Eggtimer Quantum - A WiFi-Enabled Flight Computer

Nope, just one Quantum and Project X in the BT50... running off the same compact 350 mAH 2S LiPo. Probably about 2-3 oz, which is a lot for an Estes Mongoose.

Back in post #109, you mentioned 2 Quantums. That must have been the other flight.

Shouldn't that be 'Project EggX' - for branding purposes?

cerving said:

Nope, just one Quantum and Project X in the BT50... running off the same compact 350 mAH 2S LiPo. Probably about 2-3 oz, which is a lot for an Estes Mongoose.

Click to expand...

If project X is what I hope it is, I have a project begging for it.

cerving said:

Nope, just one Quantum and Project X in the BT50... running off the same compact 350 mAH 2S LiPo. Probably about 2-3 oz, which is a lot for an Estes Mongoose.

Click to expand...

I would like to see how you mounted and wired everything to fit in a BT50. Can you take some pics and post when you release X?

Charles_McG said:

Back in post #109, you mentioned 2 Quantums. That must have been the other flight.

Click to expand...

Yes, that was the G-F flight, on a rocket based on an Estes STM012. $7 each from Estes' web site right now... added basswood fins and 29mm mount for the bottom stage.

Cris will have to launch Project X with Propellant X for a true validation flight

Kenny

cerving said:

Yes, that was the G-F flight, on a rocket based on an Estes STM012. $7 each from Estes' web site right now... added basswood fins and 29mm mount for the bottom stage.

Click to expand...

On the subject of two quantums, I'm going to be using two of them in my forthcoming frenzy xl and I'm wondering if any of the following things are currently or might in the future be possible:

1) Change the name of the wifi network. It'd be great if I could name one "rocketsam2016 frenzy primary" and the other "rocketsam2016 frenzy secondary" such that the wifi network name would be that and/or that would be displayed prominently at the top of the status pages.

2) I need physical switches if I ever want to fly this L3 under NAR (tell me if I'm wrong!), so once I'm doing that it might be fun as well to wire in some status LEDs that would indicate Off/On/Armed. Is there any easy way to hook that up to the current board? This would just be for fun - the beeping is enough to tell me they are armed and I'm assuming I'll be able to easily tell that both are beeping.

rocketsam2016 said:

On the subject of two quantums, I'm going to be using two of them in my forthcoming frenzy xl and I'm wondering if any of the following things are currently or might in the future be possible:

1) Change the name of the wifi network. It'd be great if I could name one "rocketsam2016 frenzy primary" and the other "rocketsam2016 frenzy secondary" such that the wifi network name would be that and/or that would be displayed prominently at the top of the status pages.

2) I need physical switches if I ever want to fly this L3 under NAR (tell me if I'm wrong!), so once I'm doing that it might be fun as well to wire in some status LEDs that would indicate Off/On/Armed. Is there any easy way to hook that up to the current board? This would just be for fun - the beeping is enough to tell me they are armed and I'm assuming I'll be able to easily tell that both are beeping.

Click to expand...

Each WiFi unit has its own unique identifier when you get it. You don't have to do a thing except bench test so you are assured which one is which. Here is where a checklist is helpful with the ID numbers written down so one can keep track. You'll be able to pull this off easily. If your device allows you to "rename" network wifi links, you'll have that option but frankly, I don't bother.

Personally based on the design that Cris Cerving espouses, switches are unneeded and superfluous. I hope he can convince the "Ivory Tower Boys" or the
"Powers that Be" they are absolutely not necessary for safety's sake. The "only" reason to use them would be if one is pressed on space and hence battery capacity.
In that situation, a long wait after prepping or sitting on the pad could compromise the flight. If faced with that prospect, a physical switch would allow one to activate their electronics at the "last minute" to conserve the batteries for flight. A switch is another point of failure
in an electrical circuit

Me? I always look at extra battery capacity as "useful" weight especially if needed for CG purposes or if one is trying to fly a "big" motor and keep under a waiver
limitation. It's nice to have if one has the room.

