Tag: Improvements

Making the world a better place, one piece at a time

Hotrod M2 Platform Support Stud Repair

The hotrod build platform I’m using with the Makergear M2 consists of a PCB heater bonded to a glass plate, supported by three socket head cap screws soldered into the PCB. The print quality recently took a nosedive that seemed related to the first layer height, with which I fiddled more than usual, and finally the front of the platform became obviously, visibly, no-way-around-it far too high. Peering under the platform showed that the front support stud had pulled out of the solder fillet securing it to the PCB:

M2 Hotrod Platform – support stud pullout

Those PCB patterns conduct the heater current around the mounting holes: the hotrod platform has better heat distribution than the OEM M2 platform.

The offending screw didn’t go anywhere:

M2 Hotrod Platform – support stud in spring

The wavy spring and silicone plug press on the PCB, so the solder fillet had to support all the stress. It seemed as though the solder hadn’t bonded to the stainless SHCS, but, rather than try to fix that, I decided to put a washer on the screw. That way, the spring bears on the washer and the screw head supports the strain, with the solder fillet responsible for holding the PCB and glass plate in position.

Alas, I didn’t have any washers small enough on the inside (3 mm) and big enough on the outside to support the springs, so I cut some out of a sheet steel scrap by drilling the center hole to the proper diameter, then applying a hole saw without its (far too large) pilot drill:

M2 Hotrod Platform – hole-sawing washers

That’s a lethally bad idea, as the pilot-less saw can grab the sheet and toss it across the shop. Notice the screws holding the sheet down and absorbing the cutting torque, plus the two clamps enforcing the “stay put” edict.

The other problem with not having a pilot drill in the hole saw is that it’s not guaranteed to cut a cookie that’s concentric with the center hole. Instead of taking the time to make a pilot, I just drilled and cut a few extra washers, then picked the best three of the set for finishing:

M2 Hotrod Platform – rough-cut washers

Using a screw as a mandrel, I lathe-turned the OD of the better ones to make them nice and round:

M2 Hotrod Platform – washer on mandrel

Two of the three PCB support screws were in the right place (they hadn’t come loose), so I used the M2 as an alignment fixture for the third:

M2 Hotrod Platform – aligning washers

That’s a layer of good old JB Industro Weld epoxy, rated for much higher temperatures than the platform will ever see, between the big washers and the PCB. I buttered up the head of the errant screw and the inside of the solder fillet, shoved it in, and then stacked everything together. The small washers held the big washers perpendicular to the screws while the epoxy cured.

After that, I removed the small washers, reinstalled springs + silicone plugs, tightened the nyloc nuts, aligned the platform, ran off a few thinwall hollow boxes, tweaked the alignment, and it was all good:

M2 Hotrod Platform – thinwall box alignment

The rest of the story: that mumble screw pulled loose on the Friday evening before the Mini Maker Faire on Saturday morning. I did all the shop work after supper, then let the epoxy cure overnight with the platform set to 95 °F while I got a good night’s sleep. Reinstalling and realigning the platform took the better part of half an hour around breakfast, after which I tore it all down, packed it all up, and headed off to the Mini Maker Faire.

In truth, that’s the most trouble I’ve had with the M2 and it’s not Makergear’s fault: it’s not their platform. After reinstalling the platform, the alignment was no big deal and it’s been stable ever since.

2014-12-02
Sony HDR-AS30V Audio: Fake Fur FTW!

A scrap of fake fur cut to fit the outline of the Sony HDR-AS30V helmet camera and stuck in place with a square of double-stick foam centered above (or below, in the normal orientation) the lens:

Sony HDR-AS30V – fake fur installed

Snippy remarks about what that looks like will not be tolerated, m’kay?

It reduces wind noise to an occasional rumble from strong gusts and even those don’t crush the AGC. My side of our radio conversations became clearly audible, as did shifters clicking and gravel crunching. There’s still plenty of noise, but now it comes from actual sound sources that don’t overwhelm the amp.

A layer of ordinary adhesive tape still covers the mic pores and the fur’s fabric backing extends over the tape, so the combination must muffle the sound at least a little bit. Given the source material and my hearing, it’s Good Enough; Golden Eared Audiophiles need not apply.

I also cannot detect any difference between the left and right audio channels, so the stereo separation at 15 mm isn’t worth much. I don’t know if the camera swaps the audio channels in video flip mode; that would be a nice touch.

The hairs extending outward beside the lens occasionally blew into view, so a haircut is in order:

mah00242-075 – Fake Fur in view

Perhaps a clip that snaps over the skeleton frame to hold a neat patch of fur in place without adhesive on the camera body would be even better?

2014-11-28
Shimano SPD Pedals: Cleat Oilers
Here’s the solution to creaking SPD pedals due to hardened shoe cleats gritting on hardened pedal latches:

Shimano SPD pedal – cleat oiler

Those are carefully shaped snippets of open-cell foam tucked around the springs under the movable latches, loaded with a few drops of penetrating oil, and ridden for several months. Nary a squeak or grinding sound has emerged: far better than the results after I added a drop of oil whenever either of us heard that sound.

Similar snippets tucked under the forward latch fell out without affecting the results, from which I conclude:
- The front latch doesn’t squeak
- The foam on the other side is Close Enough
- Penetrating oil oozes into a thin film over the whole pedal
The cleats don’t quite touch the ground when we walk, so we’re not leaving oily footprints.

Should I ever install new pedals, I’ll see if a larger foam block can span the gap between the front latch on the top and the movable latch on the bottom.
2014-11-25
Sony HDR-AS30V Audio vs. Wind Noise

With the Sony HDR-AS30V in its skeleton frame atop my bike helmet, the audio track for all my rides consists entirely of horrendous wind noise. You can get an idea of the baseline quality from the sound track of a recent Walkway Over The Hudson crossing.

The camera has two mics, although I’m not sure 15 mm of separation really produces meaningful stereo sound:

Sony HDR-AS30V – front view

Note that two of the five pores on each side are closed flat-bottom pits. As with earbud vents , it must be a stylin’ thing.

I added a rounded pad of the same acoustic foam that forms an effective wind noise buffer for the boom mic:

Sony HDR-AS30V – foam mic cover

That reduced the overall noise load by buffering direct wind impact, but non-radio conversations remained unintelligible; there’s just too much low-frequency energy.

Surprisingly, closing the mic pores with ordinary adhesive tape didn’t impair the audio in a quiet room:

Sony HDR-AS30V – closed mic pores

Out on the road that’s even better than foam over open mic pores; I think it reduces the peak volume enough that the internal compression can regain control. Sticking the foam pad over the tape slightly reduced the noise during high-speed (for me, anyhow) parts of the ride, but didn’t make much difference overall.

The wind noise remains too high for comfort, even if I can now hear cleats clicking into pedals, shifters snapping, and even the horrible background music when I’m stopped next to the Mobil gas station on the corner.

Next step: raid the cloth scrap box for a flap of faux fur to make a mic mop. This might be an opportunity to recycle some roadkill…

2014-11-21
Kenmore 158: Motor RPM Sensor Deglitching
The setscrew in the motor pulley lies directly in the path of the photosensor:

TCTR5000 Motor RPM Sensor – side view

Which produces a glitch in the rising edge of the digital output as the pulley rotates from the dark to the light section:

