Gas station without pumps

2017 May 27

Electric lawnmower repair

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I have a Black and Decker electric lawnmower (model MM1800 type 1), which I have used for a few years, ever since my previous electric lawnmower failed.  A few weeks ago, the lawnmower failed while I was mowing the waist-high grass in the backyard (a heavier load than the mower is designed for).  The failure mode was an interesting one, though—it blew the circuit breaker for the outdoor outlet.  I figured that some of the wet grass had gotten into motor compartment and shorting out the circuit, so I left the mower in the sun for a couple of hours to dry out and tried again.  It still blew the circuit breaker, so I put the mower away until I had time to work on it.

Last weekend, I took the cover off the mower to see if I could see an obvious short circuit.  This looked like it would be an easy job, as the cover is just held down by 6 screws, but the screws are recessed, and there was so much impacted grass built up over them that it took half an hour or more to dig out the grass enough to turn the screws.  One I got the cover off, the amount of grass inside the motor compartment was scary—after dumping out about 200 cubic inches of grass, I spent half an hour with a vacuum cleaner and a screwdriver cleaning off the stuck-on grass clippings.  Here is what it looked like after cleaning:

The mower is very simple, and looks pretty good after all the grass clippings have been removed. All those spaces between the reinforcing ribs were packed solid with grass clippings.

I thought that perhaps the huge buildup of grass clippings had been causing the short circuit, but after removing all the grass, I saw no signs of blackened wires or other evidence of arcing. I also disassembled the switch handle to look for evidence of shorts there. Again, there was nothing visible. I tried powering up the mower while it was open—still the circuit breaker blew instantly.

The lawnmower design is a simple one:

The motor driving the blade is a large brushed DC motor. The switch either provides power to the motor (on) or shorts it out (off) to brake the motor.

There is easy access to the wiring.

Here is what the rectifier looks like in situ. The four wires are on slide-on connectors, and the rectifier is screwed to a small metal plate that acts as a heat sink.

I got out my cheap ohmmeter and started checking continuity and measuring resistances. I quickly determined that the switch was working correctly, and the the motor itself did not seem to be shorted, but the bridge rectifier was acting as a short across the AC inputs, even with no load connected. I then looked online and found a site that said that the bridge rectifier was one of the most commonly failing parts for the Black and Decker mowers, and that Black and Decker charged ridiculous amounts for replacements. They also said that the part was a 15A, 400V bridge rectifier in a standard package. The one in my mower was labeled GBC2504, which is a 25A, 400V bridge rectifier (so, for that matter, is the own shown on the web page that claimed it was a 15A one). I ordered a 50A, 1000V bridge rectifier from Digikey, which cost $1 more than the closest equivalent to the one Black and Decker used, but even with shipping was half the price of the list price of the poorer rectifier from B&D. Based on the derating curves on the data sheet, the 50A bridge rectifier should be able to run about 30°–40°C hotter before it fails. My only concern is that this might be too good—that B&D was using the rectifier as a cheap point of failure at high temperatures. With the better rectifier the motor might overheat and burn out before the rectifier fails, and a replacement motor is not a $3.50 part.

This morning I replaced the bridge rectifier with the new one, being careful to clean the metal plate and put on new thermal grease to get good thermal contact to the heatsink. The mower started up right away and gave me no problems with mowing the front lawn. I’ll try tackling the waist-high grass tomorrow, but today I need to do some grading. (I have a homework set and something like 22 redone lab reports to grade during this long weekend—I think I’ll be able to clear that this weekend before getting more redone reports on Wednesday.)

2017 May 19

Baking in inequity in funding

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UCOP (University of California Office of the President) and the UC Regents recently decided to limit out-of-state students at UC campuses.  But they did not do so uniformly across all campuses.  They decided to let UCB, UCLA, UCSD, and UCI have more out-of-state students than the other campuses and to keep the extra tuition collected.