I flew an EggTimer TRS and the rocket had like a 45 minute wait on the pad. I used a single 2s Lithium to run the cpu, the pyro circuits and it was 1300mah
capacity. Had plenty of juice for the flight by the time it was launched so I was unfazed and the flight was successful.

Kurt

ksaves2 said:

Each WiFi unit has its own unique identifier when you get it. You don't have to do a thing except bench test so you are assured which one is which. Here is where a checklist is helpful with the ID numbers written down so one can keep track. You'll be able to pull this off easily. If your device allows you to "rename" network wifi links, you'll have that option but frankly, I don't bother.

Click to expand...

Yup I know they have unique identifiers and I'll have them written on my checklist, but nonetheless it'd be a very convenient ability and would reduce the risk of mistakes when using two in a single rocket (for example if the secondary charges are larger, it would be sub optimal to get the quantums mixed up and accidentally have the secondary charge fire first).

ksaves2 said:

Personally based on the design that Cris Cerving espouses, switches are unneeded and superfluous. I hope he can convince the "Ivory Tower Boys" or the
"Powers that Be" they are absolutely not necessary for safety's sake. The "only" reason to use them would be if one is pressed on space and hence battery capacity.
In that situation, a long wait after prepping or sitting on the pad could compromise the flight. If faced with that prospect, a physical switch would allow one to activate their electronics at the "last minute" to conserve the batteries for flight. A switch is another point of failure
in an electrical circuit

Me? I always look at extra battery capacity as "useful" weight especially if needed for CG purposes or if one is trying to fly a "big" motor and keep under a waiver
limitation. It's nice to have if one has the room.

I flew an EggTimer TRS and the rocket had like a 45 minute wait on the pad. I used a single 2s Lithium to run the cpu, the pyro circuits and it was 1300mah
capacity. Had plenty of juice for the flight by the time it was launched so I was unfazed and the flight was successful.

Kurt

Click to expand...

Agreed that no switches would be nice, but AFAIK they are required for an L3 flight for NAR. You're right that the other benefit is battery life - in my case I've decided I just want to use a single battery size across my rockets so I'm using a 2s 460mah lipo since one of my rockets is space constrained. That way my batteries are all interchangeable which is pretty convenient, but the downside is it won't last for hours and hours with a quantum.

But my question remains: is there an easy way to hook up leds for off/on/armed for fun?

rocketsam2016 said:

On the subject of two quantums, I'm going to be using two of them in my forthcoming frenzy xl and I'm wondering if any of the following things are currently or might in the future be possible:

1) Change the name of the wifi network. It'd be great if I could name one "rocketsam2016 frenzy primary" and the other "rocketsam2016 frenzy secondary" such that the wifi network name would be that and/or that would be displayed prominently at the top of the status pages.

2) I need physical switches if I ever want to fly this L3 under NAR (tell me if I'm wrong!), so once I'm doing that it might be fun as well to wire in some status LEDs that would indicate Off/On/Armed. Is there any easy way to hook that up to the current board? This would just be for fun - the beeping is enough to tell me they are armed and I'm assuming I'll be able to easily tell that both are beeping.

Click to expand...

I looked at customizing the SSID early on (actually, when I did the WiFi Switch...), the problem is that 1) you can only have 15 characters (not a terrible limitation) and 2) They have to be unique somehow. The uniqueness is a kicker... how do you guarantee that two people won't set "my rocket" as their SSID? The current firmware does it by adding the non-OUI part of the MAC address to a shorter name ("Quantum_"). Of course, that's no different than your home WiFi... if your neighbor has their router set to the default and it's something like "charter wifi" you might find that there are 10 of them just like that in an apartment complex. The only differentiator is the signal strength (which is hopefully strongest in your unit), and the passkey (which is hopefully unique somehow).

Since the passkey on a Quantum (or WiFi Switch) is fixed and derived from the MAC, this may not be a real problem... you would be able to see the "other" device with the same SSID, but you wouldn't be able to connect to it. That should prevent them from arming your Quantum, and vice versa. I'll look at adding this feature in a future build, but it's not likely to be in the initial airstart version.

