After that failure, I thought maybe making the spring guide pocket a bit wider and seating the spring wire in a solid plug would work. A tweak to the OpenSCAD script produced this, along with slightly larger locating ribs around the battery compartment:
A closer look at the plug spring assembly:
The hole is now slightly larger, distinct from the side of the pocket, and the partition between the pocket and plug (although something of a formality) seats the plug during assembly. The plug started out at 3 mm in diameter, as I intended to try ramming a heated wire into a length of filament. That worked, mmmm, somewhat poorly, so I drilled a hole in a length of filament:
Unfortunately, that whole bodge didn’t work any better than the spring in the first pass at a holder, so I gave up and cast the springs in epoxy. The OpenSCAD code produces a 5 mm diameter hole that should provide a larger epoxy plate with better grip than the 3 mm holes in this picture, but it probably won’t make much difference:
The alert reader will note a complete faceplant: yeah, I forgot to solder the wires into the pins before blobbing the springs in place. Fortunately, the epoxy cures slowly enough that I could:
- Take the picture
- Immediately see the obvious problem
- Ease the music wire springs out just a tidge
- Extract the pins
- Quick-like-a-bunny solder wires to pins
- Insert pins with proper polarity
- Ease springs back in place
I hate it when that happens…
With springs & wires properly in place and the epoxy cured overnight, the pins had considerably better springiness and free motion than before, although they didn’t have quite the range of travel I wanted. I think the spring wire bent slightly on the first push, as the pins never came quite as far out after that.
So this was a qualified success, but not a solid win. Time for round three…
The OpenSCAD source code:
// Holder for Canon NB-5L Li-Ion battery
// Ed Nisley KE4ZNU August 2011
include </home/ed/Thing-O-Matic/lib/MCAD/units.scad>
include </home/ed/Thing-O-Matic/lib/MCAD/boxes.scad>
include </home/ed/Thing-O-Matic/Useful Sizes.scad>
// Layout options
Layout = "Show"; // Case Lid Show Build Fit
//- Extrusion parameters - must match reality!
// Print with +2 shells and 3 solid layers
ThreadThick = 0.33;
ThreadWidth = 2.0 * ThreadThick;
HoleWindage = 0.2;
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
Protrusion = 0.1; // make holes end cleanly
BuildOffset = 3.0; // clearance for build layout
//- Battery dimensions - rationalized from several samples
// Coordinate origin at battery corner by contact plates on bottom surface
BatteryLength = 45.25;
BatteryWidth = 32.17;
BatteryThick = 7.85;
ContactWidth = 2.10;
ContactLength = 4.10;
ContactRecess = 0.85;
ContactOC = 3.18; // center-to-center across contact face
ContactOffset = 4.45; // offset from battery edge
ContactHeight = 3.05; // offset from battery bottom plane
AlignThick = 2.2; // alignment recesses on contact face
AlignDepth = 2.0; // into face
AlignWidth1 = 0.7; // across face at contacts
AlignWidth2 = 2.8; // ... other edge
//- Pin dimensions
PinTipDia = 1.6;
PinTipLength = 10.0;
PinTaperLength = 2.3;
PinShaftDia = 2.4;
PinShaftLength = 6.8;
PinFerruleDia = 3.0;
PinFerruleLength = 2.0;
PinLength = PinTipLength + PinTaperLength + PinShaftLength + PinFerruleLength;
PinHoleOffset = 13.9; // tip to spring hole
ExtendRelax = 1.5 + ContactRecess; // pin extension when no battery is present
ExtendOvertravel = 1.0; // ... beyond engaged position
//- Holder dimensions
GuideRadius = ThreadWidth; // friction fit ridges
GuideOffset = 10;
WallThick = 4*ThreadWidth; // holder sidewalls
