Switch band-less Av Bay - any experience?

[soopirV]

Hi all- I'm trying my smallest DD build yet, in a 1.6" Madcow Mini DX3. All of my other DD builds have used a conventional switch band, but this time I want to streamline it and ditch the band. By virtue of its name, the band is intended to hold the switches, ports and whatnot, but it also seems likely to transfer and spread the forces from the drogue ejection? If I secure my bandless avbay in the payload tube with 3-4 #6 machine screws into threaded inserts in the bay, the ejection/shock force will be concentrated on those small areas. I wasn't planning on fiberglassing the tubes, but if I do, then this concern is mitigated. What have others done? Am I overthinking this?

Thanks!

Dave

 

[DAllen]

I really like to make e-bays without the switch band only because this is a cleaner look. One thing I've done in addition to some sort of a mechanical connection to the upper airframe is to cut about a 1" long piece of coupler and glue it into the lower airframe right where the ebay will end. This way, the ebay will have a super duper solid point to rest against during thrust phase. Starting at post #20 in this thread:

https://www.rocketryforum.com/showt...rrior-Upscale&highlight=solar+warrior+upscale

I go into a little bit more detail on post #40 on this thread:

https://www.rocketryforum.com/showthread.php?123646-Four-inch-BSD-Thor-clone/page2

Hope that helps!

-Dave

 

[Mendal]

I'm interested in hearing what others have to say on this topic. I am starting a build on a PML Miranda that I am converting to Dual Deploy. I was planing the same thing, I was going to use plastic rivets or machine screws to hold the payload bay to the coupler/av-bay. My rocket is a 3" Quantum Tube rocket so I'm not sure if that will make a difference or not.

Mendal

 

[DAllen]

I'm interested in hearing what others have to say on this topic. I am starting a build on a PML Miranda that I am converting to Dual Deploy. I was planing the same thing, I was going to use plastic rivets or machine screws to hold the payload bay to the coupler/av-bay. My rocket is a 3" Quantum Tube rocket so I'm not sure if that will make a difference or not.

Mendal

On anything 3" or larger I am using machine screws with a blind nut attachment of some sort on the inside. I've used the rivets before and they drive me nutty. Seems like they are either way too loose or so freaking tight a tool is needed to pry them out and then with my fumble fingers I manage to scratch the paint.

 

[Worsaer]

I've had success using PEM nuts on fiberglass airframes to retain a band-free AV Bay. No problem with recovery forces, even under extreme, high-speed recovery deployment events. I prefer low profile stainless Torx machine screws.

 

[rfjustin]

I've had success using PEM nuts on fiberglass airframes to retain a band-free AV Bay. No problem with recovery forces, even under extreme, high-speed recovery deployment events.

This. Switch bands are not necessary, but some folks prefer them. OP, you wont have any issues without a switch band, just make sure you ground test your final configuration.

 

[Wizard]

I just use the plastic rivets. I'd have to look at home to see which diameter, but the ones I use fit a 5/32 hole nearly perfectly. One key for cardboard airframes is to harden the hole with CA then clean it up again with a drill bit. For 4" and smaller diameter I use 3, for 5.5"/6" airframes I use 4. Never had an issue.

David

 

[DAllen]

And don't let my opinion discourage anyone from using plastic rivets. I just don't like them as a matter of personal preference.

 

[Bat-mite]

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.

 

[soopirV]

I really like to make e-bays without the switch band only because this is a cleaner look. One thing I've done in addition to some sort of a mechanical connection to the upper airframe is to cut about a 1" long piece of coupler and glue it into the lower airframe right where the ebay will end. This way, the ebay will have a super duper solid point to rest against during thrust phase. Starting at post #20 in this thread:

https://www.rocketryforum.com/showt...rrior-Upscale&highlight=solar+warrior+upscale

I go into a little bit more detail on post #40 on this thread:

https://www.rocketryforum.com/showthread.php?123646-Four-inch-BSD-Thor-clone/page2

Hope that helps!

-Dave

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 . 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.

 

[soopirV]

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.

That's interesting, I didn't realize that's how they did it. Not sure i"d be able to do that so successfully on a small diameter, but maybe!

 

[Buckeye]

Hi all- I'm trying my smallest DD build yet, in a 1.6" Madcow Mini DX3. All of my other DD builds have used a conventional switch band, but this time I want to streamline it and ditch the band. By virtue of its name, the band is intended to hold the switches, ports and whatnot, but it also seems likely to transfer and spread the forces from the drogue ejection? If I secure my bandless avbay in the payload tube with 3-4 #6 machine screws into threaded inserts in the bay, the ejection/shock force will be concentrated on those small areas. I wasn't planning on fiberglassing the tubes, but if I do, then this concern is mitigated. What have others done? Am I overthinking this?

Thanks!

Dave

Overthinking? A little bit. A switch band is just a convenient way to mount rotary and key switches on the airframe, and to exchange ebays between different rockets. It is not necessary and provides no additional structural support. The shear forces are carried by whatever you use to hold the coupler in the payload bay - glue, rivets, screws, etc.

