Schurter switches for flight computers

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I thought the Schurter switches were sweet as can be …… Until, while I was building my Avionics bay; mine failed !!
New switch cycled maybe 25 times since I got it. Didn't even make to the flight part of its life !!

I bought Screw switches......
 
with screw switches, be sure and pinch the treads a bit with pliers so that they have more friction and don't close with vibration
I had one close and one wiggle all the way out of the screw base

What keeps the screw on a screw switch from coming loose during flight? I guess that is part of the reason to mess up the threads to help the threads hold?
 
I’ve seen occasions when a strong jerk occurs perpendicular to the long axis immediately following apogee ejection. Body parts slap into each other. Vibration acts in all directions. I’ve seen push button switches come down in pieces.
It always amazes me that people will have hundreds of dollars or more in a rocket and then be chintzy when it comes to the switches that control power to the recovery system.
Also, John DeMar is probably the very last person that any of us should lecture. 🙂

I think the twin engine airplane compared to redundant switches is a non sequitur. Apples and Oranges so to speak. I am a bit skeptical of those failure statistics also. does the poster have a source for those numbers? I'm an aviation guy. Also, the premise that ".......switches are so prone to failure (as an individual component themselves, not as part of a larger circuit with many parts and points of possible failure) that they require redundancy." is not what is being stated here either. If you have two switches and one fails you still have recovery. If you have one switch and one fails....well...you know. It would seem to follow that having two switches is asking for twice the failure rate redundancy has no place in rocket recovery at all.

I have seen the schurter switches literally fall apart when powered up on the pad. If they are only rated for 200 cycles then I would reconsider putting them in my rocket. Standard on/off switches in the R/C aircraft industry are being replaced by soft switch technology. When these switches fail, for any reason, the system stays on. If they come unplugged completely the system comes on. This move is due to the high G forces and high vibration environment that many of the aircraft are subjected to and eventually a switch is going to fail. Count on it.

My thoughts, but I too would defer to John DeMar on this particular subject.

Joe
 
I don't want to complicate this thread, but I thought I read somewhere that Schurter switches were meant for only one or two "ON-OFF" cycles.
Having said that, I use them on all my rockets, and have since 2009. No failures to date, with multiple flights on most rockets.

Has anyone else run across this caution about Schurter switches as well? Did I just "fever dream" this worry one restless night?
 
I haven't had problems with the Schurter switches, but have also switched to the Fingertech Robotics switches for my latest projects:
https://www.fingertechrobotics.com/proddetail.php?prod=ft-mini-switch
These mount using two #2 screws. Be sure to clean the terminals well before soldering to them and use a medium soldering iron tip. They also require a lot of heat, so be careful not to melt the Nylon housing (at 450℃ you have only 12s). I use a clip-on heat sink where the terminal enters the body to give me a little more time. The main failure mode of these switches is overheating them during soldering.
 
I have used the Schurter switches on numerous rockets with multiple flights on each rocket, never had a problem. They are my switch of choice.

Of course, you are just supposed to click the actuator between the 110 and 220 positions, and not rotate the actuator 340 degrees the other direction all the way around to the 220 position...;) That might result in some premature failures!

One feature I do like about the Schurters is when they are mounted on the face of the sled, the switch faces the the airframe wall and is readily accessed through a hole in the airframe for a screwdriver to turn the switch on or off.

The FingerTech switches look well made--might be a good alternative. Good pointers on the soldering technique.
 
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