This continues a pattern that has been in place at least as long as the 31 years I’ve been at UCSC of ensuring that UCB and UCLA get more funding per student than the younger campuses.  I’ve seen no evidence that UCOP or the UC Regents have any intention of ever treating the campuses equitably.  Even when they are strongly pushed to do so, they find ways to weasel out and bake in extra money for UCB and UCLA (like the “rebenching” initiative, which was touted as redressing imbalances, but ended up making them worse).

2017 April 30

Twenty-second weight progress report

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This post is yet another weight progress report, continuing the previous one, this being the 22nd since I started in January 2015.

Although I had a few days in my target range in the middle of March, my weight spiked after that and has not come back down.

 

The longer-term trend is a bit disheartening, because it suggests that even if I'm fairly diligent about my current diet, I'm likely to be back where I started within four years.

The longer-term trend is a bit disheartening, because it suggests that even if I’m fairly diligent about my current diet, I’m likely to be back where I started within four years.

The weight spike at the beginning of April was the result of my trip to Ashland for the Oregon Shakespeare Festival.  I ate too much and exercised too little on the trip.  I don’t think that this is what people have in mind when they say that “travel is broadening.”

My goal for Spring quarter is still to get my weight back down to 158 lbs, another 6-pound loss, which seems a bit unlikely in the remaining 6 weeks, as I have not even been able to hold steady at a my mid-March weight, much less lose.

My exercise for March and April 2017 was about 4.58 miles a day of bicycling, with a slightly higher pace going up hill than I usually use, though probably not enough difference to constitute more exercise, just somewhat faster exercise.

2017 April 29

Santa Cruz Mini Maker Faire 2017

Today I spent about 10 hours on the 2017 Santa Cruz Mini Maker Faire.  The hours for the Faire were 10–5, but I spent some time setting up and tearing down afterwards, so I left the house around 8:30 a.m. and had the bike trailer unpacked and everything back in the house by about 6:30 p.m.  I figure that I spent only about 10 hours earlier on setup for this Faire: applying for the Faire, setting out all the displays and testing them at home, preparing new blurbs for my book and blog, making table signs telling people how to use the interactive parts of the display, blogging about the Faire, and doing load-in last night.  That is a lot less than last year, as I was able to reuse a lot of the design from last year.

Here is the table display I ended up with:

The bare corner at the front left was reserved for the students in my freshman design course who were coming to display their muscle-controlled robot arm, but they decided to set up in back (you can see one of the lead students in the background).

I had four interactive displays (from left to right):

