Switch band-less Av Bay - any experience?

FredA said:

... To install the Ebay, you need to have the charges in place and then need to push it in and turn till in position - usually using your hand/arm. ...

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Nytrunner said:

I'm thinking more roughened tube area for the entire bay to slide past as opposed to just inserting half the bay into the tube at a break point.

Similar question for JimJarvis, are you using two recovery events? I'm also having trouble envisioning how the sequence plays out with the bay fully inserted into the tube. Do you use a bag or some other method for the main?

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Bat-mite said:

I've used the Giant Leap method. You epoxy the coupler into the payload tube. Leave about 3/5 of it out, 2/5 inside. After you prep your electronics, attach the harness to the upper bulkhead, and use the harness to lower the sled and upper bulkhead into the coupler. Once it is settled, attache the lower bulkhead. Done.

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FredA said:

how is fuzzing of tubing any bigger of an issue in this manner than in the "traditional" employment of a switchband?

Conventional dual-deploy setup with two chute bays and an Ebay in the middle - using a coupler-only Ebay (no switch ring)

Imagine a LONG tube (say 48 inches) that forms the main and drogue bays....not two tubes.
You slide the Ebay down inside the tube about 1/3 of the way so that you get 1/3 drogue and 2/3 main bays with the Ebay in the middle....no break in the tube. Then have some way to secure the EBay in place - screws or an internal bulkhead as Jim suggests.

To install the Ebay, you need to have the charges in place and then need to push it in and turn till in position - usually using your hand/arm.

With the conventional switch-ring Ebay, you aren't putting a hand down the tube with hot charges....

With the "mid-tube" Ebay, the charges are going off mid-tube. You now need to clean mid-tube and slide the Ebay in and out past the area where the charges are firing. After many flights, the tube will start binding.

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jimzcatz said:

To much trouble. I have only one removable bulk plate. Forward plate is epoxied into coupler, epoxied into payload. Ubolt on both plates. Hole drilled with wire installed in forward plate prior to installation.

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FredA said:

Yes, standard Ebay configuration with charges fore and aft. Always two charges on each end for my rockets...the backup being about twice the primary.

You gotta get the Ebay out after the flight before you can hose & brush it off.
That is usually messy and drives the debris into the walls of the Ebay and body tube.

Problematic to hose off an Ebay with avionics inside....

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FredA said:

how is fuzzing of tubing any bigger of an issue in this manner than in the "traditional" employment of a switchband?

Conventional dual-deploy setup with two chute bays and an Ebay in the middle - using a coupler-only Ebay (no switch ring)

Imagine a LONG tube (say 48 inches) that forms the main and drogue bays....not two tubes.
You slide the Ebay down inside the tube about 1/3 of the way so that you get 1/3 drogue and 2/3 main bays with the Ebay in the middle....no break in the tube. Then have some way to secure the EBay in place - screws or an internal bulkhead as Jim suggests.

To install the Ebay, you need to have the charges in place and then need to push it in and turn till in position - usually using your hand/arm.

With the conventional switch-ring Ebay, you aren't putting a hand down the tube with hot charges....

With the "mid-tube" Ebay, the charges are going off mid-tube. You now need to clean mid-tube and slide the Ebay in and out past the area where the charges are firing. After many flights, the tube will start binding.

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soopirV said:

Now THAT makes sense, and fits with JimJarvis' picture on an earlier post, thanks!...but my train-of-thought is STILL Stuck at the station- with no break, what does the aft event do? I'm supposing, perhaps incorrectly, that the fore event pushes some laundry out with the nose cone, but...there's something missing for me still! IT gets at the heart of what I'm thinking, however, which is to minimize discontinuities in airframe surface. Leads me to suppose rear-eject, but then that has its own issues...

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soopirV said:

Thanks Dave, it sure does! Nice build work, by the way, and I also like how you secured your tee nuts...I honestly hadn't though of installing them backwards, so I've been mucking about with these little tab-like weldnuts I got from McMaster View attachment 311181. The inner liner over the nut is a great idea.

Adhesion is really poor. I like the other suggestions of PEM nuts, but I have had luck so far just tapping the fiberglass and drilling a clearance hole in the airframe...don't think PEM nuts would work well on basic cardboard though.

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JimJarvis50 said:

Try this. Here's a pic with an example design. Sorry it's not too clear. There is the lower air frame with the fins, and the top of that section has a zipperless coupler. The upper air frame is a single tube that is open on either end with the Av Bay in the middle. There is no break in the tube at the Av Bay location or switch band. The lower end of the tube in the pic has some tape on it to contain the harness (I'm getting ready to fly this rocket), but imagine that this tape is not there and it's just an open tube. It slides on top of the zipperless coupler and gets shear pinned in place. The apogee event opens this section and the drogue comes out of the lower part of the upper tube. Later, the main comes out the top. Clear as mud?

Jim

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JimJarvis50 said:

It's just like Fred described. The bay just slides down part way into a longer tube as opposed to two shorter tubes. There's still a drogue chute below the bay and a main event above the bay. The bay can sit on a ring or bulkhead attached within the tube and can be held in place externally (my socket screws) or connected to the bulkhead. The only issue I have with this approach is that if the bay is a good fit to the air frame, it is necessary to clean out some of the BP residue before the bay will slide out of the air frame.

If this explanation of the two recovery events still doesn't make sense, then the confusion might be that I always use a zipperless coupler approach where the coupler that connects the upper and lower air frames is attached to the lower air frame. The upper air frame that has the bay installed in the middle of it then slides onto the zipperless coupler.

