Am I being too anal about DSub to DSub connections?

The typical method for connecting two DSub (DB9 here) connectors together is to use two #4 standoffs. You use a nut and a couple washers to secure them to one DB9 connector. You then screw the other DB9 backshell into the standoff.

You can see a standoff attached to one connector in this photo:


The connectors end up looking like this. The threads and nut of each standoff is inside the backshell on the left (some grinding of the backshell innards required).


Problem is, the other DB9 backshell is not secured to the assembly, so can wobble and strain the wires a bit. See the following video:
http://www.prettybits.com/video/DB9_Wobble.mp4

So I looked into some other solutions.

The first was to use elongated nuts from McMaster Carr that can be placed between the connectors and each backshell's screws can thread into each side of the nut. I did have to grind/shorten the backshell screws a bit to prevent them from butting up against each other in the nuts. This worked pretty well.

The elongated nuts:


Assembled:


Another option that I liked better was to simply use longer standoffs, also from McMaster. They call them Jack Screws. These go all the way through the DB9 backshells and get secured in place by washers and a nut. I put the standard washer under the jackscrew head to move it closer to the other backshell. Again, both backshells are secured firmly together.

Longer standoffs:


Assembled:


Installed on the copilot stick:


Am I overthinking this?

I think the longer standoffs will work just fine. Years ago, I read an article where the author advocated simply using the DB connectors without the shell and securing the male and female together by running a zip-tie through each ear/standoff mounting hole....

In short - looks good. looks workable. seems safe. drive on and good luck!

FredMagare said:

I think the longer standoffs will work just fine. Years ago, I read an article where the author advocated simply using the DB connectors without the shell and securing the male and female together by running a zip-tie through each ear/standoff mounting hole....

In short - looks good. looks workable. seems safe. drive on and good luck!

Click to expand...

The zip-tie thing is exactly what I do. 12 years and 600 hours with no issues.

I also purchased a bunch of those long thumbscrews from McMaster (or Newark) and found they work very well and make it very easy to disconnect when you are reaching somewhere with only one hand in an area that is difficult to get to. If you want to save weight though, nothing wrong with the zip tie method.

I didn't install the strain reliefs on any D-Subs, but rather ensured each bundle had an adequate service loop. It is a royal pain to cut shrink wrap and remove strain reliefs when you go to work on your wiring (upgrades, troubleshooting, etc.). You'd be surprised at how many certified aircraft don't have strain reliefs in stalled on the connector backshells which makes a technicians life a lot easier.

Zip ties here as well. Works like a charm and is easy to deal with.

rv8bldr said:

The zip-tie thing is exactly what I do. 12 years and 600 hours with no issues.

Click to expand...

Plus one for me too.

I am a zip tie fan also.

If you really want to get anal and expense is no object, there are
CONEC SnapLock D-SUB Hoods. I have never used them. Mouser part number: 706-16-001760E
They advertise:

CONEC SnapLock D-SUB hoods features a quick and safe locking without any additional screwing. A spring-loaded clip integrated in the hood locks in place with the locking bolt mounted to the mating connector and ensures a quick and safe connection. Locking of the locking mechanism is indicated by an audible and tangible click. The CONEC SnapLock system is especially designed for applications with high requirements to vibration and shock resistance such as applications in the railway and transport industries.

Click to expand...

The zip tie method is so simple! I do worry a tiny bit about the lack of strain relief, either on the individual pins or the whole connector. But if you secure each side well, it ought to be fine.

Those Conec Snaplock connectors are cool. Would be worth it for areas that might be connected and disconnected routinely, like the copilot stick.

Zip Ties & RTV

In a couple of tight spots with very fine wires (e.g. the electric trim) I didn't use the back shells at all and instead sealed the wires and the back of the plugs with some orange RTV for protection and security and then zip tied the flanges together. Light, strong and effective.

Orange RTV alternative

Shoe Goo or other GOOP product.

Liquid Tape?

Also available in red... This stuff works great, surprisingly so. When working on electrics, I keep one black, one red handy.

https://www.google.com/shopping/pro...sft=cm_mmc:Shopping-_-LIAs-_-D27E-_-100119178

Jerry

RTV 3145 is the most common adhesive sealant used in this application, although any RTV that does not contain vinegar will do.

There are many "aviation grade" DSub back shells that are more secure than the "computer/electronics grade" ones the OP is using.

I would use the longer standoff. Make sure the nut portion is the right height for the connectors to fully engage. There are a few heights available. I use loctite on the nuts so they don't come off too.

Concur. Loctite + Lock Washer = a very secure connection.

I did throw financial caution to the wind and ordered a few of those Conec connectors.

Zip Ties 1300hrs no problems. KISS

If you secure the wires, the zip tie method is fine. Sometimes the mass of the backshells and screwlocks makes things worse for in-line connections.

E.g.

In the interest of research, I bought a pair of the Conec DSub Backshells. They're pretty cool: They snap on and off super quickly and the pins that allow 2 backshells to connect to each other are also easy to install. Just slide them in 'til you hear/feel a little click.

Problem is, these wobble in relation to each other too. They also allow the DSub connectors to pull apart a 16th or so. Probably not a big deal, but I like my connectors fully engaged. So it'll be the standoff or zip tie methods for me, depending on the application.

Backshells and connecting pins:


Connected. You can just see that they allow the connectors to pull apart a bit: