Port and Switch Alignment

[kevin.mcgee]

Good morning,
I am going to start building my L2 project with dual deployment soon. My question is how do you make sure your static ports on AV bay align with the screw switches on the electronics sled?

 

[Donnager]

Measure 10 times, mark 5 times, drill once.

I have a couple AV bays where the sled can be rotated to align with the ports, and then tightened when the ports are aligned. This arrangement is the easiest one to get the screw switches aligned. I can tweak the sled location longitudinally to line it up the other direction.

Generally, I get a circumferential location by putting a card stock band on to trace a line, and use a couple of channels/angles to align along the rockets length.

On my fixed sleds, I seem to always be off by ~1/16" when I drill, but that is usually because of varied diameters of coupler and switch band, or bit walk if I didn't get a good start hole. I usually oversize the hole by a little because of this. I'd like to hear how others deal with it, though.

If you make a mistake, there's always more cardboard, fiberglass, epoxy, and body filler to make it right

 

[Nytrunner]

Careful design, careful measurement prior to irreversible actions, and careful placement in accordance with that design.

I make sure the switch is mounted at the appropriate vertical position on the sled, then to ensure that the switch is always aligned with the appropriate hole, I'll either make a witness mark on the lid and coupler (line drawn across the joint) or make a physical key so that the lid only fits one way

 

[Bowman]

Careful design, careful measurement prior to irreversible actions, and careful placement in accordance with that design.

I'll either make a witness mark on the lid and coupler (line drawn across the joint) or make a physical key so that the lid only fits one way

I did the witness mark on some of my rockets. Getting the sled aligned with the holes is always a challenge when prepping for flight. Sometimes requires four or five attempts to line-up.
I think future projects will incorporate the "key" approach, much more reliable to use.

 

[David Schwantz]

Before you drill any switch or vent holes, install an alignment pin between the booster section to avbay and then from payload section to avbay. This keeps everything in perfect alignment as yuou drill and install switches and vents.

 

[tfish]

Drill the hole then mount the switch to where the hole is.

Tony

 

[blackjack2564]

Drill the hole then mount the switch to where the hole is.

Tony

This!

 

[Tim51]

I don't have as much experience as some of the other posters, but personally I've found to my cost that witness marks and careful measurement that work fine on the bench can still lead to misalignments in the field - in one case at the pad, where for the life of me I couldn't access the switch and ended up standing down. Since then I've opted for keying with a small brass peg:

As you can see re @Donnager's point "If you make a mistake, epoxy, and body filler to make it right" is apposite here

 

[OverTheTop]

I have been known to use an LED inside the airframe to locate the hole position. Otherwise, as others have said, measure five times and drill once.

I also locate the airframe sections using steel or CF pins which simplifies assembly.
https://forum.ausrocketry.com/viewtopic.php?f=6&t=4612&start=51
If there are a lot of holes you can identify which had the switch with a vinyl decal.

 

[bobbyg23]

Drill the hole then mount the switch to where the hole is.

Tony

Exactly.

 

[Dudeman247.]

I have been known to use an LED inside the airframe to locate the hole position. Otherwise, as others have said, measure five times and drill once.

I also locate the airframe sections using steel or CF pins which simplifies assembly.
https://forum.ausrocketry.com/viewtopic.php?f=6&t=4612&start=51
If there are a lot of holes you can identify which had the switch with a vinyl decal.

View attachment 448278

What does RBF mean down under? Has a different meaning where I pound sand...

 

[OverTheTop]

Remove Before Flight. TLAs are context sensitive.

 

[Jimmy Neutron]

What does RBF mean down under? Has a different meaning where I pound sand...

Remove Before Flight

 

[Dudeman247.]

Remove Before Flight. TLAs are context sensitive.

Yes of course. Thanks

 

[Nytrunner]

What does RBF mean down under? Has a different meaning where I pound sand...