  • A pair of function generators and an oscilloscope showing Lissajous figures.  I changed this from last year, as I did not use the FG085 function generator this year, but one of the function generators from the Analog Discovery 2.  I still used the Elenco FG500, despite the very low quality of its waveforms, because it has a knob that is easy for kids to turn, and is easy to reset if they mess it up (unlike the jamming buttons on the FG085).  I did not use the second function generator on the Analog Discovery 2, as I did not want kids playing with just a software interface (and a rather complicated one at that).  It might even be worthwhile for me to build a simple audio sine-wave oscillator with a single big knob over the summer, so that I can have something for kids to play with that is fairly robust and that can’t be easily set into a weird state.  I could even do two, just for Lissajous figures, though having one fixed oscillator worked well this time.  I had the Analog Discovery 2 oscilloscope showing on the laptop next to the old Kikusui CRT oscilloscope, showing both the waveforms and the XY plot, so that I could explain to adults what was happening with the Lissajous figures and about the differences between classic oscilloscopes and modern USB-based ones.
    A lot of people asked me about the Analog Discovery 2, which I was very enthusiastic about—Digilent should be giving me a commission! (They aren’t, although I’m sure I’m responsible for at least half a dozen sales for them, and a lot more if we go ahead with our plan to use them in place of bench equipment in my class next year.)
  • In front of the laptop showing the Lissajous figures, I had a standalone optical pulse monitor using the log-transimpedance amplifier and the TFT LCD display.  Using the log-transimpedance amplifier worked well, as did using a lego brick to block light to the sides and back of the phototransistor.  A lot of people have trouble holding their hands still enough to get good readings (particularly children), so it would be good to have some sort of clip instead of resting a finger over the phototransistor.  I’ve tried making clips in the past, but I’m not good at mechanical design, and I’ve always ended up with either a clamp that is too tight (cutting off circulation and getting no reading) or too loose (falling off).  Ideally, I’d want a pressure between systolic and diastolic pressure, so about 12kPa (90mmHg).  People did like the use of Lego as a support, though—it provided a familiar element in the strange world of electronics.
  • To the right of the pulse monitor was a pressure sensor.  I had a mechanical gauge and the electronic sensor both connected to a piece of soft silicone tubing taped to the table top.  Kids pressed on the tubing to get an increase in pressure, visible on the gauge (about 20–60 mmHg) and on graph PteroDAQ was running on the little laptop (which we refer to as the “Barbie” laptop, because of its color and small size).  I explained to kids that the tubing was like the tubing stretched across roads sometimes to count cars, with a pressure sensor that recorded each pulse as wheels compressed the tubing.  (For some of the old-timers, I reminded them of when gas stations used to use a similar system.)
    PteroDAQ worked well for this setup, running all day at 20 samples per second without a glitch.  The only problem was occasional display sleep from the laptop, fixable by touching the touch pad.
  • At the far right end of the table, I had a phototransistor which kids could shadow with their hands, with the result visible on another channel on PteroDAQ.  This was a last-minute change, as I was getting very unreliable results from the capacitive touch sensor when I tested it out last night.  The capacitive touch sensor worked fine at my house, but in the kindergarten room at Gateway I has a different electrical environment, and it would not work unless I grounded myself. Rather than fuss with the touch sensor, I made a new table sign and put in a light sensor instead.
    I might want to experiment this summer with different ways of making touch plates—trying to get one that doesn’t rely on the toucher being grounded.  My initial thought is that if I have two conductors that are not too close together, but which would both be close to a finger if the touch plate is touched, then I may be able to get more reliable sensing.  I could try some wire-and-tape prototypes and maybe make PC boards with different conductor layouts.  (OSH Park‘s pricing scheme would be good for such tiny boards).

I also had my laptop displaying my book; some quarter-page blurbs with URLs for my book, PteroDAQ, and this blog; my 20-LED strobe; my desk lamp; and a PanaVise displaying one of the amplifier prototyping boards.

I’d like to think of a more exciting project for kids to play with next year—perhaps something I could build over the summer.  Readers, any suggestions?

In addition to my display, some of the freshmen from my freshman design seminar class demonstrated their EMG-controlled robot arm (which uses the MeArm kit):

The students built a MeArm from a kit, then programmed a Teensy board to respond to muscle signals amplified by amplifiers designed by other students in the class. The combined project had two channels: one for controlling the forward-backward position of the arm (using the biceps), the other for controlling the gripper (using muscles in the forearm). With practice, people could pick up a light object with the robot arm.

The scheduling of the Mini Maker Faire was not ideal this year, as it conflicted with the Tech Challenge, Santa Cruz County Math contest, the California Invention Convention, and the Gem and Mineral Show, all of which draw from the same audience as the Mini Maker Faire.

The Faire seemed to be reasonably well attended (rather slow for the first hour and half, but picking up considerably in the afternoon).  There was plenty of room for more exhibitors, so I think that organizers need to do a bit more outreach to encourage people to apply.  It would probably help if they were quicker responding to applicants (it took them over three months to respond to my application, and then only after I nudged them).

Some obvious holes in the lineup: The Museum of Art and History did not have a display, but I saw Nina Simons there, and she said that MAH definitely plans to do it next year, but the Abbott Square renovation is taking up all their time this year.   The fashionTEENS fashion show was April 21, just over a week ago, so it would have been good to get some of them to show their fashions again: either on mannequins or as a mini-show on the stage.  It might be good to get some of Santa Cruz’s luthiers or fine woodworkers to show—we have a lot of top-notch ones, and many do show stuff at Open Studios. The only displays from UCSC were mine and the Formula Slug electric race car team.

