Light 'n Tight II - Av Bay Rebuild - Wild Child

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GregGleason

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This is the sequel to Light 'n Tight - Av Bay Build - Wild Child, as the organization of the av bay was poorly organized. It didn't need a tweak here and there, it needed a total makeover.

So I spent a few weeks spending some time addressing the many deficiencies in the design.

So this is my design:

Av.Bay.II.Perspective.jpg

Greg
 
Thank you Mr Wrxz!

One thing I had to do is make sure that the e-match ports lined up in the caps. On the previous build, I had just made a hole in the cap with no thought to whether or not they were oriented at a natural point of egress from the altimeter. Now I had to come up with a "highway" to insure things lined up properly, and that the ports on the cap lined up with that highway.

New.Caps.jpg

Greg
 
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One problem that I needed to solve is the internal orientation. When I went to assemble it the day it flew, I discovered that I had inadvertently made a "Rubic's Cube" in that I had a seemingly infinite number of permutations to assemble it, with nearly all of them being the wrong way.

I basically had to make it so it would only come together one way, the right way.

My solution was to add internal anchors that the aluminum sleeve (seen as the light gray tube in the graphics) for the 1/4"-20 all thread could ride in (seen in blue). Also, the anchor had another hole so that a length of 4-40 all thread (seen as dark gray cylinder) could ride in to serve as an orientation pin for the cap. The cap will only go on when it is correctly aligned with the pin.

Av.Bay.II.Aft.End.1.jpg

Av.Bay.II.Aft.End.2.jpg

Greg
 
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The caps on the previous model were more or less generic and interchangeable, but since these would have a pin for orientation, the cap at top would always have to be the top and the same for the bottom cap*.

New.Cap.Design.Inside.jpg

The hole near the 3 o'clock position is the e-match port. The hole at the 6 o'clock position is for the 1/4"-20 all-thread. The pocket near the 7 o'clock position is for the 4-40 all-thread reference key.

New.Cap.Inside.jpg

The cap as milled.

Greg


* I know that it is more correct to say fore and aft WRT the rocket, but in the field you want it as simple as possible, at least that's what works for me.
 
Another task in the redesign was to make sure that there were no obstructions like I had with the first one, which were due primarily to the wires and the battery not having a defined space to reside.

So I had to do some arranging to make sure that it all fit. So I designed the sled to conform more to the walls of av bay and shifted it to one side to make room for electrical highway. I made a 1 mm obstruction area from the inner wall so that I had some room for error.

Av.Bay.II.Looking.Forward.jpg

In addition, I needed to find a permanent space for the battery to be rather than using the "find a void until it fits" strategy. It made sense to have the battery (shown as a medium green cylinder near the cap) near the power terminals on the altimeter rather than at the rear. To make room for the battery, the caps had to be shortened from 0.50" thick to 0.25" thick.

Av.Bay.II.Plan.View.jpg

Greg
 
Yes good work , I need to build a av bay for one wild child and start to build another one minus motor tube
 
After milling out the anchor references (boy, they are small), the plan was to epoxy them in place. But I had to solve another problem before I could do that: How to get the pieces properly oriented before they were positioned for the epoxy. The key reference internally is the single switch port. In my CAD program I drew a circle and trimmed away parts until I had an arc that represented the angularity between the center of the switch port to the base of the anchor. Thankfully, the CAD program has a "length" command that reports the length of an arc. So I took that information and printed out a piece of paper a rectangle, with the long side being the av bay length and the short side being the arc length. I temporary glued this into the av bay tube so I could have a reference to place the anchors. You can see a portion of the paper in the photo below (along with a penny that illustrates how space is at a premium):

Installed.Anchor.Reference.jpg

The next thing to do was to cut a length of 4-40 all thread, which I had a 3 foot length of aluminum all thread that I received from McMaster-Carr. The first attempt to cut was a bust, since my H-F digital micrometer skipped a beat and it was cut too short. Sigh. The second attempt went better and gradually ground off one end until it fit. Not only does it fit well, there is not a lot of play either. Just to make sure, I ran the 1/4"-20 all-thread through the caps to make sure there were no problems, and there were none. So now the caps can only go on one way and are properly oriented. Check.

