Magnificent marble machines

In which I shamelessly knock off a couple of videos from this page on Matthias Wandel's site.

More at woodgears.ca. Other marble machines, including Matthias' own ones, are here.

On the Domestication of Car Stereos

A reader writes:

I have been rereading some of your stuff concerning speaker building lately and have decided to possibly make it a hobby. A mate and I have a bunch of car audio stuff we pulled out of his car that we would like to turn into a garage/shed powered speaker box. I have been looking on the web and there seems to be about a million different opinions as to various aspects of the build including:

* if we can use the car amp
* if a head deck needs to be involved
* power supply – some say even an old computer PSU can be used some say that the current requirements would be better suited to a car battery with a charger attached (seems a little cumbersome)

So I thought I would send a quick email to great and powerful Tech Master who started me down on this road for some clarification. Help?

Mitch

Ludicrous car speakers
(Image source: Flickr user Nazly)
Just lever 'em out, and shovel 'em into the house!

Yes, you can make perfectly good household speakers out of car-audio components. Actually, car radio tuners can be better than the home-hi-fi kind, because the extremely variable reception conditions for mobile radio, and the lousy antennas they have to use, mean even quite cheap car stereos often have very good RF sections.

The problem with powering car amplifiers at home is, as you've already discovered, that they can want a lot of current at 12 volts.

First, definitions: You standard "car stereo" has one "head unit" in the dashboard, which combines all of the signal sources - tuner, cassette deck, CD player, line-in socket, memory-card socket for MP3s, whatever - and all of the amplifiers, in one box. These days it probably has four outputs, for two front and two rear speakers. Take such an all-in-one head unit and some speakers and a twelve-volt power supply and hook them all up at home and they'll work the same as they did in the car.

Fancier car audio systems have amplifiers separate from the head unit, and may have multiple head components as well, possibly including a separate satellite-navigation screen, DVD player, et cetera.

A separate car-audio amplifier is basically the same as a separate home hi-fi amplifier: It accepts line-level input, and amplifies it to drive speakers. The input has to come from other components. Fancy car-audio head units may have no amplifiers of their own at all. Again, though, you can run the whole system spread out on a table at home, if you want to and have a suitable power supply.

Standard cheap car-audio amplifiers, like the ones that're built into low-cost one-piece head units, have a maximum output voltage no higher than the 12 volts they run from - 13.8 volts, actually, when the engine's running. Car speakers have a nominal impedance of four ohms - home hi-fi speakers are usually nominally eight ohms - so you can use Ohm's Law to figure out the total possible output current. Ohm's Law says current equals voltage divided by resistance (I = V/R), 13.8 volts divided by four ohms gives 3.45 amps, so that's the most that such an amplifier can output per channel. Each channel is basically its own separate amplifier.

(The "nominal" in "nominal impedance" just means that that's the approximate impedance the speaker presents if you run DC electricity through it. The actual impedance varies quite widely depending on the frequency of the incoming alternating-current music signal, but overall it'll be close enough to the rated nominal impedance for rough-calculation purposes.)

13.8 volts times 3.45 amps is 47.61 watts; an amp with four output channels could therefore output 190 watts, which is more than enough to make the inside of your car very loud, even given the not-so-great efficiency of a lot of car speakers.

(Car-audio equipment of all sorts often has outrageously high "peak music power output" numbers printed on it; this problem may be even worse in car audio than it is in cheap home hi-fi equipment.)

Realistically, to avoid hideous distortion from winding the amp up all the way and to also take into account the rather-less-than-100% efficiency of all amplifiers, a ballpark figure of 25 watts of input power per channel, at the 12 volts you'll probably be running it from at home, is likely to be about the real-world maximum for a basic car-audio head unit. Call it 24 watts for a nice round number of two amps, at 12 volts, per output channel.

More powerful car amplifiers step up their input voltage so they can deliver more volts of output, and the sky's the limit for those. But you can run any amp expecting 12-volt power input from any 12-volt source. As long as you keep the volume low enough that the power supply isn't overloaded, you can probably even run some preposterous multi-kilowatt boom-car amp, at very low volume settings, from a one-amp plugpack.

