Lighter weight HPR AV bay designs..?

Tim51 · Nov 6, 2015

Hi

Does anyone have any designs for lighter weight avionics bays they are willing to share (for example, ones that use less all-thread)?

Currently researching building techniques for a scratch built Mach attempt bird based around a CTI 38mm.

Thanks in advance

--

UKRA #1895 L1

dixontj93060 · Nov 6, 2015

In many of my minimum diameter designs, I have used either aluminum hardware and/or simply Kevlar loops. Either goes a long ways in lightening the design.

rharshberger · Nov 6, 2015

Tim51 said:
Hi

Does anyone have any designs for lighter weight avionics bays they are willing to share (for example, ones that use less all-thread)?

Currently researching building techniques for a scratch built Mach attempt bird based around a CTI 38mm.

Thanks in advance

--

UKRA #1895 L1

What diameter rocket are we talking about here? Size has a lot to do with how many and what sizes of all-thread, whether or not I use 1/8", 1/4" or 1/2" Plywood for bulkheads or even aluminum or fiberglass. On small rockets I use aluminum threaded rods which I make.

The one on the left is my 3" Frenzy XL clones AV-Bay with aluminum rods and wood electronic sled, the one on the right is a Nosecone Av-Bay for my kids BAR Crayon conversions. Both use 1/4" aluminum bars instead of steel allthread, doesn't save a lot of weight but it does save some.

stealth6 · Nov 6, 2015

Kevlar loops for harness anchors are a great way to cut weight. Especially compared to the huge honkin' eyebolts that most folks use in situations that are complete overkill. I honestly don't get why folks don't use this method more often - it's at least as strong as the harness that's attached to it, it's easy/light/etc.

If you are doing a 38mm airframe, far and away the lightest (and slickest) setup is to use a Raven in a Featherweight AV Bay - the whole thing (bay, altimeter, battery, switch, hardware) weighs less than just some other altimeters out there. WAAAAAAY lighter than most anything else you could do.

If your airframe is larger than 38mm, you can still benefit from the Raven/FW setup - as I outlined in this thread: https://www.rocketryforum.com/showthread.php?43124-Simpler-lighter-AV-bay. Despite one of the comments in that thread that "it is almost the same weight as a conventional sled", my experience was that it saved a ton of weight. And it works fantastic.

s6

blackbrandt · Nov 6, 2015

Lighter weight compared to what.....

Our Children's Future (9" diameter, 17 ft tall, 100 lbs on pad) initially had 4x3/8" all thread (steel) running through it.

Bat-mite · Nov 6, 2015

Cut the sled so that it fits snugly in the coupler. No support needed. Run one piece of allthread underneath, off-center, with an eye-nut at each end. Eliminates second allthread, brass tubing, epoxy.

Tim51 · Nov 6, 2015

dixontj93060 said:
In many of my minimum diameter designs, I have used either aluminum hardware and/or simply Kevlar loops. Either goes a long ways in lightening the design.

Thanks very much - I'll look into those options.

Tim51 · Nov 6, 2015

rharshberger said:
What diameter rocket are we talking about here? Size has a lot to do with how many and what sizes of all-thread, whether or not I use 1/8", 1/4" or 1/2" Plywood for bulkheads or even aluminum or fiberglass. On small rockets I use aluminum threaded rods which I make.

The one on the left is my 3" Frenzy XL clones AV-Bay with aluminum rods and wood electronic sled, the one on the right is a Nosecone Av-Bay for my kids BAR Crayon conversions. Both use 1/4" aluminum bars instead of steel allthread, doesn't save a lot of weight but it does save some.

View attachment 275726 View attachment 275727

Thanks very much for the pictures and the description. I'm in the early stages of 2.26" diameter build with a 38mm motor.

Tim51 · Nov 6, 2015

Bat-mite said:
Cut the sled so that it fits snugly in the coupler. No support needed. Run one piece of allthread underneath, off-center, with an eye-nut at each end. Eliminates second allthread, brass tubing, epoxy.

