The Smell of Molten Projects in the Morning
Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Being that sort of bear, I (sometimes) note the date on cells when I change them, as with this notation on the AA alkaline cells in the Logitech trackball:
These Amazon Basics AA cells lasted almost exactly two years, compared with 15 and 20 months from the previous two pairs of Duracell AAs. A few months one way or the other probably don’t mean much, but the Amazon cells aren’t complete duds.
The new Amazon Basics cells have a gray paint job, so they’ve either changed suppliers or branding.
A soaker hose leaped under a descending garden fork and accumulated a nasty gash:
Mary deployed a spare and continued the mission, while I pondered how to fix such an odd shape.
For lack of anything smarter, I decided to put a form-fitting clamp around the hose, with silicone caulk buttered around the gash to (ideally) slow down any leakage:
As usual, some doodling got the solid model started:
A hose formed from chopped rubber doesn’t really have consistent dimensions, so I set up the model to spit out small test pieces:
Lots and lots of test pieces:
Each iteration produced a better fit, although the dimensions never really converged:
The overall model looks about like you’d expect:
The clamp must hold its shape around a hose carrying 100 psi (for real!) water, so I put 100 mil aluminum backing plates on either side. Were you doing this for real, you’d shape the plates with a CNC mill, but I just bandsawed them to about the right size and transfer-punched the hole positions:
Some drill press action with a slightly oversize drill compensated for any misalignment and Mr Disk Sander rounded the corners to match the plastic block:
A handful of stainless steel 8-32 screws holds the whole mess together:
These hoses spend their lives at rest under a layer of mulch, so I’m ignoring the entire problem of stress relief at those sharp block edges. We’ll see how this plays out in real life, probably next year.
I haven’t tested it under pressure, but it sure looks capable!
The OpenSCAD source code as a GitHub Gist:
| // Rubber Soaker Hose Splice | |
| // Ed Nisley KE4ZNU July 2018 | |
| Layout = "Build"; // Hose Block Show Build | |
| TestFit = false; // true to build test fit slice from center | |
| //- Extrusion parameters must match reality! | |
| ThreadThick = 0.25; | |
| ThreadWidth = 0.40; | |
| HoleWindage = 0.2; | |
| Protrusion = 0.1; // make holes end cleanly | |
| inch = 25.4; | |
| function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit); | |
| //———- | |
| // Dimensions | |
| // Hose lies along X axis | |
| Hose = [200,27.0,12.0]; // X = longer than anything else | |
| Block = [80.0,50.0,4.0 + Hose.z]; // overall splice block size | |
| echo(str("Block: ",Block)); | |
| Kerf = 0.1; // cut through middle to apply compression | |
| ID = 0; | |
| OD = 1; | |
| LENGTH = 2; | |
| // 8-32 stainless screws | |
| Screw = [4.1,8.0,3.0]; // OD = head LENGTH = head thickness | |
| Washer = [4.4,9.5,1.0]; | |
| Nut = [4.1,9.7,6.0]; | |
| CornerRadius = Washer[OD]/2; | |
| NumScrews = 3; // screws along each side of cable | |
| ScrewOC = [(Block.x – 2*CornerRadius) / (NumScrews – 1), | |
| Block.y – 2*CornerRadius, | |
| 2*Block.z // ensure complete holes | |
| ]; | |
| echo(str("Screw OC: x=",ScrewOC.x," y=",ScrewOC.y)); | |
| //———————- | |
| // 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(d=(FixDia + HoleWindage),h=Height,$fn=Sides); | |
| } | |
| // Hose shape | |
| // This includes magic numbers measured from reality | |
| module HoseProfile() { | |
| RimThick = 10.0; // outer sections | |
| RimOD = RimThick; | |
| RimFlatRecess = -0.7; // recess to front flat surface | |
| OuterOC = Hose.y – RimOD; // outer tube centers | |
| RecessM = 1.5; // back recess chord | |
