Schurter switches for flight computers

[Steven88]

Hello. Can somebody enlighten me on what is the recommended way to wire in these Schurter switches between my lipo batteries and TRS and Quark altimeters? I have one switch for the Quark and another switch for the TRS DPWR side. How for sure do the switches work? Should I wire four of the posts or only two? I was a little confused after reading this description on Apogee’s website about them. I will add the description below. Guess I’m not a wiring guru! Thanks for the help!



They have 4 terminals, and are essentially DPST with the quirk that one side of each switch is connected together in the 220V position. They can be wired as a simple SPST power switch optionally with both switch poles in parallel for even greater reliability. They can also be used to switch the common outputs of two altimeter boards as a SAFE/ARM switch for L3 projects or other airframes with redundant electronics as long as the two altimeters can handle having their starter commons tied together in the SAFE position. This allows for a "3 switch L3", and is usually ok if there are no other electrical connections between the two altimeters. Click Here to download a sample wiring diagram from a successful 3-switch L3 project if this seems complicated!

 

[Zeus-cat]

The easiest way to do this is use a multimeter to determine which two terminals are closed (near zero ohms) when the switch is in a certain position. They should be open (very high ohm reading) when the witch is turned to another position.

One altimeter manufacturer does not recommend these switches as they are not designed for high G environments. Many people use them and say they work fine.

 

[tim cubbedge]

Middle two posts. But like Zeus cat says, confirm with meter.

 

[Steven88]

Thanks guys. I am taking it to a professional to get it soldered today and I appreciate the quick reply!

 

[jsdemar]

https://www.rocketryforum.com/threads/missile-works-rotary-swich.150718/post-1856006

 

[Steven88]

Thanks for that link

 

[MoreCowbell]

Here is a diagram of the Schurter switch connections. I use these exclusively, and like them a lot. I cut off terminals 1 and 4--they don't serve any purpose for me. So on my rockets, the 110V position is "OFF", and when I rotate to the 220V position, it powers up the altimeter.

 

[Rob702Martinez]

Is it possible to use one switch to turn on 2 different computers or as 2 separate circuits?
2 and 3 would go to two different computer positive separated and 1 and 4 would be positive in from 2 different batteries?

 

[MoreCowbell]

I do not advocate powering up multiple systems with one switch. IMO each system or device should have it's own switch, and each system gets powered up individually and confirmed for flight-readiness before powering up the next system.

 

[new2hpr]

I use positions 1 and 2, so with a little sharpie magic, 110 becomes '1' and 220 becomes '0' for my on/off indications. Agreed on not using one switch for multiple systems.

 

[jsdemar]

Use one switch per device. Wire it so that the two poles form a redundant pair of switches.

For altimeters that don't have terminals for a switch, wire it to switch the positive side of the battery:


For altimeters with "Switch" terminals, wire as I showed in that link:

Including the diagram in this thread to keep it all in one place:

"230" position is OFF. Rotate clockwise to the "115" position for "ON".

 

[aerostadt]

With a continuity test you know what you got.

 

[Steven88]

Wow thanks guys! I think it’s slowly making sense

 

[Steven88]

Use one switch per device. Wire it so that the two poles form a redundant pair of switches.

For altimeters that don't have terminals for a switch, wire it to switch the positive side of the battery:
View attachment 417387

For altimeters with "Switch" terminals, wire as I showed in that link:
View attachment 417388
Including the diagram in this thread to keep it all in one place:
View attachment 417389
"230" position is OFF. Rotate clockwise to the "115" position for "ON".

Great illustration. This hopefully will help many people down the road.

 

[Steven88]

Use one switch per device. Wire it so that the two poles form a redundant pair of switches.

For altimeters that don't have terminals for a switch, wire it to switch the positive side of the battery:
View attachment 417387

For altimeters with "Switch" terminals, wire as I showed in that link:
View attachment 417388
Including the diagram in this thread to keep it all in one place:
View attachment 417389
"230" position is OFF. Rotate clockwise to the "115" position for "ON".

Do I have this right, leave the switch with two wires for redundancy and head to the altimeter, then do I merge the two wires into one wire before it connectors to the altimeter or leave two wires running all the way into the altimeter? Likewise coming into the switch off the battery I would have to solder an extra wire in to the hot off the battery to make two coming into the switch, correct? On the altimeter I have a separate switch for the DPWR versus the battery terminals.

