Tag: Repairs

If it used to work, it can work again

Tour Easy Front Fender Clip: Longer and Stronger

We negotiated the Belmar Bridge ~~connection~~ stairway from the Allegheny River Trail to the Sandy Creek trail:

Belmar Bridge Stairs - Overview — Belmar Bridge Stairs – Overview

We’re maneuvering Mary’s bike, but you get the general idea. Our bikes aren’t built for stairways, particularly ones with low overheads:

Belmar Bridge Stairs - Low Overhead — Belmar Bridge Stairs – Low Overhead

The front fender clip on my Tour Easy snapped (at the expected spots) when the mudflap snagged on one of the angles:

Belmar Bridge Stairs - First Turn — Belmar Bridge Stairs – First Turn

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:

Tour Easy front fender clip - expedient repair — Tour Easy front fender clip – expedient repair

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:

Front Fender Clip - Slic3r — Front Fender Clip – Slic3r

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,3FenderThick/cos(180/FerruleSides),10StayDia + 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();
	}

view raw Front Fender Clip.scad hosted with ❤ by GitHub

As a bonus for paging all the way to the end, here’s the descent on the same stairway:

Belmar Bridge Stairs - Descent — Belmar Bridge Stairs – Descent

No, I wasn’t even tempted …

2018-07-24

Tek A6302 Current Probe: Offset Resistor Tweakage

A package deal of two Tektronix A6302 current probes arrived from eBay, with one probe having a small crack across its case (shown in the description and bought accordingly).

The other probe worked fine and was quite clean inside:

A6302 B055461 – major sections

The cracked one couldn’t be balanced, with the twiddlepot on the AM503 amp unable to bring the signal down to 0 V from a positive offset on any of the ranges.

The current transformer might have suffered some stress on the upper-left corner of the main part (in the probe body), but it doesn’t have any obvious damage:

A6302 B032444 – ball – current transformer in place

The small ball to the left of the transfomer lid provides the slide detent; it’s an ordinary 3/32 = 0.094 inch bearing. Which, as it happens, is a Good Thing, because there’s another one exactly like it somewhere in the litter under the Electronics Workbench.

Protip: follow the disassembly procedure in the instruction manual and do it over a towel or, at least, a shallow dish. You have been warned.

Extracting the transformer from the body revealed a numeric value I didn’t recognize at the time:

A6302 B032444 – current transformer

The top slide contacts looked awful, but they’re actually covered in semi-dried contact grease and cleaned up easily:

A6302 B032444 – slide contacts

Swapping the “bad” transformer into the P6302 probe I got a while ago showed it wouldn’t balance, either, but the offset was far off into negative voltages. Putting the “good” transformer into the “bad” probe produced a similar too-positive offset. Conclusion: the transformer was probably good and Something Else was wrong.

Spending more time with the manuals produced this hint in the AM503 Amplifier circuit description:

AM503 manual – Hall offset – probe resistor selection

Fortunately, the AM503 probe connector has pin labels:

Tek AM503 Amplifier – Probe Connector – pin ID

Note the absence of pins G and I, probably to eliminate any confusion with “ground” and “one”, respectively.

Continuity checking reveals the left end of the 34.8 kΩ resistor connects to pin H:

A6302 B032444 – PCB 34.8k offset R

Huh. Even a blind pig occasionally finds a truffle: where have we seen that value before? Apparently Tek measured each transformer / Hall sensor and wrote the appropriate offset resistor value exactly where it’d do the most good.

Although I don’t pretend to know why the transformer offset has changed, if Tek can select a resistor to correct the offset, so can I:

A6302 B032444 – PCB – tweaked 82k offset R

The 82 kΩ value roughly centers the offset twiddlepot span around 0 V; it’s the result of a binary search through the resistor drawers, rather than a complex calculation.

With the resistor in place and the probe reassembled in reverse order, everything works the way it should:

Tek A6302 – 82k ohm offset – 50 mA

The lower trace is a square wave from the scope’s arb waveform generator into a (likely counterfeit) Fotek DC-DC solid-state relay, with the bench supply dialed to 5.7 V to put 5 V across a hulking 100 Ω power resistor, thus 50 mA through the probe. The purple trace comes from the repaired probe, with the other one turned off for pedagogic purposes:

Tek A6302 Calibration Setup

That wasn’t easy, but seems to solve the problem.

Dang, I loves me some good Tek current probe action …

2018-07-19
Rt 376 at Red Oaks Mill: Re-repaving

For unknown reasons, NYS DOT milled away some of the newly laid asphalt north of Red Oaks Mill:

Rt 376 Red Oaks Mill – New Pavement Milling

Then laid it down again:

Rt 376 Red Oaks Mill – New Pavement – 2018-06-14

As far as we can tell, there’s absolutely no difference, other than the opportunity for a huge longitudinal crack between the shoulder and the travel lane.

My guess: the contractor shorted them an inch of asphalt, got caught, and had to do it over again.

It’s only NYS Bike Route 9, so you can’t expect much in the way of bicycle-friendly design or build quality.

2018-07-16
Tour Easy Rack: Front Mount Screw

Long ago, I conjured a front rack mount from an aluminum bar across the seat struts on our Tour Easy recumbents, with a spherical washer soaking up the angular misalignment. The rack on Mary’s bike developed a serious wobble due to a missing screw, which was easy enough to replace:

Rack mount screw – rear

From the side:

Rack mount screw – side

It’s a 2 inch screw sawed down to 1.5 inch, ground to shape, then run through a die to clean up the threads.

The nylon lock nut over on the left should keep the screw from working its way out of the tapped aluminum bar. On the other paw, a dab of Loctite survived nearly a decade of heavy loads and vibration.

2018-07-09
Bypass Lopper

Some surreptitious brush clearing called for a tool larger than our wonderful Fiskars PowerGear pruner, so I unearthed a long-disused bypass lopper in the garage (it may have Come With The House). Alas, the pivot bolt lost its jam nut long ago:

Bypass loppers – OEM 10 mm bolt

That’s an M10x1.5 bolt, for which I lack a corresponding nut.

But 3/8-16 is approximately M10x1.5, for small values of thread engagement, and I do have an assortment of inch-sized stainless steel fasteners:

Bypass loppers – 0.375 inch bolt

The nylon lock nut jams the bolt against the left blade, with the split washer applying pressure to the tapered blade. Slobbering oil in the sliding joints restored it to perfect working order.

The weird round dingus on the far side of the pivot, up against the handles, is a bumper cushioning the fully closed position. It’s a nice touch and might work better if its rubber pad hadn’t aged out over the decades spent in the garage waiting for this very day.

It’s my kind of yard work: “What do you need killed next?”

2018-07-07
Bike Brake Pad Wear

The rear brake on my bike wasn’t stopping nearly as well as it should, even after cleaning the rim and pads with brake cleaner, so I pulled the shoes and replaced the pads:

Bike brake pad wear

It’s down a bit beyond the --WEAR--LINE-- indicator, of course.

New brake shoes on clean rims work exactly like they should!

2018-07-05
Xubuntu 18.04 vs. VNC
For unknown reasons, the Gnome-ish vino-server package for Xubuntu 18.04 no longer installs vino-preferences, so it’s not obvious how to configure the server.

After considerable flailing, I installed good old x11vnc, set up a password, then started it in .xprofile:
```
x11vnc -forever -find -no6 -avahi -usepw
```
I don’t mind having programs change, but it’d be nice if features like, say, configuration wouldn’t just vanish.
2018-06-27