Electronics advice requested

[Hal8472]

I have been experimenting with the wifi switch in preparation for lv3 electronics deployment. I have taken a long time away and just getting back into things and need some updated advice. Previously I was working on a 54mm Tomach but found the small size Avionics bay a huge challenge. One thing that took a lot of room was wires going to the case for the switches. So, exploring the wifi switch as a way to get around this problem. Of course I know that wifi and carbon fibre don't get along, and I am simultaneously considering another rocket and using a fibreglass av bay. Either way, I want to simplify the electronics process. I also know that redundancy is required for lv 3 which can be done duplicating the same setup (except my other altimeter is a raven)

Here is what I have come up with. The Wifi switch is what is used to turn on the SL100 stratologger. For safety I cant leave the ejection charges dangling. In this setup I feed the ejection charge wires through a relay. This ensures that the ejection charge cannot fire before the relay has been activated. The relay is activated at the same time as the stratologger.

With this setup I have no screws or switches to fiddle with at the side of the rocket. At the launch pad I wirelessly connect and it is ready to go. (And in construction there there no pesky wires to and from the body housing)

Can I get your thoughts on this setup?
Andrew

 

[les]

A few questions/comments/concerns

In your schematic I only see 1 lead to each ignitor, where is the other lead connected? Are they wired in series?
What are the relay contacts rated for? Mechanical or solid state relay?
If mechanical, there is a small reaction time before they actually close - not sure how quickly the stratologger checks for continuity. Depending on the size of the relay it can take 5ms ~ 25ms for the contacts to close.
Also I would be a bit concerned on the shock/vibration forces maintaining contact closure.
Last, what is the current draw of the coil? How long may the rocket sit on the pad waiting to launch?

 

[Hal8472]

A few questions/comments/concerns

In your schematic I only see 1 lead to each ignitor, where is the other lead connected? Are they wired in series?
What are the relay contacts rated for? Mechanical or solid state relay?
If mechanical, there is a small reaction time before they actually close - not sure how quickly the stratologger checks for continuity. Depending on the size of the relay it can take 5ms ~ 25ms for the contacts to close.
Also I would be a bit concerned on the shock/vibration forces maintaining contact closure.
Last, what is the current draw of the coil? How long may the rocket sit on the pad waiting to launch?

Two leads for igniters. One connects to relay the other to the strat. Wired in parallel. Just at opposite ends in the picture.

Std 12v relays, mechanical. Small reaction time to close is not an issue. They are powered up at launch, not firing. They will be in contact by time of firing.

The shock and vibration is an issue (like any switch) during the flight as a whole. However the two moments of specific concern are apogee and drouge ignition. I don't see shock or vibration happening at apogee stage. Deceleration would be the main force but should be fairly low. Similarly during fall gravity and parachute forces should lead to a constant velocity.

Good point on the draw. I will compare batteries and draw so it can sit for an hour before launch and still work

 

[ttabbal]

9V batteries are not recommended for the wifi devices. They just don't have the capacity needed to sustain the load. Add in a mechanical relay and you're asking for trouble. The coils draw more power than you might think. And the inductive kickback could also be a problem.

Mechanical relays are also a poor choice for high-G and vibration. If the contacts come loose in flight, even for a millisecond, your electronics may not recover properly. Solid state is likely fine.

With modern electronics, shunting the outputs adds more complexity than it's worth. Before connecting to the charges, connect a bare ematch and power up. If it doesn't fire, you're good to connect the real charge. If it does, the electronics have failed and need to be repaired or replaced.

If you want to use wifi devices, get the recommended 2S lipos. It really does matter.

 

[Hal8472]

9V batteries are not recommended for the wifi devices. They just don't have the capacity needed to sustain the load. Add in a mechanical relay and you're asking for trouble. The coils draw more power than you might think. And the inductive kickback could also be a problem.

Mechanical relays are also a poor choice for high-G and vibration. If the contacts come loose in flight, even for a millisecond, your electronics may not recover properly. Solid state is likely fine.

With modern electronics, shunting the outputs adds more complexity than it's worth. Before connecting to the charges, connect a bare ematch and power up. If it doesn't fire, you're good to connect the real charge. If it does, the electronics have failed and need to be repaired or replaced.

If you want to use wifi devices, get the recommended 2S lipos. It really does matter.

