Class: GearProfile

Inherits:
Shape
  • Object
show all
Defined in:
lib/rcad/gears.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods inherited from Shape

#*, #+, #-, #align, #back, #bbox, #bottom, #center, #cx, #cy, #cz, #extrude, #front, #left, #maxx, #maxy, #maxz, #minx, #miny, #minz, #mirror, #mirror_x, #mirror_y, #mirror_z, #move, #move_x, #move_y, #move_z, #revolve, #right, #rot_x, #rot_y, #rot_z, #rotate, #scale, #scale_x, #scale_y, #scale_z, #top, #transform, #xcenter, #xsize, #ycenter, #ysize, #zcenter, #zsize, #~@

Constructor Details

#initialize(pitch_dia, module_ = 4, p_angle = 20) ⇒ GearProfile

pitch_dia - effective diameter of gear

(not the same as outer diameter)

module_ - ratio of pitch diameter to number of teeth (basically the

arc length of the tooth spacing)

p_angle - pressure angle.

it seems 20 deg angle is better for torque, but
14.5 deg angle is better for backlash.



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# File 'lib/rcad/gears.rb', line 22

def initialize(pitch_dia, module_=4, p_angle=20)
  # converting everything to floats ensures that floating point
  # division will be performed later
  @pitch_dia = pitch_dia.to_f
  @module_ = module_.to_f
  @p_angle = p_angle.to_f

  if @pitch_dia % @module_ != 0
    raise ArgumentError, "non-integer number of teeth!"
  end
end

Instance Attribute Details

#module_ ⇒ Object (readonly)

Returns the value of attribute module_.



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# File 'lib/rcad/gears.rb', line 13

def module_
  @module_
end

#p_angle ⇒ Object (readonly)

Returns the value of attribute p_angle.



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# File 'lib/rcad/gears.rb', line 13

def p_angle
  @p_angle
end

#pitch_dia ⇒ Object (readonly)

Returns the value of attribute pitch_dia.



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# File 'lib/rcad/gears.rb', line 13

def pitch_dia
  @pitch_dia
end

Instance Method Details

#addendum ⇒ Object 



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# File 'lib/rcad/gears.rb', line 46

def addendum
  1.0 / diametrical_pitch
end

#circular_pitch ⇒ Object 



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# File 'lib/rcad/gears.rb', line 42

def circular_pitch
  Math::PI / diametrical_pitch
end

#dedendum ⇒ Object 



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# File 'lib/rcad/gears.rb', line 58

def dedendum
  whole_depth - addendum
end

#diametrical_pitch ⇒ Object 



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# File 'lib/rcad/gears.rb', line 38

def diametrical_pitch
  1.0 / module_
end

#num_teeth ⇒ Object 



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# File 'lib/rcad/gears.rb', line 34

def num_teeth
  (pitch_dia / module_).to_int
end

#outer_dia ⇒ Object 



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# File 'lib/rcad/gears.rb', line 50

def outer_dia
  pitch_dia + 2.0 * addendum
end

#render ⇒ Object 



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# File 'lib/rcad/gears.rb', line 71

def render
  # tooth thickness at tooth tip (TODO: is this correct?)
  tooth_tip_thickness = tooth_thickness - addendum * Math::sin(p_angle)

  # half of thickness at root/center/tip in degrees
  half_t_root_angle = Math::atan(tooth_thickness / 2 / (root_dia / 2))
  half_t_angle = Math::atan(tooth_thickness / 2 / (pitch_dia / 2))
  half_t_tip_angle = Math::atan(tooth_tip_thickness / 2 / (outer_dia / 2))

  root_r = root_dia / 2
  pitch_r = pitch_dia / 2
  outer_r = outer_dia / 2

  points = []
  (1..num_teeth).each do |i|
    angle = (2 * Math::PI / num_teeth) * i
    points << to_polar(root_r, angle - half_t_root_angle)
    points << to_polar(pitch_r, angle - half_t_angle)
    points << to_polar(outer_r, angle - half_t_tip_angle)
    points << to_polar(outer_r, angle + half_t_tip_angle)
    points << to_polar(pitch_r, angle + half_t_angle)
    points << to_polar(root_r, angle + half_t_root_angle)
  end

  polygon(points)
end

#root_dia ⇒ Object 



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# File 'lib/rcad/gears.rb', line 62

def root_dia
  pitch_dia - 2 * dedendum
end

#tooth_thickness ⇒ Object

tooth thickness at pitch dia



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# File 'lib/rcad/gears.rb', line 67

def tooth_thickness
  Math::PI / 2.0 / diametrical_pitch
end

#whole_depth ⇒ Object 



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# File 'lib/rcad/gears.rb', line 54

def whole_depth
  module_ < 1.25 ? (2.4 * module_) : (2.25 * module_)
end