Basic doubt about arming rocket electronics

[cls]

Have you ever flown a high power rocket before?

L3 in 2003. How about you?

Look, I'm talking about class 3 here, 10 inch or 15 inch diameter. There is no flight line. there is one big pad, half a mile away from everyone. not holding up anything. Sorry your experience doesn't include such projects.

You have problems. I have never had one fire accidently and you have had two. You also say it wasn't much of a safety issue. What about the person setting up their rocket on the next pad?

Many hundreds of DD flights over many years, yeah stuff happens, that's my point. 2 out of many many many is a low rate, approximately zero. Was not an issue because we all follow best practices (vertical, prep sequence), and rocketeers know each other. I hope you continue to be so fortunate.

 

[cls]

Ok, let me push reset before this gets carried away.

... Just a suggestion. Don't like it, don't use it. Something to think about, that's all.

Anyway, we're all supposed to be using shunt switches to prevent uncommanded pyro firings. Right?

Which ones do people use? Mumble mumble. I thought so. Me too. Seems like every wire junction is another point of failure.

Think through the possibilities. Do what you can to prep away from the worst. That's risk management.

 

[watheyak]

L3 in 2003. How about you?

Look, I'm talking about class 3 here, 10 inch or 15 inch diameter. There is no flight line. there is one big pad, half a mile away from everyone. not holding up anything. Sorry your experience doesn't include such projects.



Many hundreds of DD flights over many years, yeah stuff happens, that's my point. 2 out of many many many is a low rate, approximately zero. Was not an issue because we all follow best practices (vertical, prep sequence), and rocketeers know each other. I hope you continue to be so fortunate.

Yep, I'm level 3 as well. I've done kinda big rockets, but they're not my jam. I'm an altitude junkie.

I'm also looking at this from the perspective of a Prefect. When you first suggested this, it was in the same context as some pretty common "best practices" launch procedures. I'm picturing a busy launch with with multiple flyers out at the J-N lines trying to do a huge chunk of their rocket prep. There's all sorts of "less than ideal" happening in that scenario.

I'll give you that perhaps a 10g charge needs to be handled a little differently. And at an away pad, sure, you can pretty much do whatever you want.

But I definitely don't want people to start thinking they need to do any more prep than they already do at the pad. I firmply believe that all the critical prep should be done at your prep table where you can concentrate and focus on the task at hand. You know, for safety.

 

[Voyager1]

It also says:
13-8 Electronic recovery or devices shall remain inhibited until the rocket has been raised to launch position but before the launch igniter is connected to the launch control system.

Thanks Steve, I should have read further down.

 

[Steve Shannon]

Thanks Steve, I should have read further down.

We tried to put the recovery stuff together and the launch preparation stuff together, but that sometimes makes it more difficult to follow them from a sequential perspective.

 

[cerving]

By the time you get to the pad your rocket should be fully prepped with the energetics' electronics suitably disabled, and no igniters in your motor(s) (unless you have a dispensation from the RSO, i.e. for that aformentioned aerospike motor or a sustainer motor which is shunted and otherwise disabled). Deployment electronics should be energized first, then the motor igniter installed. I have seen people prep at the pad... usually followed by a long drive to dig it out of the ground with a shovel.

 

[SolarYellow]

(unless you have a dispensation from the RSO, i.e. for that aformentioned aerospike motor or a sustainer motor which is shunted and otherwise disabled).

I was going to post a question about how we organize this for electronic airstart assemblies, but then realized I still haven't digested your manual on doing that, so I STFU. Does your manual cover that area of procedures?

 

[JoePfeiffer]

An igniter using any sort of san e-match and pyrogen simply will not fire with the leads shorted (that could almost serve as the definition of "sane"). Put the rocket on the rail, insert igniter, raise to vertical, arm recovery, connect igniter.

If the field layout makes it so horizontal rockets are pointed at people (Spaceport America Cup solid pads for instance) the safety code requires the rockets be vertical when igniters are inserted. But if that isn't a factor, horizontal should be preferred.

 

[kjhambrick]

An igniter using any sort of san e-match and pyrogen simply will not fire with the leads shorted (that could almost serve as the definition of "sane"). Put the rocket on the rail, insert igniter, raise to vertical, arm recovery, connect igniter.

