Shielding An HD From Excessive Vibrations?

schematic asks: "I'm planning on building an mp3 player for my car, but a few of my buddies brought up a good point yesterday. They asked how I'd planned to mount the hard drive to protect it from vibrations (bass) and bumps (crazy driving). I've heard of a few good ideas, but I dont know what I can do to shield it from the bass, since that seems to shake the daylights outta everything. Anyone have a similar setup or an idea that works?"

Comments

Vibrational modes

[adipocere]

Your first step is to identify your vibrational modes. For example:

• Subwoofer: Assume that you will be protecting against 10 Hz to perhaps 100 Hz
• Random shocks: No guess as to the frequency of these.
• Figuring out the direction of these vibrations is important. Will they be going from side to side? Up and down? Front to back?

Examine the materials that came with your hard drive. Many of them will talk about what kinds of vibrational modes they are rated for, what they can withstand, etc. Compare to the directions of your vibrational modes to find in which to mount your hard drive. That is, if your vibrations are mostly side-to-side, mount your hard drive such that your most vulnerable direction (for example, perpendicular to the platters) is not parallel to the side-to-side vibration.

Now, another important part is that you want to damp the vibrations in multiple modes. That is, you want to guard against as many big modes as possible. If you have a contraption made from bungee cords, it will damp best against a specific frequency (and possibly some harmonics), but the damping will be less effective at other frequencies. Where the weak patches are, damp with a different material. So, perhaps bungee cords + silicone gel + foam could guard against many of them.

Test. Test again. If I were you, I would construct a "cradle" for the drive or case. Then, put something in it susceptible to vibration (a covered bowl of water, perhaps, or a leaf). Crank the bass. Have someone else drive around while you look at it. See any ripples or shaking? If so, back to the drawing board! More high-tech solutions exist for testing, etc., but I doubt you want to go there.

And, when all else fails, drivespace is cheap. Buy several replacement drives.

Re:Vibrational modes

[Tau Zero]

Your first step is to identify your vibrational modes. For example:

• Subwoofer: Assume that you will be protecting against 10 Hz to perhaps 100 Hz
• Random shocks: No guess as to the frequency of these.
• Figuring out the direction of these vibrations is important. Will they be going from side to side? Up and down? Front to back?

Some of that isn't necessary; you know that the major shocks will be from below (suspension bottoming out), and the heaviest low-frequency vibrations will likely be from the subwoofer (unless you have a REALLY loud exhaust or horrible engine mounts). All you really need to do is build your isolation mount, bolt it to something like a piece of heavy plywood, and test it.

How do you test it? Give it vibrations and shocks. If it can sit on top of your subwoofer without causing any errors, and if you can handle several G's of shock load from below (like you'd get from hitting the far side of a really bad pothole, after the car has had a chance to fall down into it), it should do. The shock-load testing can probably be done with a drop test.

The really interesting part is the suspension design. Your side loads will probably never get up to 1 G, so the mount can be very compliant in that direction. Ditto fore/aft, unless you make a habit of running into things with your car. A compliant mount will have a very low resonant frequency, and will transmit very little force from the vehicle to the drive. From below is different; you need to handle a constant 1G force and possibly spikes of 5G for short intervals (a few inches of travel) without bottoming out and shocking the drive. You probably want to use foam rubber for this. Make it in blocks separated slightly, so they can bend back and forth more easily than they crush. Use enough thickness of sufficiently stiff foam that 10 G's (ten times the drive weight) doesn't crush the foam all the way down, and make sure that turning the mount sideways (1 G side force) doesn't let the drive hit any of the sides either. Don't forget cooling requirements, and a heater to bring the drive up to a reasonable temperature before firing it up after a cold-soak is a really good idea.

I like the idea of the auto-spec CD-ROM drive; all those details are already taken care of for you.
--
Build a man a fire, and he's warm for a day.

Something to consider...

[Dr Caleb]

The toughest laptop I've ever seen is the Panasonic Toughbook. I've used it for data collection in a very high vibration area. Most other laptops would only last 12 - 18 hours in that environment. This one has been running 2 years.

The case is machined aluminum and carbon fiber, and the HD is surrounded by a very soft jelly.

It's the kind of stuff you find in ergonomic wrist and mouse pads, that really thick very soft stuff. A normal HD will survive a drop from about 1m on to concrete, but they claim that theirs will survive a 10m fall.

Perhaps you could find a couple of these at a used computer store and salvage the gel out of them?

Re:My HDD

[Detritus]

I would also be concerned about low temperatures, like when your car sits idle for long periods in the winter. The drive may not spin up if it is too cold.

What about temperature extremes?

[Ripp]

I don't think you'd have to worry about vibrations so much as it surviving temperature extremes.

Even if you stick it in the trunk, it's still going to get *damn* hot in the summer. Depending on where you live, winter is liable to kill it altogether!!!

Unless you somehow put it in a pullout chassis you can take out of the car and into the ac or heat.

Re:What about temperature extremes?

[djweis]

I don't worry too much about vibration for mine. I have it in a case in my trunk. Once my dsl comes back up, you can see it here.

Re:What about temperature extremes?

[Xenu]

Cold isn't good for motors, lubricants and bearings.

Talk to a Test lab

[CharlieG]

Ok folks, this USED to me my field of work (and I can't remember some of the source names)

If you can, try making a phone call to an "Environmental Test Lab" - they do shock and vibration testing. I've tested a few HDs over time

Vibration is going to be FAIRLY easy to deal with, IF you get lucky. There are little rubber (actually synthetic) shock mounts made - in fact, you'll see small ones on a lot of drives - the problem is I can't remember the main brand name (I haven't done this in 8 years). Your BIG worry is that the mount (ANY mount) has a resonant frequency, where it will actually amplify the input vibration. What you have to worry about is that the resonant frequency you choose for your mount can't be near any of the resonant frequencies of the drive itself.

The hard problem is SHOCK - this is usually isolated with what looks like a coil of wire (like a spring) laying on its side. This takes some space, but can work well (if you get the response frequencies right).

From watching disk drives being tested in the past (Yes, I've played with mil spec hardened drives - 200g shock? No problems - 30 gs of vibration? Cake), the BIGGEST problem is not shock (or vibration) in the X,Y or Z directions (aka, left/right, front/back,up/down), but it's TORTIONAL shock, aka, rotating about the X,Y or Z, and in particular, rotating around the axis of the spindle - this tends to drive the ends of the head arms into/out of the track.

I hope this helps