Wheelchair Brake Mods.scad

// Pride wheelchair brake lever mods
// Ed Nisley KE4ZNU 2020-11

/* [Layout options] */

Layout = "Build";					// [Build, Show, Fit, TabCap, Handle, Knob, Support]

// Hold up the knob's inside
Support = true;

/* [Extrusion parameters] */

/* [Hidden] */

ThreadThick = 0.25;
ThreadWidth = 0.40;

HoleWindage = 0.2;

function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
function IntegerLessMultiple(Size,Unit) = Unit * floor(Size / Unit);

Protrusion = 0.1;      // make holes end cleanly

inch = 25.4;

ID = 0;
OD = 1;
LENGTH = 2;

//----------------------
// Useful routines

module PolyCyl(Dia,Height,ForceSides=0) {      // based on nophead's polyholes

  Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);

  FixDia = Dia / cos(180/Sides);

  cylinder(r=(FixDia + HoleWindage)/2,h=Height,$fn=Sides);
}



//* [Basic dimensions] */

WallThick = 4.0;                                  // min wall thickness

Screw = [3.0,5.5,20.0];                           // thread, head, length under head
Insert = [3.0,4.1,8.0];                           // thread, knurl, length

//----------------------
// Brake tab cap

BrakeTab = [15,21,3.1];                           // length to wheel, width, thickness
BrakeTabSagitta = 8.0;                            // height of curved endcap

CapOAL = [BrakeTab.y + 2*WallThick,BrakeTab.y + 2*WallThick,BrakeTab.z + 2*WallThick];

module TabCap() {

  difference() {
    rotate(180/8)
      cylinder(d=CapOAL.y,h=CapOAL.z,center=true,$fn=8);
    translate([BrakeTab.x/2,0,0])
      cube(BrakeTab,center=true);
    rotate(180/8)
      cylinder(d=BrakeTab.y/cos(180/8),h=BrakeTab.z,center=true,$fn=8);
  }
}

//----------------------
// Brake lever handle
// Soft covering with rounded sides that we square off for simplicity

HandleRibs = [15,34,14];            // ignoring slight taper from end
HandleCore = [50.0,24.0,12.0];      // straight section of lever to top of ribs
HandleTipWidth = 30.0;              // ignoring actual sector height

module Handle() {

  union() {
    hull() {
      rotate(180/8)
        cylinder(d=HandleTipWidth/cos(180/8),h=HandleCore.z,center=true,$fn=8);
      translate([-HandleCore.x/2,0,0])
        cube(HandleCore,center=true);
    }
    translate([-(3*HandleCore.x/2 - Protrusion),0,0])         // extend base for ball trimming
      cube(HandleCore,center=true);
    translate([-HandleRibs.x/2,0,0])
      cube(HandleRibs,center=true);
  }

}

//----------------------
// Support structure for handle cavity inside knob
// Totally ad-hoc tweakage
// Remember it's lying on its side to match the handle

NumRibs = 2 + 1;          // must be odd
RibSpace = floor(HandleCore.z/(NumRibs + 1));

module KnobSupport() {

  color("Yellow") {              // support overlaps in the middle
    render(convexity=3)
      intersection() {
        for (k=[-1,1])
          translate([0,k*ThreadThick,0])         // shrink inward to break adhesion
            Handle();

        translate([(HandleCore.x - HandleRibs.x)/2 - HandleCore.x - Protrusion,0,0])
          cube([HandleCore.x - HandleRibs.x,HandleRibs.y,HandleCore.z],center=true);

        union()
          for (k=[-floor(NumRibs/2):floor(NumRibs/2)])
            translate([0,0,k* RibSpace])
              cube([2*HandleCore.x,HandleRibs.y,2*ThreadWidth],center=true);
      }

    translate([(HandleCore.x - HandleRibs.x)/2 - HandleCore.x,0,0])
      cube([HandleCore.x - HandleRibs.x,4*ThreadWidth,NumRibs*RibSpace],center=true);
  }
}

//----------------------
// Brake handle knob
// Largely built with magic numbers
// Includes support because it's not really optional

KnobOD = 55.0;
KnobOffset = HandleRibs.x/1;

KnobSides = 2*4*3;

module Knob() {

  difference() {
    hull() {
      resize([0,HandleRibs.y + 4*WallThick,HandleCore.x + HandleTipWidth/2 + WallThick])
        sphere(d=KnobOD,$fn=KnobSides);
    }

    translate([0,0,KnobOffset])
      rotate([0,-90,0])
        Handle();

    for (i=[-1,1],k=[-1,1])
      translate([i*KnobOD/4,0,k*KnobOD/4]) {
        rotate([90,0,0])
          PolyCyl(Insert[OD],1.5*Insert[LENGTH],6);
        translate([0,-Screw[LENGTH]/2,0])
          rotate([-90,0,0])
            PolyCyl(Screw[ID],KnobOD,6);
        translate([0,Screw[LENGTH] - Insert[LENGTH],0])
          rotate([-90,0,0])
            PolyCyl(Screw[OD],KnobOD,6);
      }
  }

  if (Support)
    translate([0,0,KnobOffset])
      rotate([0,-90,0])
        KnobSupport();

}

//----------------------
// Lash it together

if (Layout == "TabCap") {
  TabCap();
}

if (Layout == "Handle") {
  Handle();
}

if (Layout == "Support") {
  KnobSupport();
}

if (Layout == "Knob") {
  Knob();
}

if (Layout == "Show") {
  translate([60,0,0])
      TabCap();
    Knob();
}

if (Layout == "Fit") {
  translate([60,0,0])
    difference() {
      TabCap();
      translate([0,0,CapOAL.z/2])
        cube(CapOAL,center=true);
    }
  difference() {
    Knob();
    translate([KnobOD + KnobOD/4,0*KnobOD,0])
      cube(2*KnobOD,center=true);
    translate([-KnobOD,-KnobOD,0])
      cube(2*KnobOD,center=true);
  }
}

if (Layout == "Build") {
  translate([KnobOD/2,0,(CapOAL.y*cos(180/8))/2])
    rotate([0,-90,90])
      TabCap();

  for (j=[-1,1])
    translate([0,-j*0.75*HandleCore.x,0])
      difference() {
        rotate([j*90,0,0])
          Knob();
        translate([0,0,-KnobOD])
          cube(2*KnobOD,center=true);
      }

}

More details on my blog at https://wp.me/poZKh-9Et