Cluster rocket

[Huy Ton]

Hi all,

We've built our first cluster rocket with 4 C engines, but now I'm really getting cold feet. Having experienced rockets that fail to ignite before - mostly due to bad connections or shorted starters - I'm worried that a cluster would spin out of control if one or more motors fail to start. Any word of advice? 

Many thanks

[Toby Vanderbeek]

I have some ematches you could use. They have 12" tails so you can easily wire them together. Easily got my Cluster Duck to ignite all 7. 

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Regards,

Toby Vanderbeek
tobyvan...@gmail.com

[srke...@comcast.net]

Hi,

I did a >quick Google search< (!) That said an Estes igniter resistance was 0.8 ohms. The range was 0.5-2.0. I suspect the number is around 1 ohm.

Clusters frequently don't fully light because one motor lights before the rest. The typical solution is to wire the igniters in parallel and use a clip whip with heavy gauge wire.

The issue is whether the launch system can deliver the required current. Assuming 0.8 ohms, that works out to 60 amps. Assuming 1.2 ohms is 40.

LUNAR's launch system can deliver that much current, but if you use smaller than 16 ga wire in your clip whip, it might be the gating limiter. If you can't deliver all the required current, one igniter could like before the others, and suddenly the rocket's moving. Your other igniters can get pulled out before they light.

Make sure you clean all the motor nozzles of any clay dust. Use a non-metallic tool for this!

Use the correct sized igniter plug (if using Estes motors/igniters) and make sure the igniter head is touching the black powder up past the nozzle before pushing in the plug.

Wire the igniters in a bridge formation, and connect the clip whip to them as +, -, +, -.

You can also use Quest igniters. They're more like an e-match, and held in place with a small plastic tube, typically. I assume they're similar to most e-matches and closer to 1.5 ohms, so that's like 32A. Even better. And they are easier to twist together.

Just make sure you can see the BP in the nozzle. If you can't see it, it won't light. Don't use anything metallic to clean a nozzle. They chip easily, and, well... no sparks, right?

Good luck!
Steve Kendall




Sent from Xfinity Connect Application


-----Original Message-----

[Jamie Clay]

How far apart are the motors?  It might be useful to use a flash pan style of ignition. If the motors are close together it may be the easiest away to go. Black powder loves to ignite this way. :) 

Here's a 7 E motor cluster lit using a flash pan approach.

https://www.youtube.com/watch?v=7x7wdVCJyRE

--

[srkendal]

So hard to get BP these days, At least 4F. I certainly wouldn’t use mine like that. But I keep hearing that the cannon guys can get 5lb kegs of 2F pretty easily. ;-)

 

-Steve

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[Gregory Wong]

Probably doesn’t hurt to take some sandpaper and clean the crud off the clips to ensure you get a good contact.

—Greg

[Toby Vanderbeek]

https://www.grafs.com/retail/catalog/product/productId/5450

I have a lot of this powder at home. 

Regards,

Toby Vanderbeek
tobyvan...@gmail.com

[srkendal]

Good tip as usual, Greg. LUNAR usually has Scotch Bright pads available, but sandpaper is always good to have with you.

-Steve

-----Original Message-----
From: lunar-...@googlegroups.com [mailto:lunar-...@googlegroups.com] On Behalf Of Gregory Wong
Sent: Thursday, April 04, 2019 10:08 PM
To: lunar-...@googlegroups.com General
Cc: huythat...@gmail.com
Subject: Re: [LUNAR general:] Cluster rocket

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[srkendal]

Same as mine, but I didn’t pay $28/lb. ($10 shipping).  I drove to Reno and bought it there for about $18, but that was some time ago.  Back in the day, you could buy it at Dick’s Sporting goods in San Jose.  They had a vault.  But when they moved, it did not move with them. I bought it for like $12/lb. there before.

