How to install pull pin switches without arming avionics?

[Iamtannorv]

I was looking at getting and using the pull pin switches from lab rat rocketry for my avionics bay but a possible issue that has occurred to me is how would you install the pin through the av bay holes without inserting an armed sled into the av bay? My understanding is that the AV sled would have to be in place inside the bay before the switch is installed, but before installing the pin it would be powered on. How do you avoid this?

 

[DarthMuffin]

Do it before you install the motor, and before connecting battery and/or the ejection charges if possible, and just use some common sense safety. Don't put your hand on ejection charges and don't point the loaded cannon of a rocket tube at anyone, including yourself, before you can insert the pin.

If you're really worried, make a pin the width of the body tube. Insert that before anything. Then use the real pin to push that one out the other side, should stay disarmed the whole time.

 

[Steve Shannon]

Don’t add the BP until after the bay is assembled and the pull pins are inserted.

If you use a terminal strip on the bulkplate you can even wait until everything is assembled before adding the electric matches.

 

[cerving]

Don’t add the BP until after the bay is assembled and the pull pins are inserted.

If you use a terminal strip on the bulkplate you can even wait until everything is assembled before adding the electric matches.

^^^ THAT ^^^

 

[David_Stack]

I faced this same question in the build of my first bay, complicated by the fact that I was not using terminal blocks (ematches wired directly to the altimeter), nor a switch band (https://www.rocketryforum.com/threads/avionics-bay-feedback-needed-lengthy-diatribe.170864/).

Ended up implementing the solution proposed by member "Handeman": "I also add a screw switch in series with my pull pin. The access hole for that is in the should that slides into the booster. That way I can turn off everything without having to have the pull pin in place. I seldom open my av-bays so I just turn it off with the screw switch, attach the ematches. Turn on the altimeter to get a battery voltage reading and ensure 3 beeps for the two ematches. Turn off the screw switch, load the powder, insert the pull pins and turn the screw switches on when I close up the rocket before heading to the RSO."

 

[Cl(VII)]

Don’t add the BP until after the bay is assembled and the pull pins are inserted.

If you use a terminal strip on the bulkplate you can even wait until everything is assembled before adding the electric matches.

This!!!! Keep in mind that this type of switch is not suitable for every rocket. For instance, if you don't have a switch band, i.e. you have a bay that slides completely inside a body tube, these are not safe for that application as there is basically no good way to handle the bay without charges and live altimeters without adding additional means of power disconnection. I'd much rather people use the correct switch for their application, even if it isn't mine, and they stay safe.

That said, if they are suitable for your rocket, they are hella cool, and I have plenty of each variety in stock and ready to ship.

 

[Reinhard]

What I did the last time, was to ensure I can at least partially disassemble the avionics bay with the pin in place, so that I can connect and disconnect the battery without powering the altimeter.

On a club project, a member made two-part pins that screw together (think multi-part launch rods). With only the inner part of the pin installed, the avionics bay can be assembled without powering the altimeters. It feels slightly fidgety to me, but it works.

Reinhard

 

[OverTheTop]

I generally use wooden skewers in the pin switches whilst working on the avionics on the bench. They can be cut short enough so they allow the avionics to slide in and out of the airframe avionics section. I use two pin switches usually, one for safeing the eMatch and one for powering the altimeter. If either is out the BP won't go off. Once the module is assembled I can reach in through holes in the airframe with tweezers or needle-nosed pliers and pull the pin out, then quickly replace it with the real RBF pin. Repeat for the second pin and the bird is ready for flight.

I always wear a face shield when doing this, or not install the BP till later. I always wear a face shield when dealing with BP.

 

[Ted Cochran]

Those switches are double pole, right? So you could wire them to be closed when the pin was in and arm the electronics by pushing the pin in, not pulling it out.

If the switch cradle had a threaded mount at the far end, and if the pull pin was a long bolt, then you could arm the electronics by screwing in the bolt, and more importantly, disarm the electronics by removing the bolt, no special tools required. That could be helpful if someone finds the a lost rocket and wants to disarm it before moving it.

 

[OverTheTop]

Those switches are double pole, right? So you could wire them to be closed when the pin was in and arm the electronics by pushing the pin in, not pulling it out.

If the switch cradle had a threaded mount at the far end, and if the pull pin was a long bolt, then you could arm the electronics by screwing in the bolt, and more importantly, disarm the electronics by removing the bolt, no special tools required. That could be helpful if someone finds the a lost rocket and wants to disarm it before moving it.

I have been known to do that, with a note "remove screw to disarm electronics" written in permanent marker on the airframe. Very useful if a rocket is lost.

 

[Ted Cochran]

Yep. With the added advantage that the screw holds the actuator in position, making the likelihood of a bouncing contact pretty low.

 

[Cape Byron]

I have been known to do that, with a note "remove screw to disarm electronics" written in permanent marker on the airframe. Very useful if a rocket is lost.

This is now engraved on a small part of my brain for future reference. It makes a lot of sense.

