Avionics Bay and Pull-pin switch Question

[gldknght]

So, I've replaced my old push button switches with a couple of pull pin switches. But this leads me to a question. The switches powering the altimeters turn on when the pin is pulled out. So off when the pin is in. This makes arming both of my altimeters with one pull pin on the pad, very easy to do.

My question for you guys who use this type of set-up: when I'm prepping the rocket for flight, I have to install the ejection charges with the av-bay out of the rocket. I have the avionics bay closed up and the pin installed when I hook up my eject charges. But when I install the av-bay in the top half of my rocket, I will need to pull the pin out in order to slide the bay into the rocket. But this arms my altimeters with live ejection charges when I'm not at the pad. It's possible to slightly pressurized the av-bay, just sliding it into the rocket as the fit is quite tight. Then when all the holes line up, the bay could de-pressurize. This scares the B-G-bers out of me.

So how do you guys deal with this?

Please see attached photos, the switch set up is the orange thing on the right side:

 

[DarthMuffin]

How about a second power switch in series with the pull pin? Like a screw-in switch on the nearby bulkhead.
Personally I just don't put the av-bay in when the rocket body is "sealed" on the other end, for example don't put the motor in. That way if the ejection charge goes it will just pop gas out the far end. A change of underwear and you're back in action, no harm.

 

[Voyager1]

Typically you would use a switch band midway along the avbay so that you have equal aft and forward coupling either side of the switch band. The pin goes through the switch band. It appears that you don’t use one, so that does makes it trickier for you.

 

[gldknght]

Typically you would use a switch band midway along the avbay so that you have equal aft and forward coupling either side of the switch band. The pin goes through the switch band. It appears that you don’t use one, so that does makes it trickier for you.

Yeah, this rocket was built more then 10 years ago, and is all fiberglass, so no way to add a switch band. Plus, putting the switches in the canter of the av-bay sled would require a complete redesign of the sled, and I'm not certain there is even a way to do it. My av-bay sled isn't long enough because of having two altimeters.

I saw a similar thread where someone suggested using short wood dowels in the place of the pull pin when closing up the av-bay. I tested this with a couple short tooth picks, and it worked ok. I can assemble the av-bay with eject charges, the wood pins disable the altimeters. Then when the rocket is assembled, I use the RBF pin to push the wood pins out without arming anything. The wood pins just fall to the bottom of the av-bay and can be recovered post flight.

An alternate idea, I can put a dean's connector in series with the switches and route one wire off each switch out the bottom bulkhead. That way I can just disconnect the switches from each altimeter while I'm assembling the av-bay and eject charges. Dean's connectors have enough friction fit that they are not likely to disconnect from flight forces.

 

[gldknght]

Personally I just don't put the av-bay in when the rocket body is "sealed" on the other end, for example don't put the motor in. That way if the ejection charge goes it will just pop gas out the far end. A change of underwear and you're back in action, no harm.

That's good advice. I use the same procedure when using a JLCR in a rocket with a tight fitting nose cone.

 

[cerving]

Mount the pull-pin so that it lines up with the switch band. Prep everything and check continuity WITHOUT the powder in the charge wells, then close it up and put the disarming pin in. Fill up the charge wells and finish prepping your rocket. At no point in this procedure will you have power to the charges, and it will be safe until you pull the pin on the pad.

 

[gldknght]

Mount the pull-pin so that it lines up with the switch band. Prep everything and check continuity WITHOUT the powder in the charge wells, then close it up and put the disarming pin in. Fill up the charge wells and finish prepping your rocket. At no point in this procedure will you have power to the charges, and it will be safe until you pull the pin on the pad.

This isn't possible. Please re-read post number 4. Also see the photos posted in post #1.

 

[Rocketclar]

I've used pull-pin type switches and have put another switch in line for the reasons you state. However, you might be able to insert a small dowel/rod to close the switch while prepping and then when assembled you can push out the dowel with the regular pin. When ready for flight, pull the regular pin.

 

[gldknght]

I've used pull-pin type switches and have put another switch in line for the reasons you state. However, you might be able to insert a small dowel/rod to close the switch while prepping and then when assembled you can push out the dowel with the regular pin. When ready for flight, pull the regular pin.

Yes, as stated in post 4 above, I already figured that out.

 

[Handeman]

I use a screw switch in series with the pull pin that is accessable from the shoulder that inserts into the booster section. I turn that off to power everything down when installing all the matches. Once all the matches are connected, I power up the altimeter to test that the matches have the right continuity beeps. Then everything is powered off again by the screw switches and the powder charges are added. Add the shock cord connection and payload tube to the upper part of the av-bay. Once all prep is complete and the upper section with the payload and main is ready to connect to the booster with the apogee charge and chute, I install the pull pins and turn on the screw switches and immediately take the rocket to the RSO. Nothing is ever powered up after the matches are tested until it's on the pad and the pins get pulled.

The one thing that can happen is you forget to turn on the screw switches when you put the pull pins in and assemble the rocket. If this does happen, nothing will power up when you pull the pins on the pad. Been there, done that, and this is why I locate the screw switches on the shoulder close to the switch band. That way you can lift the upper section slightly without pulling it completely apart and turn on those screw switches.

 

[Rocketclar]

Sorry, I should have looked more closely to the other posts. Good luck with your setup.

Yes, as stated in post 4 above, I already figured that out.

 

[OZRoc]

You can also have a piece of material same dia as the pull pin resting inside the switch slide. Have an exit hole this can be pushed through. Do all the prep and connections and button up. Push the spare rod out with your pull pin and bob's yer uncle.
Cheers

 

[OverTheTop]

I have used a wooden skewer in place of the RBF pin during prep. After the rocket is assembled you can pull the skewer out with a dental pick and insert the RBF pin.

