Talk to me about switches and redundancy

Ok, building my first AV bay.
Question #1. What type of switch? I am looking at either Featherlight magnetic switches or LabRats double pull pin switch kit. Thoughts?
Question #2. How many do redundant altimeters? I am wanting to go all out, and for the cost (~$50) it seems cheap enough to increase my chances of success. Do those that have redundant systems, do you use different brands? I have heard that if one fails, the chance of both systems will fail if you use the same brand?
Thanks for the feedback.

I'll take a shot at this...

I personally haven't used any magnetic switches, so I can't address that. But I have used a set up very similar to the pull pin switch you posted. I liked it, it worked great. The very low mass of the switch actuator isn't susceptible to the G's your bird will encounter, this model seems easy to install and use, and has redundancy. It has the advantage of being a pull pin. Big red flag hanging off you bird, you probably won't forget to turn on the electronix.
Another alternative that worked well for me is the screw switch. Turn the screw down to contact the wires and you have continuity. Seems very resistant to vibration, and served me very well over the years.

Redundancy is your friend, and I like the way you think. I always recommended to my L3 candidates to mix electronix. If you match, and both units are from the same lot, and the manufacturer had some problem with that particular run, then both can fail, side by side. And don't think that doesn't happen, cuz it does. Keep both systems completely separate, with NO common points. Separate batteries, switches, and outputs. If there's a common point, Murphy will put the failure right there. I've got that tee shirt.

HTH. Best of luck with your project.

The featherweight mag switches work great. I have used them in countless projects. A couple of pointers: be sure you have adequate separation between two switches. I usually switch on altimeters one at a time so I can hear a startup ‘good’ beep sequence. You don’t want to inadvertently switch one off when enabling the second one.

Second, these switches default to ‘On’ when the battery is connected This is intentional, so that a temp loss of power during a flight does not result in powered off electronics. Be prepared with a magnet when connecting the battery so you can power it off.

Are switches absolutely necessary? Other than wasting battery/time by having to plug in the battery on the pad, are there any downsides to forgoing the switch totally? The more I look into it, the more headache/risk it seems switches add on smaller HPR rockets. I understand in NAR and Tripoli safety code it's called out that "[FONT=&quot]The function of onboard energetics and firing circuits will be inhibited except when my rocket is in the launching position"... would plugging in the battery on the pad meet this requirement?
[/FONT]

I have a Featherlight magnetic switch in a high power rocket and I like it.

Here are several tips for using them:

1) Before you mount the switch on an altimeter sled practice with the switch so you know where to pass the magnet over to activate it. Learn how far away your magnet can be for it to turn the switch on AND off.

2) I try to get the switch as close to the airframe as possible to ensure easy activation when the switch is inside the rocket.

3) IMPORTANT: Mark the location of the switch on the outside of the airframe so you know where to swipe the magnet. Otherwise you will look like a doofus out at the high power pad rubbing your magnet all over the outside of your rocket trying to turn it on.

4) I mounted my magnet inside a holder so it is easy to hold when passing over the rocket. The screws used to hold your switch to the sled can really attract those rare earth magnets you get with the switch.

Zeus-cat said:

3) IMPORTANT: Mark the location of the switch on the outside of the airframe so you know where to swipe the magnet. Otherwise you will look like a doofus out at the high power pad rubbing your magnet all over the outside of your rocket trying to turn it on.

Click to expand...

Do a little chant at the same time and tell people you're praying to the rocket gods.

Zeus-cat said:

I have a Featherlight magnetic switch in a high power rocket and I like it.

Here are several tips for using them:

1) Before you mount the switch on an altimeter sled practice with the switch so you know where to pass the magnet over to activate it. Learn how far away your magnet can be for it to turn the switch on AND off.

2) I try to get the switch as close to the airframe as possible to ensure easy activation when the switch is inside the rocket.

3) IMPORTANT: Mark the location of the switch on the outside of the airframe so you know where to swipe the magnet. Otherwise you will look like a doofus out at the high power pad rubbing your magnet all over the outside of your rocket trying to turn it on.