 

But that $10 shipping charge said flat rate, so if you could get 5 people to throw in, it’d only cost about $20/lb.  Same as driving to Reno without the drive! (Ok, I was on the way to Black Rock anyway…)

 

-Steve

[Doug Wade]

With so few stores carrying it, all the paperwork, etc. even when you could get it in a store in California it was $23-$25 and it’s been at least 4-5 years since I’ve managed to do that (I shoot flintlocks).  So it’s really not much more expensive to get it online even if you pay hazmat.  You wouldn’t even have to find somebody who uses black powder - a lot of the places that sell reloading components for modern ammunition carry Goex and you can tack onto their order.  Just need to find a competitive shooter or similar.

Doug

[srkendal]

I now live in Washington, in a firearms friendly area, and I can’t get it here (then again, not too many people hunting with flint locks). I haven’t looked real hard, but I know that folks in OROC and a group out of Seattle were asking around trying to find some.  They all were having issues finding it in stores.  If you’re actually shooting, it makes sense I guess to buy it in bulk or add it to an existing order.  But if you’re just using it for ejection charges, a pound can will last you 4-5 years, and that hazmat fee is kind of steep.  Get 3-4 friends to buy a pound each, there will be plenty to go around (no one will ever run out), and the fee becomes reasonable.  It’s the same when buying e-matches. Buy a case because the hazmat is by the shipping box.  Someone will buy a box or two from you.

 

Steve

[Cliff Sojourner]

Forget the flash pan and BP, use Quest Q2G2 igniters. They are very low current and made for BP motors.

[Jack Hagerty]

Haven’t they been discontinued?

 

- Jack

 

Jack Hagerty, LUNAR #0002

http://www.lunar.org

Hotline: (925) 443-8705

 

"Rocket science: A century of making everything else look easy" – James Marino

 

 

 

From: lunar-...@googlegroups.com [mailto:lunar-...@googlegroups.com] On Behalf Of Cliff Sojourner
Sent: Thursday, April 04, 2019 11:09 PM
To: lunar-...@googlegroups.com
Subject: Re: [LUNAR general:] Cluster rocket

 

Forget the flash pan and BP, use Quest Q2G2 igniters. They are very low current and made for BP motors.

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[Jack Hagerty]

You can also put your igniter leads on a stand-off a foot or so above the pads. That way the leads have to go down a foot to reach the nozzles, and if one motor lights early, that give you two feet of travel (an additional ~ 1/2 second) before the clips pull off.

Also, check the resistance of each igniter before installation and then the entire assembly after wiring up. It should come close to the parallel total of 1/(1/R1 + 1/R2 + 1/R2...+ 1/Rn) where "n" is the total number of igniters. I carry a cheap DVM in my range box if you need one. This will tell you if any of them broke during installation or didn't connect properly.

- Jack

Jack Hagerty, LUNAR #0002
http://www.lunar.org
Hotline: (925) 443-8705

"If God had meant us to be a spacefaring race,
He would have given us a moon" -- Krafft Ehricke

-----Original Message-----
From: lunar-...@googlegroups.com [mailto:lunar-...@googlegroups.com] On Behalf Of Gregory Wong
Sent: Thursday, April 04, 2019 10:08 PM

To: lunar-...@googlegroups.com General <lunar-...@googlegroups.com>
Cc: huythat...@gmail.com
Subject: Re: [LUNAR general:] Cluster rocket

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[srkendal]

You may be right.  Just did a quickie search and everyone is sold out and Quest now says to use First Fire Micros. Haven’t heard of them (in micro) but could be true. Real (regular) e-matches won’t fit in an 18mm motor hole.  The Quest igniters were smaller and would fit. They were quite reliable as I recall.  Too bad they’re apparently not making them anymore.

 

But the Estes igniters will work just fine as long as the nozzle is cleaned out and the igniter is actually touching the BP.  It’s just hard to twist those hard wire leads together.

 

-Steve

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[srkendal]

That number depends on how you measure. If you measure across the bridge you'll get 1/Rt= 1/(R1+R2) + 1/(R3+R4). If you measure across one igniter, its R1 and the other 3 are in serial and sum. But done that way, if the igniter you measure across is open, then the number will be the sum of the other igniters, a big number. A sure tell. But you have to measure them all.