Yes, NAR wants a physical switch on the deployment igniters on a L3 project. TRA is a bit more lenient, they only require that it's disabled. For an "armed" indicator, you could wire a LED with an appropriate dropping resistor in parallel with the buzzer, when it goes into the "ready for flight" mode you'll see it blink once per second. I recommend that you only do this with the newer A12f boards; the older one has the buzzer driven directly from the WiFi processor, and there isn't enough current to drive both the buzzer and a LED. The A12f board has an additional FET to drive the buzzer, there's plenty of extra current capacity.

cerving said:

I looked at customizing the SSID early on (actually, when I did the WiFi Switch...), the problem is that 1) you can only have 15 characters (not a terrible limitation) and 2) They have to be unique somehow. The uniqueness is a kicker... how do you guarantee that two people won't set "my rocket" as their SSID? The current firmware does it by adding the non-OUI part of the MAC address to a shorter name ("Quantum_"). Of course, that's no different than your home WiFi... if your neighbor has their router set to the default and it's something like "charter wifi" you might find that there are 10 of them just like that in an apartment complex. The only differentiator is the signal strength (which is hopefully strongest in your unit), and the passkey (which is hopefully unique somehow).

Since the passkey on a Quantum (or WiFi Switch) is fixed and derived from the MAC, this may not be a real problem... you would be able to see the "other" device with the same SSID, but you wouldn't be able to connect to it. That should prevent them from arming your Quantum, and vice versa. I'll look at adding this feature in a future build, but it's not likely to be in the initial airstart version.

Yes, NAR wants a physical switch on the deployment igniters on a L3 project. TRA is a bit more lenient, they only require that it's disabled. For an "armed" indicator, you could wire a LED with an appropriate dropping resistor in parallel with the buzzer, when it goes into the "ready for flight" mode you'll see it blink once per second. I recommend that you only do this with the newer A12f boards; the older one has the buzzer driven directly from the WiFi processor, and there isn't enough current to drive both the buzzer and a LED. The A12f board has an additional FET to drive the buzzer, there's plenty of extra current capacity.

Click to expand...

Good to know! Sounds like this should be a pretty safe mod then on the new boards? I may or may not do it we'll see. If I wanted to show that the quantum was on/off, would the best thing to do be to have a resistor + LED across the battery inputs and would that be pretty safe given a large enough resistor?

rocketsam2016 said:

Yup I know they have unique identifiers and I'll have them written on my checklist, but nonetheless it'd be a very convenient ability and would reduce the risk of mistakes when using two in a single rocket (for example if the secondary charges are larger, it would be sub optimal to get the quantums mixed up and accidentally have the secondary charge fire first).


Agreed that no switches would be nice, but AFAIK they are required for an L3 flight for NAR. You're right that the other benefit is battery life - in my case I've decided I just want to use a single battery size across my rockets so I'm using a 2s 460mah lipo since one of my rockets is space constrained. That way my batteries are all interchangeable which is pretty convenient, but the downside is it won't last for hours and hours with a quantum.

But my question remains: is there an easy way to hook up leds for off/on/armed for fun?

Click to expand...

If you can prove to your NAR L3CC that the devices are safed via their built in switches (Cris even has a bit in the users manual saying that iirc) they will probably only require a single disconnect switch on one leg of the battery.

My L3CC only required a single switch for each altimeter simply to disconnect the battery from the system.

cerving said:

I looked at customizing the SSID early on (actually, when I did the WiFi Switch...), the problem is that 1) you can only have 15 characters (not a terrible limitation) and 2) They have to be unique somehow. The uniqueness is a kicker... how do you guarantee that two people won't set "my rocket" as their SSID? The current firmware does it by adding the non-OUI part of the MAC address to a shorter name ("Quantum_"). Of course, that's no different than your home WiFi... if your neighbor has their router set to the default and it's something like "charter wifi" you might find that there are 10 of them just like that in an apartment complex. The only differentiator is the signal strength (which is hopefully strongest in your unit), and the passkey (which is hopefully unique somehow).