| RecessC = OuterOC; | |
| RecessR = (pow(RecessM,2) + pow(RecessC,2)/4) / (2*RecessM); | |
| RidgeM = 1.0; // front ridge chord | |
| RidgeC = 8.0; | |
| RidgeR = (pow(RidgeM,2) + pow(RidgeC,2)/4) / (2*RidgeM); | |
| NumSides = 12*4; | |
| rotate([0,-90,0]) | |
| translate([0,0,-Hose.x/2]) | |
| linear_extrude(height=Hose.x,convexity=4) | |
| difference() { | |
| union() { | |
| for (j=[-1,1]) // outer channels | |
| translate([0,j*OuterOC/2]) | |
| circle(d=RimOD,$fn=NumSides); | |
| translate([-RimOD/4,0]) // rear flat fill | |
| square([RimOD/2,OuterOC],center=true); | |
| translate([(RimOD/4 + RimFlatRecess),0]) // front flat fill | |
| square([RimOD/2,OuterOC],center=true); | |
| intersection() { | |
| translate([Hose.z/2,0]) | |
| square([Hose.z,OuterOC],center=true); | |
| translate([-RidgeR + RimOD/2 + RimFlatRecess + RidgeM,0]) | |
| circle(r=RidgeR,$fn=NumSides); | |
| } | |
| } | |
| translate([-(RecessR + RimOD/2 – RecessM),0]) | |
| circle(r=RecessR,$fn=2*NumSides); | |
| } | |
| } | |
| // Outside shape of splice Block | |
| // Z centered on hose rim circles, not overall thickness through center ridge | |
| module SpliceBlock() { | |
| difference() { | |
| hull() | |
| for (i=[-1,1], j=[-1,1]) // rounded block | |
| translate([i*(Block.x/2 – CornerRadius),j*(Block.y/2 – CornerRadius),-Block.z/2]) | |
| cylinder(r=CornerRadius,h=Block.z,$fn=4*8); | |
| for (i = [0:NumScrews – 1], j=[-1,1]) // screw holes | |
| translate([-(Block.x/2 – CornerRadius) + i*ScrewOC.x, | |
| j*ScrewOC.y/2, | |
| -(Block.z/2 + Protrusion)]) | |
| PolyCyl(Screw[ID],Block.z + 2*Protrusion,6); | |
| cube([2*Block.x,2*Block.y,Kerf],center=true); // slice through center | |
| } | |
| } | |
| // Splice block less hose | |
| module ShapedBlock() { | |
| difference() { | |
| SpliceBlock(); | |
| HoseProfile(); | |
| } | |
| } | |
| //———- | |
| // Build them | |
| if (Layout == "Hose") | |
| HoseProfile(); | |
| if (Layout == "Block") | |
| SpliceBlock(); | |
| if (Layout == "Bottom") | |
| BottomPlate(); | |
| if (Layout == "Top") | |
| TopPlate(); | |
| if (Layout == "Show") { | |
| difference() { | |
| SpliceBlock(); | |
| HoseProfile(); | |
| } | |
| color("Green",0.25) | |
| HoseProfile(); | |
| } | |
| if (Layout == "Build") { | |
| SliceOffset = TestFit && !NumScrews%2 ? ScrewOC.x/2 : 0; | |
| intersection() { | |
| translate([SliceOffset,0,Block.z/4]) | |
| if (TestFit) | |
| cube([ScrewOC.x/2,4*Block.y,Block.z/2],center=true); | |
| else | |
| cube([4*Block.x,4*Block.y,Block.z/2],center=true); | |
| union() { | |
| translate([0,0.6*Block.y,Block.z/2]) | |
| ShapedBlock(); | |
| translate([0,-0.6*Block.y,Block.z/2]) | |
| rotate([0,180,0]) | |
| ShapedBlock(); | |
| } | |
| } | |
| } |
We negotiated the Belmar Bridge connection stairway from the Allegheny River Trail to the Sandy Creek trail:
We’re maneuvering Mary’s bike, but you get the general idea. Our bikes aren’t built for stairways, particularly ones with low overheads:
The front fender clip on my Tour Easy snapped (at the expected spots) when the mudflap snagged on one of the angles:
For some inexplicable reason, I didn’t have a roll of duct tape in my packs, so the temporary repair required a strip of tape from a battery pack, two snippets of hook-and-loop tape, and considerable muttering:
It was good for two dozen more miles to the end of our vacation, so I’d say that was Good Enough.
The new version has holes in the ferrules ten stay diameters deep, instead of six, which might eliminate the need for heatstink tubing. I added a small hole at the joint between the curved hooks and the ferrules to force more plastic into those spots:
I also bent the hanger extension to put the fender’s neutral position closer to the wheel.
We’ll see how long this one lasts. By now, I now have black double-sticky foam tape!
