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Why do E-bays appear overbuilt?

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Brainlord Mesomorph

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I just bought my first eggtimer kits (haven't even started soldering yet) but I'm looking at sleds and bays, and they all look really big and heavy and overbuilt. What's with the two lengths of all-thread and steel nuts? those aren't model rocket components

I stay within FAA class 1 (LPR, and MPR?) I was assuming my ebay would be like an Estes (paper) BT60, with a balsa sled glued to estes cardbord centering rings. lightwieght nylon screws holding the circuit boards to the balsa sled. You know, model rocket parts.

Do I need steel and all-thread?
 

dhbarr

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You don't need all that heavy stuff. I've seen plenty of cardboard avbays where the harness stress is routed around or through the structure rather than beefing it up.
 

0011001100

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Do I need steel and all-thread?
Depends, the kind you are likely looking at are highpower builds where the e-bay is also structural connecting the two halves of a dual deploy rocket together. In that case the threaded rods are what are taking the deployment loads. In a small rocket you don't need such high strength components. I have a midpower build where the e-bay using a single #8 threaded rod. If you are building something that is single deploy and put the electronics in the nose then you don't need any threaded rods at all and get just 3d print the whole mount. It all depends on if it is a structural part or simply there for data.
 

Scott_650

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I just bought my first eggtimer kits (haven't even started soldering yet) but I'm looking at sleds and bays, and they all look really big and heavy and overbuilt. What's with the two lengths of all-thread and steel nuts? those aren't model rocket components

I stay within FAA class 1 (LPR, and MPR?) I was assuming my ebay would be like an Estes (paper) BT60, with a balsa sled glued to estes cardbord centering rings. lightwieght nylon screws holding the circuit boards to the balsa sled. You know, model rocket parts.

Do I need steel and all-thread?
If you’re building an Eggtimer Apogee - like I will be when my order arrives - mounting it in the nose cone looks to be the simplest way to go.
 

Brainlord Mesomorph

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If you’re building an Eggtimer Apogee - like I will be when my order arrives - mounting it in the nose cone looks to be the simplest way to go.
Actually I'm integrating a Quantum with an EggFinder TX unit (and maybe a camera to boot) and yes its all going to be in a lengthy nosecone (top half of the rocket)

Re dual deployment: couldn't the main chute come out a compartment in the aft of the nosecone? and not need a third section of body tube?
 

timbucktoo

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Why does everyone overbuild their rockets and turn them into tanks??
Mostly because I can but an overbuilt rocket will survive much better on hard landings like a road. The other day my main failed to deploy. This was a 3” FG kit. Fairly hard landing but zero damage.
 

Scott_650

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Actually I'm integrating a Quantum with an EggFinder TX unit (and maybe a camera to boot) and yes its all going to be in a lengthy nosecone (top half of the rocket)

Re dual deployment: couldn't the main chute come out a compartment in the aft of the nosecone? and not need a third section of body tube?
You’re talking about loading a fair amount of hardware into a rocket that could hit the ground pretty hard if everything doesn’t work out so something sturdy is looking likely - maybe not needing big lengths of all-thread and fiberglass but a solid platform with protection from a hard hit and the ejection charge. Which sounds like a typical e-bay whether you’re just doing head end single deployment or not. Building everything into an upper payload section with the ejection charge well mounted on the aft bulkhead (using your motor ejection charge as a backup) sounds about right - unless you’re talking about a really long nose cone I don’t think you can get that much stuff in any BT-60 cone I can recall. You may want to consider using a BT-80/2.6” based rocket like an Estes Executioner or Super Big Bertha rather than a BT-60/1.6” rocket - that extra bit of room could make it easier to build.
 

blackjack2564

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There are hundreds of ways to build av-bays correctly. Some better than others. Some complex, others simple.... like the rockets they fit into.
Each has it's place,
Find what works for your application and all is happy once again in rocket land. :)

U may not need steel althread, but others may find it absolutely needed in their project....there is no one size fits all in rocketry.
 

HHaase

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All depends on the size, weight, and forces involved. A 3" high power rocket can snap bulkheads if the chute deploys at velocity. When you start weighing launch weight in pounds instead of ounces, and velocity as a function of mach.... things escalate quickly.

But for a BT-60 cardboard rocket? Nah, I never go that bulky. Just a balsa bulkhead, a couple small screws to hold the nose cone, and maybe some anti-static bubble wrap to keep it all from rattling around.

