Black Powder Model Rocket Electronic Staging Question

I'm in the preliminary stages of designing a black powder 24mm BT-60 or -70 based model that will use something like a PerfectFlite timer in the payload
of the sustainer to ignite the second stage motor. I plan on using a motor with a delay in the booster to deploy some kind of recovery system for the booster. The recovery system for the sustainer will be deployed by the motor ejection charge. I'm thinking a design such as this could be used as a modication for the Aerobee model in Peter Alway's book and others such as a Terrier-Sandhawk and maybe even an IRIS.
Where I get a little fuzzy is coming up with a method to route the wires from the payload section to the rear of the sustainer and what type of connection to use at the aft end of the rocket to connect the igniter and how to deal with the joint between the payload bay and body tube. I'm sure there are all sorts of ways to do this in mid to HPR designs but I haven't seen much written on the subject for the size I'm considering.
I'm hoping someone here can point me to a technical publication, book or just some "been there done that advice" on how to deal with this issue.
Any assistance you can offer would be greatly appreciated.
Scott
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On Thu, 03 Nov 2005 02:42:16 GMT, "Scott Froese"

Wow. And cool, Scott!
I'd consider an external conduit for the wires. Something like a half a soda straw, properly reinforced? Thinking WAC Corporal here. I guess you could do that internally with the tube, if you are a good "ship in the bottle" kinda builder...
RE the ignitor connections, I'd think you'd almost have to wirewrap them to the leads coming down from the payload section. Or maybe some *really* weensy t-nuts as connectors down by the aft end of the sustainer stage.
Good luck, and keep us posted to your progress!
tah
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Hilty Information Systems
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I've done this using the Perfectflite timer, but I went with a very different design. The timer rode in a payload section at the front of the booster, rather than up in the sustainer. The wires ran through holes in a balsa transition up into an interstage coupler where they lit the sustainer. It worked just fine. You can see it all in the October 2005 newsletter at the WOOSH club site, at
www.wooshrocketry.org
Scott Froese wrote:

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I;m also starting on a similar project converting an Estes Sea Hawk kit into 2 stages using a PerfectFlite timer to fire the upper stage. I'm thinking of putting the timer in a payload section of the booster and running the wires up through a hole in the forward bukhead. Thanks for the link to your newsletter. That should give me some good ideas on how to accomplish it. Do you have any trouble with exhaust flame and smoke coming through the hole into the payload bay? Do you block the hole with something after the wires are in place?
Jonathan ----- Jonathan Sivier Secretary, Central Illinois Aerospace jsivier AT uiuc.edu NAR #56437 Tripoli #1906 CIA Web Site: http://www.prairienet.org/cia / Home Page: https://netfiles.uiuc.edu/jsivier/www /
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    Just that tacky putty stuff used to hang posters on the wall. I haven't had any problem with exhaust flame or smoke, and no damage to the booster, but it has only made two flights, so YMMV. The upper stage was a small BP motor in each case, as well (C6-7, IIRC).
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Howdy-
Thanks for the link. I think this approach would work fine for something with a longer booster such as Terrier-Sandhawk. If I do the IRIS, it doesn't look to me like the booster is long enough to create a large enough payload bay to do this, although I could be wrong.
My rational for carrying the electronics in the sustainer is the extra weight should help the overall stability.

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Scott Froese wrote:

I've built a couple of WAC Corporals that stage with timers. The BT-60 version runs the wire for the igniter through the WAC's "fuel-line fairing", but at the top and bottom the wire is routed back inside the airframe. The BT-20 version runs the wires entirely inside the airframe. I didn't attempt to contain the wires to isolate them from the parachute & shock cord, but rather rely on careful placing of the wires to the side out of harms way. I did the same with a Skua I built last year, running the wires entirely inside the airframe. If you keep the wires as short as possible, place them against the side, and pack the parachute neatly the wires shouldn't foul the parachute.
(The BT-20 version of the WAC actually has two pairs of wires, one pair for the sustainer igniter, another pair for a breakwire. Both pairs run down inside the WAC airframe past the parachute and shock cord. The breakwire pair is plugged into the thin brass tubes that make up the Tiny Tim/WAC interstage cage, from there a wire runs down through the Tiny Tim airframe and out the bottom where it crosses over the nozzle. At staging the wires are disconnected from the interstage tubes.)
In both models the wires plug into Molex sockets in the base of the hollow nosecone which contains the timer. With the BT-60 model I use 22-ga wire and just plug the bare ends into the Molex socket--having tinned the bare ends of the stranded wire with solder to stiffen them up. With the BT-20 model I use 30-ga wirewrap wire which I wirewrap onto a Molex "plug" (a 2-pin header). At ejection the wires are pulled from their sockets.
With the BT-60 version the aft ends of the wires terminate in short lengths of small-diameter brass tubes; I soldered the wires into the tubes for a secure connection. These tubes were then epoxied to the side of the BT-50 motor mount. Thus this wire is a permanent part of the rocket. I use a Daveyfire to ignite the sustainer, cutting the Daveyfire leads quite short--about 1" long--and crimping short bits of thinner brass tubes onto the stripped ends. These brass tube bits are a slip fit into the brass tubes on the side of the BT-50, making a good electrical connection.
With the BT-20 version, I wirewrap the aft ends of the wires to the leads of an Estes igniter. The entire wires are replaced for each flight.
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Steve Humphrey
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Steve-
Interesting information. A couple of additonal questions if I may:
1. When you say Molex connector, are you talking about the type of connector that looks like a jumper in a PC?
2. Is there a special wirewrap tool you use to make the wirewrap connections or do you mean you just manually twist things together?
It sounds like you've had pretty good luck with the wires just carefully packed in the parachute compartment. I was concerned that might risk fouling the chute and thought I needed to come up with some sort of elaborate internal conduits to route the wires to minimize the risk. My other concern was over time the insulation on the wire failing where it enters the front centering ring for the motor and creating a short that couldn't be easily repaired. Maybe I'll design a baffle into the system to prevent that from happening.

