def mount_height(self):
         return self.bracket.hole_to_side_ext
 
+    @property
+    def d_open(self):
+        return self.actuator.conn_length + self.actuator.stroke_length + self.line_length - self.line_slack
+    @property
+    def d_closed(self):
+        return self.actuator.conn_length + self.line_length
+
     def open_pos(self) -> Tuple[float, float, float]:
         r, phi, r_ = nhf.geometry.contraction_span_pos_from_radius(
-            d_open=self.actuator.conn_length + self.actuator.stroke_length,
+            d_open=self.d_open,
-            d_closed=self.actuator.conn_length,
+            d_closed=self.d_closed,
             theta=math.radians(self.motion_span),
             r=self.arm_radius,
             smaller=self.pos_smaller,
@@ -376,8 +390,8 @@ class Flexor:
 
         result = math.sqrt(r * r + rp * rp - 2 * r * rp * math.cos(th))
         #result = math.sqrt((r * math.cos(th) - rp) ** 2 + (r * math.sin(th)) ** 2)
-        assert self.actuator.conn_length <= result <= self.actuator.conn_length + self.actuator.stroke_length, \
+        assert self.d_closed -1e-6 <= result <= self.d_open + 1e-6,\
-            f"Illegal length: {result} in {self.actuator.conn_length}+{self.actuator.stroke_length}"
+            f"Illegal length: {result} not in [{self.d_closed}, {self.d_open}]"
         return result
 
 
@@ -393,7 +407,9 @@ class Flexor:
         Adds the necessary mechanical components to this assembly. Does not
         invoke `a.solve()`.
         """
-        pos = (target_length - self.actuator.conn_length) / self.actuator.stroke_length
+        draft = max(0, target_length - self.d_closed - self.line_length)
+        pos = draft / self.actuator.stroke_length
+        line_l = target_length - draft - self.actuator.conn_length
         if tag_prefix:
             tag_prefix = tag_prefix + "_"
         else:
@@ -411,8 +427,6 @@ class Flexor:
             .add(self.bracket.assembly(), name=name_bracket_front)
             .add(self.bolt.assembly(), name=name_bolt_front)
             .add(self.nut.assembly(), name=name_nut_front)
-            .constrain(f"{name_actuator}/front?conn", f"{name_bracket_front}?conn_mid",
-                       "Plane", param=0)
             .constrain(f"{name_bolt_front}?root", f"{name_bracket_front}?conn_top",
                        "Plane", param=0)
             .constrain(f"{name_nut_front}?bot", f"{name_bracket_front}?conn_bot",
@@ -427,6 +441,30 @@ class Flexor:
             .constrain(f"{name_nut_back}?bot", f"{name_bracket_back}?conn_bot",
                        "Plane")
         )
+        if self.line_length == 0.0:
+            a.constrain(
+                f"{name_actuator}/front?conn",
+                f"{name_bracket_front}?conn_mid",
+                "Plane", param=0)
+        else:
+            (
+                a
+                .addS(tension_fibre(
+                    length=line_l,
+                    hole_diam=self.nut.diam_thread,
+                    thickness=self.line_thickness,
+                ), name="fibre", role=Role.CONNECTION)
+                .constrain(
+                    f"{name_actuator}/front?conn",
+                    "fibre?male",
+                    "Plane"
+                )
+                .constrain(
+                    f"{name_bracket_front}?conn_mid",
+                    "fibre?female",
+                    "Plane"
+                )
+            )
         if tag_hole_front:
             a.constrain(tag_hole_front, f"{name_bracket_front}?conn_side", "Plane")
         if tag_hole_back:

nhf/touhou/houjuu_nue/joints.py

@@ -1067,7 +1067,7 @@ class ElbowJoint(Model):
     flip: bool = False
     angle_neutral: float = 30.0
 
-    actuator: Optional[LinearActuator]
+    actuator: Optional[LinearActuator] = None
     flexor: Optional[Flexor] = None
     # Rotates the entire flexor
     flexor_offset_angle: float = 0
@@ -1076,6 +1076,8 @@ class ElbowJoint(Model):
     flexor_mount_angle_child: float = -90
     flexor_pos_smaller: bool = True
     flexor_child_arm_radius: Optional[float] = None
+    flexor_line_length: float = 0.0
+    flexor_line_slack: float = 0.0
 
     def __post_init__(self):
         assert self.child_arm_radius > self.disk_joint.radius_housing
@@ -1087,6 +1089,8 @@ class ElbowJoint(Model):
                 motion_span=self.motion_span,
                 pos_smaller=self.flexor_pos_smaller,
                 arm_radius=self.flexor_child_arm_radius,
+                line_length=self.flexor_line_length,
+                line_slack=self.flexor_line_slack,
             )
 
     def hole_loc_tags(self):

nhf/touhou/houjuu_nue/wing.py

@@ -1291,6 +1291,10 @@ class WingL(WingProfile):
         angle_neutral=30.0,
         flexor_mount_angle_child=170,
         flexor_mount_angle_parent=-30,
+        flexor_line_length=30.0,
+        flexor_line_slack=5.0,
+        #flexor_line_length=0.0,
+        #flexor_line_slack=0.0,
         flexor_offset_angle=15,
         child_lip_extra_length=5.0,
         flexor_child_arm_radius=60.0,