Gas station without pumps

2016 October 24

Bike seat fixed

Filed under: Uncategorized — gasstationwithoutpumps @ 18:47
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This past weekend, I fixed my bike seat (see Broken bike seat and Flexible adhesives).

The idea of the fix was simple: to insert at 15mm diameter aluminum rod (6061 alloy, tempered to T6) that spans the break and the high-stress point on the other side of the clamp, which is also scored and likely to fracture, and glue it in place.

I found the rod I need at McMaster-Carr, with specifications of 15±0.23 mm diameter.  I thought it was slightly undersized at 14.7mm, measuring with my calipers, but my calipers are not so precise that I can be sure of that measurement.  Measuring with my micrometer gave 14.82±0.01mm, which is within spec.  I could have gotten a more precisely specified aluminum rod for an extra $10, but I did not think that it was worth the extra price—I may come to regret that, as the aluminum rod fits loosely, not snugly inside the tubing.  I cut the rod to length with a hacksaw (using oil to lubricate the blade) and ground the sharp edges down with a wet wheel, then sanded the rod both to round the ends and to remove most of the oxide coating and provide a rough surface for the epoxy. The rounded ends are to reduce the stress raisers at the ends of the rods, as that is now where the tubing should flex the most.

Aluminum rod: cut, ground, and sanded. The mark indicates where the break in the tubing should be.  The rod extends about 15mm past either end of where the clamp holds the tubing.  I would have extended it further, but I was worried about bending the aluminum tubing too far to open up the bike seat frame enough to get over the end of the tubing.

Aluminum rod: cut, ground, and sanded. The mark indicates where the break in the tubing should be. The rod extends about 15mm past either end of where the clamp holds the tubing. I would have extended it further, but I was worried about bending the aluminum tubing too far to open up the bike seat frame enough to get over the end of the tubing.

I sanded the inside of the tubing on the broken bike seat and the fractured ends to promote adhesion, and I cleaned both the rod and the tubing with rubbing alcohol.

In the comments on Broken bike seat, gflint suggested a silicone adhesive, but I ended up using a flexible epoxy, TotalBoat FlexEpox, that is designed for repairing boats.  It is supposed to adhere well to aluminum, have high tensile and flexural strength, and a very slow set time, plus it is fairly cheap at $18 for about 30 times more epoxy than I needed.

I mixed up tiny amounts of the epoxy in old cough-syrup measuring cups:

The cough-syrup cups did not make precision measurement of the resin and hardener easy, as both were quite viscous—I hope I got close to equal quantities. I suppose I should have gotten out the centigram scale and mixed by weight—that would probably have given a more precise ratio.

The cough-syrup cups did not make precision measurement of the resin and hardener easy, as both were quite viscous—I hope I got close to equal quantities. I suppose I should have gotten out the centigram scale and mixed by weight—that would probably have given a more precise ratio.

For the first gluing on Saturday, I coated both the inside of the tubing and the rod with the epoxy and inserted it to the desired depth. I wiped off excess (there was a lot that oozed out) with a paper towel wet with rubbing alcohol, and clamped the rod in place simple by letting the other part of the tubing press against the rod sideways. I used a little scrap of paper towel between the rod and the outside of the tubing to keep them from getting glued together:

The rod glued and clamped in place, with paper towel to keep the rod from sticking to the outside of the other part of the tubing.

The rod glued and clamped in place, with paper towel to keep the rod from sticking to the outside of the other part of the tubing.

On Sunday, I mixed more epoxy and coated the inside of the other piece of tubing and the piece of the aluminum rod sticking out, then lined up the tubing and let it close back together:

Excess glue squeezed out of the joint.

Excess glue squeezed out of the joint.

I clamped the joint together by wrapping bungee cords around the frame of the seat, and wiped off the excess glue with a paper towel moistened with rubbing alcohol:

The bungee cords provided a fairly large clamping force, but no more glue oozed out when it was added, so the springiness of the frame alone may have been sufficient.

The bungee cords provided a fairly large clamping force, but no more glue oozed out when it was added, so the springiness of the frame alone may have been sufficient.

On Monday, I worked on the clamp on the bike.

I rounded the edges of the clamp to reduce the stress raising that had led to the first failure—the edges had been quite sharp.

I rounded the edges of the clamp to reduce the stress raising that had led to the first failure—the edges had been quite sharp.