Motor Sensor – Rising Edge Glitch

The RPM signal goes to Arduino pin D2, where each falling edge triggers an interrupt handler:
```
const byte PIN_MOTOR_REV = 2;		// DI - IRQ 0 (must be D2)

... snippage...

void setup() {
... snippage ...

    pinMode(PIN_MOTOR_REV,INPUT_PULLUP);
    attachInterrupt((PIN_MOTOR_REV - 2),ISR_Motor,FALLING);			// one IRQ / motor revolution

 ... snippage ...
}
```
The maximum motor speed is about 11 kRPM, so interrupts should be at least 5.5 ms apart and the digital input should be low. If that’s true, then the code updates a bunch of useful information:
```
struct pulse_t {
 byte Counter;
 unsigned long TimeThen;
 unsigned long Period;
 word RPM;
 byte State;
};

struct pulse_t Motor;

... snippage ...

//------------------
// ISR to sample motor RPM sensor timing

void ISR_Motor(void) {

static unsigned long Now;

	digitalWrite(PIN_SYNC,HIGH);

	Now = micros();

	if ((5000ul < (Now - Motor.TimeThen)) && !digitalRead(PIN_MOTOR_REV) ) {	// discard glitches
		Motor.Counter++;
		Motor.Period = Now - Motor.TimeThen;
		Motor.TimeThen = Now;
		Motor.State = digitalRead(PIN_MOTOR_REV);		// always zero in a Physics 1 world
	}

	digitalWrite(PIN_SYNC,LOW);
	return;
}
```
The scope trace shows that the handler takes about 7 µs to get control after the glitch (the left cursor should be on the falling edge, not the rising edge), so the input read occurs when the sensor output is over 4.5 V, causing the handler to discard this spurious interrupt.

Because Motor.Period is a four-byte unsigned long, the Arduino’s CPU must handle it in chunks. Rather than disable interrupts around each use, it’s better to read the value until two successive copies come back identical:
```
//------------------
// Return current microsecond period without blocking ISR

unsigned long ReadTime(struct pulse_t *pTime) {

unsigned long Sample;

	do {
		Sample = pTime->Period;				// get all four bytes
	} while (Sample != pTime->Period);		//  repeat until not changed by ISR while reading

	pTime->Counter = 0;						// this is a slight race condition

	return Sample;
}
```
Because the interrupts don’t happen that often, the loop almost always executes only one time. On rare occasions, it’ll go back for another two values.

Converting the pulley rotation period into revolutions per minute goes like this:
```
		Motor.RPM = 60000000ul/ReadTime(&Motor);		// one (deglitched) pulse / rev
```
That’s easier than hiding the setscrew and it also discards any other glitches that may creep into D2…
2014-11-10
Kenmore 158: Power Switch Timing
The crash test dummy sewing machine now has a cheerful red momentary pushbutton in the same spot the original machine sported a 120 VAC push-on/push-off power switch:

Kenmore 158 – Digital Power Switch

It’s held in place by a dab of epoxy on the bottom. The threads aren’t quite long enough to engage the ring, so another dab of epoxy holds that in place. In the unlikely event I must replace the button, I’ll deploy a punch and hammer it out from the top; the slick paint on the sides of the straight-sided hole doesn’t provide much griptivity.

The button connects in parallel with the GX270’s front-panel button and the one on the Low Voltage Interface Board, so it operates exactly the same way. My original code didn’t include a delay before turning the power off, which meant that brushing the switch while doing something else would kill the power.

This is not to be tolerated…

You (well, I) must now hold the button down for one second to turn the power off. Releasing it before the deadline has no effect, other than blinking the green power LED on the front panel a few times.

The routine maintains a timer that allows it to yield control to the mainline code, rather than depend on a blocking timer that would screw up anything else that’s in progress:
```
//------------------
// Handle shutdown timing when power button closes
// Called every time around the main loop

void TestShutdown(void) {
	
	if (LOW == digitalRead(PIN_BUTTON_SENSE)) {			// power button pressed?
		if (ShutdownPending) {
			if (1000ul < (millis() - ShutdownPending)) {
				printf("Power going off!\r\n");
				digitalWrite(PIN_ENABLE_AC,LOW);
				digitalWrite(PIN_ENABLE_ATX,LOW);
				while(true) {
					delay(20);
					TogglePin(PIN_PWR_G);				// show we have shut down
				}
			}
		}
		else {
			ShutdownPending = millis();					// record button press time
			printf("Shutdown pending...\r\n");
		}
	}
	else {
		if (ShutdownPending) {
			ShutdownPending = 0ul;						// glitch or button released
			printf("Shutdown cancelled\r\n");
		}
	}
}
```
The normal Arduino bootloader imposes a similar delay while turning the power on, which means that you can’t accidentally light the machine up by bumping the switch. All in all, it’s much more user-friendly this way.
2014-11-06

Kenmore 158 LED Strip Lighting: Now With Improved Wiring!

