Anyone still use flash bulbs?

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icyclops

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The only information I can remember coming across on using them for recovery systems didn't use them directly, they used them to detect burnout and start some sort of timer or fuse that fired the ejection charge. Where have you found someone who claims to have used it directly?

At motor burnout your rocket's deceleration will be much greater from drag than from gravity. Your mercury will, as others have said, go to the front end of the capsule and trigger your recovery system. The length of the switch will make no significant difference in how long this takes.
[/QUOTE

Ok, got it....thanks.
 

Brian H.

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At best, a mercury switch will detect motor burnout, nothing else.
False triggering at power on is a big problem.

To use it for deployment, you will need at the very least a timer from burnout to estimated apogee time using the mercury switch as the trigger.
There are easier ways to achieve this.

AFAIK mercury switches are not allowed by TRA or NAR
 

icyclops

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At best, a mercury switch will detect motor burnout, nothing else.
False triggering at power on is a big problem.

To use it for deployment, you will need at the very least a timer from burnout to estimated apogee time using the mercury switch as the trigger.
There are easier ways to achieve this.

AFAIK mercury switches are not allowed by TRA or NAR
I went to the NAR website...read both LP and HP safety codes....no mention about Mercury switches not being allowed that I could find....
Maybe that info is located in another document....I could not find.
 

Brian H.

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I went to the NAR website...read both LP and HP safety codes....no mention about Mercury switches not being allowed that I could find....
Maybe that info is located in another document....I could not find.
I found the reference to mercury switches I thought completely banned them, but it only prohibits motor ignition.

Tripoli High Power Safety Code, page 6, Appendix A, reference A-5:
A-5 A rocket motor shall not be ignited by using:
a. A switch that uses mercury.
b. “Pressure roller” switches

I personally would stay away from them for triggering ejection charges also. I've seen too many motors chuff and cause the rocket to jump up a bit before coming to full pressure, or not ignite the motor at all.
I doesn't take much bounce to activate a mercury switch.
 

RoyAtl

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If you go back even further, you can see where John got the pairing of AG-1 and SureShot wick -- from page 6 of March 70 Model Rocketry Magazine:

And of course, you can see the NARAM 13 demonstration and R&D official flights on my Rocket Film (
). Starting at 11:40 and culminating from 33:00-35:20 with the official flight. Then at 39:30 with the first flight mentioned in the article above.
 

icyclops

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What does this movie have to do with flashbulbs and mercury switches....kinda hard to follow
 

icyclops

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Oh, i see the article now about engine ignition with a mercury switch and bulb....
 

cerving

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I don't find terminal blocks a pain to use , hiding under the tape to protect it from the debris View attachment 452273
Sure, but wouldn't it be cool to literally just plug in a new charge, swapping them out in seconds? Maybe like a pre-filled charge well with some kind of contacts, you just twist it in 1/4 turn like a bayonet bulb? (No, I'm not working on it... I just think it would be a cool idea.)
 

RoyAtl

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What does this movie have to do with flashbulbs and mercury switches....kinda hard to follow
Partly it is a response to Dave F about the history of the use of flash bulbs in rocketry, but the article "Building the Super Titan" in the PDF that is linked briefly discusses using a mercury switch (though the author chooses a mechanical method instead) . It also mentions the pairing of AG-1 flashbulbs and Centuri Sureshot igniter wicks for igniting motors, which John Langford used in Flashbulb Cluster Ignition, which is arguably the point from which all use of flashbulbs in rocketry has come. Again, most of that is for Dave, not you, but the film refers to John's article, which Dave linked to and to which I referred.

I *thought* I was going to link to another article actually about mercury switches, but I now think that article was in The Model Rocketeer, not Model Rocketry Magazine., and I don't currently have access to those issues.
 

icyclops

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Yes, I saw that after I wrote the first message, sorry. I wish I could find that article in the old roc book I had about how they used it for recovery and not wick or motor ignition....but of course I can’t find it now....
 

Ez2cDave

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I found the reference to mercury switches I thought completely banned them, but it only prohibits motor ignition.

Tripoli High Power Safety Code, page 6, Appendix A, reference A-5:
A-5 A rocket motor shall not be ignited by using:
a. A switch that uses mercury.
b. “Pressure roller” switches

I personally would stay away from them for triggering ejection charges also. I've seen too many motors chuff and cause the rocket to jump up a bit before coming to full pressure, or not ignite the motor at all.
I doesn't take much bounce to activate a mercury switch.

