PSA: Do not use an iPod or other hard drive based player in the mountains!

**coreshot-tourettes** · 05-22-2008, 10:00 AM

I have designed and built hard drive based media players from scratch.

The maximum operating altitude for an iPod is specified at 10,000 feet. There's a reason for this.

Those that use a hard drive based player like an iPod in the mountains should know that the fly height of the read/write head on the hard drive degrades significantly over 10,000 feet of altitude, as it relies on enough air flowing between head and spinning disc to keep the head from hitting the disc, in what is known as a "head crash" that will destroy data.

I have also designed and built military hard drive enclosures for use in aircraft. These enclosures are specially pressurized and sealed to prevent head crashes.

Using an iPod at altitude and under vibration (as when skiing) will significantly shorten the life of the device. If it dies within warranty, you can get it replaced. If it dies outside of warranty, you are fuX0red.

Therefore, this MP3 player designer recommends buying only flash players for use in the mountains.

(Note: Yes, I know some of you have been using iPods for years in the mountains. An intermittent head crash in music file storage will not be much of a problem, as the player will correct for those errors. If it head crashes in the file partition table, it will render the device useless.)

(Note2: I have talked with Apple engineers about their iPod battery life problems. They have zero interest in ever solving them. But that is a separate discussion.)

advres · 05-22-2008, 10:05 AM

ughh, not all iPods are HD based media players

**irul&ublo** · 05-22-2008, 10:10 AM

Originally Posted by advres

ughh, not all iPods are HD based media players

I think he knows that:

Therefore, this MP3 player designer recommends buying only flash players for use in the mountains.

**coreshot-tourettes** · 05-22-2008, 10:12 AM

Originally Posted by advres

ughh, not all iPods are HD based media players

Yes, but when people think "iPod", they think the HDD-based models.

**pechelman** · 05-22-2008, 10:16 AM

cool stuff

how much does the fly height degrade past 10k?
Isnt it something like .00005" at sea level?
I thought all enclosures had to be pressurized a bit and with very clean air.
So they actually breathe?

**coreshot-tourettes** · 05-22-2008, 10:30 AM

cool stuff

how much does the fly height degrade past 10k?
Isnt it something like .00005" at sea level?
I thought all enclosures had to be pressurized a bit and with very clean air.
So they actually breathe?

The fly height is 3-7 millionths of an inch under normal conditions. The lower the air pressure, the lower the fly height - 3 millionths at 10Kft, 7 millionths at sea level. It's not completely proportional to altitude in that range though. Older drives have higher fly heights. At zero RPM, most drive heads would rest on the drive platter surface. In a completely vibration free environment, the drive heads will not crash even at 1 millionths height. The problem comes when you jostle the drive. If the drive head hits the platter, it will often collapse the air cushion it's flying on and get stuck to the drive platter. Things act funny at small scales. When you start a hard drive, the heads start parked off the drive. The drive spins up, then the heads are shot out into the whirlwind of air over the platters and start to fly on their own.

HDDs are not pressurized, but the air is filtered. There is a very small hole on all consumer HDDs that has a tiny fiberglass fiber filter over it. If the drive were sealed, the enclosure would flex and ruin the tolerances at the read head.

A HDD enclosure for use at 60kft+ altitude is a 2 lb machined aluminum box with heavy rubber airtight seals and a Peltier heater/cooler. HDD costs about $100, box costs $5000.

**pechelman** · 05-22-2008, 10:39 AM

Originally Posted by coreshot-tourettes

The fly height is 3-7 millionths

right
isnt that what i typed above?
.1 = tenths
.01 = hundredths
.001 = thousandths
.0001 = ten-thousandths (also called "tenths" by machinsts)
.00001 = millionths (also called "mils" by machinists)

the google convert says 1micron = ~4mils???

**coreshot-tourettes** · 05-22-2008, 10:43 AM

1 millionth = .001 mils = .000001 inches.

What you typed was 10 millionths.

**bfree** · 05-22-2008, 11:05 AM

Originally Posted by pechelman

right
isnt that what i typed above?
.1 = tenths
.01 = hundredths
.001 = thousandths
.0001 = ten-thousandths (also called "tenths" by machinsts)
.00001 = millionths (also called "mils" by machinists)

the google convert says 1micron = ~4mils???

Do hundred thousandths not exist?

Anyways, good thing the pnw is all low-altitude crap, so this doesn't even matter

**pechelman** · 05-22-2008, 11:06 AM

^ ive wondered that too, but thats always been the convention when im talking tolerances and such.

advres · 05-22-2008, 11:11 AM

Originally Posted by coreshot-tourettes

The maximum operating altitude for an iPod is specified at 10,000 feet.

Originally Posted by irul&ublo

I think he knows that:

Therefore, this MP3 player designer recommends buying only flash players for use in the mountains.

