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4hv.org :: Forums :: General Science and Electronics
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Newtons, G's and Electronics Survivability.

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Patrick
Sun Jun 12 2016, 01:52AM Print
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Are there examples of electronic devices surviving high G-loads? I can only think of artillery like the M982 GPS guided round, and solid state flight recorders.

I dont think the G and Newton units are directly convertible, right? Im trying to calculate the G-force collision of a drone with a 747 or large aircraft. I guess i should be using the work-energy principle method.
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Patrick
Sun Jun 12 2016, 06:27PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Sulaiman wrote ...

Designing drone electronics to survive crashing with a 747 sounds a little odd, to say the least.
I want to know if a tiny memory card can survive, in a properly designed case.
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Bjørn
Sun Jun 12 2016, 06:50PM
Bjørn Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Two off topic posts disappeared.

Part II: Posting

A. Stay on topic. When posting in a thread, look at two things. The subject, and the first post. Those two give you an idea of what is and what isn't okay in the thread.

E. Make sure each post has a point. Unless you're in the chatting board, there's no need for a one-liner post that doesn't have any real content.

-----------

DIP chips can reliably survive 30 000 G if mounted correctly. If your drone should hit a hard surface at 900 km/h you would need about 10 cm crumple zone to reach a comparable value so it seems to be possible in theory if you can stop the card from flexing too much.
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2Spoons
Sun Jun 12 2016, 10:45PM
2Spoons Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
What do you consider high G? When I was designing military training equipment we had a laser + electronics that mounted on a gun barrel, and had to survive 800G shock loading on every shot. Biggest risk item was the crystal for the micro. I don't recall seeing any issues.
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Carbon_Rod
Mon Jun 13 2016, 12:49AM
Carbon_Rod Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
@Patrick
Normal micro SDHC memory cards are mostly wafer silicon by volume, and easily fracture when bent. Yet given its relatively low mass, there is a high probability it would remain functional for awhile if bonded to something rigid. For example, most high Mach aircraft use aluminium bonded PCBs coated with transparent fire retardant silicones to mitigate vibration fatigue. NASA has done extensive work documenting mechanical board failure modes, and JPL built on many of these same design principles.

Note, some chips already follow JESD22-B104C or Mil-Std-883:
Where method 2002.5 Cond. E is defined as 10000g’s for 0.2ms for several iterations.
Just remember from basic principles F=m*a, which suggests a lower mass package like 0402 & QFN are usually less likely to pull itself off a board or break glue bonds. Note, the solder heel fillet inspection process is very important for meeting this kind of standard.

You may find many materials exhibit piezoelectric properties under physical perturbation.
For example, tapping some scope probe lead wires or cheap ceramic components can generate noise.
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Patrick
Mon Jun 13 2016, 05:23AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
well as Bjorn said, i was looking for a range like 30,000 or 20,000 or whatever. But yours guys' comments are great.

Carbon Rod, so in aircraft they bond otherwise normal circuit boards to ridged aluminum plates, then cover with conformal silicone ?
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Carbon_Rod
Mon Jun 13 2016, 06:38AM
Carbon_Rod Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
Aluminium in PCB laminations is not that exotic these days, and can be ordered without the via holes forming fissures. Less mundane delivery vehicles where SOICs tear their own pins off if the heel is wrong, will often use this type of board for critical electronics. Coatings are another issue that can vary depending on the equipment, but flame retardant silicone dips/sprays are popular.

Note metal foams (invented at Bjorksten Lab in the 50's) were designed for impact absorption, and thus the force peaks are much less energetic.
wink
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Dr. Slack
Mon Jun 13 2016, 08:55AM
Dr. Slack Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
It's quite easy to do one's head in hoping and poking with 'do I pot it in epoxy, or something squdgy?' sort of questions.

The basic physics is quite straightforward however. You can always transform the situation into something moving being brought to rest, this seems to be the easiest way to reason about it. All the massy parts of the system will have a known amount of kinetic energy initially. This will be dissipated by them doing work on the lossy parts of the system, the crumple zone if there is an explicit structure, material losses or fractures if there isn't. The length of the crumple zone defines how much time and distance they have to do this, which controls the force. Getting the force from housing to the massy parts is the job of of a compliant system, and as you know a mass/compliant system has a resonant frequency. The ratio of stiffness and dissipation per unit displacement will indicate whether your system is heavily or lightly damped.

Put in those system terms, it's usually easier to figure out upper/lower bounds for things, and for which bits need to be stiff/lossy/light/long etc.
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Thomas W
Mon Jun 13 2016, 12:06PM
Thomas W Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276
It would be interesting to do some actual physical tests... the problem is trying to accelerate your item up to 167m/s...

Carbon did bring up a very interesting point regarding the peizo electric functions of ceramics... I woulder just how high the voltages could go from a high velocity impact such as described and how much of a concern it would be.

I would imagine the best way of securing the electronics to survive such a high velocity impact would be either securing the unit with springs in a steel case, or a material similar to what is in IGBTs.

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Patrick
Mon Jun 20 2016, 06:05PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639


1466445988 2431 FT1630 Ht Bird Strike Ll 120731 Wblog


Undesirable bird strike in an undesirable location. (737 on decent to Denver, CO)



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