Since the passkey on a Quantum (or WiFi Switch) is fixed and derived from the MAC, this may not be a real problem... you would be able to see the "other" device with the same SSID, but you wouldn't be able to connect to it. That should prevent them from arming your Quantum, and vice versa. I'll look at adding this feature in a future build, but it's not likely to be in the initial airstart version.

Yes, NAR wants a physical switch on the deployment igniters on a L3 project. TRA is a bit more lenient, they only require that it's disabled. For an "armed" indicator, you could wire a LED with an appropriate dropping resistor in parallel with the buzzer, when it goes into the "ready for flight" mode you'll see it blink once per second. I recommend that you only do this with the newer A12f boards; the older one has the buzzer driven directly from the WiFi processor, and there isn't enough current to drive both the buzzer and a LED. The A12f board has an additional FET to drive the buzzer, there's plenty of extra current capacity.

Click to expand...

Errrrrrr, ummmmm. I though NAR dropped the "safety switch" on the ematches years ago. That would mean one switch each for "off/on" and four, count 'em four! switches on each of the four ematches. Totally uncalled for and if that is the case, time
to join TRA for the certification. True one might still have to "put a switch" on the batter(ies) for the Quantum but they wouldn't have to put 4 switches on the ematches. As I said, I thought TRA and NAR both dropped the requirement years ago about the same time. Perhaps some "not so bright" Tap's or L3CC people might still insist upon "safety switches" on the deployment ematches but at least in TRA one might have some recourse.
Might be able to find some Taps who agree with Cris Cerving as I imagine there have plenty of flights that have flown without battery switches. I'd say use a single high capacity battery for the Quantum and have at it.

I can rant about shunts too but since there are those that institute those for staging that is not an issue for certification as 2 stage is not allowed.

Shunts are totally useless in preventing an ignition accident.................. Unless a user static tests the failure mode and proves it prevents the motor igniter from lighting. With an augmented low current motor igniter a lipo can blast plenty of current through a shunt and the igniter to set off an ematch augmented motor igniter. NO added safety there plus if one "tests" it, they may cook their electronic device they planned to use!

The only way around this is an electronic device that can be "turned on" remotely while the rocket is on the pad and that can give feedback via wireless that the ignition circuit is armed and ready in the sustainer so the booster can
be fired. That is the only "surefire" way to prevent a sustainer accident on the pad with a two stage. Everyone is safely out of the way while the sustainer motor is armed.

NAR requires that ematches are disconnected physically, or that the controller is powered off (i.e. disconnected from the battery).

The problem that I see is that if you have some kind of device (timer or altimeter) using a FET and the FET gets blown, it's going to fire as soon as you apply power, presumably with some kind of switch mounted on the side of the rocket, so your face and/or hands are right next to the rocket. That's not true with the Quantum, even if you blow the FET; the BJT transistor would have to turn on too, and that's not gonna happen until something tells it to. The "something" would be the processor, after you're armed and in the air.

I don't know how often this kind of thing happens, I personally haven't see it but I've heard anecdotal tales of it.

cerving said:

NAR requires that ematches are disconnected physically, or that the controller is powered off (i.e. disconnected from the battery).

The problem that I see is that if you have some kind of device (timer or altimeter) using a FET and the FET gets blown, it's going to fire as soon as you apply power, presumably with some kind of switch mounted on the side of the rocket, so your face and/or hands are right next to the rocket. That's not true with the Quantum, even if you blow the FET; the BJT transistor would have to turn on too, and that's not gonna happen until something tells it to. The "something" would be the processor, after you're armed and in the air.

I don't know how often this kind of thing happens, I personally haven't see it but I've heard anecdotal tales of it.

Click to expand...

O.k., that means an on/off switch for each "conventional" deployment device is necessary with NAR then to shut off the controllers. Like I said in the past, they required switches on the ematches themselves. Take a look in some of the older magazines of
cert attempts and you can see stuff like six switches or 6 jack and plug arrangements. Fortunately when getting into the L3 range, the rockets are large enough to accommodate whatever hardware one has to throw at them. Kurt

ksaves2 said:

O.k., that means an on/off switch for each "conventional" deployment device is necessary with NAR then to shut off the controllers. Like I said in the past, they required switches on the ematches themselves. Take a look in some of the older magazines of
cert attempts and you can see stuff like six switches or 6 jack and plug arrangements. Fortunately when getting into the L3 range, the rockets are large enough to accommodate whatever hardware one has to throw at them. Kurt

Click to expand...

