First Time AV-bay construction Thread

[Seatechnerd83]

Hello TRFers!
This is my first build thread as well as first dual deploy rocket, I hope this will become a good resource for other first-timers attempting to build their first AV-bay. Anyways here we go!




I'm using these little 2 pole WAGO flip spring splicing jigs as connectors to connect the pyro ejection charges to the separate redundant flight computers (RRC3 and Eggtimer classic if I dont mess up soldering the eggtimer) These little guys are about $8 for a pack of 10 on amazon. The advantage of these compared to screw terminals is that they're spring loaded, meaning they constantly apply pressure and wont back out. Also they dont require a flathead screw driver. (or any driver at all)



Anyways, I'm building a WM Darkstar Jr. (2.1in) and fitting 4 of these things that are about 3/4 of an inch long on a AV-bulkplate is like 3d tetris.

I figured out the best way to mount these would be to have the leads hug the 1/4-20 allthreads and proceded with dremeling out a slot for the leads:





I then test fitted the JST connector leads and verified that they would all fit and mixed up some 5 minute epoxy. I then epoxied the first two connectors in place:


The 5 min set time allowed me to fiddle with them and then let them set up to cure. About an hour later I came back and epoxied the second set of connectors and let those to set. Once those had set enough about an hour later I was finished with this stage of the construction.

Top down:

Underside:


2 JST leads come off the bulk plate, one is male and one female to make sure I dont mix up the backup and main pyro charges.


If you have any suggestions or comments please feel free to share!

 

[conneryc]

Question.....where are you going to put your pyro charges? I like the Wago connectors for work in my house. The disadvantage to use them (or terminal blocks) is that you have to have an additional hole in the bulkhead to pass the wires through into the AV bay. That's why I've always used these: Terminal Connector Binding Post But it's just my personal preference.

 

[Seatechnerd83]

Here's a picture of a spent pyro charge hooked up with one of the paddles open. I'll seal the hole with a tiny dab of hot glue (every rocket needs at least some hot glue)

 

[Handeman]

as @conneryc asked, where are the powder charges going? You have no room for charge wells.
Also, how are you going to protect the WAGO clips from the powder residue. I've found that no matter what you use, especially on the payload end, they get very dirty after the first use. That residue is also corrosive and if the springs aren't SST, they may not last too long. It's a very dirty environment that you have to consider when you select parts.

I started using Eaton 2 and 4 terminal blocks from Mouser with wire solder tabs that fit through the bulkhead. The A00110207 and A00110407 which are standard barrier, handwired, 2 or 4 poles, steel SEMS fully seated.
After attaching the matches, yes a screw driver is needed, I put some masking tape around and over the terminal block to protect it from the powder residue.


It helps to use newer RTV sealant, the old stuff doesn't go on so well.
Hot glue would probably also work well to seal the terminal.


Just a suggestion, but by all means, try what you think will work best. New ideas are always welcome. Let use know how things work out and how they work long term.

 

[waltr]

You do know about this thread:
https://www.rocketryforum.com/threads/the-avionics-bay-thread-post-your-photos.156649/
That has lots of pictures of ebays.

So far it looks like this thread is good for how not to build an ebay.
1- no room for BP ejection canisters.
2- those connector look easy to use big take up too much room. Also, am unsure as to the reliability.
3- The wires should have their own holes and not use the thread rod holes. I would be VERY worried that the threads WILL cut into the insulation and cause a failure.

You are getting good advice from the other posters.

 

[Titan II]

Charge wells/cannisters are generally not necessary.

 

[Seatechnerd83]

You do know about this thread:
https://www.rocketryforum.com/threads/the-avionics-bay-thread-post-your-photos.156649/
That has lots of pictures of ebays.

So far it looks like this thread is good for how not to build an ebay.
1- no room for BP ejection canisters.
2- those connector look easy to use big take up too much room. Also, am unsure as to the reliability.
3- The wires should have their own holes and not use the thread rod holes. I would be VERY worried that the threads WILL cut into the insulation and cause a failure.

You are getting good advice from the other posters.