For your 1.6" cardboard tube, you will be fine with 2 plastic rivets or 2 #4-40 screws and tnuts. I have done both with my LOC Weasel clone.

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.

Never heard this called the "Giant Leap" method. I like this method if I can get my arm down the tube to adjust and seat the bulkhead firmly. Though, the tiny Featherweight ebays use this method, too.

 

[Steve Shannon]

Overthinking? A little bit. A switch band is just a convenient way to mount rotary and key switches on the airframe, and to exchange ebays between different rockets. It is not necessary and provides no additional structural support. The shear forces are carried by whatever you use to hold the coupler in the payload bay - glue, rivets, screws, etc.

For your 1.6" cardboard tube, you will be fine with 2 plastic rivets or 2 #4-40 screws and tnuts. I have done both with my LOC Weasel clone.



Never heard this called the "Giant Leap" method. I like this method if I can get my arm down the tube to adjust and seat the bulkhead firmly. Though, the tiny Featherweight ebays use this method, too.

So is your arm in the tube with the charges?

 

[ksaves2]

Oh GOSH! Another thread on switches!:jaw::wink:

Um, if I want to go "switch-band-less" I epoxy a short width of coupler down the end of the the sustainer to act as a thrust block. You have a heavy glass ebay and a really hot motor you may make the holes in the upper bay tube
larger. A thrust block eliminates that. Yeah the tube will be constricted just a tad but you're just trying to get the harness and the small drogue out. You can still go switchbandless and use switches...... I've put keyswitches mid
ebay like they were in a band and cut semi-circular notches in the upper and lower tubes so the tubes meet flush. Works fine.

If one is doing small cardboard rockets I think what Justin mentions is workable and likely successful or he wouldn't have mentioned it.

Oh, keep in mind if one is using magnetic switches or WiFi deployment devices/switches it would likely not pass muster on an L3 rocket without accessible mechanical switches. NAR rules require them and
TAPs may or may not. Just came off an intense discussion about switches in another thread mainly about directly plugging the battery into a Wifi/remote switch or magnetic switch,
buttoning up the ebay, activating the device remotely and flying. Perfectly safe and no less safe than a mechanical switch. In small rockets trying to get a switch in the bay comfortably
may be hard to pull off and connecting the battery to the switch or Quantum WiFi altimeter, closing the bay activating the device and directly flying onsite is safe.

At the risk of making myself flame bait the applicable thread starts here: https://www.rocketryforum.com/showthread.php?5705-Altimeter-Bay-Pics&p=1664590#post1664590

It will either reinforce one's idea that mechanical switches are absolutely necessary or be food for thought that they don't necessarily guarantee safety. Kurt

 

[JimJarvis50]

Might not be applicable for the OP, but I don't use a break in the tube (or two of them in the case of a switch band) at the point where the bay is located. Instead, I just slide the avbay "package" into position, sitting on a ring or bulkhead, and access the on-board switches through holes in the air frame. With one exception, all of my rockets are like this.

Jim

 

[FredA]

Jim,

I've done this on a few rockets.
I've found that after a handful of flights the tubes get pretty ugly on the inside and insertion/removal of the Ebay becomes a pain.
Also - can be really hard on small diameter rockets to reach inside to position the EBay.
Not so much of a problem if you don't mind drilling more holes in your Ebay for the screws that hold it in place, but if you are trying to hit the same holes over and over, getting the Ebay positioned just perfectly can be frustration.

But this method does yield a superior strength, more aerodynamic result.

 

[jimzcatz]

Short and sweet answer, I have never used a switch band in any rocket I have built.

 

[JimJarvis50]

Jim,

I've done this on a few rockets.
I've found that after a handful of flights the tubes get pretty ugly on the inside and insertion/removal of the Ebay becomes a pain.
Also - can be really hard on small diameter rockets to reach inside to position the EBay.
Not so much of a problem if you don't mind drilling more holes in your Ebay for the screws that hold it in place, but if you are trying to hit the same holes over and over, getting the Ebay positioned just perfectly can be frustration.

But this method does yield a superior strength, more aerodynamic result.

I always clean the tubes between flights. Wouldn't work otherwise. I have several ways of attaching the bay to the tube including screws or just connecting to a bulkhead. Smaller tubes can require some creative harness work.

Jim

 

[Buckeye]

So is your arm in the tube with the charges?

Umm, yeah. And?

 

[DAllen]

Umm, yeah. And?

:y:

You do like your fingers right?

 

[Buckeye]

:y:

You do like your fingers right?

Charges are not hooked up. The top bulkead with charge gets lowered into the coupler from the top of the payload tube (this is when my arm is down the tube). Then, wires are connected to the altimeter, sled put on all-thread, and av-bay is buttoned up. Is there a better way? I am all ears.

