Carl's Deployment bay design

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Highway 101

New Member
Joined
Aug 26, 2002
Messages
3
Reaction score
0
I'm a new user of this forum so please bear with me. I was deep into a 7.5" diameter cluster project when I discovered Carl's full-scale AAmram project on EMRR. The design of the deployment bay was so elegant that I scrapped my design and got the parts to build his design. I have two specific questions for Carl and any others who may have built similar designs:
1. Carl, did you measure the diameter of the piston groove where the O-rings seat? I was planning to do it by trial and eror but if you have a measurement I'd love to get it.
2. My only planned modification of Carl's design is to route the wiring for the power switches and ejecton charge safe switches through the main chute (fore) end of the bay (instead of the aft end). I plan to use wire pass-throughs drilled through the entire closure assembly with Molex connectors recessed into the closure. This will be covered by the parachute bay base plate. Does this design have any intrinsic flaws? I'd appreciate any comments forum members may have.
I have to say that Carl's L3 page is the best laid-out and most informative site I've used in my rocketry inernet travels. If I can figure out how to build this deployment bay from reading it, it must be good!
Thanks for letting me participate in this forum - I look forward to learning a lot from the readership. All the best,

Mike Worthen
 
Mike,

I want to welcome you to The Rocketry Forum! You will find we actually talk rockets here and have a great group of rocketeers with a wide variety of talents and experiences to share...the only request is pics...we love pics and enjoy seeing eachothers work. It's probably the only place where you can display you pride and joy without feeling like your bragging, because EVERYONE appreciates the time and efforts spent, from the smallest Micromaxx to the largest of L3 projects. So as you build, remember to give us something to follow as we enjoy watching the progress and learning from your ideas. They say a picture can say a thousand words...here is living proof of it! ;)

As far as my web site goes...thanks much! My whole intent was to make it a useful tool for people and I am glad you have found it so. The deployment unit design came from a desire to build a completely self-contained unit that could be easily inserted into the rocket. All the preparation of the Alts, e-matches, ejection charges and bay sealing could be done while it was on a bench, without fighting wires and charge caps inside a bodytube. Also, it may seem a bit beefy, but that is so it can handle the "hit" of some heavy ejection charges...which could exceed 10 grams. As it sits, it has taken near 7 grams of kick without a problem and the altimeter bay appeared to be sealed well as the recording Alt's data did not show even the smallest ejection charge spikes when fired.

The O-Ring is actually a vaccum sweeper belt that you can get at nearly any store, two for about $1.50. I cut the groove for the rear "belt" O-Ring deep enough for it to just barely sit above the unit. Fine sanding was done with a Dremel and 3/8" Sanding cylinder to both the slot and the belt...yes, I said I sanded the belt a bit. ;) The reason being, at the price, the belts are pretty cheaply constructed and had some ridges and raised letters on them I wanted to get rid of; in fact, the first belt wouldn't even plug in the bay because of the raised lettering on it.

Note that most of the sealing comes from the unit bottoming out in the lower bulkhead plate...the belt was for added insurance. The same applies to the upper end of the unit; I used a 1/16" small diameter O-Ring from PML that they use for their CPR3000 on 4" rockets. I use their CPR in other rockets and had spare O-Rings around and this one fit the bill. the lip of the cavity was slightly beveled so that , when the unit is installed, the O-Ring sets itself in this "V"groove, then expanded and filled the groove when the faceplate was tightened. I guess it's not really a V, more like a 45 degree bevel.

As far as your wiring goes, it sounds just fine to me. The only reason I wired mine on the bottom was that the body tube was only 14" deep from there to the inner bulkhead, where as I would have had to reach blindly into a 25" deep cavity if I mounted it on the top. I DO like your idea very much of using the tray to protect the wires!

The only other item I had not designed was built in shunts. I spoke with advisors on this one and we agreed that it was not necessary on this rocket, as the Altimeters I was using had motion sensors integral to them, hence they did not arm until the rocket was moving forward for over 1/2 second. However, at some NAR launches, shunts may be a requirement, so as an afterthought, I have come up with a method of inserting a rod from the outside of the rocket, through the bay area and into a 8-pin Din jack on the alt bay. The rod/plug assembly has an alignment notch to keep it twisted in the right direction, while the jack in the bay has a beveled outer guide block above it to help with hitting the target. When removed, the remaining hole in the Body Tube is used as one of the holes for pressure sensing. More to come on this...

Mike, if you have any other questions I or anyone else may be able to assist with, ask away. Also expect us to tap your talents as that is what the forum is about...information, skill and idea sharing and exchange. Well, that's about it ...except for the fact that I am at it again; I am about half way through building another one of these deploy units for a Scratch 75% Scale AGM-88A Harm Missile you can find in another post. PLEASE, let us know how your construction goes and remember to get us some pics!!! :D

Cya and again, Welcome to TRF,

Carl
 
Back
Top