Aha - that's a thought that I'd been clumsily groping towards whilst staring at the pieces on my workbench (although I'd been thinking I'd need some sort of 'door stop' to prevent the sled spinning...) Thanks for crystallising it for me!

Tim51 · Nov 6, 2015

stealth6 said:
Kevlar loops for harness anchors are a great way to cut weight. Especially compared to the huge honkin' eyebolts that most folks use in situations that are complete overkill. I honestly don't get why folks don't use this method more often - it's at least as strong as the harness that's attached to it, it's easy/light/etc.

If you are doing a 38mm airframe, far and away the lightest (and slickest) setup is to use a Raven in a Featherweight AV Bay - the whole thing (bay, altimeter, battery, switch, hardware) weighs less than just some other altimeters out there. WAAAAAAY lighter than most anything else you could do.

If your airframe is larger than 38mm, you can still benefit from the Raven/FW setup - as I outlined in this thread: https://www.rocketryforum.com/showthread.php?43124-Simpler-lighter-AV-bay. Despite one of the comments in that thread that "it is almost the same weight as a conventional sled", my experience was that it saved a ton of weight. And it works fantastic.

s6

Thanks for posting - that's a great idea and very neat indeed. (Yeah.. I can't see how it would weigh the same as a conventional AVB either...)

Tim51 · Nov 6, 2015

blackbrandt said:
Lighter weight compared to what.....

Our Children's Future (9" diameter, 17 ft tall, 100 lbs on pad) initially had 4x3/8" all thread (steel) running through it.

Very good

. I suppose when I get round to that Orion style 100' wide riveted steel pusher plate project (my, err, next after the next) pesky things like AV bay mass won't matter so much. But this one's 2.26" diameter.

Buckeye · Nov 7, 2015

The battery is probably the heaviest thing in your av-bay for a MD 38. Depending on your altimeter, you can get away with much smaller batteries. I have the old Perfectflight MAWD with a big capacitor, so I use the tiny A10 9V alkaline.

RKeller · Nov 7, 2015

lipo and aluminum all thread make a huge difference. also, ditching those eye bolts for a loop of kevlar is a huge savings! this one is 38mm and uses two 6-32 aluminum rods:surprised: to be honest I'm still a little nervous about the 6-32 aluminum all thread but so far it has held up fine. the sled is 1/32" G10.

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ZaK63oMgG3O6k_wWllJJJRz19xXcSLEeNO_fSTrSvXs9DGzlPF3R9aJgBlqFgLfNcEEFdmOS-PtihFYofsoRLJ9eBAgY4wCPBCxercTLQm2uAaft3Ds2aItviTlE7GAYtyyc820Q7GNJAopSFKYe_pSsgdI8F20r-0Mp9XqecLF-PwuU96nx70OqKmA2GiOZcBPUfhtX2rUKuwXzArXrvu2opcC92bi7gXGA4TOmWlXFr8xgpxtHBrVURi2spRO_t0cUDFggAbq4F2Co2IfTHTSJfniAf53JqNbGQi901-ahu-3BZiq4gCTHpz4ZwERUKTklz6oOJhjTTk5bLOeAZLAOBySNOfM91NWjFBsFuiaaqZUXnzS52TplyBpQvHTd9Y1IsRhLzD4YoFUhCadVxOsFvjdFSaFPxaadd09HxxcpcX-FBwua6NRBEBGpKtFePGVTuJMXjO1wQYLo7W4ye4wxW6TdOyREi_E3ewikGWmq1yghpX9sW2k0FDurKE1hGL4BKgJGHUfGgo_K-gyCWEEM-Yd98KM5nf9nhCP1TTE=w890-h667-no

Thorfire · Nov 7, 2015

Here's 29mm and 38mm nose cone bays we've flown this year. The 38mm with the telemega could do dual deploy right now. Adding a quark or a strattologger CF to the eggfinder would make that bay dual deploy capable. The real issue is 0.8 oz for a small 2S lipo battery....

Tim51 · Nov 25, 2015

stealth6 said:
Kevlar loops for harness anchors are a great way to cut weight. Especially compared to the huge honkin' eyebolts that most folks use in situations that are complete overkill. I honestly don't get why folks don't use this method more often - it's at least as strong as the harness that's attached to it, it's easy/light/etc.