If the field layout makes it so horizontal rockets are pointed at people (Spaceport America Cup solid pads for instance) the safety code requires the rockets be vertical when igniters are inserted. But if that isn't a factor, horizontal should be preferred.

@JoePfeiffer --

I don't disagree with the rules but Central TX is very dry this time of year.

Our rails point away from the spectators but a land shark across the prairie could be tragic, no matter what direction the horizontal rocket is pointed ...

-- kjh

 

[cerving]

I was going to post a question about how we organize this for electronic airstart assemblies, but then realized I still haven't digested your manual on doing that, so I STFU. Does your manual cover that area of procedures?

Yes, the airstart manual for the Quantum/Quasar and airstart procedures section in the manual for the Proton cover airstart motor safety. However, it is up to the RSO (and the club) to ultimately determine what procedures should be used. If at all possible, the igniter for an airstarted motor should be left out until the rocket is stacked on the rail, and it should be shunted and/or disconnected until just before arming. Even with the added safety of the Quantum/Quasar/Proton's remote arming and electronic deployment power switch, I use a pull-pin switch with a "Remove Before Flight" banner on the airstart igniters' power.

 

[Steve Shannon]

Just a word about shunts:
In many instances a shunt will delay, but not prevent an electric match from igniting. This is especially true with LiPo batteries which have a very low internal resistance and a lightweight shunt. A shunt forms a current divider. Nearly all of the current goes through the shunt, but not all. It the connection to the shunt is poor, or if the shunt wire is a poor conductor, sufficient current may still go through the match to ignite it. Or, the shunt may burn through like a fuse; once that happens all the current goes through the match.
An open circuit to the match suffers none of these potential issues.

 

[FredA]

Just a word about shunts:
In many instances a shunt will delay, but not prevent an electric match from igniting. This is especially true with LiPo batteries which have a very low internal resistance and a lightweight shunt. A shunt forms a current divider. Nearly all of the current goes through the shunt, but not all. It the connection to the shunt is poor, or if the shunt wire is a poor conductor, sufficient current may still go through the match to ignite it. Or, the shunt may burn through like a fuse; once that happens all the current goes through the match.
An open circuit to the match suffers none of these potential issues.

Disconnect AND Shunt.
Use a Double-Throw switch contact per pyro.
NFW to fire the match once you do this.

This SHOULD be the required config, but rocket org's don't have the moxie to require this.

 

[cerving]

If you really want to ban an unsafe practice, how about banning fiddling with switches while standing on a ladder, and requiring remote arming for airstart energetics? And I'm not just saying that because I make remote switches... I'd actually love to see other manufacturers come up to the plate and come up with remote switches. If somebody is against electronic switches, how about some kind of micro servo mechanism that closes a mechanical switch? (I actually thought about doing that in 2020, while the infamous "Switch Rule" was in effect...)

 

[FredA]

And I'm not just saying that because I make remote switches...

Really???

Please make a GOOD switch.
One that DISCONNECTS AND SHUNTS.
One that does multiple (4) channels at once.
A single power switch, remote or not, is worthless and totally out of consideration.

And - if you FEAR being near your rocket when armed then there is something wrong.....just saying.....

 

[cerving]

OK Fred, would you buy a remote switch that MECHANICALLY disconnected the energetics' power?

BTW, this was adjudicated in the Court of TRF in 2020... and Tripoli decided definitively that OFF IS OFF, whether it be mechanical or electronic.

 

[cls]

This SHOULD be the required config, but rocket org's don't have the moxie to require this.

First you say this, then you note

Please make a GOOD switch.
One that DISCONNECTS AND SHUNTS.
One that does multiple (4) channels at once.

... I think you answered it: there aren't any switches like that.

Hence, the national orgs relaxed the rule.

 

[cerving]

Oh, and BTW, our WiFi Switches are some of the least expensive kits that we make, and their dollar volume represents only a few percent of our total revenue. So no, my position on remote arming is not dictated by financial means... if it was, we wouldn't have put the switch on the deployment power in our WiFi-enabled altimeters (saving us about a buck in parts per device which would go into our pockets), and we wouldn't have made them so they default to arming remotely. Ask some of your club members that use Eggtimer altimeters what they think of remote arming... I bet you'll get a 100% positive response.