(This is related to the reason why it's not dangerous to touch both terminals of a car battery that can deliver hundreds of amps into a load with a low enough resistance, like the starter motor. Your body has a far higher resistance, so far less current flows. There are also 12V power supplies with very low output ratings, like say the plugpack for an ancient calculator; you might be able to blow one of those up by just turning on a 12V amp connected to it. You also might be able to damage a 12V amp by plugging an old-style heavyweight unregulated linear power supply into it, because those deliver root-two times their rated voltage when they're unloaded, and seventeen volts might be too much for the amp. All care, no responsibility. Et cetera.)

A PC power supply actually is a pretty good 12V source for running car audio gear at home. It'll be able to deliver a decent number of amps at 12 volts (the yellow wires coming out of standard PC PSUs are +12V), and it should also deal elegantly with overload, and just shut down if you ask for too much current. Modern PSUs may have split 12V rails and other complexities, but an old one out of a superannuated Pentium II box should do nicely for most purposes. Since most home-audio listening happens at only a few watts per channel, unless you want Party Volume of want to hear the music over your power tools, this option should be fine.

A battery charger and car battery will let you run a car amp at maximum power - well, until the battery goes flat because the charger can't keep up with the amplifier load, at any rate. It is as you say not a very elegant solution, though, and the charger may get confused when you turn the amp up and it suddenly sees a strangely high load. And the output from cheap car chargers can be really filthy, noise-wise, too. Car amps generally deal very well with distortion in their incoming power, but you may still hear a whine or ticking noise.

You can also, however, plug car speakers into a home hi-fi amplifier. A given volume setting will give you more noise from a four-ohm speaker than from the eight-ohm speakers home amplifiers expect, but pretty much any amp should work fine with four-ohm-nominal speakers; some home speakers actually have six- or four-ohm nominal impedance. Any old mini-system hi-fi amp will do, too, you don't need a fancy expensive one.

Another way car-audio enthusiasts get more noise out of an amplifier is by wiring multiple four-ohm-nominal speaker drivers in parallel. Two 4-ohm drivers in parallel give you a nominal-2-ohm speaker, three in parallel give 1.33 ohms, four in parallel give one ohm, and so on. You have to be careful connecting speakers with very low nominal impedance to most amplifiers; it usually won't cause a problem if keep the volume setting very low, but one-ohm or lower speaker arrays may look like a dead short to any amp that isn't designed, as some car amps are, to drive them.

You can also get small 12V amplifiers intended for use in home and mobile applications, which are descendants of the popular, and distinctive-looking, Sonic Impact T-Amp:

T-amp and speaker drivers
(Image source: Flickr user animakitty)

The modern ones are easy to spot; they all have extruded aluminium cases, often anodised a cheerful colour, and a few chunky controls on the front:

Lepai amplifier
(Image source: Flickr user icoro.photos)

These little amps may be sonically superior to cheap car-audio amplifiers. The radio tuner in a car stereo may have to be good, but car amps can be quite noisy and distorted, because that's not very noticeable in the lousy acoustic environment of the average car. These little units all use similar class-D amplifier chips, which are good for maybe 15 clean output watts per channel or 25 watts flat out. For full power you have to run them from something with at least a five-amp power rating - so, a car electrical system or computer power supply, or a laptop-power-supply-style 12V PSU, which last is what they come with if you buy one with PSU included. Again, though, you can hook up a smaller 12V plugpack if you like, and just keep the volume low.

(Some of these little amps have a USB socket on the front panel, too. In the cheap ones, only have the power pins will be connected, so you can use that socket to charge most phones or MP3 players, but you can't play MP3s off a thumb drive.)

These little amps may or may not sound any better than a cheap car head unit, and all they are is an amplifier - no tuner, CD player or whatever. But they look a lot better indoors than a bare car head unit, and the going rate for one without a power supply is under $US20 delivered.

