AnywhereMap GPS

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Punky
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AnywhereMap GPS

Postby Punky » Fri Jun 20, 2008 11:01 am

Hey All.
I've got a Lowrance 2000c GPS right now. Nice device, runway guidance is great (use it ALL the time)... a few shortcomings but overall a nice machine.

Recently I saw an ad for AnywhereMap's ATC GPS. It's build onto the HP's Anywhere Travel Companion GPS hardware (looks like AnywhereMap developed a firmware upgrade for it). So it's got all the street level navigation as well as aviation stuff.

The website and the download-able manual all make this device look pretty damn good, good enough for me to shelf the 2000c and make a switch, but I'm a little IFFY on ordering something online (there's a restocking fee if I don't like it). The fact that's it's touchscreen looks to be a HUGE advantage. Wx capable too.

Does anyone out there have this new device? I'd love to get some feedback. Someone who's moved from a Lowrance product to this one could be particularly insightful for me. Again - it really does look like a fantastic little product but I'd like to get the real scoop on it and not just rely on it's website to help me decide.

Dave

Punky
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Re: AnywhereMap GPS

Postby Punky » Mon Jun 23, 2008 2:26 pm

Update :
So I ordered a unit late Friday.
I then decided to cancel the order over the weekend.
I found out that airspace data/dimensions for Canada are not in the unit's database.
Through no fault of theirs, NavCanada has been dragging their feet getting them the data. They have airport data but no airspace data. Kind of important for Southern Ontario ;-)

They are expecting to have it shortly, but for the time being just airport and runway information are in their database. I'm told they will probably update the website when they have Canadian data, in the mean time I've asked if I can be contacted once they have that.

Dave

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champguy
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Re: AnywhereMap GPS

Postby champguy » Mon Jun 23, 2008 9:51 pm

I've heard there can be problems running a hard drive above 10,000 feet. Devices for planes should operate off chips, not conventional hard drives which rely on a cushion of air to keep the pickup off the disk.
Remember, not all who wander, are lost.
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Punky
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Re: AnywhereMap GPS

Postby Punky » Tue Jun 24, 2008 8:31 am

Really?
You know - I think I heard the same thing, but I can't figure out why. Air density would change but I can't see how that would affect the head spacing (it's not like they would be sucked down onto the drive). A HD would have several metal discs in it, and I would guess separated by a 1/4 inch space with the head arm in between them. Maybe I'm missing something here but the discs are not going to warp closer to each other (a solid metal separator ensure that) and I just can't see how air density can bend the arms. Dunno - maybe I'm missing something here.

Anyhow, even if that were the case (and it very well could be), it's a moot point - the ATC is a solid state device, no HD.
;-)

Dave

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Re: AnywhereMap GPS

Postby JHWellington » Tue Jun 24, 2008 8:46 am

Actually Punky, my understanding is that the reduced air density does effect the how the "needle" interacts with the disc and will often crash the drive. I'm no scientist so I can't explain why, but I've read that the drives do tend to crash at altitude.
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Punky
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Re: AnywhereMap GPS

Postby Punky » Tue Jun 24, 2008 8:48 am

I should mention - that I was away of Wikipedia's claim on the 10,000 rule - I'm just not one to believe everything I read on it's face from a public source site like Wikipedia.
It notes a flying head but I thought there was a contradiction there - when the disk spins down (which can happens a lot) the head rests on the disk anyhow - so how it is that it won't cause damage then - but it will if it touches at other times. Wikipedia claims it's a "flying head" and that it's meant to stay off the disk - but it's not like the head is creating lift... it's not spinning - the disk is.

So while I believe that the head is off the disk (or at least applying so little pressure it may as well be) - I'm not convinced that it is like that because of lift (since it's not moving), and I'm not convinced that it may cause damage if it touches the disk sometimes by not others. And if I don't believe it's causing lift because it's not spinning, I can't see how air density plays any role in this.

Furthermore (I'm on a role here) - if the tolerances for disc/head separation are as tight as they claim... I would think that it would take a lot less than 10,000 feet to affect the head if it's affected at all. By the way - is that density altitude, pressure altitude or what? The fact that the distinction is not made makes me wonder - of course we pilots know the difference, and an engineer should know the difference - but it's not noted in the article.

For all I know that entry was written by someone who works for a HD manufacturer claiming to make pressurized HDs... Who knows? That's the problem with Wikipedia and the Internet on a whole.

Punky
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Re: AnywhereMap GPS

Postby Punky » Tue Jun 24, 2008 8:52 am

Hey JW.
I posted my reply before I saw yours.
I'm no scientist either ;-) but damn - I'd sure like to figure out the reasoning behind this. I almost bought into the "flying head" thing when I read it - makes sense - especially to a pilot - until I realized that the head isn't moving (other than side to side), it's the disk that moves.