Yes but he specified iPod. And the arguement that most people think of something when they hear something is bullshit. With the newer minis at 8G I know more people with smaller, non-HD ones than fullsize ones. So, I was just making a point he should be more specific and that is all.

PS. I have used my real old 60G above 10K all the time without problems. YRMV

**jon turner** · 05-22-2008, 11:14 AM

too bad I LIVE at over 10,000 feet. My ipod gets a little flakey at times, but has served me well. A reboot usually corrects it. It was flakey when I lived down in Boulder as well. I would rather get a flash based ipod more because the hard drive sucks down battery power like crazy when it's cold and the flash version seems to last a lot longer.

**njfreeskier** · 05-22-2008, 11:42 AM

wow...this might be the most technically advanced thread on tgr. thanks for the info, didn't know that about ipods. props for coming up with a new design.

**stuckathuntermtn** · 05-22-2008, 11:57 AM

this is interesting. So the new 8Gb is flash? What is flash anyway? All I've been able to get from people is that it's some magical form a storage controlled by elves. Meaning not Magnetic, I guess. Good thing I never took the Big Sky Tram. Moonlight is below 10K! (just barley). As far as battery life. A lot of it has to do with the metal back. It chills the battery.

**bfree** · 05-22-2008, 12:04 PM

^ wouldn't it also then heat the battery in the summer? If that's true, seems odd, as both of those kill battery life.

Is this just apple caring more about looks than performance?

**MOHSHSIHd** · 05-22-2008, 12:16 PM

Yeah, for skiing I just go with a little 1gb flash drive ipod. Thats enough music for one day for sure, and it keeps me listening to new stuff. Plus the battery lasts really long even in brutally cold loveland ridge weather.

**flatNshallow** · 05-22-2008, 12:23 PM

Originally Posted by pechelman

right
isnt that what i typed above?
.1 = tenths
.01 = hundredths
.001 = thousandths
.0001 = ten-thousandths (also called "tenths" by machinsts)
.00001 = millionths (also called "mils" by machinists)

the google convert says 1micron = ~4mils???

Originally Posted by coreshot-tourettes

1 micron = .001 mils = .000001 inches.

What you typed was 10 microns.

Pechelman techno-fail = 3rd sign of the Apopclypse.

**sock_monkey** · 05-22-2008, 01:09 PM

1 micron = 0.000001 meters

sheesh.

and while we're being picky 1 micron = 0.000 039 37 inches

**davep** · 05-22-2008, 01:13 PM

Holy unit failure!

METRIC UNITS:
1 micron = 0.000001 Meters (NOT INCHES, jesus) = 3.9x10^-5 inches

IMPERIAL UNITS:
1 mil = 0.001 inches (NOT 0.000001 inches, those are micro-inches)

edit: the monkey is quick

**coreshot-tourettes** · 05-22-2008, 01:21 PM

What is flash anyway? All I've been able to get from people is that it's some magical form a storage controlled by elves.

Basically, flash is memory with no moving parts, that retains its storage even when power shuts off. It's based on tiny transistors that can have data read from and written to them.

http://en.wikipedia.org/wiki/Flash_memory

As far as battery life. A lot of it has to do with the metal back. It chills the battery.

The metal back is actually good for the battery - all batteries heat up upon charge and discharge, and heat kills the Li-poly battery membranes causing self-discharge.

A lot of it has to do with Apple choosing bad battery design methodology. First, the battery will lose track of its capacity at a given voltage. It also charges the battery too fast, causing degradation. Lastly, nonreplaceable Li-poly batteries are a sucky choice for anything designed to last more than a year.

And yes, apparently I forgot my units too.

**nick > jesus** · 05-22-2008, 06:07 PM

2.5 years of using my ipod while skiing at high altitude,

**stuckathuntermtn** · 05-22-2008, 07:08 PM

my ipod has lasted longer than the norm as well. I think because mostly it's plugged into the Pioneer adapter box in my glove compartment and nothing else. Yes, I think I'm cool because I can control my ipod through my head unit.

**P_McPoser** · 05-22-2008, 07:32 PM

PSA--Also do not drop your I-pod down a 3000 foot deep mine shaft.

**leroy jenkins** · 05-22-2008, 09:46 PM

Huh, news to me.

My first gen ipod was not very durable, but I've used my 4th gen, (or fifth or whatever was the one before the current one) skiing in and out of bounds up to 14k, and in non pressurized small aircraft up to 18,000 feet, for a couple years, and it has never broken.

**critical-motion** · 05-23-2008, 09:15 AM

HD-based ipod reliability is hit and miss. I've had 2nd and 3rd gen HD-based ipods fail on me during normal use at 5000ft elevation. On the other hand, a friend of mine still has his 1st gen 5gb HD-based ipod and it works normally after 6 years of use. Needless to say, I'll stick with flash-based ipods as I have yet to break one, although I did completely wear down the battery on a 1st gen Nano.