Electronics bay configuration and building

[RocketTree]

Looking for help building altimeter bay and attempt dual deployment on the 4" G-Force. Already have the altimeters and parts to build 'coupler and switch band' or 'slide-in' bays.

Now I see there is not enough room to use a coupler and switch band, since that is all taken up by parachutes and shock cord. (see photo)

Will the bay have to be installed into the upper body tube instead, or should I add a payload bay extension to it?

Have all the parts here, but not sure where/how it should be mounted in the rocket. How is it fastened with access to power switch etc..

(edited my post to be more specific)

I also have to do these for 2.6" mirage and 1.9 Arreaux if possible

 

[Handeman]

Since the G-Force is 4" diameter, I would use a 8" long coupler and +8" piece of body tube to to extend the lower bay. Then the 9" long av-bay with 1" switch band. The av-bay attaches to the upper payload tube fits inside the lower tube.

This is the classic configuration and minor to major variation are possible.

 

[RocketTree]

Thanks for your help!

Does this look correct?

 

[boatgeek]

That arrangement shoudl do it if you need to. But...

The "normal" arrangement for dual deployment is with the main in the upper payload section and the drogue in the lower section (aka fin can). Usually it's not that hard to fit a drogue in the fin can unless you've really optimized the length and/or you have a giant motor. Can you fit the drogue below with the altimeter bay coupler? If so, I'd go with that arrangement. If not, add the 8" as described up above.

 

[RocketTree]

Thanks for your help.

Is this what you mean? I might have misunderstood the instructions a bit Added a diagram to see if I am even close... Let me know

I only have 3.5" inside the lower fin can, to slide the coupler into. From factory, the chutes and cords are located in that coupler with a bulk plate at the top of it.

This was my original design intention until realising there was not enough room:

 

[boatgeek]

If you only have 3.5" to the top centering ring, then I would definitely re-work things as follows:

Pack your drogue and drogue harness as tight as you can. Add two inches for hardware (charge wells and eye bolt) plus a little margin. Add this much more body tube to the fin can. Glue in a piece of coupler at least 4" long to make the joint (2" above and below the seam, glued in both locations). Hopefully you have an extra coupler to do this job with. If your payload section is long enough to hold your chute, the AV bay coupler, and the nose cone shoulder with the extra length of body tube removed, you can cut it out of the payload section. Otherwise, you probably need an extra piece of body tube.

You want at least one body diameter for all joints that come apart in flight. That makes it far less likely that your rocket will fold over while the motor is firing.

The other, higher skill level version of this is to make the AV bay lower shoulder 3.5" long so the coupler sits tightly on the centering ring. Then you'll put the bulkead for your AV bay right at the bottom of the switch band, which may give you enough space to put the drogue and harness in tight. You may need to replace the harness with Kevlar to make it pack smaller. Then the rest of your build can go as normal. This also gives you less space in your AV bay. You should still be OK, but you'll have to be a bit more careful with your layout.

 

[mpitfield]

Some good recommendations to consider. Another one, that is ideal for the G force is to convert the nosecone into an AV Bay for apogee eject, and use a JLCR for main. Single split with plenty of room for packing.

 

[RocketTree]

Great advice! Much appreciated. I have some more parts to order so I can get this completed. Would like to make sure I have everything needed..


Any recommendations to fasten the sections together on this example?? Is this optimal?




Maybe I could inset the electronics bay bulkhead into the coupler 2", it might allow enough room for the drogue and cord. Still have 6" inside for electronics.

update: Looks like it could work, but the heavy duty coupler is paper finish, so seems to have serious friction issue when it comes time to slide out deploy the parachute. The original coupler is glassine and much thinner (not usable for a bay). Can this be addressed somehow?

 

[boatgeek]

Great advice! Much appreciated. I have some more parts to order so I can get this completed. Would like to make sure I have everything needed..


Any recommendations to fasten the sections together on this example?? Is this optimal?

View attachment 418520



Maybe I could inset the electronics bay bulkhead into the coupler 2", it might allow enough room for the drogue and cord. Still have 6" inside for electronics.


View attachment 418524

Keeping in mind that there is no One True Way, I like most of what you did there if you want to make this a traditional dual deploy rocket. I would probably cut the lowest coupler down by 3-4" and glue it into the fin can and the 8" tube extension. That will make it so you have a full 4" of overlap available on your sliding fit at the AV bay. I'd also go to 2 shear pins at the payload bay to nose cone joint. 3 seems like overkill, though shear pins is an area where reasonable people disagree, sometimes to the point of becoming unreasonable people.