It Has Been Decided (in that place where what is decided must be) to allow a single hole in the sewing machine’s front panel:

Kenmore 158 - Front LED strip - wire routing — Kenmore 158 – Front LED strip – wire routing

The hole barely passes the 2 mm coaxial cable I’m misusing for the LED strips and is located where it:

Clears the machine’s metal frame to the upper left
Isn’t blocked by the knob’s mounting bracket to the lower right
Doesn’t snag the knob’s cam followers all over the insides
Lines up directly below the orange dot for pretty

The first three of those happen behind the front panel, inside the frame, where you (well, I) can neither see nor measure the locations. I used a large outside caliper to get a feel for where the hole could possibly fit, then got it right on the first try!

On the rear panel, it turns out that the presser foot lever doesn’t quite touch the top of its slot in the frame, so the cable for those LED strips can sneak through:

Kenmore 158 - Rear LED strips - wire routing — Kenmore 158 – Rear LED strips – wire routing

Just inside that slot, the cable turns right, passes into the endcap, then goes upward to re-emerge at the top, inside the channel used for the old 120 VAC zip cord that powered the incandescent bulb in the endcap.

I had some square cable clips lying around, so I used them, but the (yet to be designed) round versions will look better.

The grody frame tells you this is the crash test dummy machine I’m using to verify things before installing them in Mary’s machine.

The improved cable routing required different hole positions in the LED strip mounts:

Strip Light Mount - Drilled cable routing — Strip Light Mount – Drilled cable routing

The internal wire route follows the original 120 VAC zip cord’s route from the bottom of the machine to the endcap (on the left), with the new branch for the front LEDs curving over the main shaft:

Kenmore 158 - LED strips - internal wire routing — Kenmore 158 – LED strips – internal wire routing

The four-conductor ribbon cable also carries the supply voltage for the yet-to-be-built high intensity LED emitters in the end cap that will replace the 10 mm LEDs, with the ends terminated under the clamp in the middle. Those old steel wire clamps seem grossly oversized for the job, but that’s OK with me.

The ribbon cable eases past that whirling crank arm, then passes through the frame to the outside cover under the handwheel, where it just barely clears the drive belts. A few zip ties hold it out of the way.

The OpenSCAD source code offsets the wiring holes by 0.5 mm from the ends of the LED strips for easier wire bending, but is otherwise pretty much the same as before:

// LED Strip Lighting Brackets for Kenmore Model 158 Sewing Machine
// Ed Nisley - KE4ZNU - March 2014
//  October 2014 - tweak endcap length & channel position

Layout = "Build";			// Build Show Channels Strip

//- Extrusion parameters must match reality!
//  Print with 2 shells and 3 solid layers

ThreadThick = 0.20;
ThreadWidth = 0.40;

HoleWindage = 0.2;			// extra clearance

Protrusion = 0.1;			// make holes end cleanly

AlignPinOD = 1.70;			// assembly alignment pins: filament dia

inch = 25.4;

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

//----------------------
// Dimensions

LEDSegment = [25.0,10.0,3.0];		//  size of each LED segment
SEGLENGTH = 0;
SEGWIDTH = 1;
SEGHEIGHT = 2;

WireChannel = 3.0;				// wire routing channel diameter

StripHeight = 12.0;				// sticky tape width

DefaultLayout = [1,2,"Wire","NoWire"];
NUMSEGS = 0;
NUMSTRIPS = 1;
WIRELEFT = 2;
WIRERIGHT = 3;

EndCapSides = 8*4;				// endcap smoothness
EndCapShim = 0.5;				// additional space for easier wire bending

function EndCapSize(Layout) = [(2*WireChannel + EndCapShim),Layout[NUMSTRIPS]*LEDSegment[SEGWIDTH],StripHeight];

//----------------------
// 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) {

  RangeX = floor(100 / Space);
  RangeY = floor(125 / Space);

	for (x=[-RangeX:RangeX])
	  for (y=[-RangeY:RangeY])
		translate([x*Space,y*Space,Size/2])
		  %cube(Size,center=true);