-Steve

-----Original Message-----
From: lunar-...@googlegroups.com [mailto:lunar-...@googlegroups.com] On Behalf Of Jack Hagerty
Sent: Thursday, April 04, 2019 11:43 PM
To: lunar-...@googlegroups.com
Cc: huythat...@gmail.com
Subject: RE: [LUNAR general:] Cluster rocket

[THOMAS MYERS]

For what it is worth, I've built and flown numerous cluster rockets including a 2-stage 4 "D" engine cluster in each stage. It was a blast to fly....until it caught fire and burned up on the launch pad.

Anyway, I was lucky to get all 8 engines to light, but never did it spin out of control. Always flew straight and true on 3 engines. Also built and flew a 3-engine "D" cluster when only 2 of them ignited and it flew perfectly.

My 2-cents.

BTW - don't ever get cold feet when it comes to flying rockets. For me that's the real joy is building something of my own making and watching it fly regardless if it's a CATO or a perfect flight! It's all part of the hobby!!

Sent from my iPhone

[Huy Ton]

Thank you all for your advice and words of encouragement.  My engines are only 3 inches apart so I guess BP will work, assuming that LUNAR (snow ranch)  launch pad allows pan for BP. 

However, I prefer not to buy/store a large amount of BP.  

Wrt ematches, I found this on Ebay, but not sure if it's the right type.

https://www.ebay.com/i/113343344534?chn=ps 

From the pictures, it does not seem like it could be connected to the alligator clip from the Lunar launch system, so maybe it's the wrong type.

Jack's suggestions on locating the leads 1 foot above and measuring resistance sounds great.  My original plan before going on this email was to bring a bunch of alligator clips and use a meter to check for short circuiting of each igniter before connecting them in parallel with alligator clips.  I guess I can still use these alligator clips.  I'm not sure of the gauge, but the resistance of those clips should be negligible.

[THOMAS MYERS]

If your engines are 3 inches apart I personally would question whether BP would work or not w/o creating a firestorm.

In cases of large clustering efforts, the rocketeers will create basically a BP flash pan. While this tends to ignite most engines in close proximity to the powder the reliability of the method isn't that great

Your better bet is to use the e-matches previously described. That is my humble opinion.

Tom

Sent from my iPhone

[Toby Vanderbeek]

Those are the type of ematches I have. The ends are stripped or you can strip them, and wire them together or attach easily to the alligator clips at the launch pads. I also have two clip whips you can borrow.

Regards,

Toby Vanderbeek
tobyvan...@gmail.com

[srke...@comcast.net]

Personally, I think those standard e-matches might have too big of a head to fit into a C motor, plus they'll be hard to keep in place.

I still recommend using standard Estes style igniters, cleaning the motor nozzles, and using the plugs to hold them in place.

Like you said, lots of people fly clusters. Most don't go though heroic messages to do so.

Steve

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-----Original Message-----

From: sirius...@msn.com
To: lunar-...@googlegroups.com
Sent: 2019-04-05 9:14:46 AM
Subject: Re: [LUNAR general:] Cluster rocket

If your engines are 3 inches apart I personally would question whether BP would work or not w/o creating a firestorm.

In cases of large clustering efforts, the rocketeers will create basically a BP flash pan. While this tends to ignite most engines in close proximity to the powder the reliability of the method isn't that great

Your better bet is to use the e-matches previously described. That is my humble opinion.

Tom

Sent from my iPhone

[Huy Ton]

Hi Toby, 

What's a clip whip?  Is it something like this: https://www.apogeerockets.com/Cluster_Clips/2-Motor_Cluster_Cable?zenid=uelrs7oo7qnkvvrnve3gblab95

Thanks

[Toby Vanderbeek]

Yes, that is correct. Just like that. 

Regards,

Toby Vanderbeek
tobyvan...@gmail.com

[THOMAS MYERS]

Agreed, Steve!!

Sent from my iPhone

[srke...@comcast.net]

Sorry about that. I assumed. Yes, that's a "clip whip". They come in various configurations, but the goal is to power your igniter bridge uniformly.

As you can see, you can buy them, but they're just as easy to make. You just have to make sure that leads from the LUNAR launch system and your clip leads make solid contact, and all the other connections in your whip are solidly soldered together.

