Dan's Data letters #16
Publication date: 15-Dec-2002.Last modified 03-Dec-2011.
Fuzzy numbers
I've been trawling the web looking for the ultimate air cooled solution for a P4. The AVC Sunflower looks the goods, but how do you know when a heatsink has a fan rated at, say, 32 cubic feet per minute (CFM), that you actually get 32CFM passing through the unit? Do the manufacturers of heatsinks actually flow test their units? How can you measure the flow rate?
As an example, if you bolted a 32CFM fan to a duck's arse, there's no way you would get 32CFM coming out of it's beak! People are always complaining about the noise levels of high volume heatsink fans. I'm not surprised, considering the slab-sided engineering of a lot of heatsinks on the market. Units like these require a huge fan to perform adequately.
Warren
Answer:
How do you know if you're getting the full rated airflow? You don't.
Actually, you know that you aren't; heat-sink-fan (HSF) makers always seem to quote free-air flow rates for the fans on their products, which aren't anything like what the fan can manage on a heat sink which, as you say, presents a lot of resistance to air flow. Computer fans don't have much static pressure capability, so their flow always drops a great deal when they're faced with any kind of load.
To measure air flow through a CPU cooler fan, you could use a few kinds of air flow meter. A simple(ish) hot-wire anemometer in a short tube reasonably well matched to the fan inlet would probably do the trick. I've never bothered, since the cooling performance of the HSF is easier to measure, and is more important than exactly how much air actually passes over the heat sink.
Antigravity! Kinda.
Have you seen this article about antigravity "lifters"?
It isn't too bad an article, and I like the part where it says "Lifter creators' lack of interest in standard scientific procedure is tainting this topic and impeding progress toward a reliable resolution of the remaining unknowns."
Example being, to some extent: American Antigravity.
Interesting that there are still a few things which can t be quite explained.
Mike
Answer:
I hadn't read that particular piece, but I've read stuff about "lifters"
before.
So far as I can see, they're just electrostatic air-blowers. Since they weigh close to nothing (a couple of grams, for a small one), it's not very surprising that they manage to lift themselves. I doubt they'll ever be able to lift a useful power supply and payload and be sturdy enough to survive outdoors.
That said, some quite impressive ones are being built.
A pithy description of testing one is here.
Electric bike
I live in Canada. I ride my bicycle to work. This is winter here. Winter is cold. Water freezes when it's cold. Condensation water freezes inside brakes and shifter cables housing. Frozen cables don't work anymore. Therefore, gear shifter stops operating. This is bad.
Then I thought: Cables are, well, cable. Circulating current inside cables creates some temperature increase, maybe this could melt the ice?
Unfortunately, I measured a shifter cables resistance to be only about one ohm. Do you think it would be (1) feasible, (2) somewhat safe, to turn my bike into an electric chair of some sort? Am I correct in guessing that no transportable bank of cells would be enough to heat up such a cable, for any decent amount of time?
Florian
Answer:
It'd be safe enough, as long as your big battery pack doesn't manage to
short and explode.
Whether it'd actually work, though, is another question.
Connect a beefy DC power source to each end of a cable and, assuming the cable is the only current path (i.e. you're not sending much of the power uselessly through the frame, or whatever), you can indeed warm the cable up. This is a variant on the old defrost-your-water-pipes trick, where you hook up an arc welder to each end of a frozen (metal) underground pipe and leave the thing humming for a while.
The bike cables are quite long and quite narrow, though, and they're probably not well insulated from the cold air passing them as you cycle around, so you might need an unfeasibly large battery pack to keep the thing de-iced while riding.
I don't know exactly what the power requirements would be. Since you're just trying to de-ice the cable, not actually make it hot, the numbers might not be too awful. But there are lots of unknown factors - how well insulated from the air the cable is, how long the cable is, where the ice is and how much of it there is, length-of-ride and temperature-of-air, blah blah.
