I have a cold

Which is making moving hard. I caught it from Cassie, but I didn't get it as badly as she did, or I'm recovering faster maybe. I took a sick day yesterday and just reread a Laundry novel all day.

On Saturday I learned that there's an Asimov book called An Easy Introduction to the Slide Rule. My copy arrived on Monday, way faster than I expected, and I read through as much as I could follow without having a slide rule in hand.

My slide rule arrived today, fresh from eBay. It's the oldest object I own by a wide margin (fossils excepted, I suppose), a Keuffel & Esser rule made in 1940. Keuffel and Esser, after slide rules stopped being a thing, kept making regular rulers and other drafting equipment, under the name K&E, until I was a kid. My father always had a bunch of their stuff laying around from surveying.

I don't really know how to do much yet. I can multiply numbers and find square roots, that's about it. The thing is actually pretty handy: you slide the middle part so that one end is lined up with one of the numbers you're multiplying, and the answer is under the other one. The way it works is that they're not linear rulers, they're log scales. Anyway, it's an interesting tool because of what it doesn't do: in order to work at all, it only deals with numbers between 1 and 10. So, you have to track the decimal points yourself, which isn't actually that hard. It's also limited in how precise it can be (being, you know, a piece of wood and all), so really what it is is a quick way to estimate answers, more accurate than an order of magnitude (since you have to track that part yourself anyway) but less accurate than getting the actual answer with arithmetic.

House-wise, we have no internet yet, because of a dog, but we finished putting together my desk today, and moved some more boxes over. This weekend (assuming I get over being sick) I hope to move all the board games over, and the electronics table in my room.

This entry was originally posted here, where there are comment count unavailable comments.


Today I closed on the house, and got the keys. The previous owners are still moving some things out of the backyard, but it's officially mine and I can go over there whenever I want to, because it's my house.

Closing was insanely fast. The bank did it in two weeks, because they were super into getting it done in February for some reason. I got a bunch of concessions from them too, they waived almost all of my closing costs, I paid about $150 over the down payment. So that's cool.

I bought a refrigerator today too, which I'm actually more freaked out about than the house. A fancy french-door stainless steel refrigerator.

I suppose I should start packing things. Cassie has a cold so I guess that's why she's not moving things yet. She says she's going to move a bunch of stuff over spring break though.

This entry was originally posted here, where there are comment count unavailable comments.


For Christmas of 2006, my uncle gave me a Roomba. I started running it around my apartment, as you do, and after a couple days I noticed that it wasn't detecting walls right, it wouldn't follow edges correctly, that sort of thing. I took it apart to see what was up, and found that one of the leads to one of the sensors was broken off from the wire.

I went to Fry's, bought a cheap soldering pencil (no temperature control, not even a stand), some electrical tape, and a spool of solder. I did the world's worst solder joint, wrapped it in tape, and the Roomba worked again! And the electronics bug was planted.

Now, almost exactly eight years later, I have run out of solder.

In that time, I've gone from that horrible solder pencil (which I once dropped into my lap, but somehow managed to dodge away from), through two battery powered irons, three nicer temperature controlled stations, to my current station with the SMD rework gun and the smoke absorber.

What I'm a lot more proud of is, I've gone from building blinky-light kits to building much more complex kits, to designing my own things. I've built a gamepad, tweaks to my helicopter, Christmas gifts for people. I've taught myself everything from lighting up an LED with a battery to decoding radio signals. Gone from Dremeling a hole in a candy tin to printing my own enclosures. And from not even knowing what most tools do, to having a decent workbench setup.

And soon, I'm going to go from the little folding table I used in my apartment eight years ago, to having an entire room to build my stuff in, in my new house.

You know the whole thing about, to be a writer, you have to write a million (or whatever) words of bad writing before you get to start writing good things? That roll of solder was my million words. And now I'm going to take the plastic wrap off my next roll.

This entry was originally posted here, where there are comment count unavailable comments.

I already know I'm going to need this icon

Yesterday, after work, Cassie and I went to look at a couple houses. One of them was sort of lame; it had narrow little everything, old-ladyish wallpaper and woodwork and such, and a kitchen that was probably really fancy in 1977. Which was a shame because it was the one I was looking forward the most to looking at. The garage was kinda nice too, it was clearly the domain of an old man who liked to tinker with things. It was an estate sale and there was random junk everywhere, too.

Anyway, that one was a no. The second one on the other hand, was nice. You walk in, and you think "huh, this is a decent sized living room," and then you turn on the lights and you see that you're standing in an entryway, and the actual living room is the size of a small skating rink. And covered in hardwood floors. With a kitchen next to it, that's got all modern appliances and a glass-top stove.

There are four bedrooms, all with laminate floors, and the garage is converted to a den, which we'll use as a library of both books and games (and which is the future home of a Geek Chic table).

We made an offer on it yesterday, and it was accepted today, pending an inspection Wednesday. Assuming the place isn't infested with Deep Crows or something, I'm going to buy it.

So, that's the news I have to share. :)

This entry was originally posted here, where there are comment count unavailable comments.

Lost an arm

A couple days ago I bought Phoenix RC, an RC aircraft simulator. It's an amazing amount of fun, I've been playing with it like nonstop. Thursday night I stayed up Far Too Late messing with transmitter settings (on the transmitter itself; I can use my tweaks on the real quad) and last night I was playing with acrobatics (which I will likely never do with the real, $400 quad, but is a lot of fun on the imaginary one). It has a USB widget where I can plug in my actual controller, and the physics are great. It emulates different kinds of wind, you can tweak the weight / horsepower settings of the quad, simulate random equipment failures, etc.

