Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Having acquired a bunch of cheap batteries from the usual eBay suppliers for my new Canon SX230HS pocket camera, it’d be nice to measure their actual (and undoubtedly pathetic) capacity, which implies the need for a holder to make firm contact with the terminals. Sounds like a 3D printer might come in handy for that, doesn’t it?
The first step: measure the dimensions of actual batteries:
NB-5L Battery Dimensions
The terminals lie on what looks to be hard 1/8 inch centers, which must be pure coincidence. They’re recessed anywhere from 0.75 mm to 1.0 mm, depending on who made the thing, into the battery’s endplate.
The Canon charger has three spring-loaded bent-wire contacts, arranged so the (-) terminal touches first as the battery slides into the holder, then (+), and finally the thermistor (T), with about 0.5 mm between each pair. That spring loading provides enough force to hold the battery in the charger.
FWIW, the thermistor is 7.5 kΩ w.r.t. (-) at room temperature.
The plan so far: use three big old gold-plated terminal pins as contacts, with flexible wires to a PowerPole connector that matches the battery tester. Cross-drill the pins to fit music wire lever springs, because the contact spacing is smaller than the smallest coil springs in the Big Box o’ Little Springs. I only need two terminals, so maybe I can force-fit a pair of small coil springs in there, which would be nice.
For Tux pix, one should start with Larry Ewing’s drawings; I used the EPS version to get a scalable vector drawing. Run it through The GIMP, close the outline at the flippers, fill with black, save as PNG. Then import into Inkscape, trace the outline, and something like this pops out:
Tux Outline
The reason for using Inkscape is that OpenSCAD imports a very limited subset of all possible DXF files and, while Inkscape can (with some care) produce a DXF format that OpenSCAD can import, somehow the shape lacked interior fill. Sean took a slightly different approach with the same tools and managed to create a useful DXF file that produced this chunk o’ bits:
Tux Slab – solid model
The DXF import still didn’t work dependably, so I exported the Tux Slab from OpenSCAD to an STL file; if you want to extrude a solid Tux, that’s probably the way to go. Importing the STL in the next steps worked fine.
The Parametric Cookie Cutter by nateoostendorp creates thin cutter walls by subtracting a linear dimension from the X- and Y-axis extents of the shape. Unfortunately, Tux has crazy flipper feet that didn’t respond well to that; the walls developed gaps at the inflection points from self-intersections.
So I started from scratch with a Minkowski sum, which in this case amounts to rubbing a cylinder all over the Tux shape, then intersecting the resulting mega-penguin-post with a slab of the appropriate thickness sitting on the Z=0 plane. The Minkowski enlarges the XY outline by the cylinder’s radius and the Z thickness by twice the cylinder’s height, which I picked to be grossly excessive. Three Minkowskis produce the lip, wall, and tip of the cutter, which then stack up with a Tux-shaped hole subtracted from their midst:
Tux Cookie Cutter – solid model
The thicknesses and heights all derive directly from the extrusion parameters used to print the thing, because there’s not much room for roundoff. The middle section (the wall) is four threads wide, but Skeinforge divides the interior pair of threads into shorter sections with breakpoints at each sharp corner. The cutter section (the lip) is one thread wide, because I couldn’t get a good result with two threads.
The OpenSCAD preview has trouble with the Minkowski result and produces weird rendering glitches, but the CGAL model comes through fine. Note that Tux now has the opposite chirality, a gross oversight that became obvious only after the third cutter emerged from the Basement Laboratory. Here’s the second cutter:
Tux Cutter – reversed
Each cutter takes about 35 minutes to build, so I boiled the highlights down into a thrilling 6 minute movie.
The OpenSCAD source code, into which you can substitute your very own STL shape file:
// Tux cookie cutter using Minkowski sum
// Ed Nisley KE4ZNU - Sept 2011
//- Extrusion parameters - must match reality!
ThreadThick = 0.33;
ThreadWidth = 2.0 * ThreadThick;
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
MaxSize = 110; // larger than any possible dimension ...