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Scott Froese wrote:

Something like that, yes. What I use for the plug is a .100" header (like the pins on a PC motherboard where you hook up the reset switch, disk activity LED, etc.), and a Molex receptacle as a socket. Here's an example: http://dkc3.digikey.com/PDF/T053/0102.pdf (see Fig. 3). You can buy the headers in long "breakaway" strips and snap off a pair as you need them. http://dkc3.digikey.com/PDF/T053/0098.pdf (Fig. 2). There are other brands besides Molex.

Use a wirewrap tool. Here's a cheap one from Radio Shack that I haven't tried yet: http://tinyurl.com/9wcws

I use fairly thin--22 or 24 ga--stranded wire. I chuck a pair of wires into my drill, then rev up the drill to make a "twisted pair". The resulting cable flexes but generally doesn't kink. As I mentioned before, I cut the cable as short as possible--just barely past the end of the airframe so I can hold the plug while I connect it to the socket in the payload bay. It also helps to position the sockets near the edge of the shoulder of the payload bay, and don't cross the wire over the top of the parachute when sliding the payload bay into the airframe.
I solder the ends of the wires to the 2-pin header, then cover the soldered connections with a short piece of shrink tubing. The tubing not only helps avoid shorting the header, but also "streamlines" the aft end of the header a bit so there's less to snag.
I pack the parachute and shock cord in neat bundles. In cases like these I usually Z-fold the shock cord and tape it with one wrap of 1/4" masking tape--enough tape to keep the shock cord bundled during prep & boost but not enough to keep it from unfolding at ejection. I also fold the shroud lines inside the parachute.
You can add a tube to the side of the motor mount through which you route the wire. Tie a knot in the aft end of the wire to keep it from being pulled up through the tube at ejection. Or tighten a zip tie around the wire, or attach some other sort of "strain relief" to the wire. You can then replace the wire if it breaks or wears out. You could also slide a length of tubular Kevlar over the forward end of the wire to protect it from exhaust gases.
--
Steve Humphrey
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Molex connectors are more like the 4 pin power cable that goes to your hard drive, floppy, or CD (i.e. not the 40+ pin data cable). They seem to be white most of the time. Your car dashboard wiring is probably loaded with them.
Unlike phono jacks, telco, data, and other light duty connectors, Molex connectors are designed to carry heavy current loads.
--
Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
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Bob Kaplow wrote:

I think Molex makes those, too, but I was referring to the smaller .100" headers and connectors made by Molex (and others).
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Steve Humphrey
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Hey Scott,
Aside from what the others mentioned, you may want to ponder some drag separation too before firing off the second stage simply to reduce damage on the booster.
Weight tends to creep so if you're indeed going to do a BP booster with a BT-60/70 diameter, do be aware. Don't get hoodwinked by Steve... Word is he's a pretty skilled builder... ;-) <vbg> The AT 24mm rms loads may come in handy if weight gets out of hand.
Sound like fun... :)
Andy
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Andy Eng wrote:

Yeah, like on my BT-60 WAC. In my zeal to preserve "scale qualities" I left the Tiny Tim interstage open to the exhaust from the sustainer ... and then compounded my mistake by getting the stage coupler too tight. It's amazing what the exhaust from a little C11 can to a basswood nose cone. http://tinyurl.com/8tbgh
For the next flight I sealed the bottom of the stage coupler with a plywood disk. This makes the stage coupler act like a piston when the sustainer lights. Blows the booster right off!

:-P
You going to the next NARAM, Andy?
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Andy-
I'm not sure I know what you mean. Do you mean keep the fit between the booster and sustainer loose and set the timer long so?
As far as the booster motor goes, I have a AeroTech 24mm reload casing that I'm not against using for this and it sounds like I may need it based on Steve's experience.

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Hi Scott,
Scott Froese wrote:

If you're going to put in alot of time, you really don't want the sustainer to go roasting the paint off your nice looking booster...

Yes... If you pick up the model by the sustainer, the booster will still be sitting there.

Yes, probably a second or so after burnout and...

Use something like an E28 or F39. When it burns out, the sustainer should go coasting off the booster a couple feet before lighting off. The style points you gather while staring up and wondering if the sustainer will ever light is pretty neat--If you're into that sort of thing... :-)
Simply one way of many to do the project.
Regards, Andy
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