Steve


Sent from Xfinity Connect Application


-----Original Message-----

From: huythat...@gmail.com
To: lunar-...@googlegroups.com
Cc: huythat...@gmial.com
Sent: 2019-04-05 9:23:35 AM
Subject: Re: [LUNAR general:] Cluster rocket

Hi Toby, 

What's a clip whip?  Is it something like this: https://www.apogeerockets.com/Cluster_Clips/2-Motor_Cluster_Cable?zenid=uelrs7oo7qnkvvrnve3gblab95

Thanks

On Fri, Apr 5, 2019 at 9:18 AM Toby Vanderbeek <tobyvan...@gmail.com> wrote:

Those are the type of ematches I have. The ends are stripped or you can strip them, and wire them together or attach easily to the alligator clips at the launch pads. I also have two clip whips you can borrow.

Regards,

Toby Vanderbeek
tobyvan...@gmail.com

[Huy Ton]

Great!  I actually have a bunch of alligator clips that I'm planning to build same thing.  I'm planning to come to the launch in April to launch this one.   Thanks. 

[Aleksandar Milivojević]

Last year, Quest switched from BP to APCP as propellant in their motors. Hence the new First Fire Micro igniters. Were the old Q2G2 designed for BP motors? If yes, probably the reason why they are not produced anymore.

On the subject of the new Quest APCP motors and igniters. I flew the new A and B motors (but not yet the C and D). They worked great in single-motor rockets. Mike seems to be well stocked on them (I saw a ton of 'em in his trailer at one of the SARG launches). However, the First Fire Micro have much higher resistance than you average igniter. I measured 21Ω. For comparison, the First Fire Mini has only 6Ω resistance. The 21Ω is high enough to not trigger continuity light to light up on LUNAR launch setup. However they will still ignite the motor. At least in the single-rocket motor. It's just that you'd have to blindly trust that you connected everything, because continuity light will not come on (communicate to LCO that you are using new Quest igniters if they notice the light is not on).

But keep in mind much higher resistance of these new igniters if you want to try using them in a cluster.

[Sam Fineberg]

The new mjg black powder starters make a good substitute for Q2G2s

https://electricmatch.com/rocketry/see/23/6/bp-rocket-starter

The head is a bit bigger, but they fit in 18mm and 24mm motors.  They are also low current like the Q2G2s

Sam

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Sam Fineberg 

S...@Fineberg.net

[Jack Hagerty]

Doesn't that only work for a 4-element bridge? I'm not an EE, but I dimly remember that the version I posted (which has a mistake in it...the second "2" should be a "3") was universal. There are other simplifying tricks like if they are all the same resistance (which they should be) the total would be R/n, which was easier to do when I was in school in the pre-calculator days (slightly after the Earth cooled). So if each igniter was 1.8Ω then a 4-cluster parallel would be 1.8/4=0.45 Ω. An open in one of them would raise it to 0.60 and two opens 0.90. Any shorts would, of course, drop it to zero.

- Jack

Jack Hagerty, Robotic Midwives, Ltd.
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[Bill Orvis]

Hi,

I have flown 5 engine clusters before and gotten them all to light. I have had cases where one or two did not light and it still flew fine. A large part of it is making sure you have good connections to all the igniters. I use a wire wrap tool and wire wrap wire to connect all the igniters in parallel. I then connect to the wired up igniters with the igniter clips. Make sure the teeth of the igniter clips (not the tops but the teeth that grab onto the igniter) are clean and bright. I scrape a knife across the teeth before I conect them to the igniter just to be sure I have a good connection.

Bill

On 4/4/19 8:20 PM, Huy Ton wrote:

Hi all,

We've built our first cluster rocket with 4 C engines, but now I'm really getting cold feet. Having experienced rockets that fail to ignite before - mostly due to bad connections or shorted starters - I'm worried that a cluster would spin out of control if one or more motors fail to start. Any word of advice? 

Many thanks

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[Jack Hagerty]

Another option (and we’re getting into Skill Level 4 here) is if you’re building your cluster model from scratch, calculate where the CG will be and angle your motor tubes so that the thrust lines go through it.  That way, if one (or more) of the motors don’t light, there’s no pitch moment.  The rocket will still fly straight up, although it will transition sideways under boost.  The Fliskits “Tre” is this way.