AnchRef.with.4-40.All.Thread.jpg

Greg
 
I am sure that you're enjoying building these bays and all, but if you're looking for a shortcut I highly suggest you head over to www.additiveaerospace.com for an integrated solution for your MAWD altimeter orwww.missileworks.com for an RRC2+ altimeter. LiPo battery, Schurter switch (or MW's adapter for their screw switch, HIGHLY recommended), printed sled with aluminum 8-32 allthread and you have an extremely clean and lightweight solution. I have an RRC2+ in a 4" long LOC 38mm coupler in my VB Extreme 38 clone...
 
That's a good suggestion (and cool!) for most folks, but I am already going down this path and I am curious to see where it goes.

Greg
 
Next thing, epoxy the aluminum carrier tube for the 1/4"-20 all-thread to the sled. I scuffed up the side of the tube that would get the epoxy to give the surface more "tooth", then cleaned it off with alcohol. For most of the epoxy joins in this project, I am using 5-minute epoxy (Loctite/Henkel Heavy Duty).

Sled.and.Tube.jpg

Greg
 
It was time to do the initial fit for the sled with the caps. If this doesn't work, then it means back to the drawing board.

Sled.AnchRef.Check.jpg

The caps closed and set with no interference, so this is a milestone in the process.

Sled.Cap.Close.Check.jpg

I am probably more relieved than happy that it fits. That I was able to put things together in less than a minute (as opposed to about half an hour or longer with the earlier variant) and have things in proper orientation internally is to me a major achievement.

Greg
 
I must say I really like the milled/engraved markings on those endcaps.
 
As I was looking into the conduit for the e-match, I had originally spec'd out a 3/16" tubing. I also had a 7/32" tubing that looked like it would work better. The problem though with using it was that the 3/16" was already encroaching into the 1 mm warning area. My gut instinct told me to go with the bigger tube. So I checked to see if the larger tube would work at all, and it does, but just barely.


The 3/16" tubing below:

E-Match.Conduit.3%16.inch.jpg


The 7/32" tubing below:

E-Match.Conduit.7%32.inch.jpg


I also, had to adjust the stand the conduit is mounted on. I'll have to take 0.015" off the bottom to make it work. I used a chamfer bit to put a V-grove onto the edge.

Conduit.Hwy.V-Grove.jpg

Greg
 
I epoxied the 7/32" tube to the tube stand. After the epoxy set, I milled the e-match conduit, and while I was at it I placed some 4-40 taps in it, too. The main reason for tapping is that I wanted the wires to have a pinch point to hold them in place as so that if there was tension on the wire that it would tug at the pinch point rather than the terminals.

I had some 4-40 brass screws, but they were a bit too long. I didn't have any aluminum screws which would have been my preference, so I went with what I had on hand. I milled off the ends to shorten up them up so that they would fit a bit better.

E-Match.Conduit.As.Built.jpg

Greg
 
I epoxied the tube stand onto the sled, then set that aside to cure.

After a few hours, it was time to seal the wood parts. Because BP residue seems to get everywhere, I wanted to protect the wood from the start by sealing it. I am not sure what the best way to seal it and look nice, and rather than research I just came up with a process that made sense to me. So what I did was mix a 3.0 gram batch of laminating epoxy and added a pinch of milled fiber (for strength, not that it needs a lot) and added a heap of micro balloons (to clog the pores of the wood). I used an acid brush to brush it on rather than a chip brush, since the latter would soak up so much of the batch there would be hardly any left. After the first coat, I hit with a shrink wrap heater so that the pores would open up in the wood and go deep, followed by a second coat and more heat. Then I set it aside to cure.

Sealing.the.Wood.Parts.jpg

I would be interested in hearing about alternative wood sealing strategies. Always ready to learn something new, especially from those of you that have a process that you are happy with.

Greg
 
Man,

Very nice work. I did a DD AT HV Arcas but there's more room to work with. Did a single all-thread down the middle because of the space, Adept 22 and used two 3Dogs rocketry 8-32 eyenuts while they were available.
Had enough room for a magnetic switch too. The Wild Child, great planning and economy. Now don't blast it too high you don't find it.:facepalm: Kurt
 
Thank you both for your comments.

One of the biggest challenges was not only finding a space for the small battery. On the previous variant of the av bay, the battery was free floating. While it worked in theory, it was a complete dud in practice. The masking tape does not hold that well in environments are humid and your fingers are sweaty. I had to do my sweating now in the redesign phase so I wouldn't have to in the field (at least not as much). Not only did I have to find a place for the battery, I had to come up with an adequate way to secure from high g loading. I didn't trust the spring clips to do their job if things get serious with either acceleration or deceleration.

