Rotary Switch Failures?

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Fingertech Mini Power Switch is supposed to be one of the toughest / smallest, AFAIK

This thread caused me to begin considering a reliable, high current, high G rated switch. While reading the info at the link provided by dhbarr, the fingertechrobotics site had an interesting internal diagram for just such a switch.

With minimal machining skills, this type of switch could be produced inexpensively using phenolic bar and brass stock. Depending on the choice selected for the screw, either a cap screw or standard slotted head would be equally easy to use in the shop and in the field. This seems to be the simplest design for a high G capable switch within reach of anyone willing to invest an hour in some machining.

If you really wanted to invest a bit more and lower the terminal to terminal resistance, copper could be substituted for brass. But the change would be very small.

And this would completely do away with the rotary switch reliability question.

View attachment 310661
 
While it means NOTHING statistically...
I launch 2 more this weekend. A K550 and a H110 with rockets using these switches. Bought 3+ years ago.
 
This thread caused me to begin considering a reliable, high current, high G rated switch. While reading the info at the link provided by dhbarr, the fingertechrobotics site had an interesting internal diagram for just such a switch.

With minimal machining skills, this type of switch could be produced inexpensively using phenolic bar and brass stock. Depending on the choice selected for the screw, either a cap screw or standard slotted head would be equally easy to use in the shop and in the field. This seems to be the simplest design for a high G capable switch within reach of anyone willing to invest an hour in some machining.

If you really wanted to invest a bit more and lower the terminal to terminal resistance, copper could be substituted for brass. But the change would be very small.

And this would completely do away with the rotary switch reliability question.

View attachment 310661

That is an interesting design, and would likely work well. I think you would be pretty close though using a Missileworks or Featherweight screw switch, and would not need to spend an hour building it.
 
That is an interesting design, and would likely work well. I think you would be pretty close though using a Missileworks or Featherweight screw switch, and would not need to spend an hour building it.

I agree; I believe the screw switches already available work almost exactly that way except on a printed circuit board.


Steve Shannon
 
Not familiar with any of these, but just a thought. If I read correctly, sometimes 110/220V select switches are used? In general switches aren't built for more operations than are expected in a product lifetime. For a 110/220V select switch, that lifetime might be for a few dozen operations. I have seen switches with a rated lifetime of 100 operations (DIP switches IIRC) so it wouldn't surprise me to see a similar rating on these switches.
 
Not familiar with any of these, but just a thought. If I read correctly, sometimes 110/220V select switches are used? In general switches aren't built for more operations than are expected in a product lifetime. For a 110/220V select switch, that lifetime might be for a few dozen operations. I have seen switches with a rated lifetime of 100 operations (DIP switches IIRC) so it wouldn't surprise me to see a similar rating on these switches.

That's the problem I see with the Schurter switch. I posted a link to the data sheet last year for the Schurter switch. As you say it has a life measured in hundreds. If course most people don't fly rockets that many times but vibration can peel off some of those cycles, even though not actually cycling the switch.
 
Not familiar with any of these, but just a thought. If I read correctly, sometimes 110/220V select switches are used? In general switches aren't built for more operations than are expected in a product lifetime. For a 110/220V select switch, that lifetime might be for a few dozen operations. I have seen switches with a rated lifetime of 100 operations (DIP switches IIRC) so it wouldn't surprise me to see a similar rating on these switches.

That's why I chose to put jumpers instead of DIP switches on the Quark... I've seen DIP switches go out, they're relatively expensive, and they're extremely bouncy. Jumpers never fail, and if you really want high-G security you can wire-wrap or solder them in.
 
I just designed and ordered a PCB for a four channel switch based on the safe/arm switch used on the old AltAcc2C altimeters. It uses a Keystone screw terminal as the switch which are ~$0.52 each if you go for the captivated screw. Available with pretty colors on the screw heads if you like that sort of thing. :)
 
These look nice, but it looks like that spec sheet says the 6A rating is for AC and they are only rated at 0.4A for DC current? I take it you haven't had a problem though, even with lipos?

The low current rating is for the gold contacts, not strictly because it's DC.
The high current rating is for the silver contacts and AC. AC to a reactive load would be likely to draw an arc.
I use the silver contacts with solder lugs. I haven't used lipo batteries, but the current is dependent on the load, not the battery so I don't anticipate any problems.
Finally, and this is the most important thing. We don't switch these while they are under load. We switch them when the outputs are off. Trying to open the switch while the outputs are powered might be difficult on the switch, but having the switch in the closed position while the outputs close and then open doesn't stress the switch. When the outputs are open, the current is under the switch's DC rating.
https://www.mouser.com/blog/which-switch-who-cares-if-its-ac-or-dc
But, you are right; this is a consideration and I would prefer a switch rated higher for DC.
 
