// humper: a ring cam, 
// a pulley (flange) drives this cam
//  which drives a 'piston' with a cross pin up&down
//  the cross pin rides on this cam surface
//
// the cam is generated from many tall pie slices
// the height of the slice follows a cosine path
//
//05apr revisited
// the cam is correct now but stairstepped
// if i smooth it by decreasing the pie slice angle
// it appears smoother till zoomed
// is there a better way to generate this cam surface?
// i know i can tilt the surface of each slice
// andlgling from half prev delta to half next delta
// but thats another kind of step, not really smooth
//
//03apr revisited-
// TODO make the ramp smooth
//   there maybe some hints in the 'screw thread ' discussions and libraries of openSCAD
//
green=[0,1,0];
blue=[0,0,1];
bg=[0,.8,.8];

//-------- cam data
camOR=12.4;
camIR=8.1;
camAngle=40;

// each pie slice poly is between 2 chords
//  the chord at inner dia
//  and the chord at the outer dia

// each pie slice poly  has 2 sides
//  which lie on radii

// ***************  funcs to find chords ***********
// the important angle is not the sliceAngle/2 nor the rt angle
// in the half triangle from center to half chord...
//   the important angle is the angle
//    between radius and chord
// i call theta


//-------- pulley
pulleyThx=11;
pulleyRad=21;
//beltClearance = 4;
//humperFlangeThx=8.7;
humperFlangeThx=pulleyThx;
//-------- cam drives saw holder up/down

//function pi()=3.14159265358979323846;
//Deg2Rad = pi() / 180;

// vvv the birdseye pie slice angle ( tall pie slice)
s=10;// slice angle AND loop step size, every N deg

// the cam is generated above and below a central vetrical position
// this centreallized approach is useful in othe code


// vvv these funcs calc the sides of the keystone shape of the pie slice ( birdseye view)
// func theta() rtns the 'other angle' 
//   ( the angle between radius and halfchord )
function theta(sliceAngle) = (90 - sliceAngle/2);

function halfChord(dia,theta) = (dia/2)*cos(theta);

function ctr2halfChord(dia,theta) = (dia/2) * sin(theta);

function chord2circumference(dia,ctr2chord) = (dia/2) - ctr2chord;

t=theta(s);

halfChordID=2*(halfChord(camIR,t));
halfChordOD=2*(halfChord(camOR,t));

c2chordID=ctr2halfChord(camIR*2,t);
c2chordOD=ctr2halfChord(camOR*2,t);

chord2circumferenceID=chord2circumference(camIR*2,c2chordID);

chord2circumferenceOD=chord2circumference(camOR*2,c2chordOD);

// the polygon  ( a keystone shape)
wedgePts = [ 
  [ -halfChordOD,-c2chordOD ],
  [ -halfChordID,-c2chordID ],
  [ +halfChordID,-c2chordID ],
  [ +halfChordOD,-c2chordOD ] 
];
wedgePaths=[[0,1,2,3]];

// the code above solves the base polygon ( a keystone shape)
//  for later extrusion

// the code below makes a cyl-like
// form with an approx. cam top
// I'd like a smooth surface
// but this technique gets smooth
// with infinite pie-slices

// the cam drives a horz dowel pin and thus a central shaft
// the dowel pin si constrained in a vertical pill shape slot in a relatively stationary sleeve ( between cam and shaft)
//
//-------- keySlot limits vert motion
// vvv 0.57735026919 *(12.4+12.4) = 14.3182866759
keyTravel=(tan(camAngle)*(camOR+camOR));
// keyHalfTravel is 7.159143338
keyHalfTravel=(tan(camAngle)*camOR);


xtra=0.1; // avoid tissue skins after subtracts
module humper(keyHalfTravel,wedgePts, wedgePaths,s){
// 1st 180 deg of cam rises from minH
for( i = [0: s: 180-s]){
  rotate([0,0,i]){
    dH=cos(i)*keyHalfTravel;
    thisH = keyHalfTravel + dH;
    linear_extrude(height = thisH, center = false){
      polygon(wedgePts,wedgePaths,2);
    }
  }
}
// 2nd 180 deg loop drops down to minH
for( i = [180+s: s : 360-s ]){
  rotate([0,0,i]){
    dH=cos(i)*keyHalfTravel;
    thisH = keyHalfTravel + dH;
    linear_extrude(height = thisH, center = false){
      polygon(wedgePts,wedgePaths,2);
    }
  }
}
}

// the cam sits on top of of a GT2 pulley
// possible the cam is the hub but that seems like anig horz setscrew would tilt the cam, or excentric it
color(bg)
union(){
  humper(keyHalfTravel,wedgePts,wedgePaths,s);

  translate([0,0,-(humperFlangeThx/2)]){
    difference(){
      cylinder(humperFlangeThx,pulleyRad,pulleyRad,center=true);
      cylinder(humperFlangeThx+xtra,camIR,camIR,center=true);
    }
  }    
}