As I've mentioned before, you can find these amps by searching for "class D" or "class T" (Tripath's trademarked version of class D). You'll find the very cheapest ones if you just search for 12V amps, though. You can get these same chips on little amp-module circuit boards, too, for hobbyists to install in their own enclosures, like a normal sort of amplifier enclosure or powered speakers. The above search is sorted by price, so finds lots of those little modules before it gets to the assembled amplifiers.

Car speakers are a great choice if you want to play with transmission-line speakers, too. The basic transmission-line design has a single widerange driver at one end of a folded tube; here's one under construction:

Building a transmission-line speaker
(Image source: Flickr user Moisturizing Tranquilizers)

A cheap six-by-nine oval car driver with a separate tweeter and/or midrange on a bridge in the middle of it is an excellent low-cost choice for a speaker like this.

OMG P2W BS IN MWO

There is nothing that players of online games will not complain about.

In MechWarrior Online, I've started a game and heard people complaining about how the new matchmaking system has given the other team a huge tonnage advantage, so their little 'Mechs are getting murdered by mobs of heavies and assaults.

And then, the very next game, someone's complaining that the matchmaker has given their side no light 'Mechs at all while the enemy has five of them, so this time their poor giant stompy monsters are getting pecked to death by a flock of lights.

Green Atlas
This picture isn't really relevant to anything in the post. I just thought you might like to see a high-visibility Atlas.

(Somebody's probably also going to find a way to complain about the MWO change that makes it more likely that seeing yourself shooting someone actually means you're shooting them.)

Many complaints about games, especially games that're still in beta like MechWarrior Online, are valid. But someone will also venture forth upon a discussion board and proclaim a game ruined if there's a slight change to the kerning of the menu font.

(In the MechWarrior Online font, capital I looks exactly the same as lower-case L! WORST. GAME. EVER.)

Which brings me to the latest source of rustled jimmies in my favourite imaginary giant Internet robot game:

Consumables.

MechWarrior Online is going to have special things you can stick on your 'Mech that you can use in a fight, a limited number of times. Then you'll then have to buy the special consumable thing again, if you want to use them again.

The first consumable they've announced in any detail is "Coolant Flush", a thing from the tabletop game which they're implementing as a widget you can put in a module slot on a 'Mech.

If you pay in-game "C-Bill" currency for Coolant Flush, you'll be able to buy a Small and a Medium version of it, each of which will take up one module slot.

If you pay real money for "Mech Credits", though, you'll be able to buy a one-module-slot Large Coolant Flush that has the effect of both of the C-Bill ones, but only takes up one slot.

Cue the outrage and misery. This is a free-to-play game, so like all the rest of them it's constantly trying to dodge the shadow of the "Pay To Win" monster. Special improved versions of things that you can only buy with real money invariably piss off the player base.

Whether this is actually a big deal or not in this particular case comes down to the numbers.

The first important number is what Coolant Flush, and other consumables like artillery strikes, will cost.

If these things are really expensive, so pay-to-win players with deep pockets can have them every match but nobody else can, and if they give you a real large advantage, then the complaint is valid.

If they cost very little, so the only real choice is between the advantage of the consumable or the advantage of a conventional module, then even if the consumable is very powerful, it shouldn't be a big deal.

So, is Coolant Flush likely to be very powerful?

Heat management is a central mechanic of all of the "proper" BattleTech games, from tabletop to computer. Most guns make heat when you shoot them. Energy weapons that don't need ammo make more heat than guns that shoot bullets (which are another kind of consumable, but which get reloaded for free every match). If your 'Mech gets too hot, it has to shut down or run the risk of stuff exploding. So, for almost all 'Mechs, anything that can dump heat quickly is highly desirable.

Piranha haven't completely explained what Coolant Flush will do, and it is of course subject to change. They say that the effectiveness of Coolant Flush depends on the number of heat sinks in your 'Mech, and that a 'Mech with ten heat sinks (which is what you get built into every engine) will get a total cooling of 35% - 15% plus 20% for using Small and Medium Coolant Flush in succession, or hitting the key twice for the real-money Large version.