Rocket Boost Face

 

[Zeus-cat]

Magnetic switches from Featherweight. You only need to be close to get it to turn on.

 

[paulfecht]

The LED idea works. Just get a small button cell battery and an led. Mount on surface of switch with double-sided sticky tape and then close up the av bay and the led will project a circle on the translucent coupler.

 

[Tractionengines]

WiFi switches. You don't even need to wave the magnet at the right place...

 

[OverTheTop]

WiFi switches. You don't even need to wave the magnet at the right place...

Nice idea but power consumption makes it a no-go for me.

 

[mtnmanak]

A lot of great suggestions here and I would echo them. Drilling the hole, then mounting the switch to the hole is great idea, if your design allows you to do that. WiFi and magnetic switches also work very well.

However, I have been using pre-printed sleds in most of my rockets 4" and under and for my rockets 5" and up, I have been using a switch bracket design that I CNC. In those situations, you have to drill the holes to the switches.

Below are some photos of the switch bracket I made for an 8" AGM-33 Pike. The key to getting a good measurement for your switch holes is to measure radially from the center. In the photo below, the red circle shows how I lined up the switch bracket at the end of the ebay coupler and used a straight edge to measure from the center of the bracket to make the marks on the coupler. The lines were extended down the coupler and the positions of the holes drawn. Then I checked, checked and re-checked before actually drilling the holes. Also, I initially drilled 1/16" holes to ensure good alignment. The final holes in this case were 1/2". The initial 1/16" holes allowed me adjust the larger holes slightly if I was off in my initial calculations. And, I would recommend using a drill press. Final picture shows that everything lined up perfectly.

At the end of the day, there are just going to be times when you have to drill the holes to fit the switches, so getting that technique perfected is a good skill to have.

 

[ChicagoDave]

I've found a great little device that makes my life so much easier. Instead of drilling the hole where the screw switch will be, I put the screw switch where I drilled the hole. Way easier.

Surface Mount for Screw Switch – Additive Aerospace

Surface mounts for screw switch PCB's - you'll never have trouble arming a screw switch at the pad again.

Contoured to fit any tube perfectly, and holds the screw switch right at the air frame's surface.

Drill ac .3125" hole in airframe where you want the access hole.
Screw the switch to the mounting plate
Scuff the airframe ID and mounting plate with 220 grit sandpaper and clean with alcohol
Apply superglue to the mounting plate
Align and attach the surface mount adapter to ID of tube

 

[Cherrywaves89]

I've found a great little device that makes my life so much easier. Instead of drilling the hole where the screw switch will be, I put the screw switch where I drilled the hole. Way easier.

Surface Mount for Screw Switch – Additive Aerospace

I keep coming back to this post, and I understand how it’s mounted to the inside of the av bay, but I don’t understand how it’s wired up. How are you connecting this switch when you open and close the av bay?

 

[David Schwantz]

I believe the screw switch goes inside the couple and then lines up with a mating hole through the airframe.

 

[mtnmanak]

I keep coming back to this post, and I understand how it’s mounted to the inside of the av bay, but I don’t understand how it’s wired up. How are you connecting this switch when you open and close the av bay?

You need to have some kind of disconnect on the lines you solder to the screw switch and the lines you connect to the altimeter so you can connect/disconnect when you pull the e-bay apart.

Here is one where I used a JST connecter between the coupler mounted switch and the alitmeter:



I don't surface mount switches much anymore, but if I was going to do it today, I would use a longer lead to the switch and use these 3M connectors:



You can get them at Mouser:

https://www.mouser.com/ProductDetail/517-37303-A206-00EMB
https://www.mouser.com/ProductDetail/517-37103-A165-00EMB

 

[user 30299]

Drill the hole then mount the switch to where the hole is.

Tony

Amen Brother !

 

[user 30299]

When space allows it, I use a switch bridge or switch board to make the switch location and mounting easier. As stated above - drill the hole, then locate the switch.