-Hans
 

Brainlord Mesomorph

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You’re talking about loading a fair amount of hardware into a rocket that could hit the ground pretty hard if everything doesn’t work out so something sturdy is looking likely - maybe not needing big lengths of all-thread and fiberglass but a solid platform with protection from a hard hit and the ejection charge. Which sounds like a typical e-bay whether you’re just doing head end single deployment or not. Building everything into an upper payload section with the ejection charge well mounted on the aft bulkhead (using your motor ejection charge as a backup) sounds about right - unless you’re talking about a really long nose cone I don’t think you can get that much stuff in any BT-60 cone I can recall. You may want to consider using a BT-80/2.6” based rocket like an Estes Executioner or Super Big Bertha rather than a BT-60/1.6” rocket - that extra bit of room could make it easier to build.
I think the eggtimer boards are supposed to fit in a BT55, so a 60 does give me extra room.

about padding: "Great stuff" foam construction sealant? you use it to seal the water heater insulation?

I was thinking I could wrap the assembled sled in plastic, put it in a sacrificial piece of BT60, squirt a dab of that in both sides, let it dry and then cut it all apart. That should give me two custom fitted, hard, foam, pads. Hmm? Nice?

I just worry about heat buildup.
 

Flyfalcons

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There is a lot of force going through an avbay on a high power rocket during deployment.

If all you're doing is attaching an altimeter in a compartment, then minial support is fine.
 

Flyfalcons

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Actually I'm integrating a Quantum with an EggFinder TX unit (and maybe a camera to boot) and yes its all going to be in a lengthy nosecone (top half of the rocket)

Re dual deployment: couldn't the main chute come out a compartment in the aft of the nosecone? and not need a third section of body tube?
Yes this is called head end deployment and some rockets are set up that way.
 

Brainlord Mesomorph

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Yes this is called head end deployment and some rockets are set up that way.
OK then You may know this: Do i need a bulkhead and a coupler, to make that a separate compartment? or would leaving that end of the tube open and stuffing some wadding in there be enough?
 

NateB

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OK then You may know this: Do i need a bulkhead and a coupler, to make that a separate compartment? or would leaving that end of the tube open and stuffing some wadding in there be enough?
Yes, your electronics should be sealed in a separate compartment. The gasses and solid particles from the BP ejection charge burning are corrosive to your electronics.
 

cerving

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You have to consider that loads are going through the AV bay. Generally, the steel allthreads take the loads of the shock cords if the shock cords are connected to the bulkplates. You CAN run a single piece of Kevlar through the AV bay to handle the loads instead of having the bulkplates take the loads, I've done that on a few rockets where weight or space was an issue. You have to seal the exit points to keep out deployment gases... you can do that with hotmelt glue or "sticky putty".
 

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If you are used to flying paper & balsa (Estes) - larger rockets with heavier materials can seem a bit crazy. I understand where the OP is coming from.

There are alternatives.

A loop of #750 Kevlar in place of welded steel eyebolts.
Nylon all-thread from McMaster-Carr in place of steel all-thread. I have use the 1/4-20 nylon in high-power builds, it holds up just fine.

My Eggfinder-TX goes in the sealed nosecone.
Only the Quantum in the Ebay.

Better alternative - replace the Quantum and Ebay with a JL Chute release. Much easier/simpler and just as effective.


Brainlord - give us some clues... what class1 rocket are you building. Have you ever built a dual deploy rocket?
 
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Brainlord Mesomorph

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Yes, your electronics should be sealed in a separate compartment. The gasses and solid particles from the BP ejection charge burning are corrosive to your electronics.
you misunderstood, yes the electronics in separate bay.

I was thinking about the drogue streamer,and the main chute.i thought that I didn't need bulkhead between them, just wadding . it was a bad idea.

At apogee deployment would work, but with the g forces at launch, the main chute could just fall into the drogue bay... never mind.

yes i need a bulkhead.

Brainlord - give us some clues... what class1 rocket are you building, and what are you putting in the ebay?

OK, its ambitious.

an eggtimer quantum, and an eggfinder TX (i didn't want to lose the eggtimer) and I think I can take a cubecam out of its housing, and batteries. I call it an "aerospace probe" my "Odysseus Module"

Carried by a series of lifters, starting with 18mm C's and working my way up to 2 stage G's.