If Coolant Flush operates like normal heat-sink function, then a 'Mech with 20 heat sinks (the ten in the engine plus ten more separate ones) will thus get a maximum of 70% cooling, and you'd need a somewhat crazy 18 extra sinks to get almost-100% cooling.

The pretty-much-essential Double Heat Sinks upgrade makes your ten engine heat sinks the equivalent of 20 single heat sinks, and somewhat confusingly gives you number-of-other-heat-sinks-times-1.4 on top of that. So with no extra heat sinks a 'Mech with the double upgrade will get 70% cooling from using both tiers of Coolant Flush, and it'd need only six extra heat sinks to get to about 100%, to take heat from 99% to close-to-zero.

It's actually more complex than that, because, I think, adding more heat sinks also adds to the total heat capacity of your 'Mech as well as how fast heat drains away, and I don't know how that'll interact with Coolant Flush. It does seem that normal 'Mechs with realistic numbers of heat sinks will be able to get about a total heat dump from the two C-Bill Flush thingies or the single real-money one.

That definitely would give many 'Mechs a big advantage. Even if you're just one player in a random pick-up game, dumping all of your heat so you can shoot all of your guns again right away is a duel-winning advantage. A whole team of laser monsters who can drop to zero heat whenever they want, even if they can only do that once, would have a big advantage in a brawl.

But you already have to pay money to put anything into a module slot on a 'Mech. Modules are bought with C-Bills, but to unlock a module type so you can buy it you have to spend "General XP", which is created from normal "Mech XP" by spending a small number of Mech Credits. Unlocking a fancy module like the Capture Accelerator or second-tier Sensor Range will cost you $US2.50 to $US3.00, depending on which of the Mech Credit packs you bought and whether there was a sale on.

People don't complain about that, though, because once you've unlocked a module it's unlocked for good, and three bucks is not a lot of money. Modules are also not Automatic Win Machines - they just give 10%-to-25% advantages in specialised areas like how fast you can capture something by standing on it, or how long it takes before an enemy you've lost sight of drops out of your targeting system.

If there are consumable three-dollar module-things that give a big advantage, and that cost as much in C-Bills as you can possibly make in ten consecutive games, then great and valid will be the outcry.

If these things cost 20 cents each or as much many C-Bills as you can make in one game, though, the inevitable whinging won't be as persuasive.

And if they cost little in C-Bills but a lot in real money - which would, I think, be a pretty clever way to do it - complaining would be the act of a crazy person.

That still wouldn't stop 'em, of course.

UPDATE: A rethink, and clearer explanation, of how consumables may work.

Sharp edges are just good aerodynamics

Here's something I didn't know existed.

Behold, the rocket monocopter!

It's a wing on one side, and a rocket pointing horizontally on the other.

Or, in the case of this monstrous one...

...two J engines and a K in succession, as this spinning surfboard wanders the sky looking for heads to lop off.

It doesn't seem very difficult to build a small rocket monocopter, from scratch (a spare R/C helicopter rotor blade is helpful...) or a kit.

It's apparently possible for these things to get themselves into a nice flat autorotation spin on the way down, too, so you don't need a parachute.

Well, that's the theory, anyway.

One-bladed propellers are actually very desirable, essentially because the more blades you have, the more turbulence each blade must cope with from the blades in front of it.

The obvious problem with dropping to one blade is that if it's mounted on a shaft and developing thrust, then that thrust will be off-centre, spinning around the shaft with the blade, and thus ruining the shaft bearings quite quickly. So you only see single-bladed props in oddball applications like these monocopters, and extremely tweaky ultra-speed control-line models, and certain rather expensive ceiling fans.

There are also propeller-driven monocopters, where a motor and prop takes the place of the rocket in the above contraptions. With modern digital control and image-processing systems, monocopters may be useful as unmanned aerial vehicles:

Posted in Hacks, Toys. 2 Comments »

Competitively-priced small disabilities

Herewith, a combination of two of my favourite things: Imaginary giant Internet robots, and perceptual and cognitive dysfunction.