 

[DAllen]

Charges are not hooked up. The top bulkead with charge gets lowered into the coupler from the top of the payload tube (this is when my arm is down the tube). Then, wires are connected to the altimeter, sled put on all-thread, and av-bay is buttoned up. Is there a better way? I am all ears.

I donno...I've never built an e-bay that way. :confused2:

 

[jimzcatz]

All of my ebays are permanently mounted, not removable. The only rocket I have with a removable ebay was built by CJ. I use sheer pins to secure the main section.

 

[Bat-mite]

Charges are not hooked up. The top bulkead with charge gets lowered into the coupler from the top of the payload tube (this is when my arm is down the tube). Then, wires are connected to the altimeter, sled put on all-thread, and av-bay is buttoned up. Is there a better way? I am all ears.

Whether the charges are hooked up or not, you don't need to reach down inside the tube! Make sure your T-rods stick out far enough that when the sled is slid down, you can grab the T-rods and pull it into place from the other end.

 

[Steve Shannon]

Charges are not hooked up. The top bulkead with charge gets lowered into the coupler from the top of the payload tube (this is when my arm is down the tube). Then, wires are connected to the altimeter, sled put on all-thread, and av-bay is buttoned up. Is there a better way? I am all ears.

I was just wondering if your fingers were in there with charges that were connected. No criticism intended; I'm just old and cautious.


Steve Shannon

 

[Buckeye]

Agreed on pulling on the rods. Sometimes it just needs a little more force and a twist to align with the switch hole. This is often easier from the top. Hey, I can go both ways! Not that there's anything wrong with that....

 

[FredA]

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.

The secondary reason is that over time no matter how much you clean, the tube surface gets worn and pitted and installation gets harder because you need to slide the Ebay past the less-than-smooth surface. This means more time spent futzing to get the Ebay positioned which is more time futzing with the "hot end" holding the charges. I do like the idea of securing it to a bulkhead to eliminate the need for screw-hole-precision in alignment, but you still need to get the switch holes aligned, so there is always some tweaking needed, usually by putting your hand down the hole and turning which can be scary. Another reason to disconnect and shunt your charges.

But I do understand it's merits for high velocity flights - will do this on our sustainer for Balls this year.

 

[JimJarvis50]

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.

The secondary reason is that over time no matter how much you clean, the tube surface gets worn and pitted and installation gets harder because you need to slide the Ebay past the less-than-smooth surface. This means more time spent futzing to get the Ebay positioned which is more time futzing with the "hot end" holding the charges. I do like the idea of securing it to a bulkhead to eliminate the need for screw-hole-precision in alignment, but you still need to get the switch holes aligned, so there is always some tweaking needed, usually by putting your hand down the hole and turning which can be scary. Another reason to disconnect and shunt your charges.

But I do understand it's merits for high velocity flights - will do this on our sustainer for Balls this year.

I think if the tube is cardboard, some of your concerns are valid (with respect to the quality of the tube surface). That's why I don't know if the technique is applicable for the OP. However, for fiberglass or carbon, I don't recall ever having seen deterioration that would affect inserting the bay, although pulling it out after a flight can be another matter and can require a little pre-cleaning before the bay can be removed.

I have several ways of holding the bay in position. One way is to have a thick plywood bulkhead on one end of the bay or the other. This can be held in place through the air frame. I use socket screws, which results in a very strong connection (see the pics for an example). The bay can sit on a coupler ring in the tube, but it isn't even necessary to do that except as a register for positioning the bay. That is, the socket screws are sufficient to hold the bay in position, but I typically install a ring anyway.

With just a ring in the tube, the bay can be inserted with the harnesses attached on both ends. If you pull/manipulate the harnesses, it isn't hard to align the holes to secure the bay. With two- and three-stage rockets at high speeds, tube breaks are bad news.

Jim

 

[soopirV]

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.

The secondary reason is that over time no matter how much you clean, the tube surface gets worn and pitted and installation gets harder because you need to slide the Ebay past the less-than-smooth surface. This means more time spent futzing to get the Ebay positioned which is more time futzing with the "hot end" holding the charges. I do like the idea of securing it to a bulkhead to eliminate the need for screw-hole-precision in alignment, but you still need to get the switch holes aligned, so there is always some tweaking needed, usually by putting your hand down the hole and turning which can be scary. Another reason to disconnect and shunt your charges.

But I do understand it's merits for high velocity flights - will do this on our sustainer for Balls this year.

I'm having a hard time visualizing JimJ's procedure, even with Fred's additional explanation...I think I get it (in that it's similar to what DAllen mentioned at the outset), but how is fuzzing of tubing any bigger of an issue in this manner than in the "traditional" employment of a switchband? That's where I think I'm stuck...I think

 

[Nytrunner]

I'm having a hard time visualizing JimJ's procedure, even with Fred's additional explanation...I think I get it (in that it's similar to what DAllen mentioned at the outset), but how is fuzzing of tubing any bigger of an issue in this manner than in the "traditional" employment of a switchband? That's where I think I'm stuck...I think

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?