Typical HPR igniter resistances I've measured range in the 1.5 to 5 Ohm range. This includes nichrome based as well as carbon fiber/nitrocellulose pyrogen as in the Igniterman kit.

Warren

Warren.

I'm getting a tighter read on things, but haven't sampled the universe. The magnelite igniters which i use for the most part use 4-5 coils of nichrome bridge, the resistance is 1.2 +/- 0.3 Ohms. When I bothered with such, I tried rolling my own, with 34 gauge or something NiCh, then dipping them in nitrocellulose laquer--the real stuff, not dissolved ping pong balls, followed by a varity of secondary pyrogens. Never had much variability. However, some motors, specifically Ellis worst and CTI best, show various propensities to ignition.

Every davey fire chip based e-match ive seen is between 1.1 and 2 ohms and that was an outlyer. I only had three blister packs of estes but in an effort to confirm CJ's results, was unable to get an open circuit in three efforts. I used stacked Li photo batteries. But the difference between an Estes igniter and any decent HPR is literally night v day. the estes these days are low amperage devices with the most pathetic blob of pyrogen imagianable. they work in BP motors with proper installation, barely.

To the more cynical among you, i would even suggest an intended design flaw, as extra igniters cost a decent percentage of the motor themselves, no extras are included, AND ARE THE SOURCE OF HEARTBREAK EVERYWHERE. Don't get me started on crapperheads.........
J

Yeah - no kidding. As for the designed to fail? I wouldn't go that far, but they're certainly overpriced. $9 for a 3-pack of firstfires? Give me a break 🙄

Chris,
where was that? I like firstfires but last paid 6/3.Not quite designed to fail. more like no room or error..........
J

That was the last time I saw them - not sure where. I'll never use them again though, unless they came with the motor. Quickbursts work as well or better for $1 each. (about $1.50 each for the K and up igniters).

10 bucks for a pack of three FirstFires at HT in Longmont.

xman.

The jrs will work and are less money. Wildman also sells some good stuff at about 2 bucks per. I think we got you covered, don't forget the paperwork and even with the relatively mild H's you're using, its really, really, really important to have super positive motor retention with HPR clusters. There was an incident recently where a pair of high thrusting ellis H's were used. One lit late, and was literally left behind by the rocket and its brother H, so it did a little dance of its own before flying thru a car window. Luckily only property damage. Believe that was parallel wired 😉 Actually a poor choice in motors and no place for friction fit retention!

If you can a central coupler nut say #6 or 8 down the middle is perfect. Available at McGuckins in Boulder. A small washer then can be used to retain all three motors...
J

I wa concerned about the friction fit with the larger motors. I thought that a small tube clamp on each engine tube might work (after slotting to allow for the compression of the tube). I don't plan on launching this rocket more than a couple of times, so I'm not really worried about any damage the clamps may have on the tubes. This is really a prototype for things to come. Hadn't really planned on flying H's so I was going to use a friction fit with the G's (very tight though).

Worst case is I fly my other rocket with a single H. 'Nother question: I'm planning on 20' of Kevlar shock cord with the parachute being 2/3 - 3/4 of the distance to the nose cone. Will be using a Numex blanket as well. Seem reasonable?

That seems fine, and DEFINITELY, do not friction fit.

Didn't understand the central coupler until now. Great idea, but I used the center of the last (highest) clustering ring for the shock cord. Should be able to make it work though if the tube clamps aren't a good idea.

When I was a kid (more years ago than I want to admit) we used to launch home built rockets with Estes motors and cannon fuse and no launch rods - didn't know anything about CG and CP. Fortunately my brother and I and grew up in the country and didn't have to worry about much other than money - couldn't afford to buy anything 'cept the motors. We built a bunker out of scrap plywood and hay bales to protect us from errant missiles... We had a few, but learned alot.

How times have changed...

Sure hope the RSO is watching out for this one. Should be fine, at least in my understanding of what you're doing. Lofting is easy, recovery isn't. See you on the range.

Didn't understand the central coupler until now. Great idea, but I used the center of the last (highest) clustering ring for the shock cord. Should be able to make it work though if the tube clamps aren't a good idea.

The hose clamps are ok, but its not too late I think to use the coupler nut. These come in various lengths--1 to 2 inches should be fine--and are hexagonal barrel nuts--you need to pick a size that will make or come close to making contact with the three motor mount tubes. Drill a hole thru the very center of the rearmost CR and use a big gob of JB weld to keep it there. Keep the epoxy out of the threads with a screw and remove it before the epoxy sets. Then for flight, a screw with the apppropriate size washer retains all 3, hope this helps. This is gonna be a great L1 cert!
JS

OK. Here's what I did. Had some leftover things from a furniture project long ago. Don't know what they are called, but they screw into wood (large deep threads on the OD) and have 10/24 threads ID. Drilled a proper size hole in the center of the ring (after removing the layer of paint aroung the area), filled the hole with epoxy, hexed in the thing, and epoxy'd the outside. Don't think it will go anywhere and should hold as well as DenverDoc's suggestion (same idea, different application).

Provided the weather holds this Saturday, it's T-minus and counting...

Thanks for all your help.

Looking forward to meeting everyone. How do we hook up? I'll take everyone up on their offer for the use of moter casings. Just need to make sure that one of the vendors will have three H128 reloads I can buy for the launch. Lawndartman, will you have the reloads available to buy?

kp.

I can guarantee you that between GLR, Wildman, and Joe from Hobbytown that you can find 3 H128 reloads. That won't be the issue.

As for hooking up?

I'm the overenthusiastic 16 year old that shows up saturday at between 8:00 AM and 8:30 AM in a red minivan, license plate GET 101. I'll be prepping a 9 foot tall 4 inch diameter rocket first thing (a BBX). We have a blue easy-up, and if in doubt, ask a club member for Chris LaPanse (many of them know me).