Just picking a number out of the air, if you turn out to need only 10 watts of heating, then you could get it with a bit more than three volts across your one ohm cable. Three 1.2 volt NiCd cells, for instance (NiCds are good for applications like this, because you can charge and discharge them harder than NiMH; NiMH cells are lighter, though), would give you 3.6 volts, which'd be 3.6 amps across a one ohm load (volts divided by current equals resistance), which would be almost 13 watts (volts times amps equals watts), in physics-experiment-land. In the real world, your supply wires and the battery itself have resistance which becomes very significant in low-voltage, high-current circuits like this, so you'd get less.
Anyway, if you used three 5Ah D cells for this task, a full charge would last for well over an hour, you could throw a charge back into them in less than two hours, and the battery pack weight wouldn't be at all bad. But if it turns out that you need 20 or 30 watts, the pack gets bigger.
I can think of two more elegant solutions.
One, just grease the bejaysus out of the whole cable rig. No space for water, no water, end of story. Apparently, motor oil is good for this job, too. You might have to change your pants every time you ride the bike, though.
You could also try targeted heating. If the cables only freeze in some spots, then you could make up nichrome-wire heaters for those spots, which would probably work nicely.
Channeling a tank
I am considering a Tamiya 1/16 Tiger I R/C tank but would like to know if a 6 channel radio can be used with the Tamiya kit. I would like one stick to control the full motion of the tracks (CH1 and CH2 mixed) and the other stick the turret rotation and gun elevation (CH3 and CH4 mixed) and have the main gun and MG on CH5 and CH6.
Can this be accomplished with the Tamiya DMD/MF units? Or am I restricted to a 4 channel radio?
Eric
Answer:
The first part's easy enough, even without a fancy computer radio with re-assignable
channels. Just plug the DMD unit's cables into different sockets on the
on the receiver, so the turret and drive functions aren't split across the
two sticks, as they are by default.
To put the gun functions on their own channels, I think you'd have to use a fancy radio, and then just assign a more-than-full control throw (as far as the DMD unit knows...) on the appropriate channel to a switch. You couldn't control the gun elevation at the same time as firing either gun, but that'd be about it for limits, I think. I don't think there's any way to put these functions actually on another channel; the DMD unit doesn't have the inputs for it.
(Note: Readers who find all this to be Greek to them may find my review of the Tamiya Pershing, which works much the same way as their Tigers, informative.)
Speaker specs
What is the difference between home theatre speaker systems and "computer" speaker systems? I can't figure it out, and now suspect it's just marketing. Perhaps home theatre systems don't try to be as compact as systems aimed for a TV set? When shopping for a really good speaker setup for my computer for music, games, or movies, why should I shop at the local computer store (with 1 or 2 high end options), and not the stereo store, which has 20, often more compact than the "computer" systems?
It seems like it would be great to buy a high-rated, affordable system like the Kenwood HTB-504 and plug the digital output from my Audigy into the amplifier and start smiling - but I don't know anyone who does this!
Steve
Answer:
As far as the speakers and amps go, there's not much difference between
any of the relatively cheap one-carton multi-speaker rigs, whether they're
labelled as "multimedia" or "home theatre". They have the same kind of basic
features, for a given speaker-and-amps price point.
The speakers plus amps is about all there is in most computer speaker systems, though; there'll be some kind of controls (maybe a nifty cabled remote unit, maybe built into a speaker box), but there probably won't be any surround decoding features, or hi-fi-friendly connectors, or a wireless remote. You'll just get a single set of 1/8th inch stereo inputs, most likely.
Fancier computer speakers have optical inputs and surround decoders and so on, and are therefore useable as home theatre speakers as well as with a computer (or as home theatre speakers from a computer that has a DVD-ROM drive and good sound card), but most "multimedia" speakers expect the sound source to be doing all of the clever stuff.