The OpenSCAD source code as a GitHub Gist:
| // Tour Easy front fender clip | |
| // Ed Nisley KE4ZNU July 2017 | |
| Layout = "Build"; // Build Profile Ferrule Clip | |
| //- Extrusion parameters must match reality! | |
| ThreadThick = 0.25; | |
| ThreadWidth = 0.40; | |
| HoleWindage = 0.2; | |
| Protrusion = 0.1; // make holes end cleanly | |
| inch = 25.4; | |
| function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit); | |
| //———————- | |
| // Dimensions | |
| // special case: fender is exactly half a circle! | |
| FenderC = 51.0; // fender outside width = chord | |
| FenderM = 21.0; // height of chord | |
| FenderR = (pow(FenderM,2) + pow(FenderC,2)/4) / (2 * FenderM); // radius | |
| echo(str("Fender radius: ", FenderR)); | |
| FenderD = 2*FenderR; | |
| FenderA = 2 * asin(FenderC / (2*FenderR)); | |
| echo(str(" … Arc: ",FenderA," deg")); | |
| FenderThick = 2.5; // fender thickness, assume dia of edge | |
| ClipHeight = 15.0; // top to bottom, ignoring rakish tilt | |
| ClipThick = IntegerMultiple(2.5,ThreadWidth); // thickness of clip around fender | |
| ClipD = FenderD; // ID of clip against fender | |
| ClipSides = 4 * 8; // polygon sides around clip circle | |
| BendReliefD = 2.5; // bend arch diameter | |
| BendReliefA = 2/3 * FenderA/2; // … angle from dead ahead | |
| BendReliefCut = 1.5; // factor to thin outside of bend | |
| ID = 0; | |
| OD = 1; | |
| LENGTH = 2; | |
| StayDia = 3.3; // fender stay rod diameter | |
| StayOffset = 15.0; // stay-to-fender distance | |
| StayPitch = -5; // angle from stay to fender arch | |
| DropoutSpace = 120; // stay spacing at wheel hub | |
| StayLength = 235; // stay length: hub to fender | |
| StaySplay = asin((DropoutSpace – FenderC)/(2*StayLength)); // outward angle to hub | |
| echo(str(" … Pitch: ",StayPitch," deg")); | |
| echo(str(" … Splay: ",StaySplay," deg")); | |
| FerruleSides = 2*4; | |
| Ferrule = [StayDia,3*FenderThick/cos(180/FerruleSides),10*StayDia + StayOffset]; // ID = stay rod OD | |
| FerruleHoleD = 0.1; // small hole to create solid plastic at ferrule joint | |
| //———————- | |
| // 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, | |
| $fn=Sides); | |
| } | |
| //———————- | |
| // Clip profile around fender | |
| // Centered on fender arc | |
| module Profile(HeightScale = 1) { | |
| linear_extrude(height=HeightScale*ClipHeight,convexity=5) { | |
| difference() { | |
| offset(r=ClipThick) // outside of clip | |
| union() { | |
| circle(d=ClipD,$fn=ClipSides); | |
| for (i=[-1,1]) | |
| rotate(i*BendReliefA) { | |
| translate([ClipD/2 + BendReliefD/2,0,0]) | |
| circle(d=BendReliefD,$fn=6); | |
| } | |
| } | |
| union() { // inside of clip | |
| circle(d=ClipD,$fn=ClipSides); | |
| for (i=[-1,1]) | |
| rotate(i*BendReliefA) { | |
| translate([ClipD/2 + BendReliefCut*BendReliefD/2,0,0]) | |
| circle(d=BendReliefD/cos(180/6),$fn=6); | |
| translate([ClipD/2,0,0]) | |
| square([BendReliefCut*BendReliefD,BendReliefD],center=true); | |
| } | |
| } | |
| translate([(FenderR – FenderM – FenderD/2),0]) // trim ends | |
| square([FenderD,2*FenderD],center=true); | |
| } | |
| for (a=[-1,1]) // hooks around fender | |
| rotate(a*(FenderA/2)) | |
| translate([FenderR – FenderThick/2,0]) { | |
| difference() { | |
| rotate(1*180/12) | |
| circle(d=FenderThick + 2*ClipThick,$fn=12); | |
| rotate(1*180/8) | |
| circle(d=FenderThick,$fn=8); | |
| rotate(a * -90) | |
| translate([0,-2*FenderThick,0]) | |
| square(4*FenderThick,center=false); | |
| } | |
| } | |
| } | |
| } | |
| //———————- | |
| // Ferrule body | |
| module FerruleBody() { | |
| translate([0,0,Ferrule[OD]/2 * cos(180/FerruleSides)]) | |
| rotate([0,-90,0]) rotate(180/FerruleSides) | |
| difference() { | |
| cylinder(d=Ferrule[OD],h=Ferrule[LENGTH],$fn=FerruleSides,center=false); | |
| translate([0,0,StayOffset + Protrusion]) | |
| PolyCyl(Ferrule[ID],Ferrule[LENGTH] – StayOffset + Protrusion,FerruleSides); | |
| } | |
| } | |
| //———————- | |
| // Generate entire clip at mounting angle | |
| module FenderClip() { | |
| difference() { | |
| union() { | |
| translate([FenderR,0,0]) | |
| difference() { // angle and trim clip | |
| rotate([0,StayPitch,0]) | |
| translate([-(FenderR + ClipThick),0,0]) | |
| Profile(2); // scale upward for trimming | |