4) I mounted my magnet inside a holder so it is easy to hold when passing over the rocket. The screws used to hold your switch to the sled can really attract those rare earth magnets you get with the switch.

Click to expand...

You missed one of the most important tips when using magnetic switches.

Do not put the magnet in the same pocket as your credit cards.

I like the Fingertech Robotics switches. They are simple, and very robust.

I just made a lawn dart this past weekend, and the switches were one of the very few parts which were still usable. (not utterly and completely destroyed) And this was with a fire in the av bay from the LiPo batteries being mushed. There was enough impact force to remove many of the surface mount components from the boards. There was no nosecone to ease the penetration into the earth. This was a 4" diameter, sturdy bulkhead that was pile driven 16" into the ground. The nosecone landed safely, nearby in a bush. The switches still look pretty good, considering. I will not be using them again, but they are fine.

I do not see any real additional effort required between passing a magnet past a location on the airframe, and inserting a hex key into one of the switch band holes. Especially for a very dependable, old school fully 'analog' contact.

3 words - "twist and tape"

you know when you got a complete circuit, and you also can stand down your bird.
The ultimate in simplicity. Highly reliable unless you have problems twisting.....then check your wire...

cbrarick said:

3 words - "twist and tape"

you know when you got a complete circuit, and you also can stand down your bird.
The ultimate in simplicity. Highly reliable unless you have problems twisting.....then check your wire...

Click to expand...

Not reflective of my experience observing others who use the twist and tape method.

I have yet to witness a switch failure, read about them and people have told me about them, but the only failures I have witnessed first hand are twist and tape.

I really don't get it.

mpitfield said:

Not reflective of my experience observing others who use the twist and tape method.

I have yet to witness a switch failure, read about them and people have told me about them, but the only failures I have witnessed first hand are twist and tape.

I really don't get it.

Click to expand...

I'm similar, no experience with switch failures that I know of. As for twist and tape, I suspect any failures had nothing to do with the twist and tape method, but with other aspects of the systems. The same goes for switches. with all the failed DD i've seen, none was attributed to a failed switch.

With that said, my first DD was the pull pin switch and my L3 was also pull pins. Everything between has been screw switches. I haven't experienced any switch failures.
My prefered method is the pull pins in conjunction with screw switches. I like the "Remove Before Flight" ribbons hanging on the rocket. There's no doubt about whether you powered up the altimeters or not. I use the screw switches through the coupler as a master On/Off switch. It lets you turn everything off while prepping without having to have the pins inserted. You will also know exactly what you did or didn't do if you pull the pins on the pad and nothing happens.

I agree with most posts and excellent advice offered above. If cost is an issue, please realize that the magnetic switches are $25 each whereas the MW screw switch is about $3 and the featherweight screw switch is $5 each. Also, with respect to the magnetic switch separate 1s lipos (~150 mAh) is required for each switch. All of these switches in redundant fashion (along with twist and tape) are very reliable. Handeman's point about the pullpin switches with flags does make it easier to not screw up (pun intended) and to remember to activate the switch/altimeter. In addition, the pullpin switches can be attached to your sled easily (e.g. see Handeman's level 3 build-AV bay section) or by simply producing your own 3D enclosures (cost pennies) as I've printed and is displayed below. Each pullpin switch only costs in the range of $2. Good luck and have fun!
Fred,L2
ICBM member-Camden S.C.
KG4YGP

When I started using electronics a few years ago, I put switches in all my AV bays. Shruter switches, screw switches & even Wifi switches. Never any failure with the switches but just find that twist & tape is so much simpler and fewer failure points.

My favorate switch is the lowly Aerocon PCB switch. These are glued onto the sled is some manner and aligned with a hole in the air frame. The wires are soldered on and then potted in epoxy. There is literally nothing that can fail.

https://aeroconsystems.com/cart/switches/pcb-screw-switch/

I like the magnetic switches, but my experience with them is that after a time, they fail.

Jim

KC3KNM said:

Are switches absolutely necessary? Other than wasting battery/time by having to plug in the battery on the pad, are there any downsides to forgoing the switch totally? The more I look into it, the more headache/risk it seems switches add on smaller HPR rockets. I understand in NAR and Tripoli safety code it's called out that "[FONT="]The function of onboard energetics and firing circuits will be inhibited except when my rocket is in the launching position"... would plugging in the battery on the pad meet this requirement?
[/FONT]

Click to expand...