In addition to rounding the edges to reduce the stress raising, I also offset the seat by a few millimeters from where it had been, so that the glued joint is now slightly inside the clamp.

Before replacing the seat, I noticed that there was a bad rust spot behind the clamp, so I took the clamp apart to look at the frame:

The frame was quite rusty behind and inside the clamp.

The frame was quite rusty behind and inside the clamp.

I was going to sand the rust spots, prime with metal primer, and repaint the spots, but my metal primer was no longer any good, so I just did some light sanding and coated all the rusty spots with oil. I will have to buy some more metal primer and repaint in a couple of weeks when I next have time to work on the bike.

I put the bike seat back in the clamp and replaced the mesh seat, which had been washed to remove the road grime.

I plan to let the epoxy cure for another day before riding the bike (they claim a 7–10-hour cure time, 24 hours for high load, but I’ll go a little longer, as it is going to rain tomorrow anyway).

I’m hopeful that this fix, which cost under $50, will let the bike seat be usable for the next 15 years.

2016 October 13

Flexible adhesives

Filed under: Uncategorized — gasstationwithoutpumps @ 13:23
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I’ve started figuring out how to fix my bike seat (see Broken bike seat).  The idea is to insert at 15mm diameter aluminum rod (6061 alloy, tempered to T6) that spans the break and the high-stress point on the other side of the clamp, which is also scored and likely to fracture, and glue it in place. Originally I was planning to get someone to weld it, but that is looking like a bad idea—the heat-affected zone around the weld would lose 80% of its strength, unless the whole seat is retempered, which is a bit problematic with a powdercoat finish.  Also, grinding the weld down to the point where it is smooth enough to fit into the clamp would be difficult, and the result would again lose a lot of the strength.

I found the rod I need at McMaster-Carr, and it should arrive tomorrow, but I now need to choose an adhesive that is strong, flexible, and can cure in a thin film between the rod and the inside of the aluminum tube.

In the comments on Broken bike seat, gflint suggested a silicone adhesive, but most of the consumer ones are one-part adhesives that rely on exposure to moisture from the air to cure, which won’t work for a thin layer 10–15cm long between two pieces of aluminum.  There are two-part silicone adhesives that don’t rely on exposure to humidity for curing, but they are most marketed to industry, not easily available for one-shot end-user projects.  I don’t want to have to buy a $60 tool to apply the adhesive!

I started looking for flexible epoxies available to consumers.  Here is what I’ve found so far:

adhesive cost flexural modulus (stiffness) tensile strength flexural strength
TotalBoat FlexEpox $17.99 193,000psi 5,610psi 9,050psi
West System G/flex 650 $27.55 150,000psi ~2,000psi? or is that overlap shear strength?
Marine-Tex FlexSet $29.67 ? ? ?

Bob Smith Industries BSI-203H Mid-Cure

$8 3800psi
3M Scotch Weld DP-125 $41.52+applicator ? 3300psi (2200psi overlap shear) ?

There are undoubtedly many others (Bondo 280, for example), but I’m having a hard time finding any technical information about them. The costs are what I could find on Amazon.

Currently, I’m leaning towards the TotalBoat FlexEpox, which is cheap, has decent specs, and a slow set time, so I have time to reposition things.  I might have preferred a slightly more flexible glue, but I think this will work.

2016 October 5

Broken bike seat

Filed under: Uncategorized — gasstationwithoutpumps @ 17:25
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Yesterday was not a good day for me.

First, I spent most of the day struggling with the homework for the control-theory class I’m sitting in on. The course is dual listed as an undergrad and grad course, with shared lectures but different homework and projects. The undergrad part of the homework was straight-forward, and I finished it Monday night, but the two additional problems for the grad students were tough.  One of them had a simple “engineering” solution that I got quickly by formal manipulation of the formulæ, but I could not justify some of the steps, since they involved a integral that was not finite.  The other problem was not difficult, but involved a rather tedious amount of algebra to linearize the system—the professor had done the linearization in lecture notes,  and we were just supposed to check it for the homework, but he’d made an error in algebra, so I had to redo the whole thing.

Late in the afternoon, I decided to take a break and replace the sump pump that had failed sometime in the past couple of weeks.  Originally I was going to disassemble the pump and see if the problem was repairable (I think that the switch for the float is not turning on reliably, possibly from corroded contacts), but I decided that I could do that later to have a spare pump, meanwhile getting a working sump pump.  (My house is built over a seep where an aquifer comes to the surface, and the water table is about 3 inches below the surface—during wet years, the water table is sometimes right at the surface.)

