Secure, quick-release latching device for high vibration and shock environment.

[Faustie]

Hello,

I'm currently thinking of a solution to a problem which requires mounting a small avionics box to an interfacing plate. I must be able to rapidly mount the box with minimal effort (e.g., drop into place) which should securely latch, be able to rapidly dismount with low effort but never by accident, and should be capable of withstanding high vibration, shock, acceleration loads etc. (e.g., 22 g quasi-static loads in all axes, SRS of up to 1000 g at 1000 & 10000 Hz, +- 10g static acceleration limits). Ideally, the solution should be low volume and low mass, and available off the shelf.

I came across positive-locking pins such as ball locking, ball clamping, and cam locking fasteners. Would these be sensible solutions (so long as I analyse and test, of course), or have I missed an obvious better solution?

Thank you!

 

[BrianE22]

Backlash in the connection would be important I'd think. The only one of the three I've used are the ball locking pins - I wouldn't count on those if you need a pre-loaded joint.

 

[3DDave]

20 questions time.

How big a box?
How heavy a box?
What is the box made of?
How is this supposed to mount to the plate?
How rapidly is mounting to take place?

I've used expanding sleeve pins to restrain items. There is a handle actuated cam that first draws the core of the pin up until the expansion wedges it and then further motion pulls the cam down tight against whatever is being restrained. this eliminates backlash and provides substantial preload.

See

https://www.carrlane.com/product/alignment-pins/expanding-pins/expanding-pins-cam-handle

In our application we had some made with an over-sleeve for precision (0.005 or less, it's been a while) repetitive alignment. I think you may request that some expanding segments are replaced with plain spacers.

It's best to have a secondary capture on the main capture device. For the expanding pin clamps, to have a spring catch that has to be moved to let the handle loose with a very high g tolerance. For that use it could be a thin wire spring as the load from the handle will be a tensile load and the lower weight of the wire will keep it's deflection from acceleration small. Or use the wrench version so that there isn't any unlocking load.

 

[dvd]

locating pins and magnets with some sort of cam for removal comes to mind

 

[CWB1]

Simple draw latches like on a suitcase or steamer trunk are a super-common old favorite in these situations.

I'd search the latch category on McMaster for ideas.

 

[3DDave]

I found a case where some bright engineer thought to use hook and loop tape to secure a box, thinking it installs by just pushing it on and will come off by pulling it. He used a lot of it, covered the mating face of the box and matching that on the mounting plate (wall of armored vehicle.)

Turns out that the easy release of hook and loop is because the peel strength is a pound or so per inch of width, but since the box and wall were rigid it could not peel. Direct pull was on the order of 10 pounds per square inch, so it required nearly 500 pounds of pull to remove it. Not many people with fingers that strong.

 

[MintJulep]

Ball lock pins, cam locks, draw latches don't address the request for "drop in" installation.

Consider something like:

That's from Takigen:

https://www.takigen.com/

Similar latches available from:
Southco:

https://southco.com/en_any_int/latches/push-to-close-latches/remote-actuated/r4-rotary-latches

Austin Hardware:

https://www.austinhardware.com/all-products/latches/rotary-latches.html

All three of those suppliers have a wide range of products for consideration, and there are other vendors as well.

 

[Faustie]

Thanks for all the feedback! Lots of useful advice here.

Certainly looks like I was on the wrong path with the positive-lock and cam lock pins. The rotary latches look promising, especially as some have vibration damping included.

To answer the other questions above:
- Size: Roughly 30 x 10 x 10 cm
- Mass: 5 kg max
- Material: Aluminium
- Mounting method: Technician placing it in vertically. Should either drop in for a 'plug-and-play' type installation, or require minimal effort to secure especially as space is constrained and the technician will be wearing gloves. Removal is similar - needs to be manually done so it can't happen by accident, but shouldn't be too challenging for the technician.
- Speed: No more than 5 minutes worst-case for each operation, but ideally under 1 min

I'm more used to working with mil-spec electrical connectors where suitability for high-vibration aerospace/military applications is very clearly specified. Regarding using things like simple raw latches, or other types of pins, I struggle to find similar specifications for lots of these solutions - presumably it's assumed to be proven safe via rigorous testing, or am I missing something obvious?

Thanks!

 

[3DDave]

I've used a wedge mount - a keystone shape but with beveled edges on the item to be installed and a mating inverse version of it in the base plate such that the bevel is captured. With a 30 degree keystone (15 per side) and a 60 degree bevel on the edges it is almost, but not quite, self locking. Making the keystone a little steeper and the bevel to 45 degrees it may wedge tight enough to stay on its own.

If not then any of a number of clips can be used to prevent it from starting to move out of the V. For example a strip of flat spring, beryllium copper or spring steel, can be used as a one-way retainer that must be depressed to release the mount.

The nice thing about the 30 degree keystone is that one doesn't need to lift completely free of the mating part. If the overlap in the bevel is, estimating, 0.125, then lifting 0.5 should be enough to allow perpendicular travel. One might also use interrupted edges to control the amount of movement if that proves a problem.

If you give it a try, I'd recommend making a taper go the long way on the box.

 

[SnTMan]

Dzus fasteners are secure enough to mount all manner of panels to the outside of aircraft. Tool-less versions are available.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand