Cluster probem

Hi folks,

I modified a USR Banshee by using the 3X24mm adapter from a USR InterRoc and glued two 24mm tubes with aerodynamic fairings to the sides of the rocket between the fins so that I now have a 5X24mm Banshee.

I build it, so far so good. Today I tried to fly it on 5 E-9s and could not get a single one to fire.

Prior to trying this (my first attempt at clustering) I read the discussion threads that had information on the topic and I thought that as long as you wired them in parallel that it would work.

I used a metal wire about the thickness of a small piano string and made a loop tying one of each Estes igniter wires from each motor. I then made another loop and tied the other wires onto that one. I made sure that there was no contact between either wire loop and..... nothing...

I then tried removing the whole wire aparatus and just placed three Estes igniters on top of each other, tied the right wires together, then the left together, then bent the top (igniter portions) apart and placed the tips of each into the three main engines and..... nothing....

I'm using a fresh 12 v lantern battery and "Go Box" launcher. I tested the launcher with a spare igniter and it fired. I placed a spare motor and igniter under my foot and the engine lit. Not very safe, I know, but the only fun I had all day and I had to make sure the igniters would fire the engines.

I'm new to this forum, and my mistake is probably very basic to someone out there. I'd appreciate any advice.

Try using a battery with a little more current capability, like a 12V rechargeable. A small motorcycle battery will work, or something like this:https://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXL370&P=ML
Those have far more current capability, and as such, will be much better at firing multiple igniters.

And yes, as long as they are all wired in parallel, and your launch system can supply enough current (about 1A/igniter, maybe a little more for Estes), they should fire.

Although wiring the ignitors in parallel should work, I feel a more reliable method of lighting multiple motors is using a "Clip Whip", which is two 'main' wires with ignitor clips on them that lead to multiple pairs of wires. Each pair can then be connected to an individual ignitor and the main pair connected to the clips from your launch controller. They make them in varieties from 2 to 6 motors and even custom.

I get mine from Thrustline. https://thrustaero.com/prod05.htm

Imo, they're worth it. Just this last weekend I loaned one of my clip whips to fellow rocketeer for his 2 engine cluster. Both engines lit perfectly. He told me this was the first time in three launches both engines had lit; he had previously used the parallel ignition method.

Well, a couple of things.

Whether you twist the leads together, use a wire hoop (as you seemed to do) or use a clip whip, they are ALL the "parallel ignition method". In electrical terms, you only have two choices. Parallel or Series. Series won't work, parallel will.

That said, I'd like to point out a few thing that may well help:

1) The primary problem you may have had was the use of the lantern battery. Yes, it is true that you want 12 volts, but that is only half of it, you also need some serious current (especially for a 3 or 5 motor cluster) and a lantern battery just isn't going to do it. Try a motorcycle or car battery

2) You say you used a small wire similar to piano wire. I am not sure what you actually used but many processed steel wires (like piano wire) have gobs of crud on them (oils and such) that make them very poor surface conductors. I have several cluster models that work best when using a hoop of wire (like my Tres) and to assure good connection to all igniters I would take a length of tinned speaker wire, strip off all of the insulation and use that. At least I know that I am working with a wire that was DESIGNED for twisting together with other wires for good conduction.

3) In any case, also be sure to test EACH igniter before installing as your cluster will show good continuity if only ONE igniter is *good* and all fo the others broken

4) Be very aware of igniter installation. A shorted igniter (very common near the tip of the Estes igniter during installation) can result in just the problem you are seeing as it is the low current path for the electricity

Personal opinion, Clip Whips are great tools but are also prone to certain failure modes. We've all seen the case where your clips get dirty and you get a misfire. With a clip whip you have many more points of failure.

For example, if I have a 2 motor cluster and I twist the leads together properly, when I hook up the micro clips I have TWO potential points of failure (each clip)

In the same configuration using a 2 motor cluster clip whip I have SIX potential points of failure (2 clips per motor (4 clips) and the 2 clips that hook up to the clip whip) A 5 motor clip whip would have 12 potential points of failure.

If you keep your clip whips clean and in good working order they are wonderful tools, just be aware.

Hope this helps!
jim

Thanks for the feedback.

I see what you mean now about a lantern battery being 12 volts but lacking amps. I was also not being very carefull with the igniters.

I'll try these tips and let you know how it goes!

P.S. With the modifications and extra engines I added, the bottom end of the rocket feels HEAVY. I added some weight to the nose, but where should the center of gravity be. Even in the stock configuration the tail would be heavier than the nose right?

I'll post some pics soon.

Originally posted by 109rider
With the modifications and extra engines I added, the bottom end of the rocket feels HEAVY. I added some weight to the nose, but where should the center of gravity be. Even in the stock configuration the tail would be heavier than the nose right?

Click to expand...

According to the EMRR center of pressure library the US Rockets Banshee will have a CP at or around 30 5/8". This is measured from the tip of the nose cone towards the tail.

The center of gravity should be 1 to 2 calipers in front of or towards the top of the rocket from the center of pressure. One caliper equals one diameter of the body tube.

www.rocketryonline.com has a very good tutuorial for learning about the CG/CP relationship and how to measure it, as well as many other items of interest concerning rocketry.

Have Fun and Good Luck!!!

Andrew Grippo

Thanks Andrew.

You can get a 12V lead-acid lawn & garden battery for around $20 at Wal-Mart, which will deliver mondo current. Also buy a trickle charger (around $15) and a battery hydrometer (couple of bucks) to test the battery's charge level accurately. It may seem like a lot of money, but weigh that against the cost of a nice big cluster model, painstakingly built & finished...