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There are lots of snap action switches (AKA Microswitches (tm) ) like the ones Steve suggests. You can get them with rated contacts, and you can get them rated for g-loads as well as temperature extremes (winter and desert flying, for example). And they're good for millions of actuations, not dozens.

If you're really worried about g-loads (perhaps you're using a sparky motor with a lot of vibration), you can mount two of them in parallel with each other in different physical planes so that a shock in one direction won't glitch both of them and kill the power to your altimeter. You can mount them on a bulkhead and activate them by screwing a nylon thread through a hole in the body tube into a t-nut glued to the altimeter bay.

https://sensing.honeywell.com/honeywell-sensing-micro-switch-v7-basic-product-sheet-004987-3-en.pdf
https://www.grainger.com/category/s...-and-machine-safety/electrical/ecatalog/N-qjq
https://www.mouser.com/Electromechanical/Switches/Basic-Snap-Action-Switches/_/N-5g2v
https://www.newark.com/microswitch-snap-action-switches
 
There are lots of snap action switches (AKA Microswitches (tm) ) like the ones Steve suggests. You can get them with rated contacts, and you can get them rated for g-loads as well as temperature extremes (winter and desert flying, for example). And they're good for millions of actuations, not dozens.

If you're really worried about g-loads (perhaps you're using a sparky motor with a lot of vibration), you can mount two of them in parallel with each other in different physical planes so that a shock in one direction won't glitch both of them and kill the power to your altimeter. You can mount them on a bulkhead and activate them by screwing a nylon thread through a hole in the body tube into a t-nut glued to the altimeter bay.

https://sensing.honeywell.com/honeywell-sensing-micro-switch-v7-basic-product-sheet-004987-3-en.pdf
https://www.grainger.com/category/s...-and-machine-safety/electrical/ecatalog/N-qjq
https://www.mouser.com/Electromechanical/Switches/Basic-Snap-Action-Switches/_/N-5g2v
https://www.newark.com/microswitch-snap-action-switches

And with the snap action microswitch you can make your "Remove before flight" tag work!
Thank you Ted!
 
The low current rating is for the gold contacts, not strictly because it's DC.
The high current rating is for the silver contacts and AC. AC to a reactive load would be likely to draw an arc.
I use the silver contacts with solder lugs. I haven't used lipo batteries, but the current is dependent on the load, not the battery so I don't anticipate any problems.
Finally, and this is the most important thing. We don't switch these while they are under load. We switch them when the outputs are off. Trying to open the switch while the outputs are powered might be difficult on the switch, but having the switch in the closed position while the outputs close and then open doesn't stress the switch. When the outputs are open, the current is under the switch's DC rating.
https://www.mouser.com/blog/which-switch-who-cares-if-its-ac-or-dc
But, you are right; this is a consideration and I would prefer a switch rated higher for DC.
Great link, thanks! It's nice to have an explanation for the different AC and DC ratings - the difference was bothering me though I hadn't spent much time thinking about it. As you say, since we aren't switching under full load it seems reasonable to trust the AC limits. I'm going to go ahead and order a few of these.

My only nit - the battery does make a difference. A 9V battery won't stay at 9V under heavy load and will push much less current through a low resistance circuit (like an e-match) than a LiPO will. I had trouble finding canonical information, but it is noteworthy that the duracell and energizer spec sheets about battery life as a function of current don't even get to 1A (and for several batteries the data stops at 0.25A or 0.5A).
 
It took me a while to find the derating factors for electronics, but I finally found it. For high vibration and/or extreme environments (space flight, military aircraft, etc.) you decrease the expected life by a factor of 10. So if a device is expected to have a 1,000 hour mean time between failure sitting on a bench, you would give it a 100 hour mean time between failure for a military aircraft. I would call a rocket an extreme environment due to the high G and vibration.

If the device was never made for a high G environment than this really doesn't apply as you could have a failure on the first flight.. However, I wanted to show you that a high stress environment really decreases the longevity of a device.
 