Actually, the wifi switch (user manual pg 16) is rated 4-16v. It mentions 3.7v lipo as a substitute with reduced range.

While I agree that shunting adds more complexity than its worth, I understand its a requirement for lv3 electronics. Not my choice. Similarly a mechanical switch is required. Otherwise, the electronics in the altimeter would be sufficient.

For clarification, the relays only job is to provide connectivity for the ematch. They are not on the electronics inputs. Fluttering isn't an issue unless it takes place during ejection of main, or drouge (and I don't see any major forces which could affect it at that time).

As you point out the draw of the relays is significant. I will include that in testing to figure out how long it can wait before launch.

 

[rharshberger]

Keep it simple, relays may not allow the altimeter to continuity check the igniters depending on how they are setup (not sure if the SL will arm properly in that situation). NAR removed the requirement for shunts/switching the igniters and now just requires that no power be able to get to the igniters. Below is a photo of the system used in my L3 rocket, 2 screw switches (one on each battery hot leg, per the manufacturers recommendation) and the on/off switch terminal on the alts have solid wire jumpers to set the alt as permanently "ON" (at least as long as the jumper is present). Also to cut down on connection issues I wire directly to the alt terminals which means fewer connections to check if somethings not right. Depending on the wifi switch it may or may not pass the test as a safety feature (contact the manufacturer and get it in writing/email that there is no path for power to the alts/igniters while in standby). Honestly for your L3 cert I would keep it mechanical switch, then afterwards change it over to the wifi, a bonus is that the wiring complexity for a mechanical switch is simple and easy to diagnose.

Edit: all this in addition to what was said in earlier posts about mechanical relays and g-forces.

 

[ksaves2]

Mechanical relays? Whoa Nellie. Ummmmm, If you are using the WiFi switches and they default to off, why don't you just connect up the batteries without switches/relays and go?
The other thing would be to ditch the WiFi switches and just built two Quantums and be done with it? No complex wiring. Though if you use the Wifi switches you are just fine with direct connection of the batteries just before flight.

Use no mechanical switches, connect up your batteries, seal up the ebay, take rocket to the launchpad and sequentially activate each Quantum and then launch. If you expect a wait on the pad, make sure you use batteries of adequate capacity.

TRA ruled that this is reasonable otherwise there would be no advantage whatsoever for Wifi activation of one's electronics if you have to stuff a switch on everything for deployment. Don't get me mouthing off on shunts when dealing with ematches. Shunts will not work with ematches as enough current can pass in the parallel shunt situation for the match to blow so forget that. A high current igniter situation with a careful battery choice and a shunt might prevent a problem but unless one is willing to do an all up "failsafe" test and risk destroying their electronics in the process, it's false security.

It one is really panicky about going switchless, bench test this with bare contained ematches using a Quantum without a switch. Plug the battery in and out as much as you want. T'ain't nothing is going to happen.

Now if you are doing this under NAR they have a tendency to be switch happy so YMMV there. Kurt

 

[ksaves2]

Keep it simple, relays may not allow the altimeter to continuity check the igniters depending on how they are setup (not sure if the SL will arm properly in that situation). NAR removed the requirement for shunts/switching the igniters and now just requires that no power be able to get to the igniters. Below is a photo of the system used in my L3 rocket, 2 screw switches (one on each battery hot leg, per the manufacturers recommendation) and the on/off switch terminal on the alts have solid wire jumpers to set the alt as permanently "ON" (at least as long as the jumper is present). Also to cut down on connection issues I wire directly to the alt terminals which means fewer connections to check if somethings not right. Depending on the wifi switch it may or may not pass the test as a safety feature (contact the manufacturer and get it in writing/email that there is no path for power to the alts/igniters while in standby). Honestly for your L3 cert I would keep it mechanical switch, then afterwards change it over to the wifi, a bonus is that the wiring complexity for a mechanical switch is simple and easy to diagnose.

Edit: all this in addition to what was said in earlier posts about mechanical relays and g-forces.


View attachment 327383 View attachment 327384

Yup, this is where one needs to use a screw switch! Thank heavens the switch on each ematch was abandoned years ago! Kurt

 

[ttabbal]

It's not the voltage that's the problem. It's the current and the battery's ability to sustain that current level over time.