| translate([0,0,-ClipHeight]) // trim bottom | |
| cube(2*[FenderD,FenderD,ClipHeight],center=true); | |
| translate([0,0,ClipHeight*cos(StayPitch)+ClipHeight]) // trim top | |
| cube(2*[FenderD,FenderD,ClipHeight],center=true); | |
| } | |
| for (j = [-1,1]) // place ferrules | |
| translate([Ferrule[OD]*sin(StayPitch) + (Ferrule[OD]/2)*sin(StaySplay),j*(FenderR – FenderThick/2),0]) | |
| rotate(-j*StaySplay) | |
| FerruleBody(); | |
| } | |
| for (i=[-1,1]) // punch stiffening holes | |
| translate([FenderThick/2,-i*(FenderR – FenderThick/2),Ferrule[OD]/2]) | |
| rotate([0,-90,i*StaySplay]) | |
| PolyCyl(FerruleHoleD,Ferrule[OD],FerruleSides); | |
| } | |
| } | |
| //———————- | |
| // Build it | |
| if (Layout == "Profile") { | |
| Profile(); | |
| } | |
| if (Layout == "Ferrule") { | |
| FerruleBody(); | |
| } | |
| if (Layout == "Clip") { | |
| FenderClip(); | |
| } | |
| if (Layout == "Build") { | |
| FenderClip(); | |
| } |
As a bonus for paging all the way to the end, here’s the descent on the same stairway:
No, I wasn’t even tempted …
Most currents around here come in tens-of-milliamps, maybe a few hundred, tops, but it’s worth noting some curves from the Tektronix AM503 current amplifier manual for A6302 Hall effect probes:
The maximum current drops from 20 A for frequencies above 20 kHz:
There’s a 100 A·μs pulse charge limit:
Because the probe is actually a pulse transformer, its internal termination imposes a (small) load on the input circuit:
The specs are 100 mΩ at 1 MHz and 500 mΩ at 50 MHz, which means the load is essentially zilch for the circuits and signals I deal with.
The Tektronix Probes for Current Measurement Systems has some useful descriptions.
Memo to Self: Should any of those limits matter, rethink what you’re doing.
An interesting story about the AM503 design from someone who lived through it.
The top surface of the Anker LC40 flashlight serving as the daytime running light on Mary’s bike sees plenty of sunlight, particularly when it’s sitting beside her garden plots, and the black anodized finish on the screw-in battery cap has begun fading:
The bottom side of the cap is in fine shape, as is the main case, so the two parts came from different metal finishing lines.
The light on my bike, a marginally newer and essentially identical Bolder LC40, remains all black. I have no idea what “Bolder” means in this context.
Obviously, I must get out more …
Six weeks later, the mint seemed about as extracted as it was going to get and I now have nearly a liter of decidedly green mint extract:
Correspondingly, the leaves turned from bright green to dull brown:
The smaller and darker pile in the rightmost bowl came from the smaller jar (on the left) with a higher alcohol-to-leaf ratio:
Perhaps packing the jars before pouring in the alcohol doesn’t extract as efficiently. Or maybe, as in so many things, it doesn’t really matter.
A liter of mint extract may not be a lifetime supply, but it’ll suffice for quite a while!
The question occasionally comes up as to why one would want a Tektronix A6302 Hall effect current probe and AM503 amplifier. The answer is simple: non-contact, essentially non-invasive current monitoring.
I used the venerable dead-battery Astable Multivibrator to check out the rebalanced A6302 probe:
The scope screen in the background shows the two base voltages at the top, plus the overall battery current along the bottom:
The current at 1 mA/div shows plenty of noise, but the 200 ms LED pulse is barely 1 mA tall. The two AA alkaline cells have faded to 2.5 V, so the “wearable” white-LED-with-dyed-overcoat runs far under its nominal 3.6-ish V spec.
There’s basically no other way to get that result, because inserting a current-sense resistor into the circuit will alter the results, plus be intractably difficult to measure, particularly if you need the current in a non-ground-referenced branch of the circuit.
The AM503 has terrible thermal drift, by contemporary standards, but after the first half-hour or so it’s manageable for short durations. I’m thinking of epoxying a small knob to the screwdriver-adjustable twiddlepot to simplify the baseline adjustment.
Alas, even non-working probes and amps have become eBay collectables. You could, of course, buy new.
The Smell of Molten Projects in the Morning 