My new modular cluster ignition cables

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Fore Check

Well-Known Member
Sep 24, 2010
Reaction score
I wasn't sure if this should go here or in the support forum, but since I scratch built this as my first "electronics" type project, I thought I'd post it here.

I use a Pratt SureFire2 12 volt rechargeable launch system. One of the main advantages of this system is the relatively high amp delivery when you press the launch button. I wanted a more reliable, heavy duty cluster wiring system for my larger models.

You see, I just haven't been enamoured with the idea of clipping the standard set of single ignition whips to a smaller gage set of wires on a clip whip - the set that comes with the launcher is 18 gage, and most whips are "necked down" from there. Plus, you have to be quite sure that the clips on the lead cables aren't touching each other (thus causing a short) by placing them just so at the pad - leaving a higher chance factor in the mix (I've had this problem spring up on me. Shorted out my system. Had to send it in for a repair; thankfully the only cost incurred was in the one-way shipping. Thank you Pratt Hobbies!) Plus, the banana clips on the stock set were getting a bit loose in their terminal post.

Anyway, I wanted something better. So I got to dreaming this up and set out to Radio Shack and my automotive supply store and whipped this up.

Here's what I came up with.

I started off with two 24" long pieces of 10 gage wire. I soldered on a pair of premium gold plated "locking" banana clips (no more loose connection to the launcher.) I then took four 18" long pairs of 18 gage wire, split them to black and red, and attached all four pairs to the 10 gage wire (black and red side respectively) to the 10 gage using a soldered/crimped butt splice. I then soldered the other ends of the 18 gage wires to a four-pair plate of female RCA connectors mounted in a project box (all the reds on one side, all the black on the other.) This puts the same potential on all four pairs of RCA connectors.

Here's a pic of the lead line/splitter box.
I then maid four pairs of clip cables. I used a 48" long piece of 18 gage wire, with a pair of alligator clips soldered to one end, and a pair of male RCA plugs on the other. Here's a pic of one of them.
For use, simply install the banana clips on the lead/splitter lines to the launcher, lock them in, and then plug in as many sets of clip lines as I'll be using on a given rocket.

Here's a pic of the whole shooting match plugged together with all four sets of clip wires.
As I stated above, one of my primary concerns with other clip whip systems is the existence of other stray clips that will be "hot" on ignition leaving the possibility of a short. The beauty of this setup is that if I'm only launching a single engine, I only have to plug one set of clip wires in.

Here's a pic with only one installed, the other three removed.
To top it off, the system is modular even further.

I have had no problems using the smaller gage clip wires in the past, I just wanted something better (and I wanted to build this to see if I could, really.) If I wanted to go beyond 4 engines, I could get some RCA "Y" type splitters, plug them into the splitter box, and go as high as 8 (Pratt says his launcher will launch up to 9 estes igniters simultaneously.)

Further, if I ever get my hands on an Aerotech "interlock" type clip for use on copperheads, I just have to attach it to a relatively short piece of 18 gage with RCA plugs on the end, and plug it in.

The nice part is that all these wires still pack away nicely inside the Pratt launcher box, so the entire system is still self-contained for transport.
I've tested the entire system using the test lamp included with the launcher. It works great! I get a stronger, brighter light than I did on previous whips, and the audible continuity buzzer is louder and brighter than ever.

Like I said, this was just something that I "wanted," rather than "needed," but I'm pretty proud of my *very* amateur handywork and can't wait to use it.
Take this from a guy who used to design cable systems for a living....

Very nicely done.

Consider your idea stolen.

You've got a winner for sure....

My next? project is slated to be a cluster...
I tend to build from the ground support up... so it
looks like I'm on my way to RS...

Great job....(and THANKS for sharing)...

Very nice indeed!
Hows about posting the part numbers from Radio Shack for what you used. I'm sure there are plenty of us that would like to put something like this together.
Part numbers?

Ugh.... I already threw away all the packaging. Ooops.....

If I can I'll go back by there and make some notes in the next few days.
Well, that was easier than I thought - just cruised by the Radio Shack website. Here's the part numbers from them.

Banana Plugs: #278-307 ( x1 )

8 Jack Phono Board: #274-370 ( x1 )

4x2x1 Project Enclosure: #270-1802 ( x1 )

Phono (RCA-Type) Plugs: #274-319 ( x2 )

18 Gauge, 2-Conductor "Mega Cable" 25ft roll: #278-567 ( x1 )

1 3/8" Mini 'Gator Clips (5 pair package): #270-374 ( x1 )

I got my solder and solder gun from them too. I got the 10 gage wire and the solder/crimp butt splices from the automotive parts store.

The catalog says those banana plugs will take 12 gauge wire - they will take the 10.

You'll just need to cut out the lid on the project enclosure to accept the 8 jack phono board, and drill a hole in it for all the wires to pass through.

Have fun! I did. I think it turned out really nice. Thanks for the compliments!
Great looking system Forecheck!
I prefer to limit the length of the 16gage clip wires on my direct relay connections to a maximum of 24", 18inches where I can get away with it. Your module is a super idea.
I cloned you idea for myself however I did make one design change:

Instead of the RCA jacks, I used 1/4" phone plugs.

No critque of yours, just a preference.

I also built 4 alligator clip wires and one lead for the Copperhead clip.

One mod to the leads was I attached a bulldog type paperclip to rach lead as a strain relief. I clip those to either the rod or the deflector to keep the weight of the leads from pulling out the igniter.

Here is an idea I considered after the fact: Build a continuity beeper into the box so you can perform a local test before leaving the pad.

Where did you get the Copperhead interlock clip? That's all I need to complete my system...

The Pratt box has a continuity buzzer on the main box - It'd be nice to have individual lights (preferred) or buzzers on each of the four branch whips.
Thanks for the heads up! I'll watch that auction and bid if it doesn't get out of hand.

How would you put individual continuity tests (light or buzzer) on each set of clips? I'm no electrician or electrical technician by any means - but I can clip wires and operate a soldering iron....
I have not fully thought it out, however I think my design would go something like:

A SPST (three way) switch at each connector. In one position power is routed to the motor. In the other, to a contimnuity check. I'll sketch something up and post it later.

BTW, I paid $3.00 plus #1.50 S/H for mine.

I just thought of a method for use on my controller.

My box makes an audible signal when the pad is "armed" to indicate continuity.

On a cluster, I could hook up all four sets of clips at the pad, and install all of one color of the plugs at the box (lets say black.)

Then, I could install one red plug. If the alarm goes on, I have continuity. If I do, remove the plug (quieting the alarm) and proceed to the next plug. Install it and wait for alarm. If continuity alarm sounds, remove and move to next red plug. And so on. If there's continuity on all four, simply reinstall all of the red plugs (black ones are still installed) and proceed with launch procedure (stand back, install interlock key, countdown, etc.)

Not as clean as possible, but I think it would work.

In fact, if my "tests" were any indication, I wouldn't even have to plug them in entirely - just touch the jack to the plug. (I was getting enough current through my body to sound the continuity buzzer simply by grabbing the exposed metal on an alligator clip in each hand without physically touching them together. That was enough right there to tell me that all my connections were sound... :cool: )
I'm always blown away with the creativity and ingenuity in this forum. Everything from designs, repairs, electronics, pvc, chain link fence... I love it.

Great Job Fore Check. It seemed like such common sense after seeing it, somone just needed to do it.

Latest posts