From the Quantum FAQ. https://www.eggtimerrocketry.com/page64.php

The wifi switch uses the same module. It's your rocket, and it might work, but I won't fly them that way.

Shunts are not required for L3. Your L3CC/TAP has the final say, but many of them are willing to allow it if you can demonstrate that they are safe.

If I were overseeing an L3 cert, I would not allow 9V batteries with the wifi devices. Too much chance of a brownout killing the deployment electronics. Recovery is the #1 safety issue to me. If I know about it, I would make an issue of it as an RSO as well.

I did my L3 less than a month ago with a Quantum and wifi switch connected to a MAWD. Perfect flight and, more importantly, recovery. No mechanical switches, my L3CC was fine with it once I provided documentation from Eggtimer on the design. Post flight inspection showed both altimeters fired both charges and had full flight data, no brownouts.

 

[Hal8472]

I see the requirement for a switch on each ematch has changed. Thank goodness. This makes it much easier in that I don't need relays in the first place.
Ok then. And yes, the quantum becomes the solution of choice.
Thanks
Andrew

 

[cerving]

Don't use the relay, they won't handle that kind of vibration or G's and you will be hating life as you watch your L3 come in ballistic because both of the altimeters reset. You CAN use the WiFi Switch with either TRA or NAR, but you have to put a screw switch in between the battery and the switch so that all power is deactivated until arming (at least that's the NAR interpretation... TRA depends on your TAP's). You can still arm it remotely once you turn on the screw switches. To get the WiFi signal to work outside the CF AV bay, you can cut a vertical slot 1/16" wide by 2 15/32" tall... that acts as a waveguide antenna for the WiFi signal. You want it on the side opposite the rail, of course, so you also want to make sure your WiFi switches are mounted on that side too.

 

[Hal8472]

Don't use the relay, they won't handle that kind of vibration or G's and you will be hating life as you watch your L3 come in ballistic because both of the altimeters reset. You CAN use the WiFi Switch with either TRA or NAR, but you have to put a screw switch in between the battery and the switch so that all power is deactivated until arming (at least that's the NAR interpretation... TRA depends on your TAP's). You can still arm it remotely once you turn on the screw switches. To get the WiFi signal to work outside the CF AV bay, you can cut a vertical slot 1/16" wide by 2 15/32" tall... that acts as a waveguide antenna for the WiFi signal. You want it on the side opposite the rail, of course, so you also want to make sure your WiFi switches are mounted on that side too.

Granted, I don't need the relays now. However, this technical point doesn't make sense. How could a relay on the igniter leads possibly cause an altimeter to reset? It reacts well to continuity loss and regaining.

I will seek further clarification from Eggtimer regarding the NAR and tripoli interpretation. Looks like there is ambiguity. Again, Technical point is that I see no reason for a manual switch.

Thanks for the CF tip. I did not know that work around.

 

[CORZERO]

Tripoli:

"Electronics – Prior to a level 3 certification flight, the flyer shall successfully fly at least one rocket in the level 2 range using an electronic device as the primary means of recovery system deployment. Level 3 certification flights shall include at least two completely separate electronic devices, with independent power sources, wire harnesses, and ignition devices for the primary and back-up means of recovery system deployment."

Where is the ambiguity?

 

[CORZERO]

TRA ruled that this is reasonable otherwise there would be no advantage whatsoever for Wifi activation of one's electronics if you have to stuff a switch on everything for deployment. Don't get me mouthing off on shunts when dealing with ematches. Shunts will not work with ematches as enough current can pass in the parallel shunt situation for the match to blow so forget that. A high current igniter situation with a careful battery choice and a shunt might prevent a problem but unless one is willing to do an all up "failsafe" test and risk destroying their electronics in the process, it's false security.

Now if you are doing this under NAR they have a tendency to be switch happy so YMMV there. Kurt

Please cite your sources for your ruling claims and NAR opinions.

 

[JimJarvis50]

Don't get me mouthing off on shunts when dealing with ematches. Shunts will not work with ematches as enough current can pass in the parallel shunt situation for the match to blow so forget that.

Sorry for derailing the OP's thread, but...