According to OR, a two-stager with G engines, carrying about that payload, Is FAA class 1 and just breaks the speed of sound. :)

Like I said, its ambitious.
 

rharshberger

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I typically replace steel all threads with threaded 1/4" aluminum rods, that I cut and thread myself whenever projected shock loads will allow it, steel has a higher tensile strength so a lighter all thread can be used in many cases.....but 1/4-20 steel all thread is probably the most commonly/easily acquired material to fill the requirement of transferring loads through an AV bay. Easy is usually the route most people go when there is not a specific requirement for a lighter/stronger/exotic material.
 

heada

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Check out the Apogee av-bsys for smaller BT sizes. They don't use all-thread at all. Normally just the 1/8" ply that the electronics are mounted to.

 

sl98

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I fly Quarks in BT 50 / BT 55 and Quantums in BT 60 AV bays. I keep them light and tight. I use 4-40 all thread and nylon wing nuts. I use nylon fasteners to hold the electronics on 3/32 balsa or basswood. The battery sides under the sled. I also have a version that does not use all thread. Rather it uses a hatch. Finally, no heavy charge wells. I use the plastic caps that AT uses in their reload kits to hold the power. You can see pictures in the threads below.




 

OverTheTop

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I have noticed the same as the OP. Some of the 3D printed avionics bays, while being works of art, seem to be very overdesigned as far as mass. 3D printing is a wonderful technique that lets you engineer your parts and leave unnecessary parts out, which is more difficult in the traditional subtractive manufacturing.

Think about the necessary features in the design to hold whatever you want for the avionics. Design them in, add any cable routing or other features you need, and then as a final step add any other material needed to keep the necessary features together. Remember to design appropriately, as the parts still need to withstand flight and deployment forces. The design and amount of material will depend of the flight envelope and the mechanical properties of the 3D printed material. Don't forget to allow for the usually weaker z-axis bonding in most FDM printers.

I have seen designs where Kevlar harnesses feed through the bay, which is a nice low-mass option since the sled will not incur much tension and can be made lighter.

I have personally used custom length titainum bike spokes to tie avionics bays together. With a diameter of only 2mm and a breaking load of about 280kg each then can provide significant strength without soaking up too much volume or mass in the avionics area.
 
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Bill Heath

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you misunderstood, yes the electronics in separate bay.

I was thinking about the drogue streamer,and the main chute.i thought that I didn't need bulkhead between them, just wadding . it was a bad idea.

At apogee deployment would work, but with the g forces at launch, the main chute could just fall into the drogue bay... never mind.

yes i need a bulkhead.

Brainlord - give us some clues... what class1 rocket are you building, and what are you putting in the ebay?

OK, its ambitious.

an eggtimer quantum, and an eggfinder TX (i didn't want to lose the eggtimer) and I think I can take a cubecam out of its housing, and batteries. I call it an "aerospace probe" my "Odysseus Module"

Carried by a series of lifters, starting with 18mm C's and working my way up to 2 stage G's.

According to OR, a two-stager with G engines, carrying about that payload, Is FAA class 1 and just breaks the speed of sound. :)

Like I said, its ambitious.
Don't 2 G motors equal an H? No longer class 1.
 

HHaase

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Don't 2 G motors equal an H? No longer class 1.
FAA Class 1/2 doesn't line up exactly with NAR/TRA Level 1 high power. You'd be surprised how many H motors are still under the 125 gram limit and would still comply with the Class 1 limits, assuming the overall launch weight is still under 1,500 grams.

For a pair of G motors it all depends on which G's it is. Some combos will easily exceed the 125 gram limit, and some combos will be perfectly fine.

-Hans
 

Ez2cDave

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I just bought my first eggtimer kits (haven't even started soldering yet) but I'm looking at sleds and bays, and they all look really big and heavy and overbuilt. What's with the two lengths of all-thread and steel nuts? those aren't model rocket components
To the OP good question? Why does everyone overbuild their rockets and turn them into tanks??
Some examples . . .

Dave F.

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ep29030

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To the OP good question? Why does everyone overbuild their rockets and turn them into tanks??
Well, we tend to overbuild everything, so why not overbuild the av bay too? Maybe the better question is: why do not people not overbuild like the rest of us? :)
 

AfterBurners

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Well, we tend to overbuild everything, so why not overbuild the av bay too? Maybe the better question is: why do not people not overbuild like the rest of us? :)
I keep it lite for higher flights and more motor selection.
 
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