Yes, they are absolutely necessary. And no, plugging the battery in at the pad would not meet the requirement, even if this was possible.

A typical AV bay lives in a coupler tube joining two sections of airframe tubing and is bolted shut. And the batteries are usually not just plugged in on high power rockets, they are secured with additional reinforcements like cable ties, electrical tape, brackets or compartment lids to keep them from bouncing out of the battery box under extreme loads. All of this prep is done at the table...all you do at the pad is arm the electronics with some sort of switch.

And you need to think about the disarming sequence if you needed to scrub the flight. If you have to do anything more that open a switch, you are working on an armed rocket.

Chris_H said:

I like the Fingertech Robotics switches. They are simple, and very robust.

Click to expand...

+1. For mine they're the smallest footprint switch on the market that I trust. Featherweight screw switches are a similar form factor but I'm not sure I trust them for repeated use like I do the Fingertech switches. Anything larger I use MissleWorks screw switches. Historically I've used the below push button switch, both on my L3 as well as at Mach 2+ speeds. For the record they've never failed me.

Dad Man Walking said:

Yes, they are absolutely necessary. And no, plugging the battery in at the pad would not meet the requirement, even if this was possible.

A typical AV bay lives in a coupler tube joining two sections of airframe tubing and is bolted shut. And the batteries are usually not just plugged in on high power rockets, they are secured with additional reinforcements like cable ties, electrical tape, brackets or compartment lids to keep them from bouncing out of the battery box under extreme loads. All of this prep is done at the table...all you do at the pad is arm the electronics with some sort of switch.

And you need to think about the disarming sequence if you needed to scrub the flight. If you have to do anything more that open a switch, you are working on an armed rocket.

Click to expand...

I understand the avionics bay layout, however I should have been more clear on the execution. I was thinking along the lines of the arming plugs used in model aircraft, but installed on the rear bulkhead of the AV bay. Although, disarming it would involve removing the top half of the rocket to access the plug, which is unsafe.

Most everyone seems to have that one switch type that they trust, which makes choosing components for your first dual deploy setup a little daunting. I'm definitely going to research the switches posted here, I appreciate the help! Sorry for the FNG questions!

The advantage of a magnetic switch, as I can see, is that not much precision is necessary in locating the switch. The disadvantages of a magnetic switch are that it is a much more complex circuit, also involving a battery. In the real world, maybe the magnetic switches do not fail that often, or even, extremely infrequently.

A screw type switch like the fingertech, as I have just witnessed, effectively does not fail. It is like a 'twist and tuck', but with solder, almost. Yes, the fingertech switch requres a plan in order to align it with one of the vent holes in the switch band. No big deal. Part of the fun.

Wayco said:

We also use twist and tape switches for rockets that don't exceed mach 1. Sharon buried a 2.6" Blue Iguana flying on an L935 that had twist and tape switches. Ballistic from 20k ft. Sharon was not happy.
I was not happy, that was our last L935...
Most of our twist and tape rockets are short fat rockets that don't go fast. Some are rockets with small motor mount tubes, and don't go fast.

Click to expand...

Interesting. What failed?

JimJarvis50 said:

My favorate switch is the lowly Aerocon PCB switch. These are glued onto the sled is some manner and aligned with a hole in the air frame. The wires are soldered on and then potted in epoxy. There is literally nothing that can fail.

https://aeroconsystems.com/cart/switches/pcb-screw-switch/

I like the magnetic switches, but my experience with them is that after a time, they fail.

Jim

Click to expand...

I think we may be the only two users of these, because I never see them elsewhere! Super easy and solid. A long reach with a flat-blade screwdriver can be frustrating, though.

Buckeye said:

I think we may be the only two users of these, because I never see them elsewhere! Super easy and solid. A long reach with a flat-blade screwdriver can be frustrating, though.

Click to expand...

I assure you that we are not the only two.