Kurt, I previously posted the results of one of the many tests I have done looking at Shunts. It was in Post 53 here, with testing done in part due to comments you made about shunts.

https://www.rocketryforum.com/showt...ket-kit&p=1711932&highlight=shunt#post1711932

I agree that it is possible to design a shunt that doesn't provide the intended protection. It is also possible to design one that does, and it is not difficult to do. As with many things in rocketry, a little time to research the topic and to perform ground testing is necessary. It is a valuable safety technique, particularly for staged rockets.

I don't mind you expressing concerns about shunts or recommending that they not be used. However, your statement above is not true.

Jim

 

[ksaves2]

Please cite your sources for your ruling claims and NAR opinions.

P!ease read the post from another source above. I emailed TRA HQ, received said reply and also saw it in the BOD minutes that were published later. Email the BOD contact if you don't believe me.

What's the use of wireless if one can't ditch the switch to turn on altimeters.

One can have a TRS installation direct connected, no switch and no one could tell. In the wait/safe mode nothing is heard from the electronics except the "keep alive" beep at the receiver that one could keep locked away in their car while they go to the RSO.

I began pondering questions for the hierarchy as soon as I saw that these devices were going to become available. The prospect of ditching the switch for very small Rockets is very appealing. Kurt

 

[ksaves2]

Sorry for derailing the OP's thread, but...

Kurt, I previously posted the results of one of the many tests I have done looking at Shunts. It was in Post 53 here, with testing done in part due to comments you made about shunts.

https://www.rocketryforum.com/showt...ket-kit&p=1711932&highlight=shunt#post1711932

I agree that it is possible to design a shunt that doesn't provide the intended protection. It is also possible to design one that does, and it is not difficult to do. As with many things in rocketry, a little time to research the topic and to perform ground testing is necessary. It is a valuable safety technique, particularly for staged rockets.

I don't mind you expressing concerns about shunts or recommending that they not be used. However, your statement above is not true.

Jim

Yes it is. If you can test it and prove it will be safe for its intended purpose then I will agree. The problem is a neophyte can dork their Electronics in the process of testing. Unless it's actually tested in the failsafe mode it's intended to participate in you don't know whether or not the so-called shunt will absorb all the energy and bypass an ematch adequately so it will not pop. If you can't prove to me that the shunt can work then we don't know if it will serve its intended purpose.

With higher current applications of which I'm sure you're very well aware of, I believe a shunt can be more safely used. But again the failsafe mode needs to be demonstrated. Low current pass through of a shunt in a parallel fashion can pop a match. Requiring one on a deployment circuit is idiocy. Kurt

 

[JimJarvis50]

Yes it is. If you can test it and prove it will be safe for its intended purpose then I will agree. The problem is a neophyte can dork their Electronics in the process of testing. Unless it's actually tested in the failsafe mode it's intended to participate in you don't know whether or not the so-called shunt will absorb all the energy and bypass an ematch adequately so it will not pop. If you can't prove to me that the shunt can work then we don't know if it will serve its intended purpose.

With higher current applications of which I'm sure you're very well aware of, I believe a shunt can be more safely used. But again the failsafe mode needs to be demonstrated. Low current pass through of a shunt in a parallel fashion can pop a match. Requiring one on a deployment circuit is idiocy. Kurt

Kurt, the testing I posted about showed what I would consider to be a "normal" shunt. It worked fine with both a low current igniter and a LiPo battery (as it has many times in past testing). One test configuration isn't enough to prove the point (even though I have done many configurations in the past). However, it is also easy to measure the resistances of the legs, look at the worst-case battery current and the no-fire current for the ematches, and then conclude via that method that a shunt is safe. It is also possible to ground test exactly the configuration you intend to fly, and to do so without damaging your electronics. I know this because I have done it - many times. I don't understand why you maintain that "the safety of a shunt can't be proven"? This is a pretty easy one, actually. It surprises me that you seem unwilling to consider actual data or do a few simple calculations to back up your assertion.

I agree that requiring a shunt for charges in an L3 is unnecessary.

Jim

 

[ksaves2]

With the staging you do Jim I realize you are darned sure of what you are doing. My basic point is if some neophyte throws together and parallel shunt and thinks
they're safe are only deluding themselves and any potential RSO if they don't test and prove it. That's all. You've tested, I'm can't argue that. You're the
one doing the arming and don't want any surprises. I don't stage outside of BP and cannot judge except I would have to start testing out shunt situations
if it came to that.

