Category: Machine Shop

Mechanical widgetry

Sena PS410 Serial Server: Burnin’ In

The USB serial adapters I use to capture HP54602 scope and HP8591 spectrum analyzer screenshots, as well as monitor the HP Z8501 GPS time standard, lack unique identifiers and appear as unpredictable device nodes.

After putting up with this for far too long, I dropped $15 on a Sena Technologies PS410 serial server:

Sena PS410 Serial Server – interior

It needed a new lithium coin cell, of course:

Sena PS410 Serial Server – as-received CR2032

The PCB and chip date codes suggest a 2009 build, so “98” might mean August 2009. Whether that’s the manufacturing date or the best used by date, ya never know.

The eBay deal didn’t include the power supply, so I hacked a coaxial jack on the back:

Sena PS410 Serial Server – hacked power jack

A 14 VDC IBM laptop brick from the pile suits the “9 to 36 V” range printed on the case.

Poking the “factory reset” switch did what you’d expect and the “console” serial port on the front worked fine. I plugged in the scope, the spectrum analyzer, and the GPS receiver, whereupon the bench took on the unmistakable aroma of electronic death:

Sena PS410 Serial Server – charred ferrite chip

Some probing suggests FB9 used to be a ferrite bead between serial port 2’s ground pin and the frame ground.

To compress an afternoon of tinkering into one sentence, there seems to be an occasional 35 VAC difference between the spectrum analyzer and the scope, but only when one or the other is plugged into the PS410. Everything is (now!) plugged into the same branch circuit and, in fact, the same outlet via many power strips, but the difference remains. A different power supply makes no difference, either.

I managed to burn out the ferrite bead on Port 1 with only the scope and the power supply plugged in, by connecting the scope’s ground lead to the shell of Port 2. That makes no sense: there is no voltage difference between the scope’s serial ground and its probe ground.

Something Is Not Right, but I’m baffled.

I have established that the server works fine, even with the charred beads, which is a Good Thing.

2018-03-21
Bottle Cap Rehabilitation

Mary acquired this bottle a long time ago and has used it forever, so it has Historic Connotations and cannot be discarded. Alas, the cardboard-and-plastic seal in the cap finally disintegrated; I replaced it with various plastic foams and sheets, none of which worked.

Finally, I found the cork sheet stash while looking for something else and cut out a disk:

Rehabilitated bottle cap

It works perfectly, of course, because cork.

That was easy.

2018-03-17
SJCAM M20 Camera: Dimensions
The SJCAM M20 action camera came with a whole bunch of doodads:

SJCAM M20 Accessories – Manual pg 25

Including a waterproof case, some right-angle connectors, and a pipe clamp:

M20 in waterproof case – Tour Easy seat

The stack turns out to be about as flexy as one might imagine, definitely a Bad Thing for a bike-mounted camera, and a somewhat more rugged mount seems in order.

A diagram from the M20 manual shows the parts:

SJCAM M20 Overview – Manual pg 5

Some camera dimensions:
- 40.2 mm wide + 0.5 mm for the Up/Down buttons
- 21.8 mm thick + 1.0 mm cylindrical front curve + 1.0 mm rear screen
- 50.0 mm tall + 4.0 mm cylindrical top curve + buttons
- 21.7 mm OD × 6.0 mm long lens housing, 1.3 mm down from top center
All the edges have neat chamfers or radius rounding on the order of a few millimeters.

Applying the chord equation to the spans inside the rounding:
- Front radius: 162.5 mm
- Top radius: 42.5 mm
The new batteries survive for a bit over an hour, not quite enough for our usual rides. Rather than conjure a fake battery pack connected to an external 18650 cell with a wire chewed through the case, the least awful way to go may involve a relatively small battery pack (with internal 18650 cells, of course) plugged into the USB port with a right-angle cable and a rigid mount holding both the camera and the pack to the seat frame.

