Joel,
For what it is worth this an article on the damage forces and types of bumps that the type of hard drives found in DVRs are capable of surviving. The forces that cause damage are about 7 times higher in the off state. There is one well insulated drive meant for hard use but if you look at the damage forces table it only helps in the off state.
http://www.tomshardware.com/reviews/a-sturdy-companion,758-2.html
These are the compatible drives used in the 722, the Seagate is the most likely one that was installed.
Hitachi HCS725050VLA380
ST3500830SCE
WDC WD5000AAJS-57
This is the spec sheet for the Seagate which includes the on and off vibration specs.
http://www.seagate.com/docs/pdf/datasheet/disc/ds_db35_7200_3.pdf
You are the physics wizard Joel, those vibration specs will mean more to you than me. All I know is I rarely got away scot-free when thumping one of my desktop drives over the years. I have drawers that jump out onto the floor at times and I know my 722DVR has levitated in the air momentarily before doing a landing on the shelf in my rear closet :-)
Later Ed
Actually Ed, you've provided all the information needed to explain why my hard drives aren't particularly disturbed by traveling in the MH even when they are running. The article you cited states that the rated "operating" shock for most HDDs is in the 50-60G range. That's the kind of shock you get from something moving at ~0.5 m/s stopping in a hundredth of a second, like dropping a object from a height of a couple of inches onto a slab of concrete. No question that won't do your HDD any good.
But high impact forces only occur when a moving object stops suddenly. The reason the MH situation isn't nearly so bad is that everything in the MH is moving at the same speeds both sideways and up/down. So it is difficult for objects to sustain impact forces of the kind necessary to do harm. There's a huge difference between the nearly instantaneous stopping that occurs when an object falls on concrete compared to the impacts transmitted through the wheels to the inside of the vehicle.
If the MH's wheel hits a pothole the vehicle shudders but everything in the vehicle is moving together. The jolt the DVR feels is the same jolt felt by the shelf it is laying on, for the most part the objects move together. Unless an object literally goes flying and then falls back onto its shelf the impacts felt will be more in line with roller coaster forces (~5Gs) rather than impact forces. If an object does lift slightly off its shelf, the fact that it has rubber feet and probably is sitting on a carpeted shelf helps reduce any shock it may receive. Even if your entire MH goes airborne, everything in it is moving at exactly the same speed, therefore virtually no impact forces occur when the wheels make contact with the ground.
We all get jarred by the bumps our coaches go over, but the actual impact levels aren't all that high because they do ride on inflated tires and have pneumatic suspension. We see cabinets fly open, but much of that comes from distortion of the cabinet frame and latch as the vehicle flexes slightly on impact.
The lesson from this is put your DVR (or other sensitive stuff) on something that will cushion it (not something that will make it bounce)--thereby stretching out the time of any collision that occurs if the object is jostled; a piece of carpet would be fine. Better still, put a bungee cord over it to hold it on the cushioning material so it has to remain still on its shelf and can't possibly go airborne.
We've had a DVR in the MH for 4 years without issue and I've never actually considered the physics of it until now. Thanks for making me think it through; now I'm less concerned than I was previously. If someone at Dish has made a rule about DVRs in MHs they clearly don't know the physics of the situation.
Joel
