Featherweight magnetic switch turned off in flight

Walldiver7

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At our last launch, I flew a scratch built fg rocket that I had the flight computers activated by magnetic switches. Just after the drogue charge fired, one of my EasyMini flight computers shut down. Fortunately, all of my hp flights fly with two flight computers and the backup EasyMini fired it's Main chute on time. The switch functions fine on the bench and I can not detect any problem with it. After going through and verifying that all connections and the lipo are ok , I still suspect the switch.

Has anyone ever had a magnetic switch turn off their flight computer in flight? I'd really like to keep using these magnetic switches, as they have made activating the computers so much easier, but.........

Is it possible that the current flow in the lead, running to the e-match, could have created a magnetic field that turned off the switch?
 

ksaves2

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Hmmmm, First post I've seen. I've used them on single device rockets with no trouble. I take it there was no mechanical switch in the circuit? Don't laugh, I've seen it done that way. Stupid. Kurt
 

Steve Shannon

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At our last launch, I flew a scratch built fg rocket that I had the flight computers activated by magnetic switches. Just after the drogue charge fired, one of my EasyMini flight computers shut down. Fortunately, all of my hp flights fly with two flight computers and the backup EasyMini fired it's Main chute on time. The switch functions fine on the bench and I can not detect any problem with it. After going through and verifying that all connections and the lipo are ok , I still suspect the switch.

Has anyone ever had a magnetic switch turn off their flight computer in flight? I'd really like to keep using these magnetic switches, as they have made activating the computers so much easier, but.........

Is it possible that the current flow in the lead, running to the e-match, could have created a magnetic field that turned off the switch?

Is the lead coiled or wrapped around an iron core, such as a piece of all-thread?


Steve Shannon
 

Walldiver7

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Hmmmm, First post I've seen. I've used them on single device rockets with no trouble. I take it there was no mechanical switch in the circuit? Don't laugh, I've seen it done that way. Stupid. Kurt

No other switch, just the magnetic switches.
 

Walldiver7

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Right, but you asked if it was possible for the leads to have created a magnetic field. Unless you coiled it around something with iron it's highly unlikely.


Steve Shannon

Steve,... I was, by no means, making fun of your reply. Thanks for responding!
 

Coop

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Never heard of this, but I do know the switch itself needs power... could it be that the battery (-ies?) were low?

Later!

--Coop
 

Walldiver7

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Did you connect it, turn it off, button up the ebay and go launch it right away? What was the capacity of the lipo? Kurt

That was the voltage on the 400mah lipo as it sat on the pad ready for launch. The launch occurred within 5 minutes of that voltage reading.
 

warnerr

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I have experienced two types of failures with magnetic switches/ power perches. The first- used a magnet and waved it across perch area. Listened hearing raven turn on. My mistake was not waiting even longer as the swipe managed to also turn it off. The raven can run for an amazing amount of time on a momentary power up. Solution- wait a minute and see if it is still armed. That cost me a very fine rocket. The second failure is not really the switch but the perch design using those tiny 1s battery's. The battery connections are flimsy at best. Apogee event was fine but the separation caused a MOMENTARY power disconnect . The raven re powers and is waiting for launch. This rocket survived and now i have a custom wedge to hold the battery down in place and tape battery and wedge and through posts with several wraps of tape. I prefer wifi switches wherever possible today.
 

mpitfield

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I run with Featherweight Magnetic switches as well for some of my rockets, and the only failures I have had so far are wave on wave off. I know some of the altimeters will stay on a bit after they are off which can fool you if you walk away too soon. The rocket below has the same setup as you're referring to, except its a single altimeter due to the size of the AV bay, no issues thus far but it's a new build with only ground testing on it. Sadly I ground tested using the USB cable connected to my Easy-Mini and ripped the USB connected clean off the board, including the traces. I have replacement on the way.

How do you connect your wiring? I crimp a bare ring terminal to 20AWG, then solder it completely to the terminal, sandwiched in-between the stand-offs and the board. They are well secured!




 

OverTheTop

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I have flown a few flights with them and had no problems.

Are you running the same battery for the altimeter and the deployment? I could envisage a scenario where the eMatch is fired and shorts out the primary altimeter supply perhaps resetting the altimeter and/or switch.

I nowadays use separate batteries (with microswitches and pull-pins) for firing the eMatches and running the altimeter(s). That is partly to get around the problem of LiPo batteries tripping off-line if they have protection circuits built in.
 