Great link, thanks! It's nice to have an explanation for the different AC and DC ratings - the difference was bothering me though I hadn't spent much time thinking about it. As you say, since we aren't switching under full load it seems reasonable to trust the AC limits. I'm going to go ahead and order a few of these.

My only nit - the battery does make a difference. A 9V battery won't stay at 9V under heavy load and will push much less current through a low resistance circuit (like an e-match) than a LiPO will. I had trouble finding canonical information, but it is noteworthy that the duracell and energizer spec sheets about battery life as a function of current don't even get to 1A (and for several batteries the data stops at 0.25A or 0.5A).

I see what you were saying about the battery and I agree; the lipos are much closer to being a "perfect" battery, high capacity, low internal resistance. I don't think that will matter to these switches though because most rocketry altimeters don't latch their outputs closed and leave them that way.

By the way, Grayhill has some miniature slide switches that are rated well for DC. I found them last night in a search. I'll try to get you the part number. Unfortunately they don't have an actual gee rating, which is what drew me to these NKK switches.


Steve Shannon
 
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I see what you were saying about the battery and I agree; the lipos are much closer to being a "perfect" battery, high capacity, low internal resistance. I don't think that will matter to these switches though because most rocketry altimeters don't latch their outputs closed and leave them that way.

By the way, Grayhill has some miniature slide switches that are rated well for DC. I found them last night in a search. I'll try to get you the part number. Unfortunately they don't have an actual gee rating, which is what drew me to these NKK switches.


Steve Shannon

I think the quantum with the dual battery option might be close enough to a simple pass-through that runs for 1-2 seconds to exceed what a 9V could provide (the user manual mentions that the controlling transistors on the deployment circuit are rated to 20W/8A, but end up in practice limiting a short-circuit current to 3A-5A). I feel good though that it's still fine because of the good AC rating, and I think I'd rather have an explicitly high-G-rated switch. That seems like a more likely failure scenario. Agreed?
 
I think the quantum with the dual battery option might be close enough to a simple pass-through that runs for 1-2 seconds to exceed what a 9V could provide (the user manual mentions that the controlling transistors on the deployment circuit are rated to 20W/8A, but end up in practice limiting a short-circuit current to 3A-5A). I feel good though that it's still fine because of the good AC rating, and I think I'd rather have an explicitly high-G-rated switch. That seems like a more likely failure scenario. Agreed?

I agree. When not being opened the AC rating will better reflect the actual ability of the switch to pass current. If you had to open the switch under load the contacts would take a beating, but that's not the case here.


Steve Shannon
 
It would be easy for someone to do some testing to see if this is a problem. (hint, hint!)

Along those lines of “testing” has anyone shot a video on the behavior of a "failed" Schurter Rotary switch?

What about a functional one? Because it does have some operation idiosyncrasies that could lead someone to believe its failing when it is really not.

I've had good success on several flight, but not years worth. I like them because they are easy to mount and have a very discernible detent where they are either on or off.

I’ve got some of these on the bench right now, any interest in a video?
 
I recently had not just one, but two of the Schurter switches fail on the same rocket. I believe the failures were due to flying in a high moisture environment (near the coast). On inspection both seem to have very slight corrosion on the leads. When cycled they would not arm until cycled multiple times. I replaced both of them.
 
Again, my offer still stands... Anyone wanting to get rid of the horrible, unreliable Schurter switches--PM me!
 
I recently had not just one, but two of the Schurter switches fail on the same rocket. I believe the failures were due to flying in a high moisture environment (near the coast). On inspection both seem to have very slight corrosion on the leads. When cycled they would not arm until cycled multiple times. I replaced both of them.

When you say "on the leads" you mean the solder tabs on the outside of the switch?
 
With minimal machining skills, this type of switch could be produced inexpensively using phenolic bar and brass stock.

Dare I suggest 3D printing :)


I don't particularly like those Schurter rotary switches, but I have never had one fail. I don't use them. I think I have seen them a bit dysfunctional after someone tried soldering onto one. Can't remember the details.
 
Yes. When I inspected both of them and removed the heat shrink, I noticed the corrosion. I believe the internal contacts were the same. When compared to new ones they felt "gritty".
 
Does anyone still use plugs attached to "remove before flight" flags to activate switches? If not, why not? If these are still being used, where can they be purchased?
 