BaseThick = IntegerMultiple(6.0,ThreadThick); // bottom of holder to bottom of battery
TopThick = 6*ThreadThick; // top of battery to top of holder
ThumbRadius = 10.0; // thumb opening at end of battery
CornerRadius = 3*ThreadThick; // nice corner rounding
CaseLength = 2*WallThick + PinLength - ExtendRelax + ExtendOvertravel + BatteryLength + GuideRadius;
CaseWidth = 2*WallThick + 2*GuideRadius + BatteryWidth;
CaseThick = BaseThick + BatteryThick + TopThick;
//- XY origin at front left battery corner, Z on platform below that
CaseLengthOffset = -(WallThick + PinLength - ExtendRelax + ExtendOvertravel);
CaseWidthOffset = -(WallThick + GuideRadius);
CaseThickOffset = BaseThick;
LidLength = ExtendRelax - CaseLengthOffset;
//- Spring dimensions
SpringPlugDia = 5.0; // epoxy plug holding spring wire
SpringPlugLength = IntegerMultiple(1.5,ThreadThick);
SpringDia = 0.024 * inch; // music wire spring
SpringTravel = ExtendRelax + ExtendOvertravel;
SpringLength = BaseThick + ContactHeight - SpringPlugLength - 2*ThreadThick;
echo(str("Spring wire from end: ",WallThick + PinLength - PinHoleOffset));
echo(str(" from side: ",WallThick + GuideRadius + ContactOffset));
echo(str("Pin spacing on centers: ",ContactOC));
//----------------------
// 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,
$fn=Sides);
}
module ShowPegGrid(Space = 10.0,Size = 1.0) {
Range = floor(50 / Space);
for (x=[-Range:Range])
for (y=[-Range:Range])
translate([x*Space,y*Space,Size/2])
%cube(Size,center=true);
}
//-------------------
//-- Guides for tighter friction fit
module Guides() {
translate([GuideOffset,-GuideRadius,CaseThickOffset])
PolyCyl(2*GuideRadius,(BatteryThick - Protrusion),4);
translate([GuideOffset,(BatteryWidth + GuideRadius),CaseThickOffset])
PolyCyl(2*GuideRadius,(BatteryThick - Protrusion),4);
translate([(BatteryLength - GuideOffset),-GuideRadius,CaseThickOffset])
PolyCyl(2*GuideRadius,(BatteryThick - Protrusion),4);
translate([(BatteryLength - GuideOffset),(BatteryWidth + GuideRadius),CaseThickOffset])
PolyCyl(2*GuideRadius,(BatteryThick - Protrusion),4);
translate([(BatteryLength + GuideRadius),GuideOffset/2,CaseThickOffset])
PolyCyl(2*GuideRadius,(BatteryThick - Protrusion),4);
translate([(BatteryLength + GuideRadius),(BatteryWidth - GuideOffset/2),CaseThickOffset])
PolyCyl(2*GuideRadius,(BatteryThick - Protrusion),4);
}
//-- Contact pins (holes therefore)
module PinShape() {
PolyPin = false;
union() {
if (PolyPin)
PolyCyl(PinTipDia,(PinTipLength + Protrusion));
else
cylinder(r=(PinTipDia + HoleWindage)/2,h=(PinTipLength + Protrusion),$fn=6);
translate([0,0,PinTipLength])
if (PolyPin)
PolyCyl(PinShaftDia,(PinTaperLength + PinShaftLength + Protrusion));
else
cylinder(r=(PinShaftDia + HoleWindage)/2,
h=(PinTaperLength + PinShaftLength + Protrusion),$fn=6);
translate([0,0,(PinLength - PinFerruleLength)])
if (PolyPin)
PolyCyl(PinFerruleDia,(PinFerruleLength + Protrusion));
else
cylinder(r=(PinFerruleDia + HoleWindage)/2,
h=(PinFerruleLength + Protrusion),$fn=6);
translate([0,0,PinLength])
if (PolyPin)
PolyCyl(PinFerruleDia,PinLength); // very long holes to punch case
else
cylinder(r=(PinFerruleDia + HoleWindage)/2,h=PinLength,$fn=6);
}
}
module PinAssembly() {
translate([ExtendRelax,ContactOffset,CaseThickOffset + ContactHeight]) {
rotate([0,270,0]) {
PinShape(); // pins
translate([0,(2*ContactOC),0])
PinShape();
}
}
translate([-(PinHoleOffset - ExtendRelax + SpringTravel/2 - SpringDia/2 - HoleWindage/2),
ContactOffset,
(CaseThickOffset + ContactHeight - SpringLength/2 - Protrusion)]) {
cube([(SpringTravel + SpringDia/2 + HoleWindage),
PinShaftDia,
(SpringLength + 2*Protrusion)],
center=true); // spring deflection pocket
