Incremental Backup

• So far, I've lost about 55 lbs. That's 4 or 5 pant sizes, I think, plus now my winter coat doesn't fit anymore. Naturally my workplace has NOW decided to have a Biggest Loser contest. I could have won one of these fabulous prizes! I'm almost tempted to regain it all so I can lose it for the free iPhone. (Actual prize may vary.)


• The PVC piston idea doesn't work. Or rather, it works really well, but not for high temperatures. Maybe a water pumping thing might work, but otherwise it just gets gummed up with melty yuck. Also using insulation for the displacer is contraindicated as a fire hazard. /turns off smoke alarm. Needless to say, the engine was unsalvageable.


• Because of the above, I'm starting a new engine. For various reasons, probably all stupid, I'm thinking of going rhombic. I sat down the other day to quickly figure out the stroke length given stuff like the gear diameter. Just an easy little geometry problem until my face imploded. Also, finding cots (commercial/off-the-shelf) hardware that can be used for a medium-sized Stirling is non-trivial.


• This cool thing is in free beta. I hope that doesn't mean they are going to charge for it later, because then we won't have future classics like Two Regular Guys.


• I got a Moleskine "square" (i.e. graph) paper notebook for Christmas. Coupled with my mechanical drawing pencils, it is really awesome. I should post some pics of what I've been doing with it.


• Read Clock of the Long Now. It was very interesting and enlightening and life-changing and so forth, but they left out sufficient detail for my geekiness: Details on the mechanism. It's a single-function, mechanical, binary computer. Like the Difference Engine only in binary. Should be a snap to implement in Lego. I even started designing it but I just don't have enough time to do more than that.

How Do You SolveRepresent A Problem Like Mariaechanics?

First, this. (Explanation)

It would be cool to make something like that, but more general. A wider scope of problems, more construction elements, more universal attachments, etc.

The standard method of genetic programming is to represent your algorithm/whatever as a tree. The leaves are data and the nodes are operations that the "universe" supports. Then two parents producing a child via "sex" is just trading subbranches. Mutation is random changes.

That works for a linear sequence of steps because there's a standard way to traverse a tree. The question is, how do you represent a machine in a tree? It's (usually) not a linear thing.

Take a wheel and a stick. They are two leaves, I guess. The node is the operator "attach"? But where? I need to know where on the stick AND where on the wheel. And if the connection is rigid, floppy, powered or what. Where is all that knowledge stored? How can I "break out" each of those things to allow them to mutate separately? Also, you can't have a whole-organism coordinate system, for instance, because a single mutation messes it all up.

Another idea is to use an algorithm to build the machine and represent the algorithm as a tree. But what's the advantage of that? I didn't realize until this morning: This is exactly what embryology is. A machine isn't a linear object, but constructing a machine is a linear process.

So to attach a wheel and a stick, I'd have an embryology something like this:

1) Place stick
2) Locate end of stick
3) Locate center of wheel
4) Attach

Or maybe:

1) Place stick
2) Advertises marker at X
3) Locate marker
4) Locate center of wheel
5) Attach

The marker system would be key. If there's more than one stick in the structure, "locate end of stick" is ambiguous. Whereas if the stick knows that it is, say, the left shin, it can hang out cards saying "I'M THE LEFT SHIN" and "HERE IS MY LOWER EXTREMITY" and the wheel can look for that.

Could one of my graduate students get on this and give me credit so I become rich and famous but don't have to stop the N projects I'm working on to get it done? Kthx!

Discoveries

• The biggest difficulty in making something like a Stirling engine without access to a machine shop is how to make the power piston. The piston has to be precisely sized to fit inside the cylinder. However, via a YouTube video, I have discovered that it is possible to use a pair of PVC pipes to get the same effect. I made one and under breath power it worked so well it nearly knocked my teeth out. I haven't done any real testing yet, so I don't have all the construction details worked out, but basically you just get two sizes that differ by 1/4" and sand down the smaller until it fits in the larger.


• The way I'm going to test the piston is to build another Stirling. Need a bigger displacement chamber for a piston this big. Should be metal, not too thick-walled, largish, easy to make air-tight. A paint can would be perfect, except you don't want to combined leftover fumes and high heat. Turns out Lowe's sells empty paint cans! Quart- and pint-sized. That means you can even remove the lid to work on the innards and then reseal it.


• What with one thing and another, the flywheel on the new engine has to be mounted differently. I need a whole crankshaft dealie (which is something else it would be easier to make with a machine shop). Once I realized this, I realized I'd also need some kind of bearing. Idly reading something completely unrelated, I came across a mention of "skate bearings". I was thinking inline skates, but skateboards have the same thing. They are only like $1 each! And I even had an unused skateboard at home, from which I harvested 8 of them. ID ~8mm, OD ~22mm. Cute as a bug's bearing.


• I've had these drawing pencils for a while now. The leads are 2H, HB, 2B and then some high B one, I dunno what. The problem is you have to keep sharpening them like every 15 minutes. The other day I realized this is already a solved problem: mechanical pencils. The only question was, do they sell mechanical pencil leads in hardnesses other than HB? Answer: Yes. So now I have 3 mechanical pencils, each with a different lead. Makes drawing so much less of a hassle. Can't shade with the side of the lead, of course, but I never did that anyway.


• I'm not going to meet my Xmas diet goal. Scale is still going down, but too slowly to make it in time. Maybe I should aim for the secondary goal (an additional 10 lbs) at the 2 year mark (March?).