 

[Pem Tech]

I faced this same question in the build of my first bay, complicated by the fact that I was not using terminal blocks (ematches wired directly to the altimeter), nor a switch band (https://www.rocketryforum.com/threads/avionics-bay-feedback-needed-lengthy-diatribe.170864/).

Ended up implementing the solution proposed by member "Handeman": "I also add a screw switch in series with my pull pin. The access hole for that is in the should that slides into the booster. That way I can turn off everything without having to have the pull pin in place. I seldom open my av-bays so I just turn it off with the screw switch, attach the ematches. Turn on the altimeter to get a battery voltage reading and ensure 3 beeps for the two ematches. Turn off the screw switch, load the powder, insert the pull pins and turn the screw switches on when I close up the rocket before heading to the RSO."

Ohh, I like this solution.

 

[MidOH]

The pins are through my switch band. They don't interfere with the payload tube attachment.

It's not like your charges are going to blow your head off. And static electricity could still pop them during assembly regardless. Don't attach the nose cone until you get the pins in, and don't point the tube at your face.

 

[Pem Tech]

Don’t add the BP until after the bay is assembled and the pull pins are inserted.

If you use a terminal strip on the bulkplate you can even wait until everything is assembled before adding the electric matches.

Okay, I'm having a little trouble seeing this. A diaphragm or photo would be grand.

 

[Titan II]

 

[Pem Tech]

View attachment 513396

Shweet!
Thanks...

 

[Tractionengines]

The main thing with all of this stuff is respect it, not fear it. The key is exactly what is in this thread, " think thru the process " and minimize risk while not making something so "involved" that you make it more likely to have a failure. Always watch were things are pointed anytime there is "contained" black powder.

You can have an AV bay without a switch band, and still use a screw switch, or pull pin switch. Locate the pin or screw hole "RIGHT AT" the body tube joint. Use this as the alignment means for assembly of the payload bay to the booster. This way you can have the pin thru the AV Bay, slide it into the payload bay. The pin "seats" into a corresponding half circle in the payload bay tube and this should line up you screws/rivets/ etc. Then the assembly slides into the booster, and the other half of the pin "seats" into half circles there, aligning your shear pins (if used).

NOT THAT I AM SAYING SKIMP ON SAFETY... But I shoot traditional flintlock rifles. I intentionally have a flash pan worth of 4F black powder, with tiny bits of steel and flint added in for good measure; going off less than a foot from my eyes & ears . Yes at the range: safety glasses, and hearing protection, but out hunting, maybe sunglasses... Could something go wrong, yes. That is a risk I take to enjoy another one of my hobbies.

 

[Chad]

I generally use wooden skewers in the pin switches whilst working on the avionics on the bench. They can be cut short enough so they allow the avionics to slide in and out of the airframe avionics section. I use two pin switches usually, one for safeing the eMatch and one for powering the altimeter. If either is out the BP won't go off. Once the module is assembled I can reach in through holes in the airframe with tweezers or needle-nosed pliers and pull the pin out, then quickly replace it with the real RBF pin. Repeat for the second pin and the bird is ready for flight.

I always wear a face shield when doing this, or not install the BP till later. I always wear a face shield when dealing with BP.

I was just thinking. Imagine a wooden skewer cut to the length of the switch, you insert that as your assembly first step then connect power to your electronics. Then you finish putting everything together and go for flight. Then, as your last step, you insert the real pin which pushes the wooden skewer out but never arms the electronics because the real pin is right behind holding the switch closed. However, now when you pull the real pin out the wooden skewer is no longer there and the electronics arm as expected. Granted, you have a small wooden skewer bouncing around your ebay during flight but wood isn't conductive and it's not really going to damage anything.

 

[jd2cylman]

That’s a good idea. But in my case, I’ll need two short chunks, since I’ve got the dual switch mount. I used a long one then assembled the bay, then pulled it out and put the rod in. I let the altimeters power up for the allowable 10 seconds before powering down.

 

[DaHabes]

The way I'm doing it on my latest build is to use round toothpicks in the LRR switches while I assemble the AV-Bay and plug in the batteries. They are a perfect fit for the switches. The reason I am doing it this way is because it is a nose cone AV-Bay recessed into the nose cone (the main bulkhead is epoxied to the nose cone and 6 2-56 wood screws are screwed and epoxied into the bulkhead through the nose cone (the screw heads are tapered and slightly recessed into the nose cone and lightly epoxied over the top). The reason for all this is this is a short, fat rocket with a 54mm MMT and I need the space for the laundry. I need the AV-Bay for apogee deployment and my tracker, since it will be out-of-sight on the biggest motors I can put in it. I have to load the BP before I assemble the removeable bulkhead into the nose cone because there isn't enough room to add the BP afterwards (even with a 4" nose cone, just too tight). Once the bay is assembled into the nose cone, pushing the pin into the switch forces the toothpicks to fall out as the pin engages the switches (before the toothpicks release the switches).

There is no reason you couldn't use this approach on a regular DD AV-Bay as well. You use the long pin and push it all the way through the rocket. The toothpicks fall out the back side upon exiting the AV-Bay. Having a screw switch precede the LRR switches is a fine approach, but every connection point is a failure point. Minimizing connections improves reliability.