 

- Jack

 

Jack Hagerty, ARA Press

http://www.arapress.com

 

"Heaven for climate, Hell for companionship" – Mark Twain, Captain Stormfield’s Visit to Heaven

 

From: lunar-...@googlegroups.com [mailto:lunar-...@googlegroups.com] On Behalf Of Bill Orvis
Sent: Friday, April 05, 2019 8:42 PM
To: lunar-...@googlegroups.com; Huy Ton <huythat...@gmail.com>
Subject: Re: [LUNAR general:] Cluster rocket

 

Hi,

I have flown 5 engine clusters before and gotten them all to light. I have had cases where one or two did not light and it still flew fine. A large part of it is making sure you have good connections to all the igniters. I use a wire wrap tool and wire wrap wire to connect all the igniters in parallel. I then connect to the wired up igniters with the igniter clips. Make sure the teeth of the igniter clips (not the tops but the teeth that grab onto the igniter) are clean and bright. I scrape a knife across the teeth before I conect them to the igniter just to be sure I have a good connection.

Bill

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[Huy Ton]

Thank you all for your responses. Our cluster flew straight, all motors lit. It was wonderful.

[srkendal]

That’s great!  So…what method did you finally choose?  Do you have any photos?

 

-Steve

 

From: lunar-...@googlegroups.com [mailto:lunar-...@googlegroups.com] On Behalf Of Huy Ton
Sent: Tuesday, April 16, 2019 9:43 AM
To: Jack Hagerty
Cc: lunar-...@googlegroups.com
Subject: Re: [LUNAR general:] Cluster rocket

 

Thank you all for your responses. Our cluster flew straight, all motors lit. It was wonderful.

 

On Sat, Apr 6, 2019, 12:55 PM Jack Hagerty <jhag...@juno.com> wrote:

Another option (and we’re getting into Skill Level 4 here) is if you’re building your cluster model from scratch, calculate where the CG will be and angle your motor tubes so that the thrust lines go through it.  That way, if one (or more) of the motors don’t light, there’s no pitch moment.  The rocket will still fly straight up, although it will transition sideways under boost.  The Fliskits “Tre” is this way.

 

- Jack

 

Jack Hagerty, ARA Press

http://www.arapress.com

 

"Heaven for climate, Hell for companionship" – Mark Twain, Captain Stormfield’s Visit to Heaven

 

From: lunar-...@googlegroups.com [mailto:lunar-...@googlegroups.com] On Behalf Of Bill Orvis
Sent: Friday, April 05, 2019 8:42 PM
To: lunar-...@googlegroups.com; Huy Ton <huythat...@gmail.com>
Subject: Re: [LUNAR general:] Cluster rocket

 

Hi,

I have flown 5 engine clusters before and gotten them all to light. I have had cases where one or two did not light and it still flew fine. A large part of it is making sure you have good connections to all the igniters. I use a wire wrap tool and wire wrap wire to connect all the igniters in parallel. I then connect to the wired up igniters with the igniter clips. Make sure the teeth of the igniter clips (not the tops but the teeth that grab onto the igniter) are clean and bright. I scrape a knife across the teeth before I conect them to the igniter just to be sure I have a good connection.

Bill

____________________________________________________________
Melissa McCarthy Lost 132 LBs Due To Controversial Method
glancence-hality.com
http://thirdpartyoffers.juno.com/TGL3142/5ca903fc3dcdf3fa1c2fst04duc

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[Huy Ton]

I measured ohms before and after wiring to ensure all connections were good. Then I used a peg to lift up the wiring about a foot off the ground to give all igniters enough time to fire. I didn't have photos but the kids loved it and that's more than enough :)

[srke...@comcast.net]

Excellent. Glad it worked for you (it generally does) :-)

Steve


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-----Original Message-----

From: huythat...@gmail.com
To: lunar-...@googlegroups.com

[Jack Hagerty]

Way to go!  Welcome to rocket science!