One-carton home theatre speaker setups are generally better quality than 5.1 channel multimedia speaker rigs, but they're more expensive, too. They ought to come with a decent standalone surround amp (the Kenwood rig does - so you can replace the stock speakers down the track, if you like), a wireless remote control, et cetera. The proper surround amp is the big difference - it should have lots of inputs, plus video switching (press a button to switch from DVD to VCR to game console...) so you can make it the centre of a proper home entertainment system. Computer speaker setups generally only accept one or two inputs; if you want more, you have to use inelegant external switch-boxes. They never have video switching.
I've got to say, though, that one-carton home theatre rigs are designed to appeal to... unsophisticated... consumers, like the "Audio Enthusiast" who's got the top review spot on that HTB-504 review page as I write this. Make sure to replace all of the speaker cables with fancy expensive ones, especially if you're so smart it took you a while to figure out that there were protective caps on the ends of your optical cable, and that's why it didn't work. Mm hm.
Some people may not be using home theatre speakers with their PC simply because they don't know they can, but there are other reasons not to. Most people don't have any desire to get multi-channel audio from their computer, for a start, and/or don't want another bunch of speakers in the computer room, as well as in the living room. And if you've got a sound card with a digital output, it'll probably only output multi-channel audio from sources that provide such audio pre-encoded - DVDs, for instance. Don't expect the digital output to give you surround sound in games; for 5.1 channel game sound you'll probably need to hook up three 1/8th inch stereo connectors on the back of your sound card to six RCA connectors on the back of the surround amp.
That said, there's no reason at all why you can't use home theatre equipment with the PC, especially if your PC and your TV and your hi-fi are all in the same place. Consider, however, buying a separate surround amp used - it's easy to find cheap used surround receivers in excellent condition, thanks to the upgrade-mania of lots of home theatre nuts - and separate speakers to go with it. Good speakers really do make a difference, and there's no harm in just getting two good speakers to start with, plus two $10 whatever-speakers for surround, then a sub, then a centre channel speaker, if your budget doesn't stretch to getting all of that gear at once. It's really no harder to hook all that up, and you should end up with a much better system than a one-carton built-down-to-a-price job.
On the way out
I've got a Maxtor 30Gb drive on an MSI KT4 Ultra, and I've got a problem. I randomly get errors in no matter what program about corrupt files. With very random files may I add, also, it likes to not "turn on" with the rest of the computer sometimes, so I end up waiting a few minutes, or better yet, it makes a high pitched noise when I boot up but since loud noises scare me I turn the thing off before I get a chance to examine the problem.
I figured this is because my drive is going to die soon, but it's only about 2 or 3 years old. But since I'm cheap, I don't want to get a new drive unless it's a must. I'm really just looking for a second opinion: Do you think I'm in need of a new hard drive?
Andre
Answer:
Yes, you are.
Snake plagiarism?
I saw, at the bottom of your Letters #14, the link to this page.
That page is dated 11/29/2002.
I've seen these pictures elsewhere, though - on the HardOCP forums.
That thread was started 11/11/2002. I'm pretty sure the site you linked to ripped the pictures off from the HardForums thread.
Isaac
Answer:
It's possible, I suppose, but there's a clear "Voltage 230V" sticker on
the back of the PSU in both sets of pictures. Why would "Dasani",
who says he lives in Arlington,
Texas, be using a PSU that won't work from US mains power (110 volt)?
I'm thinking that the pics may well be genuine, but have bounced around the Internet for a week or three (in the usual forwarded-email fashion) before they ended up on the University of Queensland page I linked to. If that's the case, then Dasani's the guy passing off forwarded pics as his own. Not that he was really making such a claim; he could easily have been kidding. But he didn't hop back into the thread to say he was joking and just posting some goofy pics someone had e-mailed him.
I'm no snake-ID expert, so I won't hazard a guess as to the nationality of the snake (if it is a small-eyed or a red-bellied black, someone would have had to import it specially for it to end up in a Texan PC). I'll stick with IDing the PSU.
(By the way - Snopes is reserving judgement on the subject.)