Mpitfield's suggestion of putting the AV bay in the nose cone and using a Chute Release for the main is a good one, though may not be as attractive if you already have the altimeters. If you plan to fly a lot in the E-H range, you might want to pick up a Chute Release anyway.

Sliding the bottom of the AV bay up 2" would let you get away without any new parts if everything fits. I would glue in the lower (recessed) bulkhead plate, because that seems easier. There's lots of ways to skin this cat though.

What altimeters are you using? You should be able to fit two side by side in 6" of length, with the batteries on the back side and switches in the middle.

 

[RocketTree]

That looks like the best way to go about this. Will update (and probably have more questions) when I start assembling this next week. Got the Bear altimeter kits 84 and 85 model.

Have to keep the weight down, since its already heavy. Would still like to be able to fly it in original configuration for the smaller recommended motors. With the electronics bay and extension, it is overweight.

Edit: After some more work on it today, it looks like my best option is to keep the original coupler and upper body tube together for original config.

For dual deployment flights, I will get another identical upper body tube and mount it to the electronics bay coupler. Can choose between them as needed for a standard flight or dual deployment..... and will look great stacked all together on display

Update.. The 8" coupler does work at the fin can if the lower bulk plate is installed 3" up inside the coupler, allowing area for drogue and lines. Leaves me with 4.5" of height inside the coupler for equipment. Might also add a 12x12 chute protector over the motor ejection baffle for extra caution.

 

[Handeman]

+1 for boatgeek

My only advice would be to forget the shear pins altogether. They will just tear up your cardboard tubes. The plastic nose cone too for that matter.

Use friction fit. Put tape in an X pattern on the coupler in three places equally spaced around the coupler and as far from the seat joint as possible. You can add or remove pieces of tape to increase or decrease your friction. Because the thickest part is the cross of the X, you can slide the parts together easier than just adding layers of tape wrapped around the coupler. It also gives you better control of the level of friction.

The key to friction fit on the nose cone on a traditional DD, don't over do the apogee charge. It only needs to be enough to open the rocket and get the drogue into the air stream as the rocket falls. The drag of the inflated drogue chute will take care of pulling shock cord out and tight on the way down. You don't need so much charge the upper section slams to the end of the drogue shock cord.

 

[mpitfield]

My only advice would be to forget the shear pins altogether. They will just tear up your cardboard tubes. The plastic nose cone too for that matter.

Another good point for single split nosecone AV bay. Here are some links to look at for inspiration.

TRF Nosecone AV Bay
John Coker Plastic Nosecone AV Bay Conversion Video
4" Bertha Upscale with Nosecone AV Bay
AV Bay Post Your Pics

 

[RocketTree]

While some parts are on order for this 4" bay, I decided it was a good idea to build a prototype version and see if the assembly will work. Here is the design I was originally going for (Madcow bay in pic), but the use of two steel rods to sandwich the assembly is really causing a weight problem (in addition to the heavy coupler, eyebolts , fasteners, and plywood plates... etc). Tried aluminum rod, but the threads are not robust enough for repeated use.



Does anybody have a different bay design or illustration that does not require threaded rod, but still allow accessibility and disassembly of the unit in the field?

 

[swatkat]

The switch band does not need to be in the center of the bay. I do this often. (shorten one side as needed)

 

[boatgeek]

There's a few threads specifically on AV bays and switch setups on TRF:
https://www.rocketryforum.com/threads/show-us-your-av-bay-setup.56701/https://www.rocketryforum.com/threads/1-or-2-threaded-rods-in-av-bay.157213/https://www.rocketryforum.com/threads/show-us-your-switches.152456/https://www.rocketryforum.com/threads/show-us-your-hed.144744/

 

[mbeels]

Does anybody have a different bay design or illustration that does not require threaded rod, but still allow accessibility and disassembly of the unit in the field?

I'm surprised the aluminum wasn't strong enough. Some other ideas include the Apogee 4" bay with (1) threaded rod, using eye nuts instead of nuts on the threaded rod (plus eyebolts and more nuts), or even eliminating the threaded rod completely as the Apogee 2.6" bay does.

 

[RocketTree]

Those links seriously helped ^

I got a few other design ideas in mind now!


For this design below.....

