Avionics bay feedback needed (lengthy diatribe)

[David_Stack]

Good Morning all;

Working on my first avionics bay, utilizing the LOC EB-300 kit (3" diameter airframe) which includes a 'stiffy' coupler, and fear I have 'designed myself' into a corner (fortunately, apart from gluing the 'stiffy' tube into the coupler no holes have been drilled, etc.) Seeking the group's feedback in turn...

No switch band, and sampling ports would be mid-point of the coupler, right at the intersection of the airframe booster and payload bays.

Inside/comprising the bay; I had envisioned incorporating bulkhead mounted disposable charge wells like Justin featured here: https://www.rocketryforum.com/threa...hemed-build-thread.130046/page-2#post-1525111. ematches would be direct wired to the altimeter, which is a PerfectFlite Stratologger CF, powered by a 2S LiPo. LiPo has the 'factory' eFlite UMX/JST-PH connector on it, and I planned to attach a pigtail with a mating connector to the 'Batt' terminal on the Stratologger CF. Arming switch is one of the pull-pin assemblies from Lab Rat with an atmospheric sampling port doing double duty as the conduit for the arming pin; and it is this specific aspect (in concert with the absence of terminal blocks for the ematches) that has me scratching my head...

Sitting with the EB-300 on my lap, and going through the motions of how I would prep the bay for flight. I had originally thought I could insert the arming pin, connect the battery to the altimeter, and connect the ematches to the altimeter; then close up the bay. Then the 'ah ha' / 'oh sh_t!' moment; when it dawned on me that with the arming pin through the side of the coupler and into the switch, there was no way I could move the sled back and forth to terminate the ematch wires.

The only option I am coming up with (based on NO experience to date), would be to connect the ematch leads to the altimeter first (at least one set of leads would need to be long enough to allow the bay to be slid clear of the other end of the coupler) , then butt one bulkhead up to the end of the av-bay, leaving the other off, and slide the sled into final position. Insert the arming pin into the switch through the coupler wall and then reach into the open end of the coupler/bay to connect the battery to the altimeter. Lastly slip the other bulkhead over the threaded rods and secure it, closing up the bay.

I don't like the idea of needing to leave any more slack in the wires/undressed wire than I have to, especially with the wiring from the altimeter to the battery (is the ematch wiring a concern?), and I think I would need to find some way to secure the battery connector to the sled after the connection is made (to ensure they remain connected during flight), yet still be removable for post-flight disassembly.

Criticism/suggestions eagerly solicited. Is there anything I am failing to 'see' that would be a viable sequence of events? If what I am proposing is do-able, but perhaps a change to a different power connector is warranted (though I would prefer to retain the factory connectors for the balance charging it provides), what connectors would you recommend (something I can manipulate when reaching into the bay/coupler)?

Thanks as ever,
Dave

 

[Antares JS]

The only option I am coming up with (based on NO experience to date), would be to connect the ematch leads to the altimeter first (at least one set of leads would need to be long enough to allow the bay to be slid clear of the other end of the coupler) , then butt one bulkhead up to the end of the av-bay, leaving the other off, and slide the sled into final position. Insert the arming pin into the switch through the coupler wall and then reach into the open end of the coupler/bay to connect the battery to the altimeter. Lastly slip the other bulkhead over the threaded rods and secure it, closing up the bay.

This is exactly how I do it.

The one big improvement to be made here is use some kind of through-bulkhead connection, so that you don't wire the e-matches directly to the altimeter, instead wiring the inside end of your through-bulkhead connectors to the altimeter and wiring the e-match to the outside of the through-bulkhead connectors AFTER the e-bay is closed up and your arming pin is in place. This prevents the e-matches from being armed while you're closing up the bay.

Lab Rat offers a very nice through-bulkhead connector in a few common thicknesses, and you can get custom ones if you need.

https://www.labratrocketry.com/product-page/electrical-connectors

 

[Handeman]

I use the through bulkhead connector like @Antares JS stated. I use terminal strips. Makes it easy to insert the ematch wire and tighten the screw.


I also add a screw switch in series with my pull pin. The access hole for that is in the should that slides into the booster. That way I can turn off everything without having to have the pull pin in place. I seldom open my av-bays so I just turn it off with the screw switch, attach the ematches. Turn on the altimeter to get a battery voltage reading and ensure 3 beeps for the two ematches. Turn off the screw switch, load the powder, insert the pull pins and turn the screw switches on when I close up the rocket before heading to the RSO.

Here's one of my bays.


BTW, if you clamp the two wires in a vise, or twist together and put over a finishing nail, put the other ends in a drill and run the drill until your two wires are twisted as tight as you want them.

 

[David_Stack]

Thank you both for your thoughts, comments, and suggestions.

Because the disposable charge wells have the ematch leads coming straight out of the bottom of the well and through the bulkhead, terminal blocks are not needed.

That said, I REALLY like the use of the additional screw switch in series with the pull-pin switch. That would allow me to connect the battery to the altimeter initially and then go through the other preparatory actions while the bay is still open, yet not have to have the pull-pin switch installed. Looks like I need to start shopping...

Handeman; is there a reason why you wire the battery through the switches and to the Stratologger BATT terminals, instead of connecting the battery to the BATT terminals, and then your switches in series to the Power Switch terminals?

 

[Handeman]

Handeman; is there a reason why you wire the battery through the switches and to the Stratologger BATT terminals, instead of connecting the battery to the BATT terminals, and then your switches in series to the Power Switch terminals?

I do that to have a positive disconnect of the battery. I don't know how the BATT and SWITCH terminals are wired together on the altimeter board. If they are in series, the effect is the same, but I don't know that. This will also let me swap in a different brand of altimeter and still control power.