Av-Bay, Eggfinder, Upper assembly

[ActingLikeAKid]

Interested in input here. I know that a lot of folks use two all-thread rods in their av-bays, but here's what I think I'm going to try - in no small part because this is 38mm ID and 2 rods would take up a lot of room. Picture should explain it mostly, but here's what I have: The transitions (purple) are solid ABS. Plan is to get some 10-32* aluminum allthread. I'll countersink a hole at the bottom of the lower transition that will be just big enough to fit a coupler nut - 10-32 on one side, 1/4" on the other. Drill a hole through the lower transition, screw the allthread into the coupler nut, secure with loctite. Screw a 1/4" eyebolt into the other end, secure with loctite. At the top end of the av-bay**, a coupler nut (also countersunk) screws onto the allthread; I literally can screw that transition on until it's snug. More loctite there. To the top of the coupler nut in the upper transition, I screw a short piece of 10-32 allthread. That gets fillet-glued with Rocketpoxy to a piece of 1/8" birch ply; eggfinder and battery are mounted to that. Ideally the wood is just small enough to fit snugly inside the BT so it won't rattle around. The nose cone and upper BT are glued together and slide over the eggfinder, then are attached with 3 small screws (possibly going into nuts glued into the transition, depending on how fancy I want to be).

I'm wide-open to suggestions on this. I haven't put a TON of thought into how I'd do DD, but like I said in the footnote, this is mostly a placeholder for if I do decide to set up for that later. Mostly I don't want to glue and commit to SD, but I don't like the idea of 2 sets of pins in a fairly long rocket. Please feel free to tell me if I'm doing something stupid and there's a much easier way. The allthread adds 50g or so, probably 50g again for the nuts and the eyebolt. That's less than 10% of the motor-less weight and OpenRocket doesn't say it's an issue for stability (well, it's a bit overstable anyway, so it'll be REALLY stable and may weathercock a bit)



*(I wrote 10/32 some places in the pic and didn't go back to fix it. I'm talking 10-32 screw size, not 10/32")
**(which is not going to house anything right now - this is "for future use" if I want to do DD. Also allthread seemed like a slick way to secure the two transitions - way less wobbly than pins)

 

[ksaves2]

How about this: Press fit a piece a plywood for the Eggfinder so it fits perfectly with the nosecone shoulder and the front base of the transition. Either epoxy the nosecone or use screws on it too to make it removable. Ditch the all-thread. If you want this DD you'd have to put the Deployment altimeter in the bay behind the EggFinder and mount two terminals on the aft
transition. One would blow it apart at apogee and you'd have to use a cutter like that from PrairieTwister/Archtype rocketry (they still available?) to unfurl the chute.

The other alternative is get a Jolly Logic Chute release and use motor ejection at apogee and the JLCR for main "unfurling". Kurt

 

[ActingLikeAKid]

Thanks for the input! I'm planning on using my JLCR for pseudo-DD. Mostly the DD plan was for if I had something in there that wouldn't do motor-eject (or something like the CTI Vmax where NAR requires a backup charge). This would probably be a lot easier (and I could build a real DD rocket for doing DD)....

Eyebolt just goes through the lower transition and is attached with a nut. Done.
Larger BT is glued to the transition.
I cut a slot in the upper transition JUST big enough for the plywood. Plywood slips into transition, then I drill a single hole ACROSS the rocket. Upper BT and nosecone are glued together. One bolt goes through upper BT, transition, plywood, and out the other side. Everything is secure.

 

[ActingLikeAKid]

 

[OverTheTop]

The idea of aluminium allthread scares me from a cracking point of view. The root of the thread is a stress concentrator.

If you need strong skinny bits of metal consider bike spokes. Stainless steel or titanium are available. If you find a good shop that can roll the threads you can get them to whatever length you need. The rolling means the metal work hardens, than if the thread is die-cut. Thread is imperial 2-56. Breaking strain on standard 2mm Ti spokes is 280kg each . Cost for me here was about $8 ozzie dollars each.

 

[ActingLikeAKid]

Oo, hadn't thought of spokes! Which is silly, because I'm a cyclist. The more I think about it, though, the more I like the idea of an empty tube.

 

[NateLowrie]

Is 3D printing an option? Seems like the perfect choice. You could print a mount that attached to the transition with simple screws.

 

[OverTheTop]

Here is how I did a 54mm NC with telemetry a couple of years back. Simple, and seemed to work well.

 

[NateLowrie]

Here is how I did a 54mm NC with telemetry a couple of years back. Simple, and seemed to work well.
View attachment 313351
View attachment 313352

I REALLY like the tie in to the nose cone tip at the top... Great job.

 

[ActingLikeAKid]

Here is how I did a 54mm NC with telemetry a couple of years back. Simple, and seemed to work well.
View attachment 313351
View attachment 313352

Very slick, I like the U-bolt to hold the plate to the bolt. I was thinking something similar when I was going to do allthread, but since the eyebolt (or eye nut, see below) is going to be in the lower transition, I don't need a bolt going up the middle of the upper transition...As long as I can do it fairly low-profile, I like the idea of a bolt that secures the upper BT to the upper transition AND holds the bay in place....

On the eyebolt thing: Apart from it working well in this application, is there any reason to use a bolt and an eyenut vs an eyebolt with a nut on the end?

 

[OverTheTop]

I did a later version in 4" with a 3D printed NC. The sled was designed to be skinny so I can print another base and NC to suit 54mm (or whatever) airframes. Telemetry is a TeleMega.



Pulling the NC together through the sled seems to work well.

Thread is here:
https://forum.ausrocketry.com/viewtopic.php?f=6&t=5019

 

[ActingLikeAKid]

That's almost exactly what I'm thinking of. May have to ask nicely of my 3D-printer-having-friend