translate([0,(2*ContactOC),0])
cube([(SpringTravel + SpringDia/2 + HoleWindage),
PinShaftDia,
(SpringLength + 2*Protrusion)],
center=true);
}
translate([-(PinHoleOffset - ExtendRelax),
ContactOffset,
(-Protrusion/2)]) {
PolyCyl(SpringDia,(BaseThick + ContactHeight + Protrusion),4); // spring wire
PolyCyl(SpringPlugDia,(SpringPlugLength + Protrusion)); // wire holder
translate([0,(2*ContactOC),0]) {
PolyCyl(SpringDia,(BaseThick + ContactHeight + Protrusion),4);
PolyCyl(SpringPlugDia,(SpringPlugLength + Protrusion));
}
}
}
//-- Case with origin at battery corner
module Case() {
difference() {
union() {
difference() {
translate([(CaseLength/2 + CaseLengthOffset),
(CaseWidth/2 + CaseWidthOffset),
(CaseThick/2)])
roundedBox([CaseLength,CaseWidth,CaseThick],CornerRadius); // basic case shape
translate([-ExtendOvertravel,-GuideRadius,CaseThickOffset])
cube([(BatteryLength + GuideRadius + ExtendOvertravel),
(BatteryWidth + 2* GuideRadius),
(BatteryThick + Protrusion)]); // battery space
}
Guides();
translate([-ExtendOvertravel,-GuideRadius,BaseThick])
cube([(AlignDepth + ExtendOvertravel),
(AlignWidth1 + GuideRadius),
AlignThick]); // alignment blocks
translate([-ExtendOvertravel,
(BatteryWidth - AlignWidth2),
BaseThick])
cube([(AlignDepth + ExtendOvertravel),
(AlignWidth2 + GuideRadius),
AlignThick]);
}
translate([(-ExtendOvertravel),
(CaseWidthOffset - Protrusion),
(CaseThickOffset + BatteryThick)])
cube([CaseLength,
(CaseWidth + 2*Protrusion),
(TopThick + Protrusion)]); // battery access
translate([(CaseLengthOffset - Protrusion),
(CaseWidthOffset - Protrusion),
(CaseThickOffset + BatteryThick)])
cube([(CaseLength + 2*Protrusion),
(CaseWidth + 2*Protrusion),
(TopThick + Protrusion)]); // battery insertion allowance
translate([(BatteryLength - Protrusion),
(CaseWidth/2 + CaseWidthOffset),
(CaseThickOffset + ThumbRadius)])
rotate([90,0,0])
rotate([0,90,0])
cylinder(r=ThumbRadius,
h=(WallThick + GuideRadius + 2*Protrusion),
$fn=22); // remove thumb notch
PinAssembly();
}
}
module Lid() {
difference() {
translate([0,0,(CaseThick/2 - BaseThick - BatteryThick)])
roundedBox([LidLength,
CaseWidth,CaseThick],CornerRadius);
translate([0,0,-(CaseThick/2)])
cube([(LidLength + 2*Protrusion),
(CaseWidth + 2*Protrusion),
(CaseThick)],center=true);
}
}
//-------------------
// Build it!
ShowPegGrid();
if (Layout == "Case")
Case();
if (Layout == "Lid")
Lid();
if (Layout == "Show") { // reveal pin assembly
difference() {
Case();
translate([(CaseLengthOffset - Protrusion),
(CaseWidthOffset - Protrusion + WallThick + ContactOffset + ContactOC),
(BaseThick + ContactHeight)])
cube([(-CaseLengthOffset + Protrusion),
(CaseWidth + 2*Protrusion),
CaseThick + BaseThick - ContactHeight + Protrusion]);
translate([(CaseLengthOffset - Protrusion),
(CaseWidthOffset - Protrusion),
-Protrusion])
cube([(-CaseLengthOffset + Protrusion),
(WallThick + GuideRadius + ContactOffset + Protrusion),
CaseThick]);
}
translate([ExtendRelax,ContactOffset,CaseThickOffset + ContactHeight]) { // pins
rotate([0,270,0]) {
%PinShape();
// translate([0,(2*ContactOC),0])
// %PinShape();
}
}
}
if (Layout == "Build") {
translate([-(CaseLength/2 + CaseLengthOffset),-(CaseWidthOffset - BuildOffset),0])
Case();
translate([0,(CaseLengthOffset/2 - BuildOffset),0])
rotate([0,0,90])
Lid();
}
if (Layout == "Fit") {
Case();
translate([(-LidLength/2 + ExtendRelax),
(CaseWidth/2 + CaseWidthOffset),
(BaseThick + BatteryThick)])
Lid();
translate([ExtendRelax,ContactOffset,CaseThickOffset + ContactHeight]) { // pins
rotate([0,270,0]) {
%PinShape();
translate([0,(2*ContactOC),0])
%PinShape();
}
}
}
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