More pondering is in order.
2018-03-14
Paper Airplanes

Milo showed how to construct his realistic-looking paper airplane design at Squidwrench, so I had to fold an airplane pattern I learned in fifth grade:

Paper Airplanes – front view

Side views:

Paper Airplanes – side view

Bottom views:

Paper Airplanes – bottom view

His plane flies fine, but “my” airplane has the virtue of simplicity. He had a snippet left over for a fourth engine, so I cut it in half and rolled a pair; the original pattern has none.

It flies best when made from a sheet of 8-½×11 inch (Letter) paper, but anything will suffice. Here’s how to fold one from a Geek Scratch Pad half-Letter sheet.

Start with two diagonal folds:

Best Paper Airplane Ever – 1

Push the sides in and flatten:

Best Paper Airplane Ever – 2

Fold the side tips forward, then again to form pockets:

Best Paper Airplane Ever – 3

I’ve always made those folds to leave a few millimeters of clearance along the centerline, but it probably doesn’t matter.

Tear the fuselage rearward from the nose, along the center line, back to the pockets:

Best Paper Airplane Ever – 4

Tuck the nose pieces into the pockets, flatten firmly, then fold in half lengthwise:

Best Paper Airplane Ever – 5

Fold each wing downward from the pocket, upward to put the edge along the bottom of the fuselage, then fold downward to align the edge at the previous fold:

Best Paper Airplane Ever – 6

Which is harder to describe than to do. The end result should look like this:

Best Paper Airplane Ever – 7

Crisp the folds, tear a square-ish vertical-ish stabilizer, fold a triangle into the fuselage, then un-flatten the airplane into shape:

Best Paper Airplane Ever – 8

Grab just behind the pockets, toss gently upward, and it’ll fly fine the first time. Slightly bend the rear edges of the wing and stabilizer to trim the flight path until it sails gently across the room.

It’s a glider, not a dart!

Enjoy …

2018-03-13
MPCNC: Raspberry Pi Screw-down Case

Directly from 0110-M-P’s Thingiverse thing, because a Raspberry Pi in a 75 mm VESA mount case will work for me:

RPi in VESA case

The hole fits a 25 mm fan, but the thing runs cool enough it should survive without forced air; think of it as a contingency. Mounting the case on standoffs seems like a Good Idea, however, as the bottom plate includes many vent slots for Good Circulation.

The top plate builds upside-down, so I had Slic3r add teeny support plugs inside the recessed screw holes. I think button-head screws would fit neatly in the recesses, but we’re obviously not in this for the looks.

The tiny white stud is a Reset switch hot-melt glued into the slot. I plan to just turn off the AC power after shutting the RPi down, so a power-on will suffice as a reset.

2018-03-11

MPCNC: Power Supply Brick Mount

A laptop-style power brick supplies 24 V for the MPCNC’s stepper motors, but I didn’t want it wandering around on the Basement Laboratory floor and getting in trouble, so a pair of brackets seemed in order:

Power Supply Brick Mount - trial fit — Power Supply Brick Mount – trial fit

They build flat on their backs to avoid support material:

Power Supply Brick Mount - Slic3r — Power Supply Brick Mount – Slic3r

The nicely rounded corners produce a very thin line of plastic on the first layer, so the model now has thicker base plates to improve the situation. A set of mouse ears would keep the tips pasted to the glass.

The OpenSCAD source code as a GitHub Gist:

	// Power Supply Brick brackets
	// Ed Nisley KE4ZNU 2018-02-26

	Layout = "Show";

	//– Extrusion parameters

	ThreadThick = 0.25;
	ThreadWidth = 0.4;

	HoleWindage = 0.3; // enlarge hole dia by this amount

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

	Protrusion = 0.1; // make holes look good and joints intersect properly

	//– Useful sizes

	inch = 25.4;

	Tap10_32 = 0.159 * inch;
	Clear10_32 = 0.190 * inch;
	Head10_32 = 0.373 * inch;
	Head10_32Thick = 0.110 * inch;
	Nut10_32Dia = 0.433 * inch;
	Nut10_32Thick = 0.130 * inch;