To address #1, I'm not using charge canisters because i have self contained BP charges (wildman ejection lighters with the cardboard tube, then the aerotech DMS red motor eject plugs slimmed down to fit inside the smaller diameter cardboard tube). To address #2 the connectors are not that easy to open and are super hard to catch on quick links (plus if there is load on quick links, the ejection charges would already have fired), also the reliability issue, the guy I learned about them from used them on his L3 flight and have worked flawlessly on other flights of that rocket. To address #3 the slots are dremeled out a generous amount and there is almost zero insulation wear from the allthreads after many many insertions and extractions. (I also dont have any other place to put the holes so there's that.) Anyways! thanks for the suggestions, and I did just come from looking at that thread that you suggested.

 

[Buckeye]

A centrifuge vial, glove finger, etc can just hang off the terminal blocks, maybe with some tape to hold it in place.

 

[Handeman]

Charge wells/cannisters are generally not necessary.

That is very true.

If you decide not to use charge wells, you have to consider other design issues that choice creates, like how robust your terminal/mounting point has to be since the match wires can get snagged, pulled, twisted up, and exert a lot of stress on your terminal/mounting point. The whole rocket is a system and every design choice impacts other items in different and sometimes surprising ways.

 

[Seatechnerd83]

That is very true.

If you decide not to use charge wells, you have to consider other design issues that choice creates, like how robust your terminal/mounting point has to be since the match wires can get snagged, pulled, twisted up, and exert a lot of stress on your terminal/mounting point. The whole rocket is a system and every design choice impacts other items in different and sometimes surprising ways.

Thanks for the head's up! In the payload bay I'll likely snip the leads short to put the BP pressure in the right place to push out the laundry with the nosecone. (and yes I'm using shear pins) In the Booster I'll likely leave the leads long and place the electronic pyro charge near the motor BP charge to help push out the laundry instead of having the BP accidentally push it back into the booster. Also another advantage of the spring connectors is that they take a lot of force to rip out, but if it does end up getting yanked, the charge leads will slide right out, saving the AV bay from damage. (Ive done a couple yank tests and they take 20+lbs of force to pull out so youre not gonna accidentally knock them out)

 

[Handeman]

Thanks for the head's up! In the payload bay I'll likely snip the leads short to put the BP pressure in the right place to push out the laundry with the nosecone. (and yes I'm using shear pins) In the Booster I'll likely leave the leads long and place the electronic pyro charge near the motor BP charge to help push out the laundry instead of having the BP accidentally push it back into the booster. Also another advantage of the spring connectors is that they take a lot of force to rip out, but if it does end up getting yanked, the charge leads will slide right out, saving the AV bay from damage. (Ive done a couple yank tests and they take 20+lbs of force to pull out so youre not gonna accidentally knock them out)

That sounds like what I did on my L1 cert rocket. It was my first scratch build HPR and first DD rocket. It was also the last time I didn't use charge wells. I didn't have any issues with the match wires damaging the av-bay, but there were a couple times they broke near the terminal block because they got jerked hard. Just make sure the match wire comes loose or breaks before the WAGO pulls loose from the av-bay cap and starts pulling the wires through the cap.

 

[Seatechnerd83]

That sounds like what I did on my L1 cert rocket. It was my first scratch build HPR and first DD rocket. It was also the last time I didn't use charge wells. I didn't have any issues with the match wires damaging the av-bay, but there were a couple times they broke near the terminal block because they got jerked hard. Just make sure the match wire comes loose or breaks before the WAGO pulls loose from the av-bay cap and starts pulling the wires through the cap.

that sounds like an interesting rocket (this is my second HPR rocket)! There are 3 different ways the wires can disconnect from the flight computer, the ejection charge directly to the WAGO connector, the JST leads themselves, and the JST connector between the connector and the flight computer.

 

[Handeman]

that sounds like an interesting rocket (this is my second HPR rocket)! There are 3 different ways the wires can disconnect from the flight computer, the ejection charge directly to the WAGO connector, the JST leads themselves, and the JST connector between the connector and the flight computer.

If you're interested, here's the link to my L1 build back in 2007 El Juan. I wanted to learn as much about HPR as I could, and I did. I learned even more actually flying that rocket, the first 6 flights, including the L1 cert, were all I motors. It flew on a J350W at LDRS 28. It survived +80G flights on I1299N motors twice. Because of what I learned, I'll never build another rocket the way I built that one.

I hope you have as much fun with your HPR as I did and that you learn as much.

 

[David Schwantz]

The only thing I see is there enough room between the connectors for the nuts on your all thread to tighten down?

 

[Seatechnerd83]

The only thing I see is there enough room between the connectors for the nuts on your all thread to tighten down?

I made sure to have barely enough space for that. Lol.

 

[thzero]

And no, rockets do not need hot glue! :/

Seems on small side for dual redundant altimeters.

 

[Titan II]

Seems on small side for dual redundant altimeters.

Not at all. It is smart.

 

[David Schwantz]

Just a thought but you should shorten the all thread and do NOT leave the cut edge sharp like that. It will cut through a shock cord.
Also, I like to make only one end removable. The other end I sandwich with nuts on both side of the bulkhead. I also make the sled butted up to the inside nut and then lock nuts on the other end. Now you never have to line things up again. I also index all my NC, Avbays, payload, and booster joints. Again, you never have to line them up again.

 

[Seatechnerd83]

Just a thought but you should shorten the all thread and do NOT leave the cut edge sharp like that. It will cut through a shock cord.
Also, I like to make only one end removable. The other end I sandwich with nuts on both side of the bulkhead. I also make the sled butted up to the inside nut and then lock nuts on the other end. Now you never have to line things up again. I also index all my NC, Avbays, payload, and booster joints. Again, you never have to line them up again.

Clarification, the picture isnt really representative of the length, the allthread actually only sticks up about 5mm above the nut, it's unscrewed like that so that the longer allthread allows the bulkplate to sit on the AV-bay coupler and have the AV-bay lay flat on the table.

 

[Seatechnerd83]

And no, rockets do not need hot glue! :/

Seems on small side for dual redundant altimeters.

hot glue is arguably one of the most essential parts of building a rocket!!! /s


Anyways, at the end, the AV-bay should contain an RRC3, an Eggtimer classic, an Eggfinder Mini, 4 2S 450mah lipo batteries (2 are the traditional patty packs, and 2 are stick lipos that are almost the same size as an Estes 18mm motor.) 1 traditional lipo per flight computer, and 2 stick lipos wired in parallel for the Eggfinder for increased battery life.

 

[Buckeye]

Anyways, at the end, the AV-bay should contain an RRC3, an Eggtimer classic, an Eggfinder Mini, 4 2S 450mah lipo batteries (2 are the traditional patty packs, and 2 are stick lipos that are almost the same size as an Estes 18mm motor.) 1 traditional lipo per flight computer, and 2 stick lipos wired in parallel for the Eggfinder for increased battery life.

Can't wait to see how you cram all that stuff into a 54mm Av-Bay. That is very ambitious for your first one. Are those 1/4-20 threaded rods? #8 or #10 are probably good enough and much smaller. Two stick lipos and 2 altimeters are overkill as well, and you haven't even mentioned a sled or switches, yet.

I had a hell of a time designing a 54 mm x 5 in av-bay to hold one altimeter and one tracker:

https://www.rocketryforum.com/threads/wildman-mach2-hed-recovery-gear.165178/post-2167818

 

[Seatechnerd83]

Can't wait to see how you cram all that stuff into a 54mm Av-Bay. That is very ambitious for your first one. Are those 1/4-20 threaded rods? #8 or #10 are probably good enough and much smaller. Two stick lipos and 2 altimeters are overkill as well, and you haven't even mentioned a sled or switches, yet.

I had a hell of a time designing a 54 mm x 5 in av-bay to hold one altimeter and one tracker:

https://www.rocketryforum.com/threads/wildman-mach2-hed-recovery-gear.165178/post-2167818

It'll be practice for a 38-29mm minimum diameter 2 stage CTI I175-AT H13 rocket for 10k feet at LDRS this year. Also, switches are the lab rat remove before flight pull pin switches, and the sled will be 3d printed. Also yes, those are 1/4-20 threaded rods.