Forming Acrylic Mirror

I think all this information exists in previous entries, but it's nice to have all my knowledge, however little that is, dumped into one spot.

Heat forming acrylic (aka plexiglass) is pretty simple. Just get the temperature up around 220°F and it's pliable. I put it into the kitchen oven. Don't rely on the oven temperature, though, use something with a probe to tell if you've got the real temp. For one thing, you can put the probe right down where the mirror is, not just floating around in the air inside the oven. Also, when I was researching this I found some warnings about fumes. I think that's only if you overheat because I never smelled or sensed anything. Maybe I've silently shortened my life by 20 years.

I tried a couple different methods of using a form. The first couple tries were "open-faced," meaning I laid the acrylic on top of something and counted on the weight of the material itself to cause it to sag into the form. It isn't really heavy enough for that, so I moved to a two-part form. It takes longer to heat that way because of the mass of the form itself. Another disadvantage of this method is that you have to be able to force the mirror into shape before you heat it, which means no 2D curves (like a bowl, if you see what I mean). Actually, you probably could do that by putting the acrylic sheet between the halves of the form and then weighing the top part down. Like the open-faced method, but with extra weight. Drill a hole in the form so the temp probe can sit right on the acrylic.

The above should give pretty nicely formed acrylic sheet even in complex shapes. Unfortunately it's totally unworkable for acrylic mirror. I'm not sure if it's the acrylic or the mirror backing, but the heat stresses the material such that you don't get a smooth reflection anymore. For a while I thought it was imperfections in the form, but various experiments ruled that out. (You can get bumps and ridges from a rough form, though, which can be eliminated by loosening the form a little or by lining the form with some kind of bumper material. I used a sliced up silicone baking sheet.)

Also: I never got far enough to have this problem, but eventually you'll run out of space in the oven. Multi-part forms? Some other heating method?

The curve I wanted wasn't 2D, so how about cold forming (aka "bending")? I have not yet determined the point at which the acrylic cracks or deforms. I haven't even determined if there's some point short of complete destruction where the mirror breaks down, a la the heat deformation. It seems to be pretty sturdy and stable, but then I'm not making tiny radius curves. If you imagine bending a yard stick, that's about what it seems like, or maybe a little stiffer. Put another way: I have a square of acrylic mirror that's 2'x2' bent into a curve about the same as the side of a 55 gallon drum and I haven't see any problems with it. (This is the 1/8" thick stuff. There's also a 1/4" thick stuff that I've never tried.)

The trick with cold forming is that you have to hold it in place somehow. Even drilling a hole through the acrylic will deform it, although only in the immediate area surrounding the hole. I started with a sandwich method--cutting two parts and then cramming the mirror between. That works, but you have to have some method of securing the bread of the sandwich that doesn't involve drilling through the mirror. Also, you cover up some portion of the mirror surface.

Of course, you can drill through the mirror, but in that case why even have the top piece of bread? That's what I switched to: Put the mirror on an open-faced form and drill a few well-placed holes to secure it down. Don't overtighten, because the force isn't distributed over a wide area like with the sandwich, so the local area can get quite deformed. Maybe a reason to have the top piece of bread after all. Or maybe just some rubber washers or silicone baking sheet for padding.

You can't get too fancy with this method, but for a single, relatively gentle curve it works great.

Massively Unparalyzed

• I think I'm out of the summer diet doldrums. I suddenly realized that if I stayed focused, I could meet my original goal by Christmas. I have to lose 1 lb every 10 days, which seems pretty reasonable. That's just ~350 calories/day. This is the same rate my overall history has been up til now, so as long as I keep, or *cough* get back on, that average I should be good. (I say "original goal" because after I meet that goal I think I'm going to go an additional 10 lbs. But I'll have to see how things stand when I get there.)


• I needed to sense sunlight vs shadow and I'd read somewhere you can do that using an LED somehow. I got that working but they aren't made for that and so it didn't meet even the low standards of this application. Some photoresistors, even at RadioShack's redonk prices, were only $3 and work so much better.


• Also needed, or at least wanted to evaluate, pulleys. McMaster-Carr's site is so awesome, why can't my local hardware store (or even Lowe's) have a website like that? Or McMaster-Carr have an outlet near me.

  That said, my local hardware store fits an amazing depth and breadth of stuff into their store. I don't think there's been a single thing I couldn't find there that I was able to find at Lowe's, in the fields the LHS covers. (i.e. they don't sell appliances at all, so obviously they have a smaller selection of dishwashers.) And the reverse is not true--I've found things at the LHS that Lowe's didn't have. And they manage to fit all this stuff into an area that's probably literally no larger than the area devoted to just cash registers at Lowe's. Like, how is it possible that my LHS has a 9 ft² caribiners + pulleys display right next to the pumps I need (though are still more than I want to pay)?

  Oh and the staff actually know where things are and how to use them, unlike at Lowe's.

  I guess what I'm saying is, local hardware store:Lowe's::small European country:US. It may be a little more expensive, but the service and selection are great.



• How can I completely waterproof a wooden structure? How about sunproofing? Like, is it going to get baked and shrunken on one side? Probably somebody already knows all this stuff. No wonder people just build with metal. Oh wait, how about PVC? Does that degrade in the sun? Oh and it's hollow, so you can put wires in there....HMMMMM


• I was going to have an entry in here talking about all the things I suddenly (as of this morning!) have to do, but I can't even spend time enumerating them!