Cluster bug bit me. (SIMI-CATO PIC)

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Jul 28, 2004
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Hey everyone, I’ve been meaning to start posting to this group for a while not. Not long ago I got bit by the cluster bug. Since then I have been building mostly clustered rockets. Yesterday I few one of my favorite clustered rockets on 4 A10-T and 1 C6-5. The flight was great but only the A10’s lit the center engine popped out in flight. The A10’s don’t feed to the body so they have no ejection charge (they pop out in flight). The rocket nose dived and stuck in the ground (See pic)

My question is how do you do clusters? Out of 30 tried I have (almost) never had all engines light.
Originally posted by cat
My question is how do you do clusters? Out of 30 tried I have (almost) never had all engines light.

Welcome to the forum :D

A couple super-important things about clusters (particularly BP clusters):
1) You must have a high current 12V based launch controller. The Estes Electron Beam controller can barely squeeze out 6V & has very low current.

2) Get a clip whip. There are several folks here on TRF that you can buy them from or you can build your own.

Do a search for "12V launch controller", "cluster", and "clip whip"... Each of those should turn up plenty of information to get you on the path to successful cluster launches in the future :)
Sorry you had a bad flight----that picture is painful to look at.

Keep in mind, the more motors in your cluster, the bigger the chance of incomplete ignitions. There are a few tricks you can use in designing your rocket, and a few more in setting up the ignition.

It is always a good idea to have more than one of your clustered motors vented on through to the recovery section, to deploy your parachute (or whatever) in the conventional way. Once you have two or three motor mounts connected to the recovery section you could plug the rest of the mounts----or, go ahead and connect 'em, it really won't hurt anything. If you like you can stagger the delays, with the 'extra' ejection charges timed for a second or two behind the primaries. Even if you select the same delay for all motors, odds are about 1:infinity that they will all go off at the same time (or even any two at the same time) due to variations in motor performance. What you will get is multiple sequential ejection pulses until the NC pops off, and then noise from the remaining charges.

There are lots of threads here on TRF full of great advice on cluster ignition, try the search button in the header. I'll bet one of our cluster experts will jump in here anyway and give some tips?

(for starters; there are plenty more old posts on TRF)
A search will get you a ton of info on Cluster ignition techinques. I do only BP motors with a very good 98+% success rate on 2 to 8 motor clusters.
there are several reasons you cluster motors may not have all lit. the ignitor, the power source, or the power delivery to the motors.
The Best most efficent and most successful method I've found over 30+ years of Clustering BP motors is a Relay Ignition system.

Rather than go through the whole thing again, If you visit go into the library under Tech-Tips you'll find Tech-Tip 006 BP motor clustering. the article will take you step by step through the process, including wiring diagrams and parts lists for everything you'll need.
hope this helps.

Here's some cluster lift-offs as inspiration:D
aaahhhhh, clusters :D My favorite type of model rocket :)

Ditto what folks have said here. Spend some time searching TRF and see what others have said. A wealth of information here.

The short list, if I were to create one (which I will, right now :) ) would look like this:

1) start with smaller clusters (2 engine, 3 engine) and work up to 5 engine
2) always use a 12VDC power source. My personal preference is my car battery
3) Clip Whips are not a *must*, but certainly make things easier :)
4) Careful installation of ignitors, make sure you use the plugs that come with them and make sure that the ignitor is touching the propelant.
5) Make a point of putting a small ball of recovery wadding in the top of each motor and secure with tape. This prevents the ejection charge of one motor from igniting an unlit motor from the top (can gut your rocket...)

Hope this helps!

And welcome to TRF!
alittle off topic but how many engines can a 12v light successfully, ive been thinking about investing in a good bigger battery but i dont wanna jump into somehting expensive i dont need
I put together a cord that plugs into the trailer plug on the back of my pick-up, after someone passing by thought I needed help because I had the jumper cables out and stretched to the llaunch controller. I decided that a better way had to be found. It works great :D
Originally posted by rabidsheeep
alittle off topic but how many engines can a 12v light successfully, ive been thinking about investing in a good bigger battery but i dont wanna jump into somehting expensive i dont need

It's not the Volts it's the AMPS. the more amp/hr output the battery has the more motors can be lite. The general rule of thumb I've had great success with over the years is 2 amps per igniter. My advise is to purchase as hi an amp/hr rated battery your budget will allow. Gel-Cells are better for individuals who don't want to mess with Lead/Acid wet cell (Car,truckand boat)batteries. will last longer and really hold a charge.
Hope this helps.
"how many engines can a 12v light successfully?"

Well, let's do the math. Typical car battery, 630 cold-cranking amps. POS copperhead igniter, 2 amps recommended per. That gives us a theoretical 315 motor cluster capability. Just a ballpark number.

Please warn us before you try this. I would like to be at least three states away.
I guess you could twist together a FEW of the igniter leads. That could cut down the number of required microclips to a more reasonable 316, or even 210?
I have been using an Estes command control launch system with two 7.2 volt 1500ma batteries & it works great. I have also used onw 7.2 volt 1500ma hobby battery in a home made launcher & I have no problems on 2 motor clusters. On 3 I use the Estes with the 2 batteries.
Only take about 15 mon to recharge from my car!
Yes star with a 2 motor cluster with 18mm motors & work up from there.
I've generally found the old way of installing ingniters works better than plugs , I take a small wad of wadding and pack it in behind the ingniters with a sharp pencil and then cap it of with a ball of non-harding clay . also I made a launch controler which plugs into the cigerete lighter in the car works great.