Remember PPE. I keep a face shield and ear muffs on during the changeover.

After changeove the RBF tag is taped to the airframe to make sure it doesn't fall out on the way to launch.

 

[Donnager]

The ones I have like this without a switch band have either a hole drilled right at the seam or a half moon above/below it. I can have my pin in throughout assembly.

You may be able to relocate the switches a little and remove the issue, although the dowel/skewer options work.

 

[SolarYellow]

This isn't possible. Please re-read post number 4. Also see the photos posted in post #1.

I haven't handled your setup with my hands, but based on the photos you provided, you have a massive amount of space in that ebay and I have to disagree that it isn't possible. I don't really see any difficulty in doing it at all. You'd need to start over and lay out all the pieces with the goal of doing it that way, but it appears totally doable to me. The switch band around the outside of the ebay only needs to be ~1/4-inch wide, enough for the pin hole and a little on either side.

 

[Donnager]

I haven't handled your setup with my hands, but based on the photos you provided, you have a massive amount of space in that ebay and I have to disagree that it isn't possible. I don't really see any difficulty in doing it at all. You'd need to start over and lay out all the pieces with the goal of doing it that way, but it appears totally doable to me. The switch band around the outside of the ebay only needs to be ~1/4-inch wide, enough for the pin hole and a little on either side.

I think he could move the pin switch to the seam, and not even worry about the band, but that may result in bodywork/cosmetic issues. I have three without a band, and one has the pin in the LOC MMAS, inserted from the bottom/rear.

Keeping the switches closed during ebay assembly is the biggest problem I've had with these setups. The second one is keeping the pin in during transport. Because of this, I normally leave my batteries disconnected until I am at the field, and don't worry about the pins in transport. At the field, the pins go in, get taped/restrained, and then the charges and batteries are connected.

If you are using one pin for two altimeters, pull it slowly so you can hear them both. Keep your pin with you when you go for recovery.

 

[David Schwantz]

I do NOT use a switch band on many rockets. Just put the pull pin switch in the joint of the 2 tubes.

 

[David Schwantz]

Looking at your sled, I think you could easily move the pull pin switch. Remove it from its location and remount it in the space right next to those 2 empty black standoffs that are there. Lay it flat, don't stand it up. Before that, install bay into rocket and mark the spot in the joint where the pin will come out. Now, run a line around the bay at that location, install sled into bay and align where the pin will need to be on the sled. Drill hole, mount new switch location and you are done.

 

[scschulte]

I have gone to "PUSH PIN IN to arm" switches. The switches are solid and the pin cannot come out without a lot of pulling. So my rocket has "INSERT PIN BEFORE FLYING" taped on it at pad (instead of "Remove Pin"). (This has the advantage of never being armed when prepping the avbay and putting in the Black Powder charges). On redundant dual-deploy I use one of these "Insert pin to arm" switches and one screw-to-arm switch. Remove to arm type switches are, in my opinion, too easy to inadvertently remove prior to going to the launch pad. Not sure you could replace your "pull pin switch" with a "push pin" one.

 

[David Schwantz]

Not that I agree with how you are doing it, but the pull pin switch is changed to a push pin one simply by changing the solder contacts to one lead on the middle terminal.

 

[scschulte]

What don't you not agree with? Is it: "Push in a pin and leave it there during the flight to arm"?

Thanks - I'm learning all the time and appreciate any comments.

Steve Friday 10 November 2023

 

[David Schwantz]

Yes, I like pull pin. And not that you are wrong doing it your way, I just like doing a pull pin. It does not leave a pin on the outside of the airframe. Also, would not want it to vibrate out during flight and shut off altimeters. Again, with your second switch, the screw to arm one, that is also another point of failure.

 

[scschulte]

Thanks for your comments. The "push-to-arm" switch I use is solid. The pin extends 3/8" from the airframe (my cameras extend a lot more than that) and in order to remove the pin, I have to screw-in an extension to the tip of the pin, then pull it out. I've flown this 6 times in the last few months and the pin doesn't move.

I use several screw switches and agree that these can be points of failure. But the new type I'm using is not a threaded screw rather a true switch. I insert a small flat-head screwdriver and turn the switch 90° and it clicks into the ON position. Essentially impossible to have it click back to the OFF position but I'll be testing this switch in flight (only using as a backup on a redundant dual deploy for now) to see.

And I will consider a "remove to arm" pull-out pin switch. If you have any that you can recommend, I'd like to give them a try. (I made some that PerfectFlite discusses in the StrattoLogger CF manual, but find those too fragile).

Thanks again,

Steve Friday 10 November 2023

 

[David Schwantz]

I like the ones from LabRat rocketry. They come in 1,2, or 3 switch models.


https://www.labratrocketry.com/product-page/pull-pin-switch-kit

 

[Handeman]

I'll stick with the pull pins and parallel screw switch to keep if off during setup. It's simple and safe. Nothing on while prepping and only have the pull pins keeping everything off will going from the bench to the RSO to the pad.
YMMV

 

[DaHabes]

I use two different methods. For a single or double double pull-pin switch, I just use a standard round toothpick, which is the perfect length for the double switch (cut it down for the single switch). After the AV-Bay is buttoned up, push the real pull-pin into the switch and push the toothpick out the other side. For a triple pull-pin switch, I bought a 3' length of stainless steel rod from McMaster-Carr the same diameter as the pull-pin. Cut a piece to length that is slightly shorter than the diameter of the AV-Bay. Once buttoned up, push the interim pull-pin out using the real pull-pin.