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

	//– Bracket Dimensions

	Brick = [170.0,66.0,40.0]; // overall size, add details in module

	Socket = [30.0,24.0]; // IEC power socket
	Cable = [6.0,15.0]; // DC output cable ID=wire OD=strain relief

	WallThick = 3.0; // default wall thickness
	BaseThick = 4.0;

	Screw = [5.1,10.0,3.0]; // screw size, more-or-less 10-32, OD & LENGTH for head

	NumSides = 3*4;

	//———————-
	// 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);
	}

	//———————-
	// Models



	module BrickMount(End="Both") {

	difference() {
	union() {
	hull() // main block
	for (i=[-1,1], j=[-1,1], k=[0,1])
	translate([i*(Brick.x/2 + WallThick – WallThick),
	j*(Brick.y/2 + WallThick – WallThick),
	k*(Brick.z + WallThick – WallThick)])
	sphere(r=WallThick,$fn=NumSides);
	hull() // screw flanges
	for (i=[-1,1], j=[-1,1])
	translate([i*(Brick.x/2 + WallThick – BaseThick),
	j(Brick.y/2 + WallThick + 2Screw[OD] – BaseThick),
	0])
	sphere(r=BaseThick,$fn=NumSides);
	}
	for (i=[-1,1], j=[-1,1]) // remove screw holes
	translate([i*(Brick.x/2 + WallThick – Screw[OD]),
	j*(Brick.y/2 + WallThick + Screw[OD]),
	-Protrusion])
	rotate(180/6)
	PolyCyl(Screw[ID],2*WallThick,6);

	translate([0,0,Brick.z/2]) // remove center part to leave ends
	cube([(Brick.x + 2WallThick – 4Screw[OD]),2Brick.y,2Brick.z],center=true);

	if (End == "Socket")
	translate([Brick.x/2,0,Brick.z/2]) // remove cable end to leave socket
	cube([(Brick.x + 2WallThick – 4Screw[OD]),2Brick.y,2Brick.z],center=true);

	if (End == "Cable")
	translate([-Brick.x/2,0,Brick.z/2]) // remove socket end to leave cable
	cube([(Brick.x + 2WallThick – 4Screw[OD]),2Brick.y,2Brick.z],center=true);

	translate([0,0,Brick.z/2 – Protrusion/2]) // remove power supply brick from interior
	cube(Brick + [0,0,Protrusion],center=true);
	translate([0,0,-Brick.z]) // remove below XY plane
	cube(2*Brick,center=true);

	translate([0,0,Brick.z/2]) // remove AC socket
	rotate([0,-90,0])
	rotate(90)
	linear_extrude(height=Brick.x,convexity=2)
	square(Socket,center=true);

	translate([0,0,Brick.z/2]) // remove DC cable
	rotate([0,90,0])
	rotate(180/8)
	PolyCyl(Cable[OD],Brick.x,8);
	translate([Brick.x/2,0,Brick.z/4 – Protrusion/2]) // … and wire slot
	cube([Brick.x,Cable[ID],Brick.z/2 + Protrusion],center=true);
	}

	}

	//———————-
	// Build it

	if (Layout == "Show")
	BrickMount("Both");

	if (Layout == "Build") {
	translate([5,0,Brick.x/2 + WallThick])
	rotate([0,90,0])
	BrickMount("Cable");
	translate([-5,0,Brick.x/2 + WallThick])
	rotate([0,-90,0])
	BrickMount("Socket");
	}

view raw Power Supply Brick Mount.scad hosted with ❤ by GitHub

2018-03-09

MPCNC: Button Box Connector Mount

This will eventually end up on a board supporting the GRBL controller box:

Control Box - Connector Mount - Slic3r — Control Box – Connector Mount – Slic3r

It’s a direct cut-n-paste descendant of the old NEMA motor mount.