Yeah, one can see magazine covers from 10 years ago with with six jumper plugs on L3 projects, one on each altimeter and one on each of the four ematch
circuits. Those were the bad old days. Kurt

 

[cerving]

Granted, I don't need the relays now. However, this technical point doesn't make sense. How could a relay on the igniter leads possibly cause an altimeter to reset? It reacts well to continuity loss and regaining.

I will seek further clarification from Eggtimer regarding the NAR and tripoli interpretation. Looks like there is ambiguity. Again, Technical point is that I see no reason for a manual switch.

Thanks for the CF tip. I did not know that work around.

Aah, I didn't see that the relay was on the ematches. I still wouldn't trust it... rockets get thrashed around a lot and the contacts are likely to bounce. If they bounce when you're trying to fire the ematch, it may reduce the average current going to the ematch and it may not heat up enough. You could substitute a solid state relay instead, but then you still have the "electronic switch" issue, so why bother?

As far as the NAR/TRA regs, NAR is pretty adamant that there MUST be a physical switch disconnecting the power from the electronics until it's on the pad. That does not preclude putting the switch in line with the battery on the Quantum, then arming the Quantum remotely. Yes, that does defeat one of the main advantages of having the WiFi Switch/Quantum, but at least while you're doing it you know that there's no chance that something's going to pop while you're fiddling with the switch. TRA, that's a different story... it's up to your TAPs. I've spoken to a few, and it's about 50-50 whether they'd allow an electronic switch or not (ANY electronic switch... not just a WiFi/Quantum but a magnetic switch too). I'm still working on my L3 (have the rocket and the motor) so believe me, it's something that I am personally invested in too.

 

[Steve Shannon]

Aah, I didn't see that the relay was on the ematches. I still wouldn't trust it... rockets get thrashed around a lot and the contacts are likely to bounce. If they bounce when you're trying to fire the ematch, it may reduce the average current going to the ematch and it may not heat up enough. You could substitute a solid state relay instead, but then you still have the "electronic switch" issue, so why bother?

As far as the NAR/TRA regs, NAR is pretty adamant that there MUST be a physical switch disconnecting the power from the electronics until it's on the pad. That does not preclude putting the switch in line with the battery on the Quantum, then arming the Quantum remotely. Yes, that does defeat one of the main advantages of having the WiFi Switch/Quantum, but at least while you're doing it you know that there's no chance that something's going to pop while you're fiddling with the switch. TRA, that's a different story... it's up to your TAPs. I've spoken to a few, and it's about 50-50 whether they'd allow an electronic switch or not (ANY electronic switch... not just a WiFi/Quantum but a magnetic switch too). I'm still working on my L3 (have the rocket and the motor) so believe me, it's something that I am personally invested in too.

At LDRS 36 the Tripoli BoD was asked whether the WiFi switch is allowable. Kurt sent the question to Deb Koloms. Based on information you provided about the circuit, we stated that we have no problem with it. With that said, you're correct; a person's TAPs (and the RSO) must also be comfortable with it before allowing it. That's a matter of familiarity I think.




Steve Shannon

 

[jderimig]

With the staging you do Jim I realize you are darned sure of what you are doing. My basic point is if some neophyte throws together and parallel shunt and thinks
they're safe are only deluding themselves and any potential RSO if they don't test and prove it. That's all. You've tested, I'm can't argue that. You're the
one doing the arming and don't want any surprises. I don't stage outside of BP and cannot judge except I would have to start testing out shunt situations
if it came to that.

Yeah, one can see magazine covers from 10 years ago with with six jumper plugs on L3 projects, one on each altimeter and one on each of the four ematch
circuits. Those were the bad old days. Kurt

Shunts are an advanced safety technique. All shunts will allow current to flow through the ematch, its just a question of how much will. To KNOW that you have to KNOW the resistance of the shunt, the resistance of the ematch, the output impedence (resistance) of the power source at the altimeter output (not just the battery resistance) and the resistances of all the connections. The KNOW is the tricky part, especially the output resistance of the altimeter output if there is energy storage (capacitance) there.

Opens are alot easier to analyze. 0 current will flow in a open circuit. The is also less to KNOW to have confidence in this safety approach.