Today's patch for MechWarrior Online, you see, didn't just add a mildly interesting new 'Mech...

Trebuchet BattleMech

...and a large new map.

Alpine Peaks screenshot

Besides that, it also fixed a few bugs which most players, me included, should have noticed. But didn't.

The second-most-coveted "Elite" efficiency upgrade for your 'Mechs is "Fast Fire", which makes your weapons recycle to fire again 5% faster. Everybody with a 'Mech that, you know, has guns, buys Fast Fire as soon as they can.

Except, until now, it didn't work.

Worse, it worked backwards. It made your weapons recycle 5% slower.

They've fixed that, now.

But I never noticed. I've bought Fast Fire for, what, two dozen 'Mechs so far? If you'd asked me, I would have said it worked.

(The most desirable elite upgrade is "Speed Tweak", which raises your top speed by ten per cent. That always worked, though it used to only boost you 7.5% before they bugfixed that too, a few patches ago. Well, I think it always did something. Maybe it just changes the speedometer to tell you 100 kilometres per hour is now 110...)

And it was actually even worse than that, because there were several other screw-ups in the upgrade system.

People noticed some of them, like how you still have to buy the Basic upgrade "Arm Reflex" if you want to get to the Elite upgrades, even if your 'Mech is a Catapult or something that does not actually have articulated arms.

But Arm Reflex and "Twist Speed" were backwards, until now. Each actually gave the other's upgrade.

And the reason the Fast Fire problem was even worse is that when you bought Fast Fire it didn't do anything to your fire rate at all. Because, like Arm Reflex and Twist Speed, Fast Fire and "Pin Point" were reversed too!

If you bought Fast Fire you got Pin Point, and if you bought Pin Point you got Fast Fire. Which was, once again, actually Slow Fire. But when you bought it you didn't get it. Which was actually helpful, since it didn't work. Stay with me, here.

And the doubled Basic efficiencies you got from getting to Elite weren't doubled properly! And there's more!

MechWarrior Online is still in beta, so you should expect stuff like this. If there weren't bugs, even quite egregious bugs, then it wouldn't be a beta.

But you'd think errors like this would be the talk of the town. I mean, it'd be the work of a moment to do a little science to detect such things. Time some gun-shooting, or screenshot how far your 'Mech's torso can twist, or whatever. Then buy a new upgrade that's meant to change whatever you did, and test again.

But, clearly, almost nobody did that. I certainly didn't. So almost nobody noticed the bugs. This may have something to do with how long it's taken these bugs to be fixed - we're almost four months into the open beta now.

The moral of the story is, once again, that if you want to see if something is true or not, you have to do science. And science is not restricted to incomprehensible white-coated boffins who look at brightly-coloured liquids in the background of wrinkle-cream advertisements and who also dogmatically pursue the formula for the perfect biscuit dunk. Science is just careful experimentation, observation and thinking, which anybody can do, any time they like.

Some differences are blatantly obvious enough that you don't need to set up a formal experiment. You don't have to do science to determine whether it is safe to cross the road when something that looks very much like a car, but could be a hologram or hallucination, is coming. And if there were some upgrade in MechWarrior Online that was meant to make your 'Mech twice as tall or twice as fast, you'd be able to tell if it was working pretty easily with informal observation. (Though you wouldn't be able to easily determine if it were only making you 1.95 times as tall or fast...)

When something is subtle or elusive, though, as many concepts in the real world are, there is no substitute for science. And it's surprising how often it's needed.

New Frontiers in Duck-Feeding

Bread is not good for birds. It's not deadly poison for most of the wild birds that humans commonly feed, but it's basically empty carbohydrates. Wild birds usually have plenty of opportunities to burn off calories, but it's still a better idea to feed them something that more closely resembles what they naturally eat.