Anyway, after doing that for two days, and today being the first nice day in a week, I took it out and immediately lost an arm. I was practicing zooming as fast as I could toward the construction site and then back, and I flew too fast too close to the ground and crashed.

That construction site makes me sad, too: we used to have this enormous field behind our office, but now past about 50 yards it's a muddy construction site. For what I'm sure is going to be Joe's Pine Tree, Doberman, and Swimming Pool Emporium or something equally unfriendly to fly over.

It was a pretty impressive crash, to be fair. Even from about 30 yards I could see little bits fly into the air, the thing flipped and rolled a couple times, it was very photogenic, unlike when I lost a prop flying it into a ping pong table. I managed to find all the bits that fell off, and I snapped an arm in half.

Funny thing: the props, including the ones that dug into the ground, were perfectly fine. Carbon fiber is some tough shit. The arm was toast but the prop on it still looks (and works) great.

I have eight (now seven) spare arms, so it's already flying again. But, first major crash! Woo!

This entry was originally posted here, where there are comment count unavailable comments.

Of helicopters and hand grenades

I was talking to Cassie today about RC flying culture, and how quadcopters are changing it. Unlike planes, quadcopters don't need an airstrip or a lot of space to fly, so you don't need to be part of a club to fly one. This change has been made possible by two major new developments: cheap microcontrollers (a quad without a computer-controlled autoleveling system is a crash looking for a place to happen) and Lithium-ion polymer batteries. The amount of power needed to run, essentially, four RC airplane power systems at once would have been too much to lift with those systems, until batteries got much smaller and better.

How much smaller and better?

Well, the batteries I use are fairly medium-sized ones, with 3000 milliamp-hours of charge, meaning that they can put out 3000 milliamps for an hour, or 6000 mA (6 amps) for 20 minutes, and so on. There's an upper limit to how fast they can be safely discharged, but let's ignore that and just look at the total power available.

If we know the voltage the battery provides, which the label tells us (and a meter confirms) is 11.1 volts, we can convert that to watt hours: 3 amp-hours times 11.1 volts is 33.3 watt-hours. One watt-second is a joule, so 33.3 watt-hours times 3600 seconds in an hour is 119880 joules. Let's round that off a bit and say 120 kJ.

Now, something to compare it to:

One gram of TNT is, Google conveniently informs me, 4184 joules. It's a bit harder to find the TNT-equivalent of modern grenades, but Wikipedia says that the stereotypical "pineapple" grenade seen in a thousand world war II movies contained 57 grams of TNT (the real ones, I mean, not the ones in the movies. Those were fake, I hope). That means a grenade in the '40s would put a total of 4184 joules-per-gram times 57 grams, or 238488 joules of energy into the Nazi tank of your choice.

So again, let's round that off for convenience and say 240 kJ. What that means is, the little blue battery pack on top of my quadcopter is the energy equivalent of half a hand grenade.

For a fun exercise, look up the specs on your smartphone. It's probably got a LiPo battery, just like my quadcopter. How much TNT do you carry in your pocket?

This entry was originally posted here, where there are comment count unavailable comments.

Remote control lights!

I made the lights on the quadcopter operate by remote control. Here's how that went:

There were two general problems to solve here: one is, I needed to control 12 volts to the lights, with a 5 volt signal from the receiver. So there's the voltage mismatch. The second is, the signal from the receiver isn't a simple on-off, it's a pulsed signal, so I needed some way to decode that to decide whether the receiver was saying "lights on" or "lights off."

First, the voltage. The usual way to control one signal with another one is a transistor, so that's the first thing I tried, but the normal kind of transistor (that I have a drawer full of) really wants the signals to be the same voltage. If there's too much of a difference between the base voltage (that controls whether the transistor is on or off) and the source voltage (that the transistor allows through, or doesn't) then the source voltage just goes through the base. I burned up a resistor last weekend playing around with this.

The solution to this problem is called a MOSFET: metal oxide semiconductor field-effect transistor. The difference between a normal transistor and a MOSFET is that once a little voltage starts to go through, that sets up a reinforcement effect that lets the rest through. So a small voltage to the base starts this avalanche going, and so a 5 volt signal will turn on or off a 12 volt signal.

Next problem, the pulses. RC aircraft are designed to have a bunch of analog signals to control servos: some level for the throttle, an angle for ailerons or whatever. An on-off signal isn't very useful on an RC plane, so RC equipment isn't really set up to produce it. What happens instead is you get a pulse: if the throttle (say) is at 0, then you get a pulse 1000 microseconds long followed by 1500 microseconds of nothing; if it's at 100% you get a 2000 microsecond pulse followed by 500 microseconds of nothing. But it's never fully on or off: the minimum pulse is 1000 us, the maximum is 2000 us. So I need something to decode that.

There were a few solutions to this: build an analog circuit which will charge a capacitor with the long pulse but the short pulse won't charge it enough, for example. Or buy another component called a speed controller, which is meant as a go-between to translate this kind of signal for an RC aircraft engine (which the copter already has four of). In the end, I cheated, and took a more expandable approach: I used an Arduino.

The Arduino reads the pulses, looks at the width, and either writes (or doesn't) to an output pin, which is connected to the MOSFET. This is kind of cheating since I used a fairly powerful computer where a few cents of passive components would do, but on the other hand now that I have this, I can use the same board do to other things later, like landing gear or control a camera or whatever.

But for now, what I have is, a board sitting on top of my copter that allows me to flip a switch and turn some lights on or off in flight. Which is kinda useless (I know when I take off whether it's dark enough for lights or not) but also kinda cool.

This entry was originally posted here, where there are comment count unavailable comments.