 

[JimJarvis50]

Shunts are an advanced safety technique. All shunts will allow current to flow through the ematch, its just a question of how much will. To KNOW that you have to KNOW the resistance of the shunt, the resistance of the ematch, the output impedence (resistance) of the power source at the altimeter output (not just the battery resistance) and the resistances of all the connections. The KNOW is the tricky part, especially the output resistance of the altimeter output if there is energy storage (capacitance) there.

Opens are alot easier to analyze. 0 current will flow in a open circuit. The is also less to KNOW to have confidence in this safety approach.

John, what I do is measure the resistances of the legs, assume that the battery voltage won't drop (even though it will), and set a criteria that the maximum current through the match can't be more than half of the no-fire current. Do you see any flaws with that approach?

Jim

 

[cerving]

At LDRS 36 the Tripoli BoD was asked whether the WiFi switch is allowable. Kurt sent the question to Deb Koloms. Based on information you provided about the circuit, we stated that we have no problem with it. With that said, you're correct; a person's TAPs (and the RSO) must also be comfortable with it before allowing it. That's a matter of familiarity I think.




Steve Shannon

Thanks for that, Steve. I didn't make it to LDRS 36 so I was not aware of that. So, can it be stated that TRA does not explicitly disallow electronic switches on deployment electronics for L3 attempts, subject to TAP approval?

 

[jderimig]

John, what I do is measure the resistances of the legs, assume that the battery voltage won't drop (even though it will), and set a criteria that the maximum current through the match can't be more than half of the no-fire current. Do you see any flaws with that approach?

Jim

Jim, like I said it is tricky and you have to make the measurements like you are doing. Every case is different and what is safe for one instance may not be for another.

A question that I have is are you running the shunt in parallel with your ematches with a series resistor between the power source and your parallel circuit?

In otherwords do you include a dropping resistor that the shunt works against to drop the voltage across the match?

 

[Charles_McG]

Does it take any special kind of meter to read those low resistances?

 

[ksaves2]

Shunts are an advanced safety technique. All shunts will allow current to flow through the ematch, its just a question of how much will. To KNOW that you have to KNOW the resistance of the shunt, the resistance of the ematch, the output impedence (resistance) of the power source at the altimeter output (not just the battery resistance) and the resistances of all the connections. The KNOW is the tricky part, especially the output resistance of the altimeter output if there is energy storage (capacitance) there.

Opens are alot easier to analyze. 0 current will flow in a open circuit. The is also less to KNOW to have confidence in this safety approach.

Yup, I didn't mean to infer they didn't work. If one doesn't know what they are doing it can be a false sense of security. Obviously when used for staging motor purposes it carries greater importance to work as expected in the failure situation
it's expected to protect one from. Kurt

 

[ksaves2]

John, what I do is measure the resistances of the legs, assume that the battery voltage won't drop (even though it will), and set a criteria that the maximum current through the match can't be more than half of the no-fire current. Do you see any flaws with that approach?

Jim

Is it also safe you assume you have to consider your battery source/type and the maximum current it can deliver and how much ones electronics can deal with? Kurt (This is getting interesting seeing what it takes for an effective, safe shunt.)

 

[ksaves2]

At LDRS 36 the Tripoli BoD was asked whether the WiFi switch is allowable. Kurt sent the question to Deb Koloms. Based on information you provided about the circuit, we stated that we have no problem with it. With that said, you're correct; a person's TAPs (and the RSO) must also be comfortable with it before allowing it. That's a matter of familiarity I think.




Steve Shannon

Thanks for posting that Steve. It's not so much of what a TAP is "comfortable" with it's more so how this would affect everyday flying. I've flown several switchless rockets with Cris' remote products and mag switches. As you point out it was considered
acceptable. As far as L3, keep the TAPs and RSO's happy. As far as staging goes that's another ball of wax. As far as deployment electronics goes the current offerings are pretty darned good considering safety.

Besides there more than likely will be more fliers with smaller diameter MD rockets that are going to be going very high with trackers, with little room for outside accessible switches. It won't take an M motor to do an extreme flight anymore. Kurt

 

[Steve Shannon]

Thanks for that, Steve. I didn't make it to LDRS 36 so I was not aware of that. So, can it be stated that TRA does not explicitly disallow electronic switches on deployment electronics for L3 attempts, subject to TAP approval?

Absolutely. It should be part of the minutes also which are in the Tripoli Report for that period.