other topics - launch system safety

[OzHybrid]

I can build that

Not yet speedy..... and @rocket_troy A 1W test lamp would test that you had enough current to guarantee firing an igniter. Unfortunately, that's not what you are testing for. What you are testing for is "is there any voltage present with sufficient minimal current to accidentally set off an igniter?" That is if I connect an igniter to these leads, will they potentially exceed the MINIMUM SAFE CURRENT for an igniter. That level you test for should be the level for the MOST CURRENT SENSITIVE igniter you will connect.
In this case, The power source is close to the pads on a remote box, so it's not a long lead and the test is performed at effectively the relay output, or first bit of wire connector after. If it were 100m of wire with a switch and a battery at the firing end it would be more tricky.

What are those numbers? Well, read the data sheet for the ematch or igniters you may use and pick the lowest. A 1W bulb is NOT SENSITIVE ENOUGH.

PM me if you want to discuss it. This thread is going off topic.

 

[rocket_troy]

Not yet speedy..... and @rocket_troy A 1W test lamp would test that you had enough current to guarantee firing an igniter. Unfortunately, that's not what you are testing for. What you are testing for is "is there any voltage present with sufficient minimal current to accidentally set off an igniter?" That is if I connect these leads, will they potentially exceed the MINIMUM SAFE CURRENT for an igniter. That level you test for should be the level for the MOST CURRENT SENSITIVE igniter you will connect.
What are those numbers? Well, read the data sheet for the ematch or igniters you may use and pick the lowest. A 1W bulb is NOT SENSITIVE ENOUGH.
PM me if you want to discuss it. This thread is going off topic.

Well, 1W @12V is <100mA current. If your igniters or Ematches are sensitive enough to fire at those currents, then they're too hazardous for the purpose.

Irrespective, you're detecting if the channel is live ie. if a relay is stuck closed or if a short has occurred somewhere or the channel's somehow activated inadvertently, so it should be okay to detect in amps. You don't need to over complicate things or introduce false positives to detect a very high % of hazardous scenarios that in themselves only happen very seldom.

TP

 

[OzHybrid]

Well, 1W @12V is <100mA current. If your igniters or Ematches are sensitive enough to fire at those currents, then they're too hazardous for the purpose.

Irrespective, you're detecting if the channel is live ie. if a relay is stuck closed or if a short has occurred somewhere on the circuit so it's okay to detect in amps. You don't need to over complicate things or introduce false positives to detect a very high % of hazardous scenarios that in themselves only happen very seldom.

TP

You have exceeded the MAXIMUM test current by a factor of 2.5 for a J Tek match. (40ma) or by a factor of 3.3 for the 30mA test for a BP igniter. Although you are below the minimum no fire current.
I agree that if it were to light up when the output was off, then you would say it's definitely NOT safe. But if it did not light, you could NOT say it definitely WAS SAFE, because you are above the MAXIMUM test current. Personally, I would not want to be the one explaining why the max safe test current was knowingly exceeded and approved as ok.
If you have designed a system that gives you false indications of whether it is safe, fix that design.

 

[SDramstad]

Most of these ideas sound good at first but would completely screw up the continuity test.

 

[jsdemar]

This is discussed over the other:
https://www.rocketryforum.com/threads/energetics-safety-circuits.182064/
There should always be an arming switch at a pad box which completely disconnects any source of high current.

My “stuck relay” alarm circuit is fairly simple. See my schematic. It will be screaming even before you arm the pad. I’ve been using this for 25 years.

 

[FredA]

Wow did this thread go OT.

 

[cerving]

This is discussed over the other:
https://www.rocketryforum.com/threads/energetics-safety-circuits.182064/
There should always be an arming switch at a pad box which completely disconnects any source of high current.

My “stuck relay” alarm circuit is fairly simple. See my schematic. It will be screaming even before you arm the pad. I’ve been using this for 25 years.

I agree... and this needs to be codified. In the case of a remote launch system, BOTH sides need an "off" switch... the last man out should be responsible for arming the pad box, from a reasonably safe distance from the pads.

 

[RocketPro]

Why not just hook up the igniter BEFORE you put it into the motor? Seems like that would be a failsafe method…

 

[Sooner Boomer]

Or, you could put a big knife switch between the battery and the remote launch box. That's what we've done. When you approach the pad to "rack" a rocket, the first thing you do is to open the switch. The rocket then goes on the rod/rail and leads are hooked up. Retreat to battery and close knife switch. If something has stuck and the leads are live, you're at least 15 feet from the pad. If all's well, do continuity test, and leave area. Launch rocket as per usual.

 

[John Kemker]

Why not just hook up the igniter BEFORE you put it into the motor? Seems like that would be a failsafe method…

That's exactly what the @prfesser recommends in his book, Experimental Composite Propellant.

 

[AlexBruccoleri]

One thought is to bring an LED or e-match with you and hook that up to the leads as a check instead of the spark test. Hooking up the igniter first is not a bad idea but there is the chance of it going off when someone else is testing something. I think the best approach is to insert the shorted igniter into the rocket and secure as necessary, then move the leads a bit away (as long as possible), confirm the leads are off and then hook it up. Keep your hands and face as far as possible from the potential exhaust and fins during the whole process.

 

[AlexBruccoleri]

Hooking up the igniter outside the rocket is not a good idea. Larger igniters can form a large fireball and throw off hot debris for quite a distance... such as on your hands and face. Plus, it could start a fire with dry grass around.

I've made a simple buzzer that won't go off with just the test current. I use this to test the launch system after setting it up. It could be used to connect to the clips to check if the (poorly designed) launch system has a stuck relay.

All these post should be pared off and put in another thread like was done earlier (on energetics). We're no longer talking about hotel rooms!

I think the more general point here is to be careful. Agreed that igniters present some hazards and the bigger ones even more so. The incident in the original post shows what happens when you essentially do multiple dubious actions in violation of the safety code and common sense. I agree with you that hooking up the igniter is not ideal but if you had no other decent way to check against current, it would be better than putting it in the motor first. It is far better off going off outside the motor than in, in a setting where people are right there. Also it is not a bad practice with staged rockets to do a full arming check with the pyros connected but igniters removed from the motor. That being said staged and complex rockets are no doubt more dangerous than standard simple rockets and the people in the prep area need to be limited and on high alert.

A buzzer, LED, etc is a nice way to do this. I think the reason most fliers go with the spark test is it is simple and easy.

 

[cwbullet]

Safety measure to prevent ematch lighting link at NSL