 

[JohnCoker]

Do I have this right, leave the switch with two wires for redundancy and head to the altimeter, then do I merge the two wires into one wire before it connectors to the altimeter or leave two wires running all the way into the altimeter?

I suggest as short and few wires as possible. (Tangling is another risk, even in large spaces and there never seems to be enough space.)

 

[wsume99]

I am not familiar with how most altimeters integrate the switch inputs into the power circuitry. Question, with the Tripoli requirement for a physical switch to break the power between the battery and the energetics, does using the switch inputs on an altimeter satisfy the requirement? Or would you need to install the switch on the battery connections or on the charge side?

 

[Steve Shannon]

I am not familiar with how most altimeters integrate the switch inputs into the power circuitry. Question, with the Tripoli requirement for a physical switch to break the power between the battery and the energetics, does using the switch inputs on an altimeter satisfy the requirement? Or would you need to install the switch on the battery connections or on the charge side?

It depends on the altimeter. Some altimeters have switch contacts that are simply in series with the battery. For those, the switch contacts are fine. Others have used switch contacts as a sort of soft switch to place the processor into an idle loop. That’s not a substitute for the physical break. Talk to the manufacturer.

 

[Cameron Anderson]

Is it possible to use one switch to turn on 2 different computers or as 2 separate circuits?
2 and 3 would go to two different computer positive separated and 1 and 4 would be positive in from 2 different batteries?

Have you met Marc? He uses a 2 position 3 pole switch (I think that's what it's called, maybe it's 6 pole) to turn on both his altimeters and his GPS with one switch. Everything off to everything on.
Don't listen to the redundancy naysayers - complexity statistically increases your chance of failure more than anything else and makes user error (the most common reason for an altimeter failure) that much more likely.

 

[beeblebrox]

All those things above are all well and good, but remember the KISS rule. Keep It Simple Stupid.. The more complex, the more prone to error. Use these:
https://www.amazon.com/WGCD-Latching-Button-Switch-Flashlight/dp/B07BMNYJ13/
Mount so that the button is flush with the airframe. I measured the approximate force, over 1 lb to press. If you have a multiple battery system, like the Eggfinder TRS for example, use common ground, then switch the ground wire. (Mine has 7.4v lipo for circuitry, 12v A23 battery for the chargewell outputs) The button fits smoothly in a 3/16" hole. It extends about 0.050" from a round area about 0.34" dia. There are other similare ones available too... and UBER Cheap!!!

 

[jsdemar]

All those things above are all well and good, but remember the KISS rule. Keep It Simple Stupid.. The more complex, the more prone to error. Use these:
https://www.amazon.com/WGCD-Latching-Button-Switch-Flashlight/dp/B07BMNYJ13/
Mount so that the button is flush with the airframe. I measured the approximate force, over 1 lb to press. If you have a multiple battery system, like the Eggfinder TRS for example, use common ground, then switch the ground wire. (Mine has 7.4v lipo for circuitry, 12v A23 battery for the chargewell outputs) The button fits smoothly in a 3/16" hole. It extends about 0.050" from a round area about 0.34" dia. There are other similare ones available too... and UBER Cheap!!!

Those cheap switches may work if everything goes well on a mild flight, but they are susceptible to vibration and snapbacks. A pound is too small a force for a pushbutton switch. You will get bouncing and power drop outs. Depending on the altimeter's power protection, it might not be noticed... or it might reset the altimeter.
Also, it is not recommended to switch the ground wire on a power source. There may be other paths to ground that may not be obvious in some designs. There may be other paths from the way someone wires staging igniters or shares ground with other electronics. I've seen N-N staged min diameter flight ignite both motors at liftoff due to a misinterpreted ground path.
The cost of the whole flight justifies more than a few pennies for a switch, IMO. I have to admit that I often "twist wires" for a switch if it's a critical connection.

 

[jsdemar]

Have you met Marc? He uses a 2 position 3 pole switch (I think that's what it's called, maybe it's 6 pole) to turn on both his altimeters and his GPS with one switch. Everything off to everything on.
Don't listen to the redundancy naysayers - complexity statistically increases your chance of failure more than anything else and makes user error (the most common reason for an altimeter failure) that much more likely.

A single switch for all electronics is a risky single point of failure. If you want fully redundant/independent altimeters for deployment, don't share a single switch.