After giving this quite a bit of thought, I recently (as in the last few days) came up with a way that I thought might work. I don't know yet since I haven't fully modeled everything, but at least it is worth a shot.

Using two pieces of 0.500" x 0.0625" aluminum angle, they could be placed in such a way that would provide stops for the most likely g loading. The two pieces would have to be carved up a bit to work, but at least it is a possibility.


Here is the "open" position:

Battery.Well.Open.jpg


Here is the "closed" position:

Battery.Well.Closed.jpg

Hopefully I'll know soon if this is a viable solution.

Greg
 
Great build! TOUGH making small AV Bays- truly an art form. That battery looks well supported with your unique solution. Thanks for posting.
 
Are the milled out circles with the center still in place when you are going to attach your charge cups?
It was time to do the initial fit for the sled with the caps. If this doesn't work, then it means back to the drawing board.

View attachment 182741

The caps closed and set with no interference, so this is a milestone in the process.

View attachment 182742

I am probably more relieved than happy that it fits. That I was able to put things together in less than a minute (as opposed to about half an hour or longer with the earlier variant) and have things in proper orientation internally is to me a major achievement.

Greg
 
This is truly a very elegant design. I understand your "want" to build it yourself, I find the build and design more than half the fun.

I have a question about the aluminum tube epoxied to the "sled". If you made it long enough to come all the way through the bulkhead caps, would that allow the caps to be indexed and allow the deletion of the alignment rod? Could it also be accomplished using the ematch highway tube? I know you are past that now, but do you think that would work?
 
That ought to do it wit the battery. What kind of cell you using? Kurt

The battery is known by many names, so I'm not sure which one is the predominant name. But some are 10A, A10, E10A, G10A, GP-10A, GP10A, L1021, L1022, and WE10A. It has a L x D of 21.6 mm x 10 mm and is a 9V battery at 38 mAh. The inspiration for this attempted build can be found with this link. The battery can be used for two flights. Maybe.

Great build! TOUGH making small AV Bays- truly an art form. That battery looks well supported with your unique solution. Thanks for posting.

Your welcome! This is the hardest thing I have had to design to date.

Are the milled out circles with the center still in place when you are going to attach your charge cups?

Yes. They are milled to accept K&S brass tubing. It's 13/32" x .014" x 12" as bought, then I cut it to length. The cups will be different lengths on different ends, based on the amounts of BP they will hold. I spent a couple of hours yesterday coming up with calculations to determine the length that those tubes should be. I won't bother posting the math unless someone wants to see it!

Here is a picture of the caps after a firing test from the earlier variant:

Av.Bay.Caps.After.Ground.Test.jpg

This is truly a very elegant design. I understand your "want" to build it yourself, I find the build and design more than half the fun.

I have a question about the aluminum tube epoxied to the "sled". If you made it long enough to come all the way through the bulkhead caps, would that allow the caps to be indexed and allow the deletion of the alignment rod? Could it also be accomplished using the ematch highway tube? I know you are past that now, but do you think that would work?

Thanks!

The more that I think about it, the more I think that it would work. It may be even a better design than the one I came up with. Hats off to you!

Greg
 
Yes. They are milled to accept K&S brass tubing. It's 13/32" x .014" x 12" as bought, then I cut it to length. The cups will be different lengths on different ends, based on the amounts of BP they will hold. I spent a couple of hours yesterday coming up with calculations to determine the length that those tubes should be. I won't bother posting the math unless someone wants to see it!

Here is a picture of the caps after a firing test from the earlier variant:

View attachment 182990



Thanks!

The more that I think about it, the more I think that it would work. It may be even a better design than the one I came up with. Hats off to you!

Greg[/QUOTE]

Thank you, I don't know about it being better, just different. I always enjoy your creations and they have inspired things I have built. I am trying to come up with a "core" design that will work on the smallest and then have adapters to fit into larger air-frames. The thrill of the chase for the "perfect" Av Bay keeps me daydreaming. Thanks again, great build project.
 
After the sled had cured, I tried to put it in the av bay and then it hung up. So I backed it out.

I was pretty sure I knew what the culprit was, so I removed the brass screws and tried again and it fit fine. Barely. So I will either need to mill down the heads or put slots in some 4-40 studs. Or not use them at all. I'll defer that decision.

Greg
 
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