feat: Torsion joint
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229
nhf/joints.py
229
nhf/joints.py
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@ -1,5 +1,7 @@
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import cadquery as Cq
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from dataclasses import dataclass
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import math
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import cadquery as Cq
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import nhf.springs as NS
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def hirth_joint(radius=60,
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radius_inner=40,
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@ -174,54 +176,205 @@ def comma_joint(radius=30,
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result.faces('>X').tag("tail_end")
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return result
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def torsion_spring(radius=12,
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height=20,
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thickness=2,
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omega=90,
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tail_length=25):
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"""
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Produces a torsion spring with abridged geometry since sweep is very slow in
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cq-editor.
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"""
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base = (
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Cq.Workplane('XY')
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.cylinder(height=height, radius=radius,
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centered=(True, True, False))
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)
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base.faces(">Z").tag("mate_top")
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base.faces("<Z").tag("mate_bottom")
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result = (
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base
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.cylinder(height=height, radius=radius - thickness, combine='s',
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centered=(True, True, True))
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.transformed(
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offset=(0, radius-thickness),
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rotate=(0, 0, 0))
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.box(length=tail_length, width=thickness, height=thickness, centered=False)
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.copyWorkplane(Cq.Workplane('XY'))
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.transformed(
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offset=(0, 0, height - thickness),
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rotate=(0, 0, omega))
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.center(-tail_length, radius-thickness)
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.box(length=tail_length, width=thickness, height=thickness, centered=False)
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)
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return result
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def comma_assembly():
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joint1 = comma_joint()
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joint2 = comma_joint()
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spring = torsion_spring()
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spring = NS.torsion_spring()
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result = (
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Cq.Assembly()
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.add(joint1, name="joint1", color=Cq.Color(0.8,0.8,0.5,0.3))
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.add(joint2, name="joint2", color=Cq.Color(0.8,0.8,0.5,0.3))
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.add(spring, name="spring", color=Cq.Color(0.5,0.5,0.5,1))
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.constrain("joint1?serrated", "spring?mate_bottom", "Plane")
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.constrain("joint2?serrated", "spring?mate_top", "Plane")
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.constrain("joint1?serrated", "spring?bot", "Plane")
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.constrain("joint2?serrated", "spring?top", "Plane")
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.constrain("joint1?tail", "FixedAxis", (1, 0, 0))
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.constrain("joint2?tail", "FixedAxis", (-1, 0, 0))
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.solve()
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)
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return result
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@dataclass(frozen=True)
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class TorsionJoint:
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"""
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This jonit consists of a rider puck on a track puck. IT is best suited if
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the radius has to be small and vertical space is abundant.
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"""
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# Radius limit for rotating components
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radius = 40
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disk_height = 10
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radius_spring = 15
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radius_axle = 10
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# Offset of the spring hole w.r.t. surface
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spring_hole_depth = 4
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# Also used for the height of the hole for the spring
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spring_thickness = 2
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spring_height = 15
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spring_tail_length = 40
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groove_radius_outer = 35
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groove_radius_inner = 20
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groove_depth = 5
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rider_gap = 2
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n_slots = 8
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right_handed: bool = False
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def __post_init__(self):
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assert self.disk_height > self.spring_hole_depth
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assert self.radius > self.groove_radius_outer
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assert self.groove_radius_outer > self.groove_radius_inner
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assert self.groove_radius_inner > self.radius_spring
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assert self.spring_height > self.groove_depth, "Groove is too deep"
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@property
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def total_height(self):
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return 2 * self.disk_height + self.spring_height
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@property
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def _radius_spring_internal(self):
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return self.radius_spring - self.spring_thickness
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def _slot_polygon(self, flip: bool=False):
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r1 = self.radius_spring - self.spring_thickness
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r2 = self.radius_spring
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flip = flip != self.right_handed
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if flip:
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r1 = -r1
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r2 = -r2
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return [
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(0, r2),
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(self.spring_tail_length, r2),
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(self.spring_tail_length, r1),
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(0, r1),
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]
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def _directrix(self, height, theta=0):
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c, s = math.cos(theta), math.sin(theta)
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r2 = self.radius_spring
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l = self.spring_tail_length
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if self.right_handed:
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r2 = -r2
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# This is (0, r2) and (l, r2) transformed by rotation matrix
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# [[c, s], [-s, c]]
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return [
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(s * r2, -s * l + c * r2, height),
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(c * l + s * r2, -s * l + c * r2, height),
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]
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def spring(self):
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return NS.torsion_spring(
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radius=self.radius_spring,
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height=self.spring_height,
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thickness=self.spring_thickness,
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tail_length=self.spring_tail_length,
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)
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def track(self):
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groove_profile = (
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Cq.Sketch()
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.circle(self.radius)
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.circle(self.groove_radius_outer, mode='s')
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.circle(self.groove_radius_inner, mode='a')
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.circle(self.radius_spring, mode='s')
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)
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spring_hole_profile = (
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Cq.Sketch()
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.circle(self.radius)
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.polygon(self._slot_polygon(flip=False), mode='s')
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.circle(self.radius_spring, mode='s')
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)
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result = (
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Cq.Workplane('XY')
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.cylinder(radius=self.radius, height=self.disk_height)
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.faces('>Z')
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.tag("spring")
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.placeSketch(spring_hole_profile)
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.extrude(self.spring_thickness)
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# If the spring hole profile is not simply connected, this workplane
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# will have to be created from the `spring-mate` face.
