Adapters

Posted on by Brian Garthwaite
Extruded aluminum telescope pier.
Expensive equipment goes on here.

A great many jobs in the daily work of a shop consist of riffs on this: can you make item A connect to item B? It might be physical connections, electronic and/or digital signals, or even the relatively abstract interpretation of transitioning a lab space over from one experiment to the next without disruption. The simplest ones are when someone can’t locate the proper connector cable. (There are so many different kinds!) Less simple are those times when two things are supposed to fit, but don’t.

Just straight-up don’t.

At the Tressler lab, we have the luxury of permanently-installed piers which support our telescope mounts. For our purposes, this is an excellent improvement over the default, a very stable yet heavy tripod. Now in the process of upgrading our mounts, we find that the tapped mounting holes on the pier don’t match the drilled and counterbored corresponding holes on the custom-made mount adapters. By 1/8″ or more in some cases. Sounds small. Is actually huge. Is will-not-fit-even-with-brute-force huge.

Note: not made in-house. We could try to guess where the error might have arisen, but our job is to fix it.

Also note: the previous mounting plate was not precisely machined to the proper dimensions, either, but was close enough that it was fastened by brute force. Sensing a theme here, which is this: precise measurements are crazy hard.

Pier with adapter plate.
Fix holes with more holes.

Getting to the adapter-for-the-adapter called for more than one CNC-milled plastic prototype. Measure, mill, test. Rinse, repeat. Polyethylene, as one might imagine, is cheap stuff.

A few test runs later, we have a custom-machined (in-house!) sheet of 1/2″ aluminum to connect to the 5/16″-18 tapped holes on the pier, which then sets up a new series of 1/4″-20 holes in this plate and the mount adapter to hold everything rock solid. Holes drilled and tapped, counterbored for a clean surface with all of those socket screws.

And all carefully measured and aligned on the milling machine to within 0.001″.

Telescope mount adapter, in place.
No one notices the unused holes in the dark.

You don’t appreciate the precision of reliable machinery and sharp tooling until the pieces slip together effortlessly. Whoa! Goosebumps!

Best part? The adapter is functionally invisible for anyone who doesn’t know to look for it. Few things feel as rewarding as solving a problem before (almost) anyone else realizes it’s there.

“The Perfect Cleaner”

Posted on by Brian Garthwaite
Capital Metal Polish can.
Buddy Brand!

Sometimes, stuff just lingers. It’s unclear how long it’s been sitting on this or any shelf, whether it has any use anymore, how on earth to dispose of it, etc. Of course, those odd objects tend to sport some of the coolest old labels.

So much to enjoy here! Buddy the dog, holding a flag with his name, but also helpfully labeled below as “Buddy,” just in case it wasn’t obvious enough. Directions for using metal polish on non-metallic surfaces, which – to be fair – might not be obvious. (Still mostly amounts to wipe on with a soft cloth, wipe off with a soft cloth.) The prime visual real estate for “Non-Inflammable,” which is an entertaining reminder of the flammable/inflammable quirk of the English language. What a country!

It’s not entirely clear if the yellow color was an original choice or has been caused by many years of aging paper.

Capital Metal Polish can back.
Seems pretty straightforward.

At any rate, the steel cap is thoroughly corroded shut, so there’s no telling what remains inside. Whether that corrosion is caused by or despite the contents of the Capital Metal Polish container, we’ll never know.

Colorful candy

Posted on by Brian Garthwaite
Box of bags of M&Ms.
Inside: milk chocolate, a statistics lesson, some artificial colors.

New concepts work better when there’s a hands-on element to engage students. It might be rockets, bouncy balls, lasers, or in the case of basic statistics concepts: candy. Specifically colorful candy. The physics labs have a long history of using M&Ms, though we hear that Skittles and Starbursts have their partisans, too. One bag for each student, TA, and instructor.

It’s a lot of milk chocolate.

The trick is that while each bag contains about the same number of M&Ms – there’s a statistics question all its own – they come in a range of different and unevenly distributed colors. How many blues are in your bag? Opening one won’t tell you much about how many to expect in another bag, but two might. Or thirty. Or three hundred. The more data you collect, the better you can understand the range of possible blue M&Ms and the likelihood of any particular value.

It’s very helpful in a variety of topics in physics and astronomy. It’ll show up later for those students who study radioactivity, which functions in a completely random fashion on an atom-by-atom level, not revealing its predictable patterns until you look at large populations. It’s critical for understanding uncertainty in measurements, because they’re never perfect. It’s foundational for techniques in astronomy used to separate out faint signals from distant celestial objects among the electromagnetic noise of the universe.

Plus they get to eat them when they’re done.

Blue M&M on the floor.
Included in the data set, or not?

Rockets

Posted on by Brian Garthwaite
Estes rocket.
Assembled. May or may not be recovered post-launch.

It’s nearly rocket day! Okay, well, it’s nearly time for a physics lecture on momentum conservation – good ol’ Newtonian mechanics – and nothing livens up a discussion of theory and mathematical modeling like making stuff shoot up into the sky. Or, quite possibly, fail to shoot up into the sky, but we’ve been running some advance tests and prepping backup plans because we really, really want things to go zoom.

Zoom, not boom. It’s much more of a hissing zzziiippp than anything else.

The demonstration usually shows three different rockets in succession, each more impressive than the last. The first one, a soda-bottle water rocket, actually illustrates the principle best. Pressurized water shoots out and down, so the rocket moves up. Mass, velocity, terrible aerodynamics. Occasional light spray, so keep your distance.