Does the lower plate with threaded rods get glued into the coupler, so only the top plate and sled come out?
https://www.rocketryforum.com/threads/show-us-your-av-bay-setup.56701/


(google image)

 

[DaHabes]

There is a thread here somewhere that covers what to replace steel all-threads with (primarily to avoid creating interference when adding a GPS tracker to the AV-bay). I didn't mark the thread to watch it, but captured the options.

One guy uses nylon all-threads: https://www.grainger.com/product/GR...d-1ENZ5?opr=APPD&pbi=1ENZ5&analytics=altItems

One guy uses titanium rods ($$$) - https://www.amazon.com/s?k=titanium+threaded+rod+1/4&ref=nb_sb_noss

One guy uses titanium bike spokes: "Only 2mm diameter and breaking load is around 280kg each. Find a good bike shop and they make them to custom length for you. They roll-form the threads, which results in work hardening and strengthening in that area. If you thread a rod with a die it actually creates stress raisers and greatly weakens the rod. I paid about $USD5 each for them a couple of years back. The amount of space saved by the smaller diameter can really provide much more space in the avionics area."

 

[Speaknoevil]

Those links seriously helped ^

I got a few other design ideas in mind now!


For this design below.....

Does the lower plate with threaded rods get glued into the coupler, so only the top plate and sled come out?
https://www.rocketryforum.com/threads/show-us-your-av-bay-setup.56701/

View attachment 419001
(google image)

I typically use adhesive on one of the bulkplates. Usually the forward one that is screwed into the airframe. Why? I just don't like taking off one set of wing nuts and having everything clanking around. The exception is when I have the bay permanently glued into place when I have less than one caliber insertion length due to space constraints in the payload bay.

 

[kbRocket]

If you need to eliminate the threaded rod to reduce weight, see:
https://www.rocketryforum.com/threads/three-electronics-bays.157884/post-1967912/

 

[Kelly]

I like the idea of eliminating the rods, holding the bulkplates on by screwing them into the sled itself, and then using either the sled (protruding through the bulkplates) or a kevlar cord (running through the center of the bay) to take the tensile force from one end to the other. The 'three-electronics-bays' thread mentioned above shows the first approach, and this thread shows the second:
https://www.rocketryforum.com/threads/3-av-bay-v-2.159199

 

[RocketTree]

These are all great suggestions. I have been reading through them and making some notes. The biggest thing is keeping it light weight and retain easy access to the electronics area. I should have mentioned earlier - the total mass must be kept below 1500g (Rocket and G80 motor = 1050g according to manufacturer). This leaves a safe 350g for electronics and room for error & additional recovery hardware. Here are the weights of assembled bay with different materials I have on hand:

Dual 1/4" steel rods, 1/4" eye bolts, steel fasteners, 9V battery,
altimeter, single sided sled, plywood bulk plates, heavy coupler and switch band
= 355g

Dual 1/4" aluminum rods, 3/16" screw eyes, steel nuts nylon washers, 9v batt,
altimeter, single side sled, plywood bulk plates, heavy coupler, switch band
= 297g

Single 1/4" steel rod, 1/4" eye nut, steel fasteners, 9v batt,
altimeter, single side sled, plywood bulk plates, heavy coupler, switch band
= 291g

Dual M8-32 steel rods, 3/16" screw eyes, steel nuts nylon washers, 9v batt,
altimeter, single side sled, plywood bulk plates, heavy coupler, switch band
=277g



Solid wood sled with upper bolt (no rods) (approx 260g), and some aerofiber bulk plates (if you can even buy them?) might get it down to around 220g which sounds great to me.

 

[mbeels]

I was a bit concerned about your aluminum all thread test results, because one of my rockets uses a single length of 1/4" aluminum rod to hold the AV bay together. I hooked one end on a nail in my basement ceiling, and I can hang from the other end, so at least my hardware seems ok. I weigh about 155 lbs, so that should be good for 50 G deployment events for a 3 lb rocket. Just another test result.

 

[RocketTree]

I was a bit concerned about your aluminum all thread test results, because one of my rockets uses a single length of 1/4" aluminum rod to hold the AV bay together. I hooked one end on a nail in my basement ceiling, and I can hang from the other end, so at least my hardware seems ok. I weigh about 155 lbs, so that should be good for 50 G deployment events for a 3 lb rocket. Just another test result.

Good to know. I believe this ended up being the 1/4 plain steel nut having excessive clearance in the threads of the rod. Will certainly try this again knowing that it can be done.