Of the local fab labs, Cabrillo College Fab Lab and Idea Fab Labs were present, but The Fábrica and the Bike Church were not.  I thought that Cabrillo did a great job of exhibiting, but Idea Fab Labs was a little too static—only the sand table was interactive.

It might be good to have Zun Zun present their Basura Batucada show (entirely on instruments made from recycled materials) and have a booth on making such instruments.  It might be hard to get Zun Zun to volunteer, but they used to be very cheap to hire (I hired them to give a show at my son’s kindergarten class 15 years ago—they were very cheap then, but I don’t know what their prices are now).

One problem my wife noted was the lack of signs on the outside of classrooms, so that people would know what was inside.  The tiny signs that the Faire provided (I think—I didn’t get one) were too small to be of any use.  It may be enough to tell makers to bring a poster-sized sign to mount.  I had my cloth banner behind my table, but a lot of the displays were hard to identify.  Instructions or information mounted on tables would also have been good—again these would have to be provided by the makers.  I did not see people carrying maps this year—they can also be helpful in getting people to find things that were tucked away in odd corners.  Not many people made it back to the second kindergarten room where FabMo and the Lace Museum activities were.

Update 2017 May 1: It turns out that there were some things I missed at the Faire.  The principal of Gateway sent me email:

… we did have 4 of the Fashion Teens exhibit their creations on the stage at 11:30—might be cool to have them put those on mannequins and have a booth next year. Also we had two more UCSC projects—Jim Whitehead and the Generative Art Studio, and Project AWEsome from the School of Engineering. We would LOVE to have more UCSC-related projects …

 

2017 April 16

Recent theater events

Filed under: Uncategorized — gasstationwithoutpumps @ 20:46
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I have been so busy lately that I haven’t had a chance to do a blog post about the theater I’ve seen lately. The electronics course has mostly been responsible for my being busy—from March 20 to March 27 I was grading the huge pile of design reports for BME 51A, and classes started again on April 3.  Two weeks into the new quarter, I’ve just finished grading the third set of homeworks for BME 51B, and I’m already tired of grading.  (There are still six sets of exercises and five 5–10-page lab reports to come.)  I have a non-course pile of “grading” to do also: I’m on a committee to evaluate 22 project reports from across the School of Engineering for Deans’ and Chancellor’s Awards.  I’ve looked at four of them so far, and I have about a week to finish them.  They are a bit bigger than the little design reports (7–67 pages), but generally better written, and I don’t have to read them closely—just rank them to figure out which are the most award worthy.

But since I have my homework graded, I’ll take a break to list some of the plays I’ve seen lately:

date title playwright theater company
March 25 Dance of Death Strindberg Jewel Theatre
March 29 Julius Ceasar Shakespeare Oregon Shakespeare Festival
March 29 Shakespeare in Love Norman/Stoppard/Hall Oregon Shakespeare Festival
March 30 Henry IV, Part One Shakespeare Oregon Shakespeare Festival
March 31 Hannah and the Dread Gazebo Jiehae Park Oregon Shakespeare Festival
March 31 Mojada: a Medea in Los Angeles Luis Alfaro Oregon Shakespeare Festival
April 15 The Nether Jennifer Haley SeeTheatre

 

The Strindberg play did not quite sell out the Colligan Theater, but it was well attended by the usual crowd of white-haired theater goers.  Julie James gave herself one of the leads (what’s the point of owning a theater company if you don’t get to play lead?), but this time she was well-cast in a part that matched her skills, unlike some of her earlier attempts to play parts for women 20 years younger. The play was well-acted, but the directorial decision to use MP3 players and laptops jarred with the text in several places.  The set was a bit generic, but the costumes were good. Overall, I think that we all enjoyed seeing the play, but have no particular desire to see another production of it ever—it just isn’t that gripping a story.

Over  Spring break, my son and I both traveled by bus with people from Santa Cruz Shakespeare (staff, board members, and donors) up to Ashland, Oregon to see 5 plays there, to get a backstage tour, and to get a tour of the new production facilities in Talent, OR. My wife was unable to go, as her spring break is a week later than UCSC’s and UCSB’s.