I'm a software developer with a few patents - so I have access to some technical people - I'll have to run it past them but I have an idea that they won't have answers either... you may be right - perhaps only an engineer or scientist can produce the math to make sense of that claim.

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champguy
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Re: AnywhereMap GPS

Postby champguy » Tue Jun 24, 2008 10:50 am

As I understand it, the head is held off the disk by a boundry layer of air present because of the relative motion between the spinning disk and the head.
Less air, less separation. Anyone who has had a hard disk crash, and dealt with the consequences, wouldn't be having this conversation. It is not like landing a sailplane in a corn field, its like an engine out over hostile terrain.
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Punky
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Re: AnywhereMap GPS

Postby Punky » Tue Jun 24, 2008 12:43 pm

Hard drives crash from bad motors... very much like airplanes come to think of it haha.

You may get bad sectors, hell every HD out of the factor has bad sectors - they're marked at the factory and avoided... rechecking the drive will mark additional bad sectors as they appear - although when you start getting more and more bad sectors - it's usually a sign of the motor going or the head arm seeking mechanism has failed. A sudden drop knocks the innards around - it doesn't mark the disc (which by the way seem pretty indestructible judging by the way they get flung around the warehouse here from time to time haha).

That whole air thing just doesn't seem to wash. The distance is still the same between the head and the disc - regardless of air pressure, is still the same, unless they are pressurized.
Think of a plastic bottle... now pop the top off and dive down 100 feet. The diameter inside is still the same - it makes no difference that you're at 5 times the atmospheric pressure at that depth (btw - what's the atmospheric pressure at 10,000?). Of course, if you sealed the bottle with air at the surface the thing would contract but that's because you're dealing with water which is exerting a pressure/weight on a "pressurized" container. Unpressurized and the pressure the water inside the bottle exerts the same pressure as what's being pushed on from outside the bottle.

Following this logic - it would seem to me that a "pressurized" hard drive would suffer from expansion (albeit slightly) as you ascend. Unpressurized - it makes no different... the distance between the head and the disc is the same - it's just the number of air molecules has done down under the head - but at the same time - the air molecules pushing against the air has also gone done. I would think the effect of gravity has WAY more effect on the head's spacing from the disc than the air molecules - and yet a HD will operate fine on the side or upside down.

Man - I feel like a jerk here - but it just seems like there's a whole in that 10,000 ft logic. I don't get it. ;-) But then again - there's a lot I don't get so no surprise. ;-)

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JimP
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Re: AnywhereMap GPS

Postby JimP » Sat Jun 28, 2008 10:23 pm

Recently became a listener, and just registered on the forums to respond to this question. I used to work for IBM, and was once given the opportunity to tour the facility where IBM hard drives were made. (They were trying to hire me to write software that controlled the manufacturing process.) We got an in-depth explanation on how they work from one of the engineers. The hard drive technology does, in fact, involve "flying" heads.

A pair of read/write heads are attached to U-shaped actuator arms, which apply a slight "clamping" force to hold the head together, so that they would tend to "clamp" onto the media platter. As the hard drive is powered off - well before it is stopped - the heads are mechanically "retracted" away from the spinning disk platters, and the arms (with read/write heads attached) are "wedged" slightly wider apart than the width of the platter, so that there is no possibility of contact between the heads and the platters. When the drive is powered back up, firt the disk platters spin up to speed, then the heads are moved back over the spinning platters. As they do so, the mechanical retractor also releases the "wedge" to allow them to "press together" against the platter. However, a boundary layer of air spinning with the platter actually keeps the heads from making physical contact with the platters -- they "fly" on that boundary layer, kind of like a car tire hydroplaning over the road on a thin film of water.

So why the "limitation" of 10,000 feet? They did the calculations on the density of the air, and above 10,000 feet, there is insufficient boundary layer pressure to totally counteract the "clamping" effect of the head mounting system... Above that altitude, the drive might work under "normal" circumstances, but even minor shocks to the system could result in catastrophic contact between the heads and the platters (known as a "head crash"). Turbulence, or even normal maneuvering might cause the heads to make contact and destroy the drive's utility.

If you were to look at a drive that has had a "head crash", you would see exactly where the heads first made contact with the disk -- there would be a "ring scar" where the magnetic media plating is literally scraped off the platter, then you might also see a couple more smaller "rings" as the head is retracted towards the outside of the drive, bouncing off the surface of the disk along the way. By the way, both the upper and lower surfaces of the disk platter receive the "scar", because the heads for upper and lower sides are on the same "retractor"...

Just like airplanes, you can (or at least used to be able to) buy "high altitude" drives that effectively have their own "pressurized cockpits" - meaning that the drives have an impeller that boosts the pressure inside the drive case so that the heads continue to "fly" at higher altitudes. These were quite expensive, and I haven't seen any for years now...

As pointed out by one of the other forum members, solid-state drives have pretty well eliminated the need for these drives.
Jim Parker
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