I put the old pump in my panniers and headed down to hardware store, when my bike seat suddenly failed.  I tried riding for a block with the failed seat and gave up and returned home.  The failure was right at edge of the block that holds the horizontal crossbar at the front of the seat:

Here is a view from the front showing the tubing displaced vertically from where it belongs.

Here is a view from the front showing the tubing displaced vertically from where it belongs.

A closer view shows a very clean break right at the surface of the block that clamps around the tube.

A closer view shows a very clean break right at the surface of the block that clamps around the tube.

I probably should have had some warning about the imminent failure, as the bike has been creaking a bit more than usual when I pedal for the past several months, but I was never able to track down the creaking. I’m not sure I could have seen the crack that was probably propagating, since it was flush with clamp block.

The seat on my Longbikes Vanguard is not a standard, off-the-shelf component, so I’m probably going to have to custom order a new seat from the manufacturer (who no longer make the Vanguard model, so probably has no spare seats built) and wait weeks or months for one to be built.

I got my old upright bike down from the garage wall, inflated the tires, adjusted one of my panniers to fit the different rack, and headed off to the hardware store, carrying the old pump in the pannier. At the hardware store, I could not find a sump pump with the same outlet size as the old one (they all had bigger outlets). I needed to match, in order to hook the sump pump up to the existing plumbing. Luckily, they did have a reducer that would adjust for the difference.

After buying the pump, I went out to my bike and realized that I couldn’t fit both pumps into one pannier—in fact the new boxed sump pump wouldn’t fit into the pannier even by itself. Normally I carry a bungee cord or two for strapping stuff onto my rear rack, but those were left on the other bike. So I had to go back into the hardware store to buy some new bungee cords—not a big deal, but an irritation.

The bike was a bit wobbly on the way home—I’d forgotten how much difference a high center of gravity makes on an upright bike—and the bike has much twitchier steering than my recumbent anyway—but I got home without incident.

On getting home, I immediately attached the pluming to the new sump pump and lowered it into the sump. Let me correct that—I tried to lower it into the sump, but it wouldn’t fit. The pump was a couple of inches wider than the old pump and though the hole at the top was more than wide enough, it narrowed significantly where the bottom of the foundation for the house spread out, and the remaining hole was simply too small for the new pump. This was particularly frustrating for me, as I was meeting my wife downtown for dinner in less than an hour, and I was going to have to walk rather than bike, so I only had about 10 minutes to come up with a fix.

I then remembered something that should have occurred to me much earlier—I had another one of the small sump pumps in a different sump in the back garden. Quickly pulling it out and attaching the plumbing got the main sump working again (though I still need to recheck the plumbing for leaks). And it turned out that the garden sump was wide enough to accept the new pump—problem solved!

I cleaned up, grabbed a backpack so I could do some shopping after dinner, and walked down to the library to meet my wife. After the stresses of the day, I felt the need for comfort food, so we went to Betty’s Noodles, a hole-in-the-wall Chinese restaurant in the bus station. This restaurant has taken over the niche that Little Shanghai used to fill of providing cheap, tasty Chinese fast food (noodles and rice bowls).  I had ma-po tofu over Chow Fun noodles, which went a long way to de-stress me.  Going to Mission Hill Creamery for a plum sorbet cone afterwards helped also.

On the walk home, a couple blocks before we got home, I realized that I had not done my shopping! I decided not to go back downtown, but to do without my chocolate soymilk for a couple of days, until I can go shopping again.

This morning I finished the homework and submitted it. I’m still a bit bothered about the inverse Laplace transform problem that  can be formally solved but that ends up with a function that doesn’t have a Laplace transform, but I’m pretty sure I did what was expected. After turning in the homework, I realized that there was a possible different interpretation of part of the linearization question than what I did, so I queried the professor about what he really meant.  (The homework isn’t due for a week, so if there is a clarification needed, he can get it to the grad students before the homework is due.)

The TA does not grade my homework, since I’m just auditing, but I’m doing the homework using Python instead of Matlab, so I’m sharing it with the TA and professor anyway, so they can see whether it would be worth switching to free tools.

Currently, the scipy.signal package and matplotlib seem as easy to use at Matlab, but there is no equivalent of SIMULINK, which the professor is relying on for students doing simulations.  I can do the simulations in Python, but setting them up is all text-based, and requires thinking explicitly about the state vector, rather than having a GUI that does all the setup for you.