//- Cookie cutter parameters
Size = 100;
TipHeight = IntegerMultiple(8,ThreadThick);
TipThick = 1*ThreadWidth;
WallHeight = IntegerMultiple(7,ThreadThick);
WallThick = 4*ThreadWidth;
LipHeight = IntegerMultiple(1.5,ThreadWidth);
LipThick = IntegerMultiple(5,ThreadWidth);
//- Wrapper for the shape of your choice
module Shape(Size) {
Tux(Size);
}
//- A solid slab of Tux goodness in simple STL format
// Choose magic values to:
// center it in XY
// reversed across Y axis (prints with handle on bottom)
// bottom on Z=0
// make it MaxSize from head to feet
module Tux(Scale) {
STLscale = 250;
scale(Scale/STLscale)
translate([105,-145,0])
scale([-1,1,24])
import_stl(
file = "/mnt/bulkdata/Project Files/Thing-O-Matic/Tux Cookie Cutter/Tux Plate.stl",
convexity=5);
}
//- Given a Shape(), return enlarged slab of given thickness
module EnlargeSlab(Scale, WallThick, SlabThick) {
intersection() {
translate([0,0,SlabThick/2])
cube([MaxSize,MaxSize,SlabThick],center=true);
minkowski() {
Shape(Scale);
cylinder(r=WallThick,h=MaxSize);
}
}
}
//- Put peg grid on build surface
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);
}
//- Build it
ShowPegGrid();
//cube(5);
difference() {
union() {
translate([0,0,(WallHeight + LipHeight)])
EnlargeSlab(Size,TipThick,TipHeight);
translate([0,0,LipHeight])
EnlargeSlab(Size,WallThick,WallHeight);
EnlargeSlab(Size,LipThick,LipHeight);
}
Shape(Size); // punch out cookie hole
}
The wheel fits the shaft with a 4-40 setscrew to hold it in place. The post has 4-40 mounting holes for one of those optical switches, plus a big hole for the wiring. The solid models look about like you’d expect:
Wheel and post solid model
I located the post’s holes on the baseplate with a spindly pair of transfer punches, after transferring the wheel’s centerline by eyeballometric guesstimation:
Locating holes with transfer punches
Then aligned the baseplate on the Sherline, located the holes, and drilled ’em with manual CNC to get the proper spacing:
Drilling opto switch post holes
And then it went together quite smoothly:
Dyno with sync wheel
What’s really nice about 3D printing is you can build stuff like this without too much fuss & bother: figure out the solid model, walk gingerly through the software minefield, and (usually) assemble the parts later that day.
A bit of wiring to power the LED and pull up the phototransistor should do the trick.
The OpenSCAD code, including a few tweaks that rationalize spacings and sizes and suchlike:
My first pass at the NEMA 17 motor mount bracket used additive modeling, glomming together several blocks made from cube primitives:
The motor mounting plate, less five holes
Two side struts to stiffen the motor plate
The baseplate, minus two mounting holes
Makes perfect sense to me; perhaps I’m an additive kind of guy. That produced an OpenSCAD model with positive surfaces for the various parts and negative surfaces inside the holes:
NEMA 17 Mount – additive model
Compile that through CGAL, export as STL, inhale into RepG 25, and you (well, I) get what looks to be a fine object in the preview pane:
NEMA 17 RepG preview – additive
Then run it through Skeinforge 40, which emits a flurry of messages along these lines:
[19:11:08] Warning, the triangle mesh slice intersects itself in getLoopsFromCorrectMesh in triangle_mesh.
[19:11:08] Something will still be printed, but there is no guarantee that it will be the correct shape.
[19:11:08] Once the gcode is saved, you should check over the layer with a z of:
[19:11:09] 0.165
The usual searching suggested that sometimes Skeinforge has problems with coincident surfaces, such as between the motor mount plate and the struts and the base, or coincident edges where two blocks abut. Judging from the messages, the problem ran all the way to the top of the struts. Oddly, Skeinview didn’t show any problems, so the G-Code was (presumably) OK.
Error messages tend to make me twitchy, though. I modified the OpenSCAD code to extend the struts 0.1 mm inside the base and ran that model through the software stack, which produced not a single complaint about anything, anywhere.
Success!
However, painful experience has caused me to review the G-Code for every single object with the Skeinlayer plugin, which, right on cue, revealed this interesting anomaly:
NEMA 17 Mount – Skeinview – Bad gcode
That happened for every layer in the square motor mount plate: the lower right corner is fine, the upper left seems to be the negative of the actual solid model. The holes are filled, the plate is empty. The Skirt outline ignores the smaller holes, goes around the large one, and continues on its merry way.
I putzed around for a while and discovered that the failure seems acutely sensitive to the side strut thickness. Yeah, like that makes any sense.
Any variations along those lines that I tried generated either:
A flurry of mesh error messages, with seemingly good G-Code
No error messages whatsoever, with totally bogus G-Code
Running the STL files through netfabb Cloud Service produced the same diagnostic for both:
Number of holes: 3
Number of shells: 2
Mesh is not manifold and oriented.
We unfortunately have not yet enough experience with the occuring server loads, that we can securely enable shell merging at the moment.