 

[beeblebrox]

Those cheap switches may work if everything goes well on a mild flight, but they are susceptible to vibration and snapbacks. A pound is too small a force for a pushbutton switch. You will get bouncing and power drop outs. Depending on the altimeter's power protection, it might not be noticed... or it might reset the altimeter.
Also, it is not recommended to switch the ground wire on a power source. There may be other paths to ground that may not be obvious in some designs. There may be other paths from the way someone wires staging igniters or shares ground with other electronics. I've seen N-N staged min diameter flight ignite both motors at liftoff due to a misinterpreted ground path.
The cost of the whole flight justifies more than a few pennies for a switch, IMO. I have to admit that I often "twist wires" for a switch if it's a critical connection.

Switching ground can be common practice. It is used extensively as long as the entire system follows that when there are multiple voltages. (The Eggfinder recommends two batteries so that the fire current does not overload the main batteries and cause the GPS to reset.) As for the switches mentioned above, you are overlooking the big picture...the button is only a few tenths of a gram, it would take over 1000 g's of acceleration - sideways... to make it push in and then open the circuit. And, with the button flush or below the surface, if you dropped it on the ground, the likely hood of something directly hitting that button is as close zero as hitting the lottery... It is horizontally mounted not vertically. that switch type has worked perfectly in every flight I have used it, including my J520 powered L2 cert flight. I have worked in the electronics industry and have performed all types of environmental testing. G-Force from a flight is along the axis not sideways... Remember this when installing battery holders for round batteries, like AA, A23 for example... The spring should be towards the nose cone, or mounted horizontally. Acceleration could momentarily cause the battery + terminal come off the contact.

 

[Steve Shannon]

Th

Have you met Marc? He uses a 2 position 3 pole switch (I think that's what it's called, maybe it's 6 pole) to turn on both his altimeters and his GPS with one switch. Everything off to everything on.
Don't listen to the redundancy naysayers - complexity statistically increases your chance of failure more than anything else and makes user error (the most common reason for an altimeter failure) that much more likely.

That’s a very poor understanding of redundancy and complexity. Two separate simple circuits, each with an SPST switch, provide redundancy without complexity. As soon as any one element is shared you have created a single point of failure.

 

[Steve Shannon]

Switching ground can be common practice. It is used extensively as long as the entire system follows that when there are multiple voltages. (The Eggfinder recommends two batteries so that the fire current does not overload the main batteries and cause the GPS to reset.) As for the switches mentioned above, you are overlooking the big picture...the button is only a few tenths of a gram, it would take over 1000 g's of acceleration - sideways... to make it push in and then open the circuit. And, with the button flush or below the surface, if you dropped it on the ground, the likely hood of something directly hitting that button is as close zero as hitting the lottery... It is horizontally mounted not vertically. that switch type has worked perfectly in every flight I have used it, including my J520 powered L2 cert flight. I have worked in the electronics industry and have performed all types of environmental testing. G-Force from a flight is along the axis not sideways... Remember this when installing battery holders for round batteries, like AA, A23 for example... The spring should be towards the nose cone, or mounted horizontally. Acceleration could momentarily cause the battery + terminal come off the contact.

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.

 

[Cameron Anderson]

Th

That’s a very poor understanding of redundancy and complexity. Two separate simple circuits, each with an SPST switch, provide redundancy without complexity. As soon as any one element is shared you have created a single point of failure.

Two-engine aircraft suffer single engine failures at twice the rate of single engine planes. Why? Two engines mean two things that can fail. That's not a poor understanding of redundancy, that's just math. Not option - hard unyielding fact across aircraft types and engine manufactures. It is truth.

The demand for redundancy is related to chance of failure and is directly tied to risk reduction. I've argued countless times that the "risk reduction" methods common to high power rocketry do little if anything to improve safety. They are window dressing steps that aren't aimed at true safety improvement and are often highly unscientific.

What are the things I am worried about getting right with my electronics more than a switch failing?
1. Properly securing a battery so it won't come loose during flight (something that happens more than a switch failing, and probably the biggest cause of altimeter failure)
2. Users failing to set their altimeter properly (yet another thing that happens far more than a switch failing)
3. Improperly sized and tested ejection charges (yet again, something else that happens more than a switch failing)
4. Improperly securing the altimeter in the av bay/on a sled (something far more common than a switch failing)

Of all the possible points of failure in a rocket system, redundant switches, while simple (no argument there) and not burdensome (to design in terms of build or cost), are perhaps the most unnecessary and least safety-conscious requirement I can think of.

