Blue Raven blew BP charges instantly when switched on

[Mason T]

Thanks for the help Adrian, we'll be in touch via email.

And thanks all for the comments, we use 3s Lipos when we're launching 2-stage rockets because we use Aerotech FirstFire ignitors that need 12v. I understand it makes a lot more sense to use different ignitors that need less voltage but that's tricky over here in the UK. Commercial vendors only stock these Aerotech ignitors and thinking about making your own ignitor is a big no no from RSO's.

We have recently been moving towards Cesaroni motors for our sustainers as they come with ignitors that can ignite with a 1s, but this limits us to certain motor configs so we are trying to find alternative solutions to our ignitor problems. Any tips/recommendations would be appreciated!

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I was initially questioning if those igniters needed 12V. Igniters need current to ignite and from what I have seen they have low resistance ~1Ω and with ohms law you can get a fair amount of current with low voltages. The website does say that it needs 12V. Does anyone know if these have a current limiting resistor built into the igniter? Or are they just not a sensitive pyrogen?

There are options out there for you.

1. Find an flight computer that will operate on a 3S Lipo. (Simplest solution)
2. Use your 3S Battery, add a voltage converter to get you to 3.7-4.0V to give you a 1S voltage to power the flight converter. You then can use a properly spec'd MOSFET to switch the 3S voltage to the igniter. The output of the flight computer can drive the gate to switch it on and off. Depending on if the flight computer is high or low side switched will change the circuitry on the gate. (More complex, added points of failure, and more testing required) I don't know your appetite for electronics work and the rules of that you need to fall under.

 

[ksaves2]

I always, always, always ground test a new altimeter with bare ematches to make sure they will perform nominally. On the other hand, if one is using
an Rf tracker, deployment altimeters can be messed with if they aren't designed properly (grounded appropriately on the pc board, nothing the flier could remedy) and ematches can blow as soon as the tracking transmitter is turned on! Or they may blow in mid flight or not blow at all. I've been there and done that and saw folks who had to deal with it also. A 16 inch O powered rocket coming in ballistic with three of the same type altimeters leaves a big hole in the ground when a Garmin dog tracker transmitter didn't play well with the deployment electronics and the flier (not me) didn't ground test.

Some altimeters don't work well with Rf trackers. I will say again, ground test, ground test and ground test. I believe most of the egregious deployment altimeters are out of production now but best to test on the ground in a controlled situation before flying a new installation.

Plus if a dd rocket has a hard landing, best to ground test the electronics before flying again. Easy to do. Just use contained ematches on the deployment circuits and ground test. Kurt

 

[g.pitts]

I always, always, always ground test a new altimeter with bare ematches to make sure they will perform nominally. On the other hand, if one is using
an Rf tracker, deployment altimeters can be messed with if they aren't designed properly (grounded appropriately on the pc board, nothing the flier could remedy) and ematches can blow as soon as the tracking transmitter is turned on! Or they may blow in mid flight or not blow at all. I've been there and done that and saw folks who had to deal with it also. A 16 inch O powered rocket coming in ballistic with three of the same type altimeters leaves a big hole in the ground when a Garmin dog tracker transmitter didn't play well with the deployment electronics and the flier (not me) didn't ground test.

Some altimeters don't work well with Rf trackers. I will say again, ground test, ground test and ground test. I believe most of the egregious deployment altimeters are out of production now but best to test on the ground in a controlled situation before flying a new installation.

Plus if a dd rocket has a hard landing, best to ground test the electronics before flying again. Easy to do. Just use contained ematches on the deployment circuits and ground test. Kurt

I wish you'd mentioned the importance of ground testing...

 

[Tractionengines]

FYI.. if your municipality installs one of the gunshot monitoring systems...DON'T Ground test in your yard. The deployment charge acoustic pressure profile is close enough to trip the automated system depending on how close the sensors are to you, and what direction the mic is facing. ( Which they won't tell you.)

 

[ksaves2]

I wish you'd mentioned the importance of ground testing...

I and others have been burned on this back in the day hence my stressing it. Many DIY electronics (P6K) were notorious with this. Fly without a tracker and
worked fine nominally. Certainly you're being facetious.

 

[ksaves2]

FYI.. if your municipality installs one of the gunshot monitoring systems...DON'T Ground test in your yard. The deployment charge acoustic pressure profile is close enough to trip the automated system depending on how close the sensors are to you, and what direction the mic is facing. ( Which they won't tell you.)