However, the repaired STL files produce correct G-Code: evidently OpenSCAD spits out bogus STL data. The fact that RepG/SF treats the two files differently suggests improved diagnostics would be in order, but that’s in the nature of fine tuning.
So I junked the additive model and went subtractive, chewing the recesses out of one huge block:
NEMA 17 Stepper Mount – solid model
That worked:
Number of holes: 0
Number of shells: 1
Mesh is manifold and oriented.
I like processes that don’t emit error messages or result in mysterious failures, although it’s not obvious that subtractive modeling will always produce correct results. Heck, I’m not sure I can think in terms of negative volumes all that well.
The OpenSCAD code for the additive model, with a highlight on the conditional that will trigger the two errors:
OpenSCAD depends on CGAL for all the 3D heavy lifting, which puts any STL export problems further upstream. I suppose I could open Yet Another RepG ticket to get better diagnostics, but the others haven’t gotten much attention so far and I suppose it’s not really their problem anyway.
I’d waited for a few days for the silicone to cure, then put the clamps back in their home. When I went to use them, the pads were firmly affixed to the plate. Evidently, the copper-loaded silicone gasket compound takes a few days longer than forever to cure, which is not what I gathered from reading the label.
It may well be that adhesive has aged out, because when I went to try it again, the first half-inch inside the tube had turned into solid gum. Yes, it cures inside the tube and not outside.
Other than that, it seems like good stuff; I may pick up another tube and give it a second chance. Who knows? It might be useful in a plastic extruder or something like that.
As described there, the buttons on the back of my pocket camera stopped working, but the obvious laying-on-of-hands repair (i.e., wiggling the cables) didn’t improve things. I later discovered out that two other buttons on the side that didn’t go through the same flex cable were also dead, which suggested that the common failure was on the CPU board deep inside the camera. I gave it to my Shop Assistant with some handwaving about how she could maybe fix it by delving deep inside, tracing the cables, and doing some jiggling: if she could fix it, she could have it.
The first step was to take both covers off, which required a Philips 00 bit:
EX-Z850 front cover removed
Then the side plate comes off, which requires maneuvering the spring-loaded battery latch out of its recess, at which point the lug for the carry strap will fall out:
EX-Z850 battery latch and carrying lug
En passant, we discovered why the clock dies while changing the battery pack. It seems the miniature rechargeable lithium (?) NiMH (?) cell has rotted out:
EX-Z850 internal battery corrosion
Fortunately, it charges in a cradle, so the main battery can remain in place indefinitely. We’ll replace that thing at some point.
The CPU board has two flex cable connectors on the front surface and two on the back. My Shop Assistant released the clamps, removed the cables, wiped down the contacts with DeoxIT Red, gave it a test run with the covers off, and came bounding up the stairs as happy as I’ve ever seen her: the camera worked perfectly again!
Not being used to these things, though, she managed to crack one of the side latches on the far connector. I’ll admit to doing exactly the same thing, so I knew how to fix it: a dab of acrylic adhesive holds the fragment in place with a bit of springiness to hold the latch down.
EX-Z850 connector repair
The connector in question comes from the flash control board, to which those other two buttons (Ex and Drive mode) connect. The inside of the camera is a maze of connections, so I guess that was the simplest way to get the conductors through the body.
She reassembled the camera and it continued to work; we declared the job a complete success.
Shortly after that, I promoted her from Shop Assistant to Larval Engineer, First Instar, and we installed her in her new socket at college, where that camera should come in handy for something.
I think she’ll ace the Freshman Engineering Practicum, wherein her compadres will learn how to solder components to circuit boards, use multimeters & oscilloscopes & other instruments, and generally survive in a laboratory. Maybe she can wrangle a job as a Lab Assistant?
So I picked up a new mower blade that sported a sticker claiming it probably fit my Craftsman mower. Got it home, took off the old blade, and it actually fit the mower; the holes matched the hub’s drive pins, although the bolt hole was oversized.
The old blade was a replacement, too, with a square hub hole and an adapter to fit the bolt. The blade had slots for the drive pins, so the adapter was required.
Seeing as how nothing exceeds like excess, I rummaged around in the heap to find something that would serve as an adapter in the central hole. It’s not really necessary, but I’m that type of guy.
As it turned out, an ordinary lockwasher for a 3/8 inch bolt was just about perfect. I crunched one in a short bolt with two nuts jammed in place …
Lockwasher ground for mower blade
… introduced it to the coarse side of Mr Grinding Wheel, and, after a few shots with a hammer, it became a perfect fit:
Lockwasher in blade
Bolted it on the mower, put in two hours of yard aerobics, and it worked just fine. Sliced the top off a root that evaded the attention of the previous blade, too.
The Smell of Molten Projects in the Morning 