(Conservationists usually argue that the best thing to feed to wild birds is nothing, to prevent stress and injuries from squabbling over an unnatural pile of food, dependence on humans, and over-breeding. But screw you, I like feeding birds.)

There's also that possible canard, ha ha, that says if a duck eats dry bread and then has a drink, the bread can swell in its throat and choke it, so you should always chuck your duck-bread in the water and not on dry land. I find this more plausible than feeding Alka-Seltzer to pigeons in order to cause them to explode, but I imagine there'd be pretty strong selective pressure against ducks living in human settlements who choke on bread.

In any case, I resolved to attempt to kill some ducks with astonishment, by feeding them something that's actually moderately good for them.

I got a degree on this subject from an intensive five-minute study program at the University of Google. Then, when I next went to pick up twenty tons of seed for the cockatoos from the local farm-stuff shop, I also bought a bag of "layer pellets".

Layer pellets in hand

Layer pellets are feed for egg-producing chickens. They're a compound feed made from various grains and maize and suchlike, generally with a lot of calcium, for eggshells.

Naturally, ducks like the Pacific Black Ducks at my nearest good-sized lake dabble around on the bottom of the lake with their tails pointing up ridiculously, and eat water-plant seeds, along with the occasional insect or snail or bits of plant matter they can find both in the water and on land.

(Digression: If you'd like to identify some bird you just saw in Australia, the Birds in Backyards Bird Finder is a good first stop. They even have a page for the emu, which makes me wonder if anybody has actually ended up there from the Bird Finder, after perhaps attempting to determine whether the six-foot fluffy dinosaur in their back yard is some kind of pigeon. Perhaps someone has at some point needed to determine whether the looming thing in their back yard is an emu or a casssowary.)

You can get various other prepared food mixtures for poultry, like "grower pellets" for instance; those have more protein and fat, to build meat fast. (There's also "mash", which is just the ingredients mixed together and not pressed into pellets.)

Layer pellets seem a pretty natural kind of food for ducks, though. There's endless debate over what people who keep ducks of their own should feed them, and of the niceties of wild-animal food intake in a world that contains humans tossing stale bread and rubbish bins full of fascinating stuff for animals equipped to fish it out. But layer pellets, for ducks, certainly seem to be close enough for government work.

I tried one of the pellets myself. If you were to draw a Breakfast Cereal Nutrition Versus Flavour graph with the X axis for "healthiness" and Y for "flavour", corn flakes might score something like 5 and 6 respectively, and Frosted Flakes of Nothing would score 1 and 8. Layer pellets taste like a cereal that would score 10, and 0.2.

Would the ducks like them more than I did? Would they even recognise these things as food?

Throwing chook pellets to ducks

Yep, looks like it.

Feeding ducks

Both the ducks and the eurasian coots that inhabit Wentworth Falls Lake were entirely delighted with the layer pellets.

(The coots, by the way, have extraordinary feet.)

Ducks eating chook pellets

The pellets are denser than water. If I threw them in the lake then I suppose the ducks might dabble them up again, but it was more fun to just scatter food near our picnic blanket. Ducks' beaks were stabbing away at the ground like little pneumatic drills.

They were even almost brave enough to eat pellets from my hand, but all any of them ever actually managed was a vague bite at the end of one of my fingers. No part of a duck seems to be particularly pointy, so I was in no danger of...

Cockatoo wrist damage

...what happens when a cockatoo decides to perch on my arm.

(I tried layer pellets on the cockatoos, too. They were very confused. One scattered the little pile of pellets with his beak to see if there was some actual food underneath.)

All in all, a very successful day out. Layer pellets aren't expensive, either. Highly recommended.

Posted in Birds. 6 Comments »

Raining rocks

A reader writes:

If you're up for it, I'd really love an article on why the size of that meteorite varies from 10 tons to 10,000, why the rarity of it is 1 in 5 years to 1 in 100, and why the explosion is everything from 1 to 500 Hiroshimas (I hadn't realized that was a new standard measure until today).

