« The uneven performance of cameras in rugged handhelds and tablets | Main | Thoughts about Computer Benchmark Testing »
October 1, 2019
How the rugged PC "drop spec" just became different
The Department of Defense significantly expands drop test definitions and procedures in the new MIL-STD-810H Test Method Standard
You wouldn't know it from looking at almost all of the published ruggedness testing results, but the good old DOD MIL-STD-810G was replaced by the MIL-STD-810H in January 2019. And if you thought the old MIL-STD-810G was massive in size, the new one is bigger yet. While the old MIL-STD-810G document was 804 pages, the new one has 1,089. That's 285 extra pages of testing procedures.
The new standard brings quite a few changes in ruggedness testing. In this article I'll take a first look at one of the marquee tests as far as rugged mobile computing equipment goes, the transit drop test. It was described in Method 516.6 Procedure IV in the old MIL-STD-810G, and now it is under Method 516.8 Procedure IV in the new MIL-STD-810H. The drop section has grown from two to six pages, and there are some interesting changes.
Drop surface: Steel over concrete
The basic approach to drop testing remains the same. Items must still be tested in the same configuration that is actually "used in transportation, handling, or a combat situation." What has changed is how testing is done. Procedures are described in more detail.
Under the old MIL-STD-810G, lightweight items such as mobile computing equipment had to be dropped onto two-inch plywood backed by concrete, and only really heavy gear weighing over 1,000 pounds directly onto concrete. That has changed. The DOD was apparently concerned about repeatability of results, and surface configuration can have a substantial impact on that. The DOD wanted to test the most severe damage potential, that of "impact with a non-yielding mass that absorbs minimal energy."
Since plywood hardness can change and affect results, under MIL-STD-810H the default impact surface is now steel plate over concrete. For mobile computing gear purposes, the steel plate must be at least an inch thick, have a Brinell hardness of 200 or more, the concrete underneath must be reinforced, have a minimum compressive strength of 2500 psi, and the steel must be bonded or bolted onto the concrete to form a uniform, rigid structure.
This seems drastic. Clearly, what the DOD is concerned here is that it is the dropped item that must absorb the impact and not the surface that something is dropped on, hence the steel instead of plywood. Fortunately, the DOD realizes that there is a big difference between dropping light and very heavy gear, and also what something might fall on. On an aircraft carrier, for example, it would almost always be steel. Out there in the field, it's more likely asphalt or dirt.
So the supporting notes allow that "concrete or 2-inch plywood backed by concrete may be selected if (a) a concrete or wood surface is representative of the most severe conditions or (b) it can be shown that the compressive strength of the impact surface is greater than that of the test item impact points." Whew. But steel is actually a very good idea.
Different drop scenarios
The MIL-STD-810H recognizes that not all drops are equal. The "transit drop" in the old MIL-STD-810G seemed to primarily assume that something falls off a truck when loading and unloading equipment. This really didn't have much relevance to the most likely drop scenario in mobile computing -- dropping a tablet or laptop while using it in the field. So whereas the old standard only had one drop scenario -- transit drop -- the new MIL-STD-810H standard has three.
There is the "logistic transit drop test" that states drop conditions for "non-tactical logistical transport" i.e. dropping things off the proverbial truck. The "tactical transport drop test" includes scenarios associated with "tactical transport beyond the theatre storage area. And, finally, there's a "severe tactical transport drop test" where items pass as long as they do "not explode, burn, spread propellant or explosive material as a result of dropping, dragging or removal of the item for disposal."
Now what does all that mean?
The "logistic transit drop" test is, in essence, the same as the old MIL-STD-810G transit drop test. Items where the largest dimension is no more than 36 inches (i.e. all mobile computing gear) must pass 48-inch drops on "each face, edge, and corner; total of 26 drops." These 26 drops may be among no more than five test items.
The "tactical transport drop" offers five scenarios (ship, unpackaged, packaged, helicopter, and parachute), where only one scenario applies to conventional ruggedness testing of mobile computing gear "unpackaged handling, infantry and man-carried equipment." There, the drop height is five feet. And instead of 26 drops, there are five standard drop orientations (drop to flat bottom, left end, right end, bottom right edge at 45 degrees, and top left end corner at 45 degrees), with each item exposed to no more than two drops.
The "severe tactical transport drop" test really only applies to items being dropped from significant heights, like helicopters, aircraft, cranes and such. There, the drop height starts at 7 feet (falling out of a helicopter, unpackaged) to 82 feet (shipboard loading onto an aircraft carrier). This rarely applies for the purposes of rugged mobile computers, but for bragging rights, some makers of rugged computing gear will undoubtedly perform those tests (you know who you are!).
Guidance systems
If you've ever wondered how one can drop an item so that it lands exactly on a mandated edge or corner, the MIL-STD-810H offers help and a suggestion. "Guidance systems which do not reduce the impact velocity may be employed to ensure correct impact angle, however, guidance shall be eliminated at a sufficient height above the impact surface to allow unimpeded fall and rebound." We've never seen any such system, and it should be interesting if someone will come up with such a drop test guidance mechanism.
Evaluating results
Now how does one perform, document and evaluate the drops? That has always been the weakest point in drop testing, and the new MIL-STD-810H brings no change.
It's simply recommended to "periodically" examine an item visually and operationally during the testing, to help in the follow-up evaluation. It's recommended to document the impact point and/or surface of each drop and any obvious damage. And that's it.
So although the "drop test" section in the new MIL-STD-810H has grown considerably in length, new categories have been added, and testing methods mandated in more detail, much remains quite vague. That's to be expected of a testing procedure that covers a vast variety of different items that may be packaged, unpackaged, and ranging in weight from very light to thousands of pounds. And so the section ends with "conduct an operational checkout in accordance with the approved test plan."
My recommendations
What do we learn from all this? In essence, that it all depends, even under the more detailed guidelines of the new MIL-STD-810H.
What's important with mobile computing gear is that it still works after you drop it. Whether it's operating during the test or not used to matter back when mobile computers had hard disks. With solid state storage it functionally really doesn't matter whether testing is done with the system on or not.
I suggest doing the tests with the unit operating. That way it's immediately obvious if a drop killed the unit or not. And leaving it on alleviates the need to start it up after every drop.
I would not split the mandated number and types of drops on five units. That makes no sense. Instead, I would do all mandated drops on the same unit, but do all those drops on five successive units. All five must pass, i.e. still work after all drops. That way, one can be reasonably sure that results were not a fluke.
As far as the surface goes, most units will fall on carpet or wood indoors, and natural surfaces all the way to concrete outdoors. Using the suggested steel over concrete shows you're taking the testing serious. Using plywood is a bit of a cop-out because it's much softer and less likely to damage a unit. And the hardness of plywood varies.
Doing the 5-foot "tactical transport drop" test definitely gets extra credit. When using a handheld computer as a phone it'll fall from five or six feet. And even tablets can easily fall from more than four feet. Besides, the "tactical transport drop test" for "infantry and man-carried equipment" (presumably the DOD means women-carried as well) much better describes the real world drop scenarios of mobile computing gear.
Passing the "severe tactical transport drop" test that starts at seven foot drops gets extra credit.
So hit the books and study the pertaining sections of the new MIL-STD-810H. You don't want to be the last to switch. -- Conrad H. Blickenstorfer, September 2019
Posted by conradb212 at October 1, 2019 6:06 PM