 

- Jack

 Jack Hagerty, Section Advisor

LUNAR #0002

http://www.lunar.org

Hotline: (925) 443-8705

 "Our main goal for a long time [developing the V2] was to make it more  dangerous

to be in the target area than to be part of the test crew."  -- Wernher von Braun

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[Paul Pittenger]

I loved seeing that and how you modified it, it is great to see something unusual from the build night come to life.  That was really cool, glad you had fun with it.

Paul

[Les Niles]

Not exactly.  The sideways motion means that the aerodynamic forces will still cause it to pitch toward the dead motor.  Maybe not as quickly as the pitching if the thrust lines are aligned with the rocket's axis, but it will still pitch.  

Out of curiosity, why not wire the igniters in series?  It would need batteries in series to fire, but would avoid the failure modes where an igniter is disconnected, or has a high resistance connection so takes longer to light. A shorted-igniter failure would be an issue but that should be easier to prevent by physical arrangement of the wiring.   

  -Les

[Jack Hagerty]

Technically true, but the times I’ve seen this phenomenon, the lateral velocity has been only a few ft/sec.  It only builds up to maybe 10 fps by the time the motor(s) burn out so there’s very little pitching.  It sort of depends on the polar moment around the CG.

 

- Jack

 

Jack Hagerty, ARA Press

http://www.arapress.com

 

"Heaven for climate, Hell for company" – Mark Twain, Notebook

 

From: lunar-...@googlegroups.com [mailto:lunar-...@googlegroups.com] On Behalf Of Les Niles
Sent: Tuesday, April 16, 2019 10:50 PM
To: LUNAR General <lunar-...@googlegroups.com>
Subject: Re: [LUNAR general:] Cluster rocket

 

Not exactly.  The sideways motion means that the aerodynamic forces will still cause it to pitch toward the dead motor.  Maybe not as quickly as the pitching if the thrust lines are aligned with the rocket's axis, but it will still pitch.  

 

Out of curiosity, why not wire the igniters in series?  It would need batteries in series to fire, but would avoid the failure modes where an igniter is disconnected, or has a high resistance connection so takes longer to light. A shorted-igniter failure would be an issue but that should be easier to prevent by physical arrangement of the wiring.   

 

  -Les

On Saturday, April 6, 2019 at 12:55:38 PM UTC-7, Jack Hagerty wrote:

Another option (and we’re getting into Skill Level 4 here) is if you’re building your cluster model from scratch, calculate where the CG will be and angle your motor tubes so that the thrust lines go through it.  That way, if one (or more) of the motors don’t light, there’s no pitch moment.  The rocket will still fly straight up, although it will transition sideways under boost.  The Fliskits “Tre” is this way.

 

- Jack

 

Jack Hagerty, ARA Press

http://www.arapress.com

 

"Heaven for climate, Hell for companionship" – Mark Twain, Captain Stormfield’s Visit to Heaven

 

From: lunar-...@googlegroups.com [mailto:lunar-...@googlegroups.com] On Behalf Of Bill Orvis
Sent: Friday, April 05, 2019 8:42 PM
To: lunar-...@googlegroups.com; Huy Ton <huythat...@gmail.com>
Subject: Re: [LUNAR general:] Cluster rocket

 

Hi,

I have flown 5 engine clusters before and gotten them all to light. I have had cases where one or two did not light and it still flew fine. A large part of it is making sure you have good connections to all the igniters. I use a wire wrap tool and wire wrap wire to connect all the igniters in parallel. I then connect to the wired up igniters with the igniter clips. Make sure the teeth of the igniter clips (not the tops but the teeth that grab onto the igniter) are clean and bright. I scrape a knife across the teeth before I conect them to the igniter just to be sure I have a good connection.

Bill

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[Anthony Cooper]

Series igniters means:

1. current is limited to the battery voltage divided by the series resistance. If there is enough resistance, you'll never burn any of the igniters. 
2. igniters are designed to work on 6v+ systems. Each series igniter drops that voltage. i.e. 4 igniters in series, equals 3v/igniter in a 12v system, ignoring system losses. 
3. all current stops once the first igniter burns. Not good. 

Parallel igniters means:

1. current to each igniter is only limited by the power supply.
2. current keeps flowing as each igniter burns and if the power supply is a limiting factor, more current is available to the remaining igniters as each one burns. 
3. are the only way to go. 

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