I don't remember about NAR but TRA got rid of that rule years ago. NAR got rid of it too at sometime. To paraphrase, it read every ematch circuit had to have a "safety" switch between it and the altimeter on an L3 cert flight. Most used pull plugs. My prefect had to pull six pull plugs in proper order to get "everything" to work right on the pad for his L3 project. It was ABSOLUTELY a stupid, stupid, stupid rule that thankfully was discarded some years ago. He had to pull 4 pins on the ematch circuits then two pins to activate the altimeters. Shoot, most electronic deployment altimeters at the time wouldn't work for the continuity checks without live ematches online! Both groups hierarchies at the time to put it mildly, "Where academically uninformed dunces."

Now if you want to use a pull plug(s) to activate an altimeter(s) in this day and age, I don't think anyone will slam you to turn on altimeter(s) with 'em but make sure you use good quality "jacks and pins". Last I looked over 10 years ago most were guaranteed to like 4G's. But hey they worked in even higher G situations. I can't tell you which ones to get as I and other abandoned that modality but if the product is dirt cheap, performance can't be guaranteed in a rocket.

One would do better with a keyswitch as there are a myriad out there and I've seen folks comment here about which is the best but that was a long time ago and there are probably better keyswitch products out there now. Bottom line is you get what you pay for. Good luck Kurt
 
Does anyone still use plugs attached to "remove before flight" flags to activate switches? If not, why not? If these are still being used, where can they be purchased?
I assume the "plugs" you are talking about are the pins as I call them. In my case, 2" x 3/32" cotter pins. As @Steve Shannon linked, Lab Rat Rocketry carries them. I have a bunch of the microswitches so I just mount my own and epoxy a small brass tube on the sled as a guide for the pin.

I first used them in 2007 because that is how Perfectflite describe the way to wire up a HiAlt45, which was my first altimeter. I went to screw switches after that, but went back to microswitches and pull pins with my L3 in 2015 and every DD rocket I've built since.

I now use screw switches in series with the microswitches between the battery and altimeter. The microswitches are wired to the normally closed contacts so the pins actually open the microswitch and turn off the altimeter when inserted. The screw switch allows me to turn off the altimeters while prepping without having the pins and flags in the way and possibly getting bent or breaking something inside the av-bay. The screw switches are accessed through the lower coupler of the av-bay so they are covered by the booster BT when assembled.

The last thing I do when prepping the rocket is insert the pull pins, turn on the screw switches, slide the av-bay coupler into the booster BT, insert any shear pins, then take it to the RSO.

I find that just pulling the pin to turn on altimeters is so much faster and easier than fumbling with screw drivers, magnets, or my phone when out at the pad. YMMV

Primary side.jpg

20220816_132108.jpg
 
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I find that just pulling the pin to turn on altimeters is so much faster and easier than fumbling with screw drivers, magnets, or my phone when out at the pad. YMMV
Right. I was thinking the same thing. Carrying a pocket full of extra tools out to the away pads is NOT my thing. And I have the world's dumbest cell phone, not even sure it would make a wi-fi switch work!

Right now my level 3 rocket (work in progress) has the rotary switches for the electronics mounted in a switch band. They will work, but it means there is a lot of extra wire in there so I can slide the avionics sled out of the av bay. I'm not 100% on that loose hanging wiring floating around in there, so am considering altering the set up.

I also like the idea of having a visual (flag) reminder to turn the switches on before leaving the pad. I don't know how that would be possible with the rotary ones. I do have a launch checklist, but...
 
Right. I was thinking the same thing. Carrying a pocket full of extra tools out to the away pads is NOT my thing. And I have the world's dumbest ceGrizzly.com® -- Homell phone, not even sure it would make a wi-fi switch work!

Right now my level 3 rocket (work in progress) has the rotary switches for the electronics mounted in a switch band. They will work, but it means there is a lot of extra wire in there so I can slide the avionics sled out of the av bay. I'm not 100% on that loose hanging wiring floating around in there, so am considering altering the set up.

I also like the idea of having a visual (flag) reminder to turn the switches on before leaving the pad. I don't know how that would be possible with the rotary ones. I do have a launch checklist, but...
I carry one tool out to the pads with me and its taped to the side of the rocket, a small phillips screwdriver, its kind of like a remove before flight pin. I have found screw switches to be very reliable and robust, the screw driver is the same rough size as a Remove before flight tag and pin.

I abandoned the Schurter Rotary switches long ago, for the very reasons that @cerving stated either in this thread or another one, they are intended to be used once and not touched again in most applications and so have a very short life when cycled on/off frequently.
 
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