The nut threads onto the connector behind the bulkhead, so you must either wire it in place or make very sure you can feed all the terminations through the hole:

Given the previous hairball, I think in-situ soldering has a lot to recommend it:

The OpenSCAD source code as a GitHub Gist:

	// Circular connector bracket
	// Ed Nisley KE4ZNU 2018-02-22

	//– Extrusion parameters

	ThreadThick = 0.25;
	ThreadWidth = 0.4;

	HoleWindage = 0.3; // enlarge hole dia by this amount

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

	Protrusion = 0.1; // make holes look good and joints intersect properly

	//– Useful sizes

	inch = 25.4;

	Tap10_32 = 0.159 * inch;
	Clear10_32 = 0.190 * inch;
	Head10_32 = 0.373 * inch;
	Head10_32Thick = 0.110 * inch;
	Nut10_32Dia = 0.433 * inch;
	Nut10_32Thick = 0.130 * inch;

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

	//– Mount Sizes

	Connector = [14.6,15.5,4.0]; // connector thread; ID = dia at flat
	Screw = [5.1,10.0,3.0]; // screw size, more-or-less 10-32, OD & LENGTH for head

	MountWidth = IntegerMultiple(2*Connector[OD],ThreadWidth); // use BCD for motor clearance
	MountThick = IntegerMultiple(Connector[LENGTH],ThreadThick); // for stiffness

	WallThick = 3.0; // default wall thickness

	StandThick = IntegerMultiple(WallThick,ThreadWidth); // baseplate
	StrutThick = IntegerMultiple(WallThick,ThreadWidth); // sides holding motor mount

	UprightLength = MountWidth + 2*StrutThick;

	StandBoltHead = IntegerMultiple(Head10_32,5); // bolt head rounded up
	StandBoltOC = IntegerMultiple(UprightLength + 2*StandBoltHead,5);

	StandLength = StandBoltOC + 2*StandBoltHead;
	StandWidth = 2*StandBoltHead;

	StandBoltClear = (StandLength – UprightLength)/2; // flat around bolt head

	Recess = StandWidth – MountThick;

	echo(str("Stand Base: ",StandLength," x ",StandWidth," x ",StandThick));
	echo(str("Stand Bolt OC: ",StandBoltOC));
	echo(str("Strut Thick: ",StrutThick));

	//———————-
	// 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);
	}

	//———————-
	// Model

	module MotorMount() {

	difference() {
	translate([StandThick/2,0,StandWidth/2])
	cube([(MountWidth + StandThick),StandLength,StandWidth],center=true);

	translate([-Protrusion/2,0,StandWidth – (Recess – Protrusion)/2])
	cube([(MountWidth + Protrusion),MountWidth,(Recess + Protrusion)],center=true);
	translate([0,0,-Protrusion])
	PolyCyl(Connector[OD],StandWidth,4*4);
	for (j=[-1,1]) // cutouts over bolts
	translate([-Protrusion/2,
	j*((StandLength – StandBoltClear)/2 + Protrusion/2),
	StandWidth/2])
	cube([(MountWidth + Protrusion),
	(StandBoltClear + Protrusion),
	(StandWidth + 2*Protrusion)],center=true);
	for (j=[-1,1]) // stand bolt holes
	translate([(MountWidth/2 – Protrusion),j*StandBoltOC/2,StandWidth/2])
	rotate([0,90,0])
	rotate(180/6)
	PolyCyl(Clear10_32,StandThick + 2*Protrusion,6);

	translate([0,-(UprightLength/2 – ThreadWidth/2),StandWidth/2])
	rotate([90,180,0])
	linear_extrude(ThreadWidth,convexity=10)
	text(text=str(Connector[OD]),size=6,spacing=1.20,font="Arial",halign="center",valign="center");
	}
	}

	//———————-
	// Build it

	MotorMount();

view raw Connector Mount.scad hosted with ❤ by GitHub

2018-03-08

Category: Machine Shop

Sena PS410 Serial Server: Burnin’ In

Bottle Cap Rehabilitation

SJCAM M20 Camera: Dimensions

Paper Airplanes

MPCNC: Raspberry Pi Screw-down Case

MPCNC: Power Supply Brick Mount

MPCNC: Button Box Connector Mount