The first pass at a holder for a Canon NB-5L battery didn’t quite work, but the failure was instructive. The overall layout was fine; the battery fit well, it’s just that the pins and springs didn’t function properly.
I thought a simple straight music wire spring pushed into a hole with a pocket to limit the pin travel would suffice. Watching it build showed that the pocket came out too small and the spring hole was almost completely closed, despite a bit of HoleWindage.
Here’s a closer look at the spring arrangement, with a pocket at the bottom for an epoxy blob after it became obvious the ABS couldn’t properly anchor the pin.
Drilling out the holes to allow free pin movement ended up with #52 for the tip, #40 for the shaft, and #31 for the ferrule at the end; choose for an easy slip fit.
I used 0.024 inch (0.6 mm) music wire, which fit neatly into the pin’s inspection hole. Drilling that (#73 drill) into the nearly closed hole through the bottom showed that things weren’t working well: far too much resistance along what should be a half-open channel.
With the pin in place and a stub of wire pushed upward into the pin, the pins moved very stiffly and tended to not return to their rest position. Minus the spring wire, they slid freely.
After a bit of this and that, I tried 0.020 music wire, which didn’t have enough return force at all.
The end of the spring wire moved around a lot more than I think it should have, gradually turning the hole into an oval. I drilled two pockets in the bottom (and changed the solid model to match what you see above) and cast a dab of epoxy into each hole; that solved the moving-around problem, but the pins were still too stiff.
The weird orange color comes from a few layers of Safety Orange filament that melded into white in mid-flight. No reason to use fancy filament on a prototype, methinks; that’s what was in place when I started.
But I glued the cap on anyway to see if the pins would work well enough to run some early battery tests. This is what it looked like before gluing the cap:
The Powerpole connectors came from one of those packs, with the wires soldered into the ends of the pins so as to not block the inspection holes that I’m using for the music wire springs.
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
//- Spring dimensions
ExtendRelax = 1.5 + ContactRecess; // pin extension when no battery is present
ExtendOvertravel = 1.0; // ... beyond engaged position
SpringDia = 0.024 * inch; // music wire spring
SpringTravel = ExtendRelax + ExtendOvertravel;
SpringLength = 4.0 + PinShaftDia/2; // free length below pin centerline
//- 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;
SpringPlugDia = 3.0; // filament snippet holding spring wire
SpringPlugLength = IntegerMultiple(1.0,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]) { // pins
rotate([0,270,0]) {
PinShape();
translate([0,(2*ContactOC),0])
PinShape();
}
}
translate([-(PinHoleOffset - ExtendRelax + SpringTravel/2),
ContactOffset,
(CaseThickOffset + ContactHeight - SpringLength/2 + Protrusion/2)]) {
cube([SpringTravel,
(2*SpringDia),
(SpringLength + Protrusion)],
center=true); // spring deflection pocket
translate([0,(2*ContactOC),0])
cube([SpringTravel,
(2*SpringDia),
(SpringLength + Protrusion)],
center=true);
}
translate([-(PinHoleOffset - ExtendRelax),
ContactOffset,
(-Protrusion/2)]) {
PolyCyl(SpringDia,(BaseThick + ContactHeight + Protrusion)); // spring wire
PolyCyl(SpringPlugDia,(SpringPlugLength + Protrusion)); // wire holder
translate([0,(2*ContactOC),0]) {
PolyCyl(SpringDia,(BaseThick + ContactHeight + Protrusion));
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();
}
}
}
The Smell of Molten Projects in the Morning 
Comments
3 responses to “NB-5L Holder: Internal Springs”
[…] The Smell of Molten Projects in the Morning « NB-5L Holder: Internal Springs […]
[…] that failure, I thought maybe making the spring guide pocket a bit wider and seating the spring wire in a solid […]
[…] twice failed to make music-wire springs work, I rummaged around in the Big Box o’ Small Springs […]