Then it’s off to model rocket land, with high-velocity solid fuel instead of water. Less mass but at a much, much higher velocity, and in no time that B-size engine has launched the little cardboard-and-plastic rocket high enough to be a speck that’s hard to discern. As long as the weather isn’t terrible, though, a standard B launch is not only recoverable, but entirely possible to catch before it reaches the ground, drifting lazily beneath its parachute.

Scaling on up to a C-size engine, we’ll have our final launch. Bigger engine, more momentum, and even the slightest breeze ensures it’ll drift far beyond our sight and ability to track. Anyone so lucky as to find the rocket afterward can keep it.

If it’s you, maybe stop on by and let us know?

Vectors

Posted on by Brian Garthwaite
Force table apparatus.
Three-way tug of war.

The humble force table. A flat surface, graduated with single-degree marks. Three pulleys which may be clamped at any position. Loops of string connected to a central ring surrounding a post, each of which is pulled by a mass hanger of 50 grams.

Move those pulleys about, slip on some extra masses, and try to keep the central ring from touching the post!

If you’re going by gut intuition (and not just doing the silly trivial 120° spacing with equal masses), be prepared to make mistakes and incremental adjustments. There’s no way you’re nailing this on the first attempt. Slowly making corrections, adding and removing masses, trying to get that central ring to hover just right, it’s fun. Yes, folks, vectors and statics can be genuinely enjoyable.

The students get to explore that, of course, but it’s also an opportunity to learn a bit of Excel. Build your spreadsheet properly, and you can predict the precise angles and masses needed for equilibrium. Set it up and, presto, it works!

As a test, they run it in the opposite direction, too. Set some angles, add some masses, get it to balance. Type those numbers into the spreadsheet, and… it’s not quite right. The math says it’s off, but the ring says it’s fine. Weird! It’s a handy introduction to measurement uncertainty, a tactile illustration of a critical concept.

It’s very cool.

Bird droppings

Posted on by Brian Garthwaite
Bird dropping on telescope.
Yes, this telescope can rotate all the way around.

Telescopes don’t work when they’re not at the same temperature as the surrounding air. They don’t work if there is glass between them and the sky. (Okay, they work, just not very well.) So: you use them outside, and any space used to protect them from the elements is best if it’s as much like outside as possible.

Observatory domes, retractable roofs, etc.: all very fancy ways to keep the rain off.

Wildlife has a habit of getting into these spaces, especially the small critters. Spiderwebs are a frequent feature. Birds appreciate the shelter from the elements, and will happily build nests if given sufficient access. It’s amazing what they’ll squeeze through, if for no other reason than to leave a stark white splotch on an all-black telescope. At least it seems that way.

This doesn’t include the exterior-only wildlife population that brightens up the occasional observation session. Nocturnal critters get used to the quiet around daytime spaces, so it’s best to keep alert for opossums and skunks and other adorable visitors when out late at night. That black-and-white blur is probably just a feral cat, but you know what? Best not find out for sure.

Force table

Posted on by Brian Garthwaite
Force table with acquisition info.
More yellow paint!

Some equipment just keeps on working, year after year. This force table – an apparatus used to illustrate static equilibrium and vectors in a way that’s loads more fun than Excel, but the students still have to learn Excel – was purchased in February of 1957 for the not-insignificant sum of $87.50.

Today’s dollars: $935.89.

Circuit Boards

Posted on by Brian Garthwaite
Broken circuit board.
Guts.

Ah, the printed circuit board. Svelte. Densely packed with teeny marvels of modern electronics. Those parts big enough to be labeled usually require magnification to read the text. The really little ones? It’s not really possible to replace those anyway, so just trust that they’re working as intended.

Until the whole gizmo isn’t working as intended, of course.

When that happens, it’s time to make an assessment of what can be fixed. Sometimes it’s a loose wire. Sometimes it’s a frayed cord, or a bad switch that’s not part of the circuit board itself. Not that these are likely, but it’s best to be thorough.

Assuming you can get the housing open to inspect it. These suckers aren’t built with repairs in mind, given that purchasing a whole new item is less expensive than the cost of labor plus the replacement value of what’s 98% of the whole item. So many tiny screws. So many snap-fit plastic parts. At some point you realize how much thought and effort went into designing this object for quick assembly, and how little went into ease of disassembly.

Pictured above, a faulty motion sensor, has no obvious loose connections or broken parts. It simply fails to collect consistent data, with erratic drop-outs punctuating the signal. Oh, well. Maybe it’s good for parts?

“The Pit”

Posted on by Brian Garthwaite
Bilco door.
Feed the pit.

When you have a regular need to open lots of doors – accessing equipment, supplying labs and classrooms, helping coworkers find their misplaced keys – the powers that be may be kind enough to cut you a master key. Saves time, effort, and several pounds of metal on a keyring. They are, of course, master keys with a limited range. Certain doors are off-limits.

The access door to the elevator-base maintenance? That’s a place we don’t need to be. It’s only important that we don’t stack anything of substance on top. (The roll of plastic seen here could be blown away by a light breeze.) Not that it wouldn’t be neat to have a look inside – after all, who wouldn’t like to check out some new kind of specialized machinery? – but if the elevator’s working, maybe let it be.

That said, it’s hard not to be fascinated by the accompanying light switch:

Pit light switch.
“Pit Light”

Sure. Of course. How else would you label it? Dark, forbidden basements should always get the proper horror movie styling.

And then there’s the nubbin of a switch. Makes one wonder. Can’t possibly be from overuse. (Can it?) Implies that someone did that on purpose.

Maybe the answer’s down in the pit.