Good gosh! Great point! I live out in the sticks in a semi rural town and no problem here for me with I, H or less motors for testing. Bigger stuff, I drive around the corner to a municipal golf driving range. On the south side of the driving range off to the side, the city reserved a portion of the field for R/C stuff. Nobody flies R/C out here anymore because the locals are a bunch of old people. (I used to fly R/C and regret selling all my stuff off.) I ground test bigger motors out there on Sunday mornings. Being Catholic, I can go to church Saturday night and go out and fly modrocs and test larger motors. With good weather early Sunday morning, the "backsliding or Catholic" golfers are out on the links so I don't have to deal with them often. If some guys or gals are out early Sunday morning hitting balls, I approach them before I fly and ask if I wave a flag that they stop hitting balls until I recover a rocket. They are always happy to do that. The field is so large my rockets don't land very often on the driving range proper. More than once when flying a small dual deploy or a chute release the folks have come over and ask me, "How did you do that? We thought it was going to crash!" I then get a chance to be an ambassador for rocketry and talk about engines and electronics. Folks generally have amazed looks on their face. Even had police and sheriff's deputies stop and watch me fly. They knew it was legal to do but were very interested to see a small rocket tumbling down and then a main chute opening at a lower chute release altitude.
A lot of folks are familiar with the whoosh, pop, whoosh pop and whoosh pop of Estes BP rocket motors but are unfamiliar when they see a dual deploy or chute release rocket do a nominal flight. They are amazed.
Seeing a dual deploy rocket perform nominally whether it's yours or someone else's is really cool. First time I saw one, I knew I had to learn to do it. Kurt

 

[Adrian A]

After doing a bunch of testing yesterday and today with a 3S 550 mAhr Lipo battery, ematches, a Raven, and a Salae Logic Pro 8 logic analyzer, I was not able to reproduce an ematch going off at power-on, but I did find and record a mechanism that could explain the observed firings under more adverse circumstances. The effect is a brief "Miller effect" turn-on of the output MOSFET when high dV/dT is applied. This mechanism partially turns on the switch for a fraction of a microsecond at a time. I think in a corner case with a noisy turn-on of a screw switch that applies 12V on and off very quickly, that it could explain the observed result. I'll have a full write-up about this phenomenon in a new thread tomorrow, but in the meantime I'll give the spoilers and some conclusions:

1. Powering with a 1S lipo battery completely avoids the phenomenon.
2. Using a 9V alkaline battery avoids 95% of the effect, which likely eliminates the risk because an ematch needs more current to fire than I was able to reproduce in the worst case in my 12V experiments.
3. Applying 12V power with a single screw switch to power the altimeter and the output ematch at the same time, caused the most unintended current to the ematch. This was the OP's configuration.
4. Turning on the altimeter separately before applying power to the an output igniter reduces the unwanted current. This is also a good method for verifying safe inhibits while powering up for a HPR airstart.
5. If an igniter needs a 12V battery to light, it's very unlikely to be affected by this phenomenon, but I have ordered some FirstFire igniters for follow-up testing to verify.

If you need a high-current 12V power source for FirstFire igniters for an airstart, I believe the risk from this effect can be reduced and probably eliminated by putting 1, 4, and 5 together and powering the electronics and the deployment ematches with a 4V battery, and then giving airstart igniters their own 12V power source on their own switch that is turned on after the altimeter is powered on and the deployment charges are verified ready to go.

More on this tomorrow.

 

[OverTheTop]

The capacity is separate from the voltage. The recommended type is a 1S battery (4.2V full charge), with 9V acceptable... they are using a 3S that has a full charge voltage of 12.6.

Replacing 1S 300mAh with 1S 3000mAh has the same voltage just a MUCH LONGER run time. Replacing it with a 3S 300mAh battery applies much more "stress" to the electronics from the higher voltage. While not adding any longer run time.

Replacing the 1S 300mAh with a 3000mAh one also means it can deliver much more current to the igniter, possibly damaging the driver during normal use. The larger batteries have a lower internal resistance than the smaller capacity ones. As mentioned upthread an appropriate series resistor mitigates this problem.

 

[Adrian A]

Replacing the 1S 300mAh with a 3000mAh one also means it can deliver much more current to the igniter, possibly damaging the driver during normal use. The larger batteries have a lower internal resistance than the smaller capacity ones. As mentioned upthread an appropriate series resistor mitigates this problem.

This is not an issue for the Blue Raven, which internally limits the current and can tolerate firing into a short circuit with lipo batteries with any mAhr capacity rating.