Jim

Chris_H said:

I just made a lawn dart this past weekend,

Click to expand...

Wayco said:

Sharon buried a 2.6" Blue Iguana flying on an L935 that had twist and tape switches. Ballistic from 20k ft.

Click to expand...

This thread is also about redundancy. Were both of these flights with redundant/multiple electronics? Hmmm.

I have both the single and double pull pin switches from Lab Rat. Very nicely made, even include quality mounting hardware all very reasonably priced. I also use an Eggtimer Quantum/Eggfinder mini combo for my nose cone av bay which technically requires no physical switch...arms over wi fi

Buckeye said:

This thread is also about redundancy. Were both of these flights with redundant/multiple electronics? Hmmm.

Click to expand...

Yes, and ironically, both on the L935.

I had no problems with electronics, that all worked fine. It was a complex design with the motor passing well into the av bay. I needed more ground testing of charges, and really, a simpler design, a rocket that the motor actually fits in. Apogee deployment did not bring separation. Main deployment at 1000' led to the chute exploding with a boom that could easily be heard a half mile away. This also snapped the 1/2" tubular nylon shock cord which allowed the nosecone to land safely in a sage bush, unscathed. GPS tracking was lost before it hit the ground, likely on the way up. Miraculously, the RF transmitter will fly again, otherwise I would have never known what happened. Except, if I ever hear that noise again...

The Fingertech Robotics switches still make and break continuity, and look like they would fly again just fine if the fire residue was cleaned off of them.

As for the question of redundancy and multiple electronic systems, had I upped the backup charge sufficiently, the flight would have landed safely. The electronics worked fine.

The screw switches that Mike Fisher (Binder Design) makes are the most robust I've seen, he has used these on ridiculously high-G flights with zero problems.

I use the twist and tuck technique.

KC3KNM said:

I understand the avionics bay layout, however I should have been more clear on the execution. I was thinking along the lines of the arming plugs used in model aircraft, but installed on the rear bulkhead of the AV bay. Although, disarming it would involve removing the top half of the rocket to access the plug, which is unsafe.

Most everyone seems to have that one switch type that they trust, which makes choosing components for your first dual deploy setup a little daunting. I'm definitely going to research the switches posted here, I appreciate the help! Sorry for the FNG questions!

Click to expand...

Got it...I didn't think about just extending plugs outside of the AV bay. You might be able to get away with that on a small rocket, but still not recommended for the reason you mention...having to lift the upper section completely off of the booster, then connect the plug. If something were to go wrong, your face and hands are right next to the charges. I'd rather turn a switch from outside of the rocket. If something goes boom unexpectedly, a part of the rocket will separate but hopefully I'm mostly out of the way when the parts come back down.

FWIW, I've used the Missileworks and Featherweight screw switches. Both work great, the only failure I've had with them was when I got a bit ham-fisted on a Featherweight and broke the nut free on the back of the board. Now I put a small dab of epoxy on the nut so that it's bonded to the board with more than just solder...no problems since then.

Twist & Tape for 17yrs....never, never failed. [when done correctly!!!!!]
I have had 3 switch failures......Key switch-screw switch-shurter switch.
Over the years figured I would try them.

T&T good for around mach2-2.3 [at least for me tape stayed put]
For everyday sport flying I like T&T for simplicity and reliability. [Tons of my friends use it]

For Xtreme flights I use the combat robot switch [fingertech robotics] which I believe I may have introduced them here, many years ago.

There is a bit of art to T-T...not done correctly you can bounce power or worse loose it during flight. YOU MUST cross wires first, then squeeze them while twisting BOTH around each other...like so: [2 altimeters]

Keeps the power positively contacted during twist...

...then tape to outside of payload/switchband so it can be disconnected if need be. My tape has held to around M-2.3 at stated. Depends on quality/stick-um of electrical tape used.
Note I start the twist with insulated portion also.

The incorrect way happens when one wire gets mostly twisted around the other. As improbable as it seems, done this way is NOT a good connection & can "bounce" or loose/regain contact several times during flight, causing many types of altimeters to "re-set" during flight...not a good thing..."crash" or stay disconnected, though looks like a good contact.