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Shock of 75 G. and 350 G.

Posted on 2006-07-21
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Last Modified: 2012-08-13
All,

It has been pointed out to me that there is a warranty notice on some Seagate drives that says "Varranty void if ... , or if drive experiences shock in excess of 350 Gs.". Could people give me examples of an event that could cause a 350 G shock to a hard drive? Realistic, creative or hilarious would be perfectly acceptable.

http://backbytes.computing.co.uk/2006/07/hard_driving.html

The quote mentions 75 G too so some examples of that would be good. Mine reads 350 G.

Paul
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Question by:PaulCaswell
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11 Comments
 
LVL 84

Expert Comment

by:ozo
ID: 17152721
Drop it from 75cm, and stop it in 1cm.
Drom it from 350mm, and stop it in 1mm.
0
 
LVL 16

Author Comment

by:PaulCaswell
ID: 17152747
Thanks ozo,

Any ideas exactly what I could stop it with to stop it at 1cm and 1mm? I could imagine a 1cm deep dent in a plank of wood but that would not appear as a result of a 75 cm or 350 cm drop.

If it was in my car and I hit a brick wall and the normal crumple process occurs, how fast would I need to be travelling to achieve these two values?

Paul
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LVL 16

Author Comment

by:PaulCaswell
ID: 17152784
If I drop it into water, say, how high would I have to drop it from? Assume normal salinity seawater and a predictable impact orientation.

Here's the details of the drive:

                    Height (inches/mm):    1.03/26.1
                    Width  (inches/mm):    4.00/101.85
                    Depth  (inches/mm):    5.78/147.0
                    Weight      (lb/g):     1.2/550

I guess it depends on the orientation on impact so a range from 26.1 X 101.85 to 101.85 X 147.0 would be good.

Paul
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LVL 22

Expert Comment

by:grg99
ID: 17153011
If you drop it onto a  hard surface, it can end up stopping in considerably less than one millimeter.  Let's assume it stops in .1 millimeter.  that means a 3.5cm drop will accelerate it enough to cause 350G decelleration in 0.1 millimeter.  That's only about 1.3 inches.  

So almost any drop onto a hard surface is a bad thing.

If you drop it into salt water, it's not likely to survive.  Salt water is bad for electronics.  Not to mention the water will contaminate the filter and maybe seep inside the drive.


To have it survive, you need some kind of shock mounting, so no matter how quickly the outer case stops, the drive has a few millimeters of jounce-room over which to spread out the decelleration.  Look up "Lord mounts", that company makes shock mounts to mount all kinds of things-- from nanites to jet engines.  Or mount it hanging from some thick rubber bands.  Or if it's a tiny cool drive, just wrap it in about an inch of bubble wrap.  Doesnt work for PC-sized drivers, they run too hot for this treatment.





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LVL 84

Expert Comment

by:ozo
ID: 17153126
38.3m/s or 138km/hr with a 1m crumple would be 75g
but crumpleing .99m to decelerate from 38.3m/s to 8.3m/s then
decelerating from 8.3 to 0 in the last .1m would be over 350g


If the surface does not deform when supporting 192.5kg per 2658 sq mm, it could impart 350g to a drive droped on end.
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LVL 84

Expert Comment

by:ozo
ID: 17153262
About 26m/s through water on the small end, or 11m/s on the big end should generate 350g of drag
About 12m/s through water on the small end, or 5m/s on the big end should generate 75g of drag

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LVL 18

Accepted Solution

by:
JR2003 earned 125 total points
ID: 17153774
A 1200 rpm spin dryer could produce about 350g

http://www.msu.edu/~venkata1/gforce.htm
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LVL 6

Expert Comment

by:infex
ID: 17156564
If it drops on a hard material ... (see before)

However if it is packed in some chock absorbing materials thing are quite different. I have actually seen how the transporters throw with boxes of "fragile" materials ...

Hope this helps
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LVL 16

Author Comment

by:PaulCaswell
ID: 17157125
>>A 1200 rpm spin dryer could produce about 350g
Now THAT's the sort of thing I was looking for! A real-life repeatable situation.

I dont want it to survive, I just want it to experience 350G (and 75 G) in an everyday or at least an uncontrived event such as being dropped from a plane or spun in a spin dryer. :-)

Good work all! Just a couple more fine examples of Seagate Hard-Drive abuse that would void your warranty.

Paul
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LVL 84

Expert Comment

by:ozo
ID: 17158912
Vibrating at 40.5KHz (the resonant frequency of a .147m block of steel) with a displacement of 0.0000447 mm would require an acceleration of 75g
and a drive of that size vibrating like that would produce about a 90dB tone
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LVL 16

Author Comment

by:PaulCaswell
ID: 17159568
Thanks ozo, in what situation might this be made to happen? A very loud rock concert?

Paul
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