}

//-- The negative space used to thread wires into the endcap

module MakeWireChannel(Layout = DefaultLayout,Which = "Left") {

	EndCap = EndCapSize(Layout);	// radii of end cap spheroid

	HalfSpace = EndCap[0] * ((Which == "Left") ? 1 : -1);

	render(convexity=2)
	translate([0,LEDSegment[SEGWIDTH]/2,0])
		intersection() {
			union() {
				cube([2*WireChannel,WireChannel,EndCap[2]],center=true);
				translate([-2*EndCap[0],0,EndCap[2]/2])
					rotate([0,90,0]) rotate(180/6)
						PolyCyl(WireChannel,4*EndCap[0],6);
			}
			translate([HalfSpace,0,(EndCap[2] - Protrusion)]) {
				cube(2*EndCap,center=true);
			}
		}
}

//-- The whole strip, minus wiring channels

module MakeStrip(Layout = DefaultLayout) {

	EndCap = EndCapSize(Layout);	// radii of end cap spheroid

	BarLength = Layout[NUMSEGS] * LEDSegment[SEGLENGTH];				// central bar length

	echo(str("Strip OAL: ",BarLength + 2*EndCap[SEGLENGTH]));

	hull()
		difference() {
			for (x = [-1,1])						// endcaps as spheroids
				translate([x*BarLength/2,0,0])
					resize(2*EndCap) rotate([0,90,0]) sphere(1.0,$fn=EndCapSides);
			translate([0,0,-EndCap[2]])
				cube([2*BarLength,3*EndCap[1],2*EndCap[2]],center=true);
			translate([0,-EndCap[1],0])
				cube([2*BarLength,2*EndCap[1],3*EndCap[2]],center=true);
		}

}

//-- Cut wiring channels out of strip

module MakeMount(Layout = DefaultLayout) {

	BarLength = Layout[NUMSEGS] * LEDSegment[SEGLENGTH];

	difference() {
		MakeStrip(Layout);
		if (Layout[WIRELEFT] == "Wire")
			translate([(BarLength/2 + EndCapShim),0,0])
				MakeWireChannel(Layout,"Left");
		if (Layout[WIRERIGHT] == "Wire")
			translate([-(BarLength/2 + EndCapShim),0,0])
				MakeWireChannel(Layout,"Right");
	}
}

//- Build it

ShowPegGrid();

if (Layout == "Channels") {
	translate([ (2*WireChannel + 1.0),0,0]) MakeWireChannel(DefaultLayout,"Left");
	translate([-(2*WireChannel + 1.0),0,0]) MakeWireChannel(DefaultLayout,"Right");
}

if (Layout == "Strip") {
	MakeStrip(DefaultLayout);
}

if (Layout == "Show") {
	MakeMount(DefaultLayout);
}

if (Layout == "Build") {

	if (false) {					// original no-drill wiring
		translate([0,(3*LEDSegment[SEGWIDTH]),0]) MakeMount([1,2,"Wire","Wire"]);		// rear left side, vertical
		translate([0,0,0]) MakeMount([5,2,"Wire","NoWire"]);				// rear top, across arm
		translate([0,-(3*LEDSegment[SEGWIDTH]),0]) MakeMount([6,2,"NoWire","Wire"]);	// front top, across arm
	}

	if (true) {						// front: drill panel, rear: route through foot lift lever
		translate([0,(3*LEDSegment[SEGWIDTH]),0])
			MakeMount([1,2,"NoWire","Wire"]);				// rear left side, vertical
		translate([0,0,0])
			MakeMount([5,2,"Wire","Wire"]);					// rear top, across arm
		translate([0,-(1*LEDSegment[SEGWIDTH]),0])
			rotate(180)
			MakeMount([6,2,"NoWire","Wire"]);				// front top, across arm
	}
}

2014-10-29

Tag: Improvements

Hotrod M2 Platform Support Stud Repair

Sony HDR-AS30V Audio: Fake Fur FTW!

Shimano SPD Pedals: Cleat Oilers

Sony HDR-AS30V Audio vs. Wind Noise

Kenmore 158: Motor RPM Sensor Deglitching

Kenmore 158: Power Switch Timing

Kenmore 158 LED Strip Lighting: Now With Improved Wiring!