Now I'm confused. Cris - I interpreted your response as saying that it is sufficient to have the altimeter physically disconnected from the battery by a switch. If so, the Quantum is still safe when you throw the switch since it has the BJT transistor.

If you disconnect the battery, it's 100% safe... no juice to fire the igniter. That's the way the NAR thinks, and it's hard to argue with.

The Quantum is different than other altimeters because there are two electrical paths required to activate a deployment device... the FET and the BJT. The FET is basically an electronic switch on the deployment power, the BJT's (one for each channel) controls the firing. There is much less chance of having any kind of accidental firing than you would have with a device with only a single path. If for some reason you fry something, the other path is there to prevent it from triggering accidentally.

FET's have a habit of failing short-circuited when overloaded. If a FET switch fails that way, it's essentially always on. BJT's fail open when blown... they're always off. From a pad safety point of view, it's safer to have an open-circuit failure than a closed-circuit failure. All Eggtimer Rocketry altimeters use BJT's in their deployment circuitry, for that reason. Most other altimeters use FET's. FET's for a given size will handle more current and don't create as much heat, because they're a near-zero resistance device, whereas BJT's are basically a variable resistor as far as the load is concerned. Everything in electronics design is a trade-off... in this case, I chose a "safer" route vs the more established convention.

The problem that I see is that if you have some kind of device (timer or altimeter) using a FET and the FET gets blown,

Click to expand...

Cris, I was wondering the other day if the Quantum checks for power on the downstream side of the power feed FET as part of its startup tests? If it does, it could alert the owner that a FET was blown and to not fly the altimeter. Testing the individual channel FETs might be a little trickier, but that would show up during normal ground testing I think.

BTW, finally got around to assembling the WiFi switch and a Quantum flight computer that I got in the sale last November. Very easy to assemble and work well (in ground testing so far). Thanks for your efforts in developing these devices.

No, but it would be really hard to blow the FET. You'd probably blow the BJT first. It would take some circuitry to do this, with the current board there's really no room and there are no available I/O ports on the processor. Maybe I'll sacrifice one of my early ones to see if I can blow the FET...

No worries Cris. It was just a thought when I was running failure modes in my head. FETs are a lot better than they used to be.

Of note. I emailed a question specifically on the "switched" vs. "switchless" about a month ago to TRA and received a courteous reply it was a good question and the BOD is going to consider it specifically with these devices.
I have several small projects with mag switches and EggTimer products I connect up the battery and activate on the pad. The TRS especially in a minimum diameter I have wired with one battery in parallel. I had the room to put
a screw switch in that controls the juice into the pyro circuit. I leave it open, plug in the battery to the TRS and let it pair and get into standby mode. The system is silent and nobody knows there is no switch on the battery.
On the pad, I close the pyro switch, activate for launch and insert the igniter.

Same thing can apply for the Quantum in a small project. I have no reservations flying that completely switchless.

The thing I do like about the Quantum is if one wants to use a unit to fly for staging that is a situation where I would insist on a switch to the Quantum battery on the device that is wired to ignite an upper stage motor.

That way the "upper stage ignition"Quantum can be "turned on" at the pad with the mechanical switch by one person. That person can then step away a distance and "arm" the motor ignition Quantum with some space between them and the rocket.

Personally, when I am going to fly switchless, I test the electronics each time before I am going to fly that rocket with contained bare ematches. If it passes that test, ie. no popping, I proceed to prepping for flight adding BP etc. This can be done well in advance under relaxed conditions.

