Archived from groups: alt.comp.hardware.pc-homebuilt (
More info?)
Al Dykes wrote:
> In article <kpBFc.18942$IQ4.1820@attbi_s02>,
> John R Weiss <jrweiss98155@.comNOSPAMcast.net> wrote:
>
>>"Raff" <NOSPAM_raff.m@eudoramail.com> wrote...
>>
>>>I would to install a computer in my car. I want to use an hd too, just i'm
>>>worried if it can work fine because vibrations. do you think a 2"5 hd can
>>
>>go
>>
>>>better?
>>
>>A 2.5" HD would be preferable for 2 reasons: smaller size; and better
>>adaptation to motion, because it was initially designed as a mobile unit.
>>
>>That said, the motion of a car is much more significant overall than that
>>seen by a laptop computer in normal use. You should do some research into
>>vibration damping and shock mounting. You might look into the Panasonic
>>Toughbooks and other "hardened" laptops, and the components and enhancements
>>used in them.
>>
>>
>
>
>
> If you get the spec sheet for the HDD model you are considering from
> the manufacturer's web site you will see the G-force limits (and
> temps) for operating and non-operating conditions. I think you will
> find that your disk is good to several 10's of G's while running, and
> much more when off. Considering that you've probably never felt
> anywhere near 1 G in any car you've ever been in, you're OK.
Your interpretation of the spec is a bit optimistic. Those 'multiple 10s'
of Gs you speak of are for a 2ms half sine wave and you won't see shock in
a car that's only 2ms in duration.
And, btw, it doesn't take all that much momentum to look like 20Gs when
it's constrained into 2ms. Which is why dropping an object onto something
'soft' is safer than onto something hard. The exact same amount of momentum
that's 'safe' onto a soft landing gets turned into astronomical Gs when the
falling object stops 'instantly' on the hard surface. The point is, what to
your soft pliable butt, sitting on a soft pliable seat, feels like a 'minor
bump' can be a huge G shock to something rigidly mounted to the car.
The more relevant numbers are the vibration specs, of which there are two:
Linear: 20-300 Hz, 0.75 G (0 to peak) and, the more real world
representative one, Random: 10-300 Hz, 0.004 g2/Hz.
Those are not 'sustained' global Gs, though, as you are thinking when you
say "you've probably never felt anywhere near 1 G in any car you've ever
been in." No, you don't 'feel' it because they're shock/vibration (not a
skid pad test) and your body gives with the shock/vibration, and absorbs
them. But to something rigid they're 'multiple Gs' nonetheless.
> You need
> to use some rubber mounts to isolate low amplitude-high frequency
> vibrations, but that doesn't take much.
Rubber mounts are a bad idea because they'll resonate and actually amplify
certain vibration frequencies.
> A toughbook (a wonderful PC, BTW) is probably designed to take a 3 ft
> fall to concrete, with G forces much higher than you'll ever see in
> car, possibly even in a crash, because the car has crumple zones
> designed in.
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