 

[FredA]

I think you answered it: there aren't any switches like that.

Of course there are - used in every rocket I build.
Called a 4PDT switch. Switchcraft makes the brand I use.

Convenience always wins customer likes....but that doesn't imply safety.

 

[Buckeye]

Newbie poster from Brazil asks a question about arming recovery electronics while the rocket is vertical, then gets an earful about motor igniters, packing black powder, and switches and shunts. Awesome!

Funny thing is everybody agrees on the answer to the original question: Yes, rocket should be vertical on the pad before arming recovery electronics. All the disagreements involve the other topics.

Also, the OP spent all of 12 minutes on the forum between joining and last seen! Sweet!

 

[jsdemar]

Of course there are - used in every rocket I build.
Called a 4PDT switch. Switchcraft makes the brand I use.

Convenience always wins customer likes....but that doesn't imply safety.

https://www.rocketryforum.com/threads/nar-l3-requirement-argument.67896/post-735980

 

[jsdemar]

Fred's old post:

https://www.rocketryforum.com/threads/nar-l3-requirement-argument.67896/post-735980

No specs on vibration.

 

[cerving]

Of course there are - used in every rocket I build.
Called a 4PDT switch. Switchcraft makes the brand I use.

Convenience always wins customer likes....but that doesn't imply safety.

Wouldn't it take at least 5 poles if you were going to shunt both charges and turn off power? Two poles each to short the charges (OFF) and connect them to the altimeter (ON), and at least one pole if you're going to use it as an SPST switch?

 

[user 30299]

Wouldn't it take at least 5 poles if you were going to shunt both charges and turn off power? Two poles each to short the charges (OFF) and connect them to the altimeter (ON), and at least one pole if you're going to use it as an SPST switch?

So two Poles walk into a bar, and the bartender says he'll short the charges if at least one Pole switches to a . . . .

 

[FredA]

Wouldn't it take at least 5 poles if you were going to shunt both charges and turn off power? Two poles each to short the charges (OFF) and connect them to the altimeter (ON), and at least one pole if you're going to use it as an SPST switch?

Yes.
I usually use two of the same 4PDT switches.
One does the disconnect and shunt for all four pyro channels.
The second handles power using multiple (2 or 4) sets of contacts for the altimeter & tracker.
Thus power vibration concerns are handled by the multiple contacts and the on-board capacitors in the flight computer.
Vibration for pyro's is a don't care unless the FC is stupid about continuity.

 

[SolarYellow]

I did a quick search on 4PDT switches and found many that are ON-NONE-ON. So it should be possible to wire up each pole so that in one position, everything is on and in the far position, the charges are shunted. Sounds like that's what Fred is doing.

 

[Steve Shannon]

I usually use two of the same 4PDT switches.
One does the disconnect and shunt for all four pyro channels.

That would not be acceptable for the redundancy needed for L3 certification.
Two DPDT switches would.

 

[FredA]

Don't really care about L3 redundancy rules, but thanks for being clear about that.

Here is how one output channel's Double-throw set of contacts are wired. Sorry for crude drawing.
Twist your Pyro's too....always wise.

 

[cerving]

And here's how you would wire a 5PDT switch to turn off power and shunt the charges when OFF, and connect everything up when ON. Use one per altimeter... 100% satisfies both the Tripoli/NAR redundancy rules and performs your shunting.

 

[rcktnut]

A couple more ideas:

Can wire up the empty charges and check continuity etc with much reduced risks.

Fill the charge containers with BP at the pad. Then turn on everything and insert the igniter, etc.

Mine are filled the same place I assemble my motors, at home. After filling they are stored in anti-static bags.

 

[SolarYellow]

And here's how you would wire a 5PDT switch to turn off power and shunt the charges when OFF, and connect everything up when ON. Use one per altimeter... 100% satisfies both the Tripoli/NAR redundancy rules and performs your shunting.

View attachment 599664

Quick check of Newark shows no 5PDT switches, only 4PDT and 6PDT. The 6P slide switches max out at 300mA. There is a 6PDT ON-ON toggle with a 10A rating that is 34x55mm on the main housing. They are only $23.45 each. Could be used in a big enough rocket, I guess.