I have heard stories where folks have flown a DD rocket and had a hard landing for one reason or another. They prep for a future flight and when they turn the device on at the pad, the charges blow due to some failure that occurred on the prior flight. I think cycling one's electronics with bare contained matches before every flight is prudent and would nearly completely minimize the risk of on pad deployments or upper stage motor firings. Kurt

I recommend doing the continuity tests at work worktable BEFORE you put the powder in the charge wells. If you're going to have a problem, it's going to show up then. I have yet to see a scenario (short of a soldering problem that would show up before you ever got to that point) that would cause a Quantum to fire a channel without arming.

cerving said:

I recommend doing the continuity tests at work worktable BEFORE you put the powder in the charge wells. If you're going to have a problem, it's going to show up then. I have yet to see a scenario (short of a soldering problem that would show up before you ever got to that point) that would cause a Quantum to fire a channel without arming.

Click to expand...

Right. I mentioned doing this with "contained ematches" which in my case is ematches epoxied in a hole at the bottom of those plastic ultra-centrifuge sample tube with the cap on and "NO" powder of course. If no pop, the device is intact.

Then move on to powder. One's electronics of course will run through the continuity test when turned on at the pad and one will need to confirm either visually (ie. Quantum WiFi) or aurally (ie. other devices with piezos or beepers) that the matches are connected with continuity. Heck I do have an ematch tester I use but Geez Louise even then I will not test an ematch as long as it's in contact with BP period! Never ever do that.
If using an ODT ematch tester use it before adding BP. If the altimeter then beeps a continuity fault, could be you made a bad connection somewhere in the circuit.

The Featherweight Parrot altimeter had a serious flaw in that it beeped the same continuity beep whether one or three channels were connected. I lost a rocket when on the pad, I thought there was supposed to be
some sort of warbling that both channels were connected. Shut off the Parrot, disconnected the Apogee charge and remembered, "Stupidhead, that's the way it's supposed to sound!" I reattached the apogee charge but since this was
"before" cataract surgery, I MISSED one leg of the ematch and the main blew on a ballistic descent. I didn't get the remains back for 18 months. Serious design flaw there.

I forgot to add that even a small charge like 1.5grams blown outside of a rocket will be REALLY loud. So there is a bit of power there. Kurt

cerving said:

If you disconnect the battery, it's 100% safe... no juice to fire the igniter. That's the way the NAR thinks, and it's hard to argue with.

The Quantum is different than other altimeters because there are two electrical paths required to activate a deployment device... the FET and the BJT. The FET is basically an electronic switch on the deployment power, the BJT's (one for each channel) controls the firing. There is much less chance of having any kind of accidental firing than you would have with a device with only a single path. If for some reason you fry something, the other path is there to prevent it from triggering accidentally.

FET's have a habit of failing short-circuited when overloaded. If a FET switch fails that way, it's essentially always on. BJT's fail open when blown... they're always off. From a pad safety point of view, it's safer to have an open-circuit failure than a closed-circuit failure. All Eggtimer Rocketry altimeters use BJT's in their deployment circuitry, for that reason. Most other altimeters use FET's. FET's for a given size will handle more current and don't create as much heat, because they're a near-zero resistance device, whereas BJT's are basically a variable resistor as far as the load is concerned. Everything in electronics design is a trade-off... in this case, I chose a "safer" route vs the more established convention.

Click to expand...

Keep in mind also that the NAR rule which requires a "physical break" is only in the Level 3 procedure. It doesn't apply to any other flights.

There are advantages to a physical switch with the quantum:
1) it let's you set things up ahead of time without the battery draining. You prepare the avbay the night before, flip the switch(es) at the launch site sometime before the launch, and then arm as usual on the pad. Depending on the rocket, this can be a nice time savings when you have an AVBay that is prepared ahead of time (except for charges) and doesn't need to be opened on site.
2) It let's you cut power without opening the av bay after the flight to save the batteries, stop the post-flight beeping and/or reset for a new flight
3) If using a pair of quantums for redundancy, an external pair of switches makes it easy to be sure you are connected to the right one with configuring flight settings.