If you are doing a 38mm airframe, far and away the lightest (and slickest) setup is to use a Raven in a Featherweight AV Bay - the whole thing (bay, altimeter, battery, switch, hardware) weighs less than just some other altimeters out there. WAAAAAAY lighter than most anything else you could do.

If your airframe is larger than 38mm, you can still benefit from the Raven/FW setup - as I outlined in this thread: https://www.rocketryforum.com/showthread.php?43124-Simpler-lighter-AV-bay. Despite one of the comments in that thread that "it is almost the same weight as a conventional sled", my experience was that it saved a ton of weight. And it works fantastic.

s6

Hi again. I was wondering whether your design only works when the electronics are in a separate tube to the kevlar cord (as in your pictures) or whether you had tried any designs with, say, the kevlar running under the Av sled - I see there's a potential problem with the latter in ensuring the ejection charge gases don't get to the electronics through the kevlar hoop holes in the bulk heads. I was wondering whether tight fitting but removable O rings would sufficiently seal the holes? I would appreciate any thoughts / experience you can share on this.

KenECoyote · Nov 25, 2015

Here's a "Crazy Coyote brainstorm" idea...how about skipping the all-thread and running a long shock cord straight through the AV bay (just one long cord from bt to nose)? Just add a knot on the bottom before the bay, zip-tie the board the electronics are mounted on to the cord, slide into bay, some means to seal the top (either another knot, some sort of clip or bolt lid into bay), fly. :grin:

sig warnings apply.

Tim51 · Nov 25, 2015

KenECoyote said:
some means to seal the top (either another knot, some sort of clip or bolt lid into bay), fly. :grin:

As Han Solo says - 'well, that's the real trick isn't it?'

K'Tesh · Nov 25, 2015

Ok, forgive me if this doesn't make sense, I've been awake for less than 5 minutes.

Replace one of the all thread rods with two dowels or two pieces of carbon fiber tubing (arrow shaft?). The dowels would align with holes in the bulkhead and pin the sled in place (so switches could be aligned for easy external access), and one all thread (going down the center) could tie everything together.

Then again, you could skip the dowels, and just make short pins that would do the same.

KenECoyote · Nov 25, 2015

Tim51 said:
KenECoyote said:

some means to seal the top (either another knot, some sort of clip or bolt lid into bay), fly. :grin:

As Han Solo says - 'well, that's the real trick isn't it?'

Click to expand...

Not really...can just use a double knot...first one loose, slip down, tighten and then a second knot just to be sure.

KenECoyote · Nov 25, 2015

The beauty of my idea is that you don't have to worry about two separate cords pulling your AV bay apart (why we often use all-thread anyway...for strength). You're basically using a long shock cord a la single deploy, but putting the bay around the cord. YMMV - do lp tests first.

Worsaer · Nov 25, 2015

Here are some pics of an AV Bay designed for my a 54 minimum diameter fiberglass rocket, with it all fitting in the nose cone coupler. It uses a single all thread in the center. I use the same principle in most of my builds, one all thread rather than two.

Featherweight Raven + mag switch, and BRB GPS.

Tim51 · Nov 25, 2015

Worsaer said:
Here are some pics of an AV Bay designed for my a 54 minimum diameter fiberglass rocket, with it all fitting in the nose cone coupler. It uses a single all thread in the center. I use the same principle in most of my builds, one all thread rather than two.

Featherweight Raven + mag switch, and BRB GPS.

Beautiful - thanks!

Tim51 · Nov 25, 2015

KenECoyote said:
The beauty of my idea is that you don't have to worry about two separate cords pulling your AV bay apart (why we often use all-thread anyway...for strength). You're basically using a long shock cord a la single deploy, but putting the bay around the cord. YMMV - do lp tests first.

Thanks. My initial thoughts were to use a single offset alu all thread, and feed the kevlar loop strip through a wider section of tube that would poke through the bulkhead as below (literally 'back of the envelope' thinking here... )

My concern with off-setting either the loops or the all thread was whether uneven tensions at deployment would tend to prise the lid off the av bay.