Of the five plays we saw, Shakespeare in Love was the most fun, Mojada had the strongest emotional impact, and Hannah and the Dread Gazebo  was the most thought-provoking.  The two Shakespeare plays were the weakest productions.

The Julius Ceasar was a rather lack-luster production, with little attempt to get inside the characters’ heads, just showing us the public faces.  I found the Brutus (played by Danforth Comins) particularly disappointing, portraying Brutus as a weak and vacillating figure, rather than a man of strong principles who was so moral that he attributed high principles to everyone around him.  The dance theater elements really left me cold—it felt like I was watching a poorly produced music video on YouTube. The kata at the end seemed endless and monotonous. Others in our group had much more positive reactions to the play, and the reactions seemed to split based on whether or not people liked to watch dance.  The dance fans loved the play, and the non-dance fans did not.

The Henry IV, part 1 had a good Falstaff (G. Valmont Thomas) who was an excellent physical comic, and they really played the Eastcheap tavern scenes for all they could milk out of them, but the second half of the play fell flat.  Some of the cross-gender casting worked well (Lauren Modica as Glendower, for example), but I was not thrilled by Alejandra Escalante as Hotspur.  Don’t get me wrong—Ms. Escalante did a superb job of acting, but the machismo of the part made it very difficult.  (Note: I’m not at all opposed to cross-gender casting—last year’s female Hamlet at Santa Cruz Shakespeare was by far the best Hamlet I’ve seen.)  I think it would have been more interesting (though even more difficult) to make Hal be the female character—the father’s disappointment at not having a worthy son and Hal’s subsequent attempt to live up to the father’s dreams could have worked quite well as a female role, though the desire to keep the same actor for Henry IV, part 2 and for Henry V would have required a much bigger commitment to a female lead.  Some of our party thought that Falstaff’s comic acting was too much like minstrel shows, with too much caricature of black culture.  Others were uncertain whether Mr. Thomas was being directed to this caricature, or whether it was just his style of comic acting—I’m sure that black comics actors are forever wrestling with the dilemma of how to be funny to a wide audience without being disrespectful to their peers.  I’d be interested in hearing how black theatergoers react to his Falstaff.

Shakespeare in Love is a delightful romp through a lot of Shakespearean references (as well as big parts of Romeo and Juliet), and the actors and actresses all seemed to be thoroughly enjoying themselves.  The play is pretty close to the movie (at least as I remember the movie), which is unusual in a stage-play adaptation of a movie.  I was impressed by the teen actor playing John Webster (Preston Mead)—he did a good job of portraying a particularly ghoulish character.I think that this play will have the widest audience appeal of any of the five we saw.

Hannah and the Dread Gazebo was the strangest play I’ve seen in some time, with a lot of dream sequences and non-linear story telling. All the money for the set was spent on a massive wall that tilted down to make a rooftop.  We were told that the counterweight for the wall weighed 8000 pounds, and that combined with the rest of the wall, the total weight was around 10000 lbs.  The counterweight was not taken out of the theater on the twice daily set changes, but the rest of the set was. I was particularly impressed with the lighting design (by David Weiner), as the set took on very different characteristics with no change in the set pieces, just from the lighting.  The only disappointing set piece was the “gazebo” at the end, which was symbolically represented by a chandelier—this felt like a we’ve-already-overspent-our-budget move, rather than an artisitic choice. The quick costume changes needed by the Shapeshifter (Jessica Ko) were also technically very challenging (some of the changes had to happen on stage, as there was only 5–10 seconds for them). The play had an emotional resonance for some of the Asian-Americans in our group and perhaps a few other second-generation immigrants, but I found it more of an intellectual puzzle than an emotional play (despite being a second-generation immigrant myself).  I really needed more time to ponder it, but we had Mojada to see the same evening, which rather cut short my time for rumination.