Ignoring things that are unsafe is dangerous, but moreso is creating artificial boogie men and safety issues where none exists.

Single switches for multiple electronics...not a real concern.

 

[Cameron Anderson]

A single switch for all electronics is a risky single point of failure. If you want fully redundant/independent altimeters for deployment, don't share a single switch.

How many good switches (not cheap e-bay Chinese crap, or twist and tuck wires) have you ever had fail? Have many have you heard of failing?

Personally, I've never had any. Nor have I heard any. Bad batteries, bad soldering, batteries coming disconnected...now those things happen all the time. Even schurter switches (which I use) are only rates for a certain number of turns (200 if memory serves); after that, failure is possible, and I have had a schurter that wouldn't hold it's position after lots of use. But a failure in that case would be due to exceeding design tolerances, not a switch build to spec failing spontaneously.

Focus on the right points of failure, switches aren't it.

 

[Reinhard]

Two-engine aircraft suffer single engine failures at twice the rate of single engine planes. Why? Two engines mean two things that can fail. That's not a poor understanding of redundancy, that's just math. Not option - hard unyielding fact across aircraft types and engine manufactures. It is truth.

But that's not the point of redundancy. The increased possibility that an engine fails is more than outweighed by the decreased possibility that *all* engines fail. That's the reason why, for example, you aren't allowed to fly a single engined helicopter over many metropolitan areas. Airliners are multi-engined and historically they had to have 3+ engines for most flights over oceans (see ETOPS).

Dissimilar redundancy saved my L3, because it turns out my until then trusted primary altimeter was not compatible with high altitude launch sites like Black Rock (fixed in later firmware versions).

Of course, redundancy is not an excuse to build sloppy e-bays. Piling up unreliable systems will often make it worse.

Reinhard

 

[Steve Shannon]

Two-engine aircraft suffer single engine failures at twice the rate of single engine planes. Why? Two engines mean two things that can fail. That's not a poor understanding of redundancy, that's just math. Not option - hard unyielding fact across aircraft types and engine manufactures. It is truth.

The demand for redundancy is related to chance of failure and is directly tied to risk reduction. I've argued countless times that the "risk reduction" methods common to high power rocketry do little if anything to improve safety. They are window dressing steps that aren't aimed at true safety improvement and are often highly unscientific.

What are the things I am worried about getting right with my electronics more than a switch failing?
1. Properly securing a battery so it won't come loose during flight (something that happens more than a switch failing, and probably the biggest cause of altimeter failure)
2. Users failing to set their altimeter properly (yet another thing that happens far more than a switch failing)
3. Improperly sized and tested ejection charges (yet again, something else that happens more than a switch failing)
4. Improperly securing the altimeter in the av bay/on a sled (something far more common than a switch failing)

Of all the possible points of failure in a rocket system, redundant switches, while simple (no argument there) and not burdensome (to design in terms of build or cost), are perhaps the most unnecessary and least safety-conscious requirement I can think of.

Ignoring things that are unsafe is dangerous, but moreso is creating artificial boogie men and safety issues where none exists.

Single switches for multiple electronics...not a real concern.

That’s a terrible comparison. Two engine planes use both to load balance; they don’t reserve one as a backup in case the other fails, which is what true redundancy is about.

 

[Cameron Anderson]

But that's not the point of redundancy. The increased possibility that an engine fails is more than outweighed by the decreased possibility that *all* engines fail. That's the reason why, for example, you aren't allowed to fly a single engined helicopter over many metropolitan areas. Airliners are multi-engined and historically they had to have 3+ engines for most flights over oceans (see ETOPS).

Dissimilar redundancy saved my L3, because it turns out my until then trusted primary altimeter was not compatible with high altitude launch sites like Black Rock (fixed in later firmware versions).

Of course, redundancy is not an excuse to build sloppy e-bays. Piling up unreliable systems will often make it worse.

Reinhard

I agree with your assessment on why redundancy is necessary in systems, I disagree 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.

I am also a fan of dissimilar redundancy (in thinking that hopefully if fault X causes failure in system A, system B will be fault X tolerant), but if both your dissimilar altimeters were wired through one switch (a mechanically sound properly wired, securely wired) you would have been fine since the error was in the altimeter and not the power circuit.

My point is redundant switches creates more points of failure than it does increase safety margin .