UhClem · Nov 25, 2015

KenECoyote said:
Here's a "Crazy Coyote brainstorm" idea...how about skipping the all-thread and running a long shock cord straight through the AV bay (just one long cord from bt to nose)?

You mean like this?

That has a 38mm tube down the middle with o-ring seals at each end.

stealth6 · Nov 25, 2015

These suggestions about dispensing with all-thread and using a continuous length of kevlar - this is exactly what I did, and referenced/linked in post #4. Works great.

The main thing that the allthread does in a traditional AV is provide strength. But by design you don't need any more strength than whatever your shock-cord is rated at. So, a piece of shock cord is EXACTLY the amount of strength you need - nothing more, nothing less. But is IS less weight than most allthread designs. And it's pretty easy to do, so why not?

By the way, this same principle applies to harness attachment points on ends of regular ebays, nosecones, etc. Typically we all use a big honking (and very heavy) steel eyebolt or somesuch. But again, a simple loop of kevlar cord is EXACTLY the strength required, and a whole lot lighter. I use this method a lot instead of eyebolts - it's lighter, takes up less room, is easy to do, and I almost always have a scrap of cord laying around that suits my purpose and so it's sort of cheaper too.

s6

KenECoyote · Nov 25, 2015

UhClem said:
You mean like this?

That has a 38mm tube down the middle with o-ring seals at each end.

stealth6 said:
These suggestions about dispensing with all-thread and using a continuous length of kevlar - this is exactly what I did, and referenced/linked in post #4. Works great.

The main thing that the allthread does in a traditional AV is provide strength. But by design you don't need any more strength than whatever your shock-cord is rated at. So, a piece of shock cord is EXACTLY the amount of strength you need - nothing more, nothing less. But is IS less weight than most allthread designs. And it's pretty easy to do, so why not?

By the way, this same principle applies to harness attachment points on ends of regular ebays, nosecones, etc. Typically we all use a big honking (and very heavy) steel eyebolt or somesuch. But again, a simple loop of kevlar cord is EXACTLY the strength required, and a whole lot lighter. I use this method a lot instead of eyebolts - it's lighter, takes up less room, is easy to do, and I almost always have a scrap of cord laying around that suits my purpose and so it's sort of cheaper too.

s6

Ah! Sorry...I didn't click on the link and didn't recall reading of such before. Great minds think...well, you know. :wink:

stealth6 · Nov 25, 2015

I think the quote you are looking for is:

"Great minds think alike..........and ours do too!"

s6

watermelonman · Nov 25, 2015

Tim51 said:
Hi

Does anyone have any designs for lighter weight avionics bays they are willing to share (for example, ones that use less all-thread)?

Currently researching building techniques for a scratch built Mach attempt bird based around a CTI 38mm.

Thanks in advance

--

UKRA #1895 L1

My standard design is a single length of threaded rod with eye nuts on each end, and two regular nuts for adjustment and cinching.

mpitfield · Nov 25, 2015

stealth6 said:
as I outlined in this thread: https://www.rocketryforum.com/showthread.php?43124-Simpler-lighter-AV-bay.

Maybe I am just having one of my brain dead moments! If you pull on the Kevlar from the direction that the force would be expected, away from the AV bay on either end of the bay, then wouldn't the force pull the AV bulkhead off? I would of thought that a knot on either side of the AV bay bulkhead would prevent this, which of course would then be a bit of a hassle for opening the bay as well as hard to tie while keeping the AV bay tightly sealed, so generally a poor design.

Maybe a better explanation would help?

KenECoyote · Nov 25, 2015

watermelonman said:
My standard design is a single length of threaded rod with eye nuts on each end, and two regular nuts for adjustment and cinching.

My Punisher bay also uses a single rod through the middle, but it's not that light weight due to the use of heavy couplers (I built it for strength and simplicity); however it is still lighter than two rods along with eyebolts and you can always use a lighter backing piece.

Lighter weight HPR AV bay designs..?

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