Jim

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JimJarvis50 said:

Try this. Here's a pic with an example design. Sorry it's not too clear. There is the lower air frame with the fins, and the top of that section has a zipperless coupler. The upper air frame is a single tube that is open on either end with the Av Bay in the middle. There is no break in the tube at the Av Bay location or switch band. The lower end of the tube in the pic has some tape on it to contain the harness (I'm getting ready to fly this rocket), but imagine that this tape is not there and it's just an open tube. It slides on top of the zipperless coupler and gets shear pinned in place. The apogee event opens this section and the drogue comes out of the lower part of the upper tube. Later, the main comes out the top. Clear as mud?

Jim

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soopirV said:

BINGO, thanks! I thought you had zero breaks in the airframe, from fins to cone. This makes a lot more sense to me now, with the zipperless booster/fin can. Sorry it took so long for me to get there!

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FredA said:

If you setup your rockets as Jim Jarvis suggested with the Ebay set mid-tube, you have little option but to install the Ebay by sliding it down the tube and rotating it into position with the charges installed.
This is one of the primary reasons I don't like this method as you need to reach down the tube with the charges in place.

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manixFan said:

Unless I missed it I'm surprised no one has mentioned the PML CPR3000 system. (Just the mounts, not the coupler.) I've used it in a fair number of rockets and it does not require a switchband - I use screw switches to arm my electronics so all I have to do is make sure the holes are lined up. I have a half-dozen altimeters mounted on sleds that all use the same switch location so I can pretty much move them between rockets without any issue. I've even used it on an internal e-bay that slid into the middle of the A/V body tube and was held in place with plastic rivets. My Level 3 rocket used 2 mounts side-by-side in a 6" airframe. In 15 years of using this method I've never had any real issues other than a few broken parts to replace. It only works in 54mm or larger body tubes though.

Most of the time for larger rockets I don't use the charge holders provided by PML. I pack the charges appropriately and just run the wires through the mounts.

Just another way to get it done.


Tony

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soopirV said:

Can you share some photos? I've never built a CPR kit but have read about it on PML's website. Would like to get a deeper understanding.

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manixFan said:

Sure, below are several photos (the first 3 are back from 2007) that show how it can work. Some are pretty small but should be enough to make sense of how it works.

For the sleds, I use cable ties and then a wrap of electrical tape to hold the batteries in place. I seal the holes the wire pass through with some sticky-tack to prevent gas from getting into the bay. The holes that allow access to the screw switch also act as the altimeter vent holes. There are o-rings that are installed on the mounts that also seal against gas blow-by. If the charge is too big to fit in the charge holder I just run the wires through as normal but use a larger container to hold the charge. One thing I've learned is to not let the recovery harness wrap around the charge holders otherwise the charge holders can break off. I now cover the holders with a nomex blanket and then load in the recovery gear.

I've even screwed two sleds together to make a redundant setup for a 3" min diameter 3" rocket. I also have a couple of sleds that have a Raven and Stratalogger CF with lipo batteries so I can do dual deploy with a single sled. In the photo of a few of my altimeters you can see the screw switch epoxied in place. I also have sleds with Ravens and even an old ARTS 2. On the bottom altimeter the screws have been inset into an aluminum mount.


Tony

View attachment 311415View attachment 311416View attachment 311417View attachment 311418

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soopirV said:

Makes more sense now when you said earlier that you use the mounts but not the coupler. It seems then that PML sells the components separately? I like the modular nature since now that my fleet is growing I'm tying up more and more "motor money" in buying electronics, so I'm not messing about switching a computer from one rocket to another. It seems that this system is really useful on larger frames- 3" is the smallest possible in your experience?

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manixFan said:

I've used it with 54mm rockets. A tight fit but possible. As long as the screw switch is in the same place, the mounts move easily between rockets. With the newer, smaller altimeters it's a lot easier to get things to fit, especially using lipo batteries. Years ago a local hobby store went out of business and I bought all the CPR stuff they had at a good price which helped me standardize on this system. I'll try and post a setup in a smaller rocket later tonight.


Tony

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Steve Shannon said:

I've used the CPR3k system down to 54mm rockets also, but using the aluminum couplers. I like them and once went through a phase or fitting them to almost all of my rockets 4 inch and below, but with the aluminum couplers there is a weak point where the aluminum coupling abuts the centering ring. If the phenolic tube shears there the altimeter or its sled becomes a structural member for a short time.
If the male thread coupling half had a rebated shoulder and could be let into the centering ring it would completely prevent that. An alternative would be to use a G12 tube instead of the slotted phenolic one PML provides. Hawk Mountain used to sell a CPR3k upgrade kit that did just that.
For smaller electronics the Estes plastic motor retainers could be made to work. For much larger electronics a 54mm threaded retainer could also be made to work.


Steve Shannon

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manixFan said:

Since the OP asked about smaller diameter, here's what I did for 38mm. The CPR system won't work smaller than 54mm so I decided to go with magnetic switches. Attached is a photo of the sled I used for a 38mm Min Dia rocket that flew on a Loki K627 to about 15,000' at BALLS last fall. It had redundant dual deploy in a very small area. A coupler was epoxied into the aft end of the ebay. The sled slid into the A/V tube and the fore end was retained by a reinforced coupler that was held in place with plastic rivets. So no all-thread was needed. I used the same design in two 38mm rockets and it worked well but was a pain to wire the ejection charges. The other rocket flew on a CTI Mellow Yellow I55.

Both altimeters used magnetic switches so no holes were needed to arm the electronics. It took a bit of experimenting but using the smaller magnet I was able to arm each switch separately. Both flights were successful and I plan on flying them again this fall except with a CTI J150 Mellow Yellow in place of the I55.

Yet another way to get it done.


Tony

38mm Dual deploy redundant altimeter setup. Using LiPo for power and Featherweight magnetic switches. (Hold-down for smaller LiPo is not shown, but you can see the screw hole for the retainer.)
View attachment 311458

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