You still get most of the benefits of the quantum - a visual and outside-the-rocket view of the settings, continuity and arming status, as well as the ability to arm the electronics while stepped back a few feet or more and do safe remote ground testing. I'm building my current rocket with switches so that it can be used for an L3 NAR cert, but these benefits mean I'll probably still use physical switches with quantums in future builds as well.

rocketsam2016 said:

There are advantages to a physical switch with the quantum:
1) it let's you set things up ahead of time without the battery draining. You prepare the avbay the night before, flip the switch(es) at the launch site sometime before the launch, and then arm as usual on the pad. Depending on the rocket, this can be a nice time savings when you have an AVBay that is prepared ahead of time (except for charges) and doesn't need to be opened on site.
2) It let's you cut power without opening the av bay after the flight to save the batteries, stop the post-flight beeping and/or reset for a new flight
3) If using a pair of quantums for redundancy, an external pair of switches makes it easy to be sure you are connected to the right one with configuring flight settings.

You still get most of the benefits of the quantum - a visual and outside-the-rocket view of the settings, continuity and arming status, as well as the ability to arm the electronics while stepped back a few feet or more and do safe remote ground testing. I'm building my current rocket with switches so that it can be used for an L3 NAR cert, but these benefits mean I'll probably still use physical switches with quantums in future builds as well.

Click to expand...

Very good thoughts. That's the kind of judgement I enjoy seeing in an L3 candidate.

You can easily put a switch on the deployment channel power, if you're using the single-battery configuration you just run it between the two "jumper" pads. That way you can check it on your table without the powder, turn it off, put in your powder, and you don't have to touch it until you get to the pad. This also applies to the TRS, too.

cerving said:

If you disconnect the battery, it's 100% safe... no juice to fire the igniter. That's the way the NAR thinks, and it's hard to argue with.

The Quantum is different than other altimeters because there are two electrical paths required to activate a deployment device... the FET and the BJT. The FET is basically an electronic switch on the deployment power, the BJT's (one for each channel) controls the firing. There is much less chance of having any kind of accidental firing than you would have with a device with only a single path. If for some reason you fry something, the other path is there to prevent it from triggering accidentally.

FET's have a habit of failing short-circuited when overloaded. If a FET switch fails that way, it's essentially always on. BJT's fail open when blown... they're always off. From a pad safety point of view, it's safer to have an open-circuit failure than a closed-circuit failure. All Eggtimer Rocketry altimeters use BJT's in their deployment circuitry, for that reason. Most other altimeters use FET's. FET's for a given size will handle more current and don't create as much heat, because they're a near-zero resistance device, whereas BJT's are basically a variable resistor as far as the load is concerned. Everything in electronics design is a trade-off... in this case, I chose a "safer" route vs the more established convention.

Click to expand...

I should have said earlier that I really appreciate this level of an explanation, Cris. This makes it easier for me to understand.

cerving said:

You can easily put a switch on the deployment channel power, if you're using the single-battery configuration you just run it between the two "jumper" pads. That way you can check it on your table without the powder, turn it off, put in your powder, and you don't have to touch it until you get to the pad. This also applies to the TRS, too.

Click to expand...

As I mentioned previously, I use one battery on a TRS with a screw switch connected to the pyro side. I also tested it completely switchless and no surprises there.
I liked the idea of saving the battery although with a 1300mah battery there can be a long wait time on the pad before that becomes critical. Nonetheless, switched or switchless no one can tell aurally what shape the rocket is in because in standby mode there is nothing heard from the TRS. Yes there is a keep alive beep heard
and the receiver but that is it. The business about a switch on a Quantum is moot. So what! You can look in your hand at the status. If flying with conventional
mechanically switched electronics one is going to stand there and wait for the proper beeping signals and continuity before inserting the igniter anyways.

The only advantage with a switched Quantum is if being used for staging or air starting. In that case, I believe the extra layer of safety for outweighs the inconvenience of a mechanical switch if the Quantum controls a low current augmented igniter to a large motor. I am not a believer in shunts unless a person actually tests the failure mode with the shunt in place. Unless one proves the shunt prevents firing it's a total false assurance. I'm with Cris that a needless switch (barring staging and airstarting) is another unneeded point of failure.

Kurt