Timothy

Right after everybody started goggling at YouTube videos of lights in the sky over Chelyabinsk, and blessing once again the everlasting source of comedy and horror that is the Russian dash-cam phenomenon, a lot of reporters were probably hitting the telephones. (Or just Twitter, now that having the first story is so much more important than having the first correct story.)

Anyway, early on there was an estimate allegedly from the Russian Academy of Sciences that said the meteoroid was only about ten tons. I don't know who at the Academy first said that to a journalist, since there doesn't seem to be an official press release or anything, but that mass estimate seems tied to them.

Since this estimate came before anybody had pulled together enough reports and readings to know for sure the size, velocity and explosion altitude of the rock, it's not surprising they were way off. I presume they just estimated a relatively low airburst of a relatively small rock, enough to do this sort of damage...

...without requiring the meteoroid to be a one-per-century size.

Around the same time, the European Space Agency similarly estimated the rock to be relatively small, with the caveat that they didn't yet have "precise information on the size, mass and composition of the object".

But then NASA estimated the rock was much bigger and heavier and blew up much higher. Since then, better readings have caused NASA to estimate it was a little larger again, putting it in the one-per-century category. I think this pretty conclusively overrules the early, low estimates.

This may also make it fortunate that this meteoroid came in at a grazing angle, and exploded so high up. I'm no expert on meteorite dynamics, but if the Chelyabinsk rock had managed to get down to ten kilometres or lower before it exploded, it would have Tunguska-ed the city, not just outshone the sun and then broken lots of windows.

This may have been impossible, especially if this meteoroid was one of the common stony types. Nickel-iron meteoroids are much rarer than stony ones, but also much more likely to make it to the surface without "exploding". The explosion effect when a meteoroid disintegrates in the atmosphere comes from the much greater surface area per mass of the fragments; they decelerate faster and heat up more, creating the kaboom. Whatever bits survive this process are generally small enough that they're only travelling at terminal velocity when they hit the ground.

I think gigantic dinosaur-killer meteorites can't help but make it to the surface largely intact, and ruin everybody's whole week. At the other end of the size chart are the tiny micrometeorites that drizzle down constantly, which anybody can harvest from the roof of a building.

I agree that using the Hiroshima bomb as an explosion-size yardstick is a bit silly, since it's not as if many people now living have a personal, visceral understanding of what that means. You might as well say something like "the meteoroid weighed more than 9000 tonnes, as much as fifteen thousand adult bluefin tuna".

I propose we use the PEPCON explosion instead.

The two biggest explosions there, which happened almost simultaneously, added up to only about 2.7 kilotons of TNT. The Chelyabinsk meteoroid explosion was, according to NASA's corrected estimate, close to 500 kilotons.

UPDATE: Phil Plait, the moderately famous actual astronomer who you should obviously have listened to about this stuff before you wasted minutes of your life on the above, has a couple of articles about the Russian meteor here and here.


Psycho Science is a... sort of... regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Brief imaginary Internet robot update

As I write this, MechWarrior Online has a slightly belated Valentine's Day sale on, with cheaper experience-point conversion, a discount on the rather ordinary Yen-Lo-Wang "hero 'Mech", and, more importantly, another free day of "premium time", giving you a 50% money and experience-point boost for 24 hours.

(The observation that Wang is cheap on Valentine's day is... widespread.)

For new players: The current trial 'Mechs are pretty decent by the very low standards of those 'Mechs. (Trial 'Mechs are the ones you can jump straight into whether you've bought any 'Mechs of your own or not. Play trials for a little while and you'll very soon have money to buy your own.) But the current trials include the iconic, gigantic, terrifying, Atlas AS7-D.

A new player should NOT jump straight into that hundred-ton monster. It's too slow, and it has too many weapon systems for a newbie to manage.

As is usual for big slow trial 'Mechs, trial Atlases are generally assumed to be piloted by a small gurgling baby. They are treated, with good reason, as slightly dangerous experience-point farms.

If you're new, drive something faster, and you'll learn more and have more fun.