 

[Buckeye]

Also, switches are the lab rat remove before flight pull pin switches

Also very large compared to other switches. This will be an interesting build!

 

[bad_idea]

I'm using these little 2 pole WAGO flip spring splicing jigs as connectors to connect the pyro ejection charges to the separate redundant flight computers (RRC3 and Eggtimer classic if I dont mess up soldering the eggtimer) These little guys are about $8 for a pack of 10 on amazon. The advantage of these compared to screw terminals is that they're spring loaded, meaning they constantly apply pressure and wont back out. Also they dont require a flathead screw driver. (or any driver at all)

Question: is there any motion required to move the lever other than simply flipping it up? If not, how much force is required to open them? Since seeing these WAGO connectors in a Joe Barnard video, I've wondered if those mounted on the bottom of an avbay would open on their own on a very high g flight. (E.g., one of our local fliers is fond of flying the H999 in a tiny minimum diameter rocket that pulls hundreds of Gs off the pad.) Of course they could always be mounted sideways if that was a concern.

 

[David Schwantz]

I fly the H999 in "Lil Glory". It hits 283 Gs. My JL Alt 2 does not even survive that. These connectors would not be in my rocket. For one thing, they would not even fit

 

[Seatechnerd83]

I fly the H999 in "Lil Glory". It hits 283 Gs. My JL Alt 2 does not even survive that. These connectors would not be in my rocket. For one thing, they would not even fit

If we were gonna put money on this topic, I'd bet for them surviving, for one thing the spring is quite strong, for another, force from G-load is only relative to the weight of the part, the part weighs less than a gram and the weight distribution is opposite of the torque required to open the switch, plus if we assume the part of the switch is 1 gram, the opening force is much greater than 283 grams. (I have no way of calculating the force, but I can attest they require more than 8oz of opening force.)

 

[Raythain]

plus if we assume the part of the switch is 1 gram, the opening force is much greater than 283 grams.

Your math is off by a factor of 9.81.

Gram is a unit of mass. The weight force holding it closed would be 9.81 mN. Under 283 Gs, it would experience a force of 2.776 N. I’d be more concerned with the connectors buckling from the stresses than the opening force. Useful data points would be things like crush forces.

 

[Handeman]

I don't think the OP is planning anything close to a 283G flight so that whole discussion if irrelevant.

Like most of us, he is trying to design an av-bay his way. As some experienced posters have pointed out, there are flaws in the design as presented, but they may not be fatal flaws and until he tries to fly the rocket, no one really knows.

 

[bad_idea]

I don't think the OP is planning anything close to a 283G flight so that whole discussion if irrelevant.

Irrelevant to his flight, yes, but not irrelevant to the connectors themselves. I asked a question about a detail of the connectors because he has them and I do not, same as I might see you building a rocket with a particular nose cone and ask you a question about the cone in case I might want to use it someday. I agree that with the question answered, we can move on.

 

[Seatechnerd83]

Hello again! Update time! Took a small break, and have been making incremental progress. There was alot of slightly dangerous dremeling happening too. I 3d modeled out an avionics sled, and 3d printed it. It needs some changing, but was actually a quite good first prototype sled. First thing I had to do was dremel out sections for the eye bolt posts to fit into the sled:

It ended up bumping up against the eggtimer classic mounting pegs, and future iterations will have the eggtimer classic mostly centered. (If I decide to go with the eggtimer and I can actually make it stop giving an error) I was also able to prove that I AM able to fit 4 450mah lipo batteries inside the avionics bay, I just needed to take a bit of plastic off of one side of the sled as shown.

I was also able to figure out how I will go about mounting the Lab Rat pull pin switch. I will remove one of the bottom ET classic mounting pegs and use it as a mounting peg with a spacer (or maybe not) between the 2 mm of gap for the mounting holes.
I also made the decision to not add a second set of WAGO connectors on the drogue end of the avionics bay, since the motor will act as a backup then and is pyrotechnically triggered and timed so an (almost) failsafe setup.
I have yet to procure the RRC3, but that can wait until I have the AV bay more finished (and I get my paycheck, new phones aren't cheap)



As always, comments, suggestions, and angry rants are welcome.