Mojada was definitely a gut-punching play (as you would expect from any adaptation of Medea). The script kept many of the elements of Euripedes’s play, though a number of characters were conflated to reduce the cast size.  The acting was strong, but I found the set rather distracting—trying to make an L.A. slum apartment look like Baba Yaga’s hut was a little too strained.  They might have been better off producing the play on a bare stage.

The high point of the trip to Ashland was not the five plays (though they were definitely worth seeing—or the 3 non-Shakespeare ones were).  The high point was visiting the production facilities in Talent, OR. The custom-built space is a Makerspace par excellence for theater lovers. They have all the usual tools: 3D printers, laser cutter, CNC router, CNC lathe, machine shop, two wood shops (props and scenery), spray paint booth big enough for a car, robotics workshop, … with huge amounts of space. One wall of the paint shop has a grid large enough to hang the largest flies that any of their theaters can use, with theatrical lighting for it so that they can paint the backdrops vertically, rather than having to lay them on the floor. Their scene shop has a full-size mockup of the theater stages, complete with a 14-foot-deep pit for testing lifts to the stage, and that mockup is a small fraction of the whole scene shop.

Almost half the building is taken up with storage for costumes and props. The costume collection is amazing, and they rent out everything to theater companies and schools (with a big discount for community theaters and schools).  Almost everything is photographed and indexed on the web (https://www.osfcostumerentals.org/OSF-Costume-Rentals).  The props are not so well indexed nor do they have a formal rental program, though they have occasionally rented out pieces on a case-by-case basis.

This wall of shoes is part of the shorter wall of the room—the long wall would not fit in any of my pictures, nor would the many rows of racks double-height racks of clothes.

I took a few pictures in the costume storage area, but none were able to capture the sheer magnitude of the space and the overwhelming number and variety of costumes. This picture shows just a tiny fraction.

The most recent play I’ve seen is Jennifer Haley’s The Nether, which is still showing at Center Stage (through April 29). The play is intended to be thought-provoking (about what standards should apply to online entertainments), but the themes are a bit tough for many audience members: child abuse and murder of virtual characters.  Like in many science fiction works, there was a bit too much exposition, but the actors managed to keep things moving despite that. The highlight of the play was the performance by Olivia Gillanders, a fourth-grade student who played the role of Iris, the child avatar that is abused and murdered (off-stage). Nick Bilardello as Mr. Doyle and Andrew Davids as Mr. Sims were also quite good.  I felt that the April Bennett (as Detective Morris) and Robert Gerbode (as Woodnut), did decent jobs, but were not up to the caliber of the rest of the cast—their delivery was sometimes a bit wooden, and the characters lacked the intensity of the others.  Part of that may be in the script—the characters didn’t have as good lines—but they could have done more with what they had to work with.

The set was very simple, being split between an interrogation room (stage right) and the virtual world called the Hideaway (stage left).  The interrogation room was done in greys and ultra-utilitarian furniture, while the Hideaway attempted to be a lush Victorian parlor (not quite successfully, as the theater company lacked the budget, but well enough to give the impression of a virtual-world Victorian parlor).

I felt a little sorry for the actors, as the house was only about half full last night (I don’t think I’ve ever been to a production at Center Stage that was not sold out before, as the house only seats 89 including the wheelchair spot). The play is worth seeing, and there are two more weekends (tickets at http://www.brownpapertickets.com/event/2729920). I recommend that people buy tickets, even if they can’t go, in order to keep small theater companies from going bankrupt in Santa Cruz.

In addition to these plays, other recent cultural events include Viva La Lehrer IV (April 8 @ Kuumbwa Jazz, a celebration of Tom Lehrer songs) and a visit to the crochet coral reef on display at the Porter Sesnon Gallery at UCSC (which my wife and I went to April 14).

The Lehrer songs were fun, though I could quibble with some of their selections and how much time they gave to the weaker performers compared to the stronger ones—I don’t feel any need to go to Viva La Lehrer again for about another 5 years.

The CO2CA-CO2LA Coral Reef exhibit runs at the Sesnon gallery until May 6.  I recommend it for kids as well as for adults (one part is mounted in a dark room that you explore with flashlights).

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