NOTE : This mechanism uses NO MERCURY, yet functions in the same manner . . .

Dave F.

I - CROP.jpg


H.JPG



I.JPG
 
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icyclops

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Yes, I read that diagram and info from the link earlier. I don’t think I would ever use a Mswitch in HP anyway. Very interesting constructed technique/device. Thanks for this information.
 

icyclops

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Thanks for the PM and the data too. Will keep it in my files for good info.
 

Ralph S.

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I have 2 or three boxes of flashbulbs, one of the old CPR systems used them.
I believe Badass Rocketry is working on a Plugin type ejection for one of his future products.
 

caveduck

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Flashbulbs would work OK for ejection ignitors, but they are bulkier than e-matches.

There is one other safety issue: flashbulbs have a *very* low no-fire current, 20-30 mA if I remember right. Continuity circuits can fire them unless carefully designed. Back when flashbulb ignition was popular, you had to be very careful that the club launch system would not pop the bulb upon a continuity check.

Modern altimeters have really low continuity current and should be OK, but you definitely want to verify and test before flight, keeping in mind that everything now is designed with e-matches in mind, where the no-fire current is more like 200 mA.
 

Ez2cDave

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There is one other safety issue: flashbulbs have a *very* low no-fire current, 20-30 mA if I remember right. Continuity circuits can fire them unless carefully designed. Back when flashbulb ignition was popular, you had to be very careful that the club launch system would not pop the bulb upon a continuity check.
"Back in the day" ( mid-1970's ), our club, BCMRA ( Broward County Model Rocketry Association - Section # 217 ) used to do a separate "Countdown to Continuity Check", in case it fired the flashbulbs. A couple of years later the system was upgraded with a separate Continuity Circuit, specifically for Flashbulb Ignition.

Dave F.
 

icyclops

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I’m a little confused. The continuity check from the pad controller usually checks the motor ignitor. The flash bulb is on a different system??? A bulb connected to a mercury switch or g switch then to a capacitor...how does the pad cont check even access that. Maybe you mean using a altimeter....does the cont check connect to that? I have never used one but how can a cont check jump from motor ignition to recovery ejection system....their is no electrical connection. Please clarify.
 

jimzcatz

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A continuity check sends current through the system. That miniscule amount of current can set off dozens of flashbulbs. Always check in advance. I never used flashbulbs for anything but BP clusters. One bulb per motor. Same issue if hooking to an ejection charge, the POST can set them off. I have never has a problem but I did try an estes controller just as a test, bulb flashed when key was inserted.
 

dhbarr

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I’m a little confused. The continuity check from the pad controller usually checks the motor ignitor. The flash bulb is on a different system??? A bulb connected to a mercury switch or g switch then to a capacitor...how does the pad cont check even access that. Maybe you mean using a altimeter....does the cont check connect to that? I have never used one but how can a cont check jump from motor ignition to recovery ejection system....their is no electrical connection. Please clarify.
Many flight computers do their own continuity checks.
 

Ez2cDave

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I’m a little confused. The continuity check from the pad controller usually checks the motor ignitor. The flash bulb is on a different system??? A bulb connected to a mercury switch or g switch then to a capacitor...how does the pad cont check even access that. Maybe you mean using a altimeter....does the cont check connect to that? I have never used one but how can a cont check jump from motor ignition to recovery ejection system....their is no electrical connection. Please clarify.
The issue of low current firing flashbulbs was already addressed by Jim Scarpine.

Now, as for the onboard system, there is no continuity check circuit. The rocket is "hot" and if anything closes the circuit, the flashbulb ( or electric match ) WILL fire !

A Mercury Switch functions by aerodynamic drag slowing down a rocket, allowing the Mercury to travel upwards to complete the circuit.

A "G-Switch" functions to arm electronics ( such as a timer ), AFTER a rocket has lifted off. But, it does not fire the igniter itself.

A capacitor is used to reduce the weight and is charged through a "plug", AFTER the rocket is on the pad. "Back in the day", rocketeers commonly used HEAVY 9-volt "Transistor Radio Batteries" in their onboard systems.

Dave F.
 
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