I bicycled up to campus today on my old upright, after adjusting my other pannier to fit the rack.  I had forgotten how uncomfortable an upright bike is.  This evening my neck and shoulders are sore, and I have chafing on the inside of my thigh.  I really hope I can get the recumbent seat replaced quickly, so that I can go back to riding comfortably!  It might even be worth taking the seat to a local frame-builder and finding out whether they could replace the tube, even if only for a temporary fix. (Although most of the bike is chrome-moly steel, the seat appears to be all aluminum tubing.)

2016 October 1

Nineteenth weight progress report

Filed under: Uncategorized — gasstationwithoutpumps @ 09:08
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This post is yet another weight progress report, continuing the previous one, this being the 19th since I started in January 2015.

For the past year, the trend line has had a slope of 3.76 lbs/year.

For the past year, the trend line has had a slope of 3.76 lbs/year.

weight-2016-oct-01

 

Exercise has been very low the past two month, with only 2.63 miles/day of bicycling. It is picking up again, as I’m cycling to campus 3 or 4 times a week to sit in on classes during my sabbatical. (I’m taking feedback control theory, something I’ve been meaning to learn on a formal basis for some time now.)

I skipped the report at the end of August, because I was embarrassed about the whole month being above my self-imposed target range, and I thought that September would bring me back in range.  Of course, the upshot was that September was even worse than August, so I now have two solid months above my target range. The really big spike in mid-September may not be a sudden change in weight—we moved the scale to weigh my son’s luggage before his return to college, and the scale always changes its readings after being moved. (I think that the larger  measurement is the more accurate one, though.)

I’d like to lose 5 pounds to get back to the middle of my target range, but I’m less hopeful that I’ll succeed at that than I was 2 months ago, as my trend lines keep getting steeper.

2016 September 10

Seven UC campuses in top 30 on Sierra Club list

Filed under: Uncategorized — gasstationwithoutpumps @ 11:30
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In the Sierra Club list of “Cool Schools” for 2016, seven of the ten University of California campuses rank in the top thirty for sustainability.

rank campus score
  3 UCI  734.38
  8 UCD  714.50
 18 UCSC  670.87
 24 UCSD  657.99
 27 UCR  656.65
 29 UCB  655.00
 30 UCSB  649.18
 62 UCLA  595.56
 84 UCM  571.16

Note: UCSF is not ranked, because it has no four-year undergraduate program, just a med school.

Because the Sierra Club relies heavily on self reports by the campuses, it is not clear that the numbers are really directly comparable. Different standards will be applied in answering the questions, with some colleges really stretching the definitions in order to appear sustainable, and others having very strict standards in which well above average behavior and facilities are deemed inadequate.

Their point system is based on the Sierra Club’s particular beliefs about what is important (giving a lot of points for divestment from fossil fuel companies, compared to the points given for low use of fossil fuels, for example).

They also reward reductions in water consumption and energy usage “since an established baseline period”, but there doesn’t appear to be any uniformity in when the baseline was established nor any reward for having always been a low consumer.  A water-usage per student and energy-usage per student measure would probably paint a very different picture, with places like UCSC (which have always been sparing in both their energy and water usage) moving way up in the ranking.  Of course, energy usage varies a lot with the climate, and coastal California campuses should be able to use a lot less energy than ones in Michigan and Minnesota—but sustainability measures should not start out by giving bonuses for building in places that require unsustainable practices.

Some of their standards are a bit strange, giving as many points for a “bike-sharing program” as for “bike storage, shower facilities, and lockers”, and nothing for bike lanes/paths.  Bike-sharing programs are pretty much PR fluff on a college campus, but bike parking is crucial (though for commuters policies that allow bikes in the office are often better than lockers or bike storage facilities).

UCI, UCB, UCSD, and UCSC all do better in their transportation rankings than UCD, but I suspect that UCD actually has the lowest per-student or per-employee transportation impact, because the very much larger share that bike commuting has there.  They may be giving more points for public transportation than for bicycling, which would explain Columbia University being at the top of their ranking.

Unfortunately, the Sierra Club does not seem to have made the raw data from which they did the scoring available, so it would be difficult to redo the rankings based on different weighting of the criteria, and difficult for student organizations to determine where their campus is missing the mark, in order to push for improvements.

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