Walldiver7

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I have experienced two types of failures with magnetic switches/ power perches. The first- used a magnet and waved it across perch area. Listened hearing raven turn on. My mistake was not waiting even longer as the swipe managed to also turn it off. The raven can run for an amazing amount of time on a momentary power up. Solution- wait a minute and see if it is still armed. That cost me a very fine rocket. The second failure is not really the switch but the perch design using those tiny 1s battery's. The battery connections are flimsy at best. Apogee event was fine but the separation caused a MOMENTARY power disconnect . The raven re powers and is waiting for launch. This rocket survived and now i have a custom wedge to hold the battery down in place and tape battery and wedge and through posts with several wraps of tape. I prefer wifi switches wherever possible today.

The EasyMini s that I fly have no caps of any significant value to power itself for any length of time. When the power goes away, the EasyMini is off. But, I do verify that the EasyMini is on and stays on because I also know very well that those mag switches can turn on and off in a single swipe. Connections... the Achilles Heel of all well-designed Av-bays! All connections were solid and verified.... over and over.
 

Walldiver7

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I have flown a few flights with them and had no problems.

Are you running the same battery for the altimeter and the deployment? I could envisage a scenario where the eMatch is fired and shorts out the primary altimeter supply perhaps resetting the altimeter and/or switch.

I nowadays use separate batteries (with microswitches and pull-pins) for firing the eMatches and running the altimeter(s). That is partly to get around the problem of LiPo batteries tripping off-line if they have protection circuits built in.


Post flight, I went right to the Lipo to make sure I had not accidently used a lipo that still had the protection board. That was not the case; I had flown one without. Now, your first scenario of a shorted e-match, could very likely be the culprit since I fly with one lipo for power and pyro events. I will do some testing to determine if this is the cause. The question is: Will a shorted e-match cause the EasyMini to shut down even if the lipo has no protection circuitry employed? Thanks.
 

Walldiver7

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I run with Featherweight Magnetic switches as well for some of my rockets, and the only failures I have had so far are wave on wave off. I know some of the altimeters will stay on a bit after they are off which can fool you if you walk away too soon. The rocket below has the same setup as you're referring to, except its a single altimeter due to the size of the AV bay, no issues thus far but it's a new build with only ground testing on it. Sadly I ground tested using the USB cable connected to my Easy-Mini and ripped the USB connected clean off the board, including the traces. I have replacement on the way.

How do you connect your wiring? I crimp a bare ring terminal to 20AWG, then solder it completely to the terminal, sandwiched in-between the stand-offs and the board. They are well secured!





Very nice... ! I solder my leads directly to the Mag switch.
 

OverTheTop

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The question is: Will a shorted e-match cause the EasyMini to shut down even if the lipo has no protection circuitry employed?

You mention that the altimeter you use has no significant capacitance, so the answer is possibly. Ground testing, as you mention, is a way of getting some confidence one way or the other.

I just use small 120mAh or 180mAh 2S LiPos for the pyro circuit. Typically the same 180mAh for the altimeter (Ravens normally). I would use smaller for the pyros but these ones are easy to get.
 

UhClem

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Is it possible that the current flow in the lead, running to the e-match, could have created a magnetic field that turned off the switch?

Perhaps, but only if the wire were touching the sensor.

I don't know the part number used but a 1A current in a wire 1mm from the sensor gets into the ballpark of some devices sensitivity.
 

mpitfield

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Please identify your components left to right.

Thank you.

Altus Metrum TeleGPS, Featherweight Mag switch space to mount a LiPo, Altus Metrum EasyMini, Featherweight Mag switch, followed by a space to mount the altimeter LiPo. The TeleGPS mounts on a removable daughter board and the whole assembly slides on the "Shotgun" AV bay for a MD GLR Mariah 38.

33261349132_01e9c742bf_b.jpg


The antenna slides through a hole in the end of the AV bay and just clears the end of the nosecone.


 

Adrian A

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Perhaps, but only if the wire were touching the sensor.

I don't know the part number used but a 1A current in a wire 1mm from the sensor gets into the ballpark of some devices sensitivity.

The part number is Murata AS-M15KAH-R, with a 1.2 mT sensitivity.

Waldiver7, could you post a picture of your av-bay?
 
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