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.faces('>Z')
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.placeSketch(groove_profile)
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.extrude(self.groove_depth)
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.faces('>Z')
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.hole(self.radius_axle)
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)
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# Insert directrix`
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result.polyline(self._directrix(self.disk_height),
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forConstruction=True).tag("directrix")
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return result
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def rider(self):
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def slot(loc):
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wire = Cq.Wire.makePolygon(self._slot_polygon(flip=False))
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face = Cq.Face.makeFromWires(wire)
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return face.located(loc)
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wall_profile = (
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Cq.Sketch()
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.circle(self.radius, mode='a')
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.circle(self.radius_spring, mode='s')
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.parray(
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r=0,
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a1=0,
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da=360,
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n=self.n_slots)
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.each(slot, mode='s')
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#.circle(self._radius_wall, mode='a')
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)
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contact_profile = (
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Cq.Sketch()
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.circle(self.groove_radius_outer, mode='a')
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.circle(self.groove_radius_inner, mode='s')
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#.circle(self._radius_wall, mode='a')
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.parray(
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r=0,
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a1=0,
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da=360,
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n=self.n_slots)
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.each(slot, mode='s')
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)
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middle_height = self.spring_height - self.groove_depth - self.rider_gap
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result = (
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Cq.Workplane('XY')
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.cylinder(radius=self.radius, height=self.disk_height)
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.faces('>Z')
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.tag("spring")
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.placeSketch(wall_profile)
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.extrude(middle_height)
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# The top face might not be in one piece.
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#.faces('>Z')
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.workplane(offset=middle_height)
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.placeSketch(contact_profile)
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.extrude(self.groove_depth + self.rider_gap)
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.faces(tag="spring")
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.circle(self._radius_spring_internal)
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.extrude(self.spring_height)
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.faces('>Z')
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.hole(self.radius_axle)
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)
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for i in range(self.n_slots):
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theta = 2 * math.pi * i / self.n_slots
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result.polyline(self._directrix(self.disk_height, theta),
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forConstruction=True).tag(f"directrix{i}")
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return result
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def rider_track_assembly(self):
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rider = self.rider()
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track = self.track()
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spring = self.spring()
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result = (
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Cq.Assembly()
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.add(spring, name="spring", color=Cq.Color(0.5,0.5,0.5,1))
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.add(track, name="track", color=Cq.Color(0.5,0.5,0.8,0.3))
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.constrain("track?spring", "spring?top", "Plane")
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.add(rider, name="rider", color=Cq.Color(0.8,0.8,0.5,0.3))
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.constrain("rider?spring", "spring?bot", "Plane")
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.constrain("track?directrix", "spring?directrix_bot", "Axis")
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.constrain("rider?directrix0", "spring?directrix_top", "Axis")
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.solve()
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)
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return result
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@ -0,0 +1,42 @@
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import math
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import cadquery as Cq
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def torsion_spring(radius=12,
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height=20,
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thickness=2,
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omega=90,
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tail_length=25):
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"""
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Produces a torsion spring with abridged geometry since sweep is very slow in
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cq-editor.
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"""
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base = (
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Cq.Workplane('XY')
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.cylinder(height=height, radius=radius,
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centered=(True, True, False))
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)
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base.faces(">Z").tag("top")
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base.faces("<Z").tag("bot")
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result = (
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base
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.cylinder(height=height, radius=radius - thickness, combine='s',
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centered=(True, True, True))
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.transformed(
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offset=(0, radius-thickness),
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rotate=(0, 0, 0))
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.box(length=tail_length, width=thickness, height=thickness, centered=False)
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.copyWorkplane(Cq.Workplane('XY'))
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.transformed(
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offset=(0, 0, height - thickness),
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rotate=(0, 0, omega))
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.center(-tail_length, radius-thickness)
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.box(length=tail_length, width=thickness, height=thickness, centered=False)
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)
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result.polyline([(0, radius, 0), (tail_length, radius, 0)],
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forConstruction=True).tag("directrix_bot")
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c, s = math.cos(omega * math.pi / 180), math.sin(omega * math.pi / 180)
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result.polyline([
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(s * tail_length, c * radius - s * tail_length, height),
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(c * tail_length + s * radius, c * radius - s * tail_length, height)],
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forConstruction=True).tag("directrix_top")
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return result
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@ -15,6 +15,11 @@ class TestJoints(unittest.TestCase):
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nhf.joints.hirth_assembly()
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def test_joints_comma_assembly(self):
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nhf.joints.comma_assembly()
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def test_torsion_joint(self):
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j = nhf.joints.TorsionJoint()
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assembly = j.rider_track_assembly()
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bbox = assembly.toCompound().BoundingBox()
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self.assertAlmostEqual(bbox.zlen, j.total_height)
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class TestHandle(unittest.TestCase):
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