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Clip whips and multiple-motor continuity testing

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Joshua F Thomas

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My 12v launch controller has one defect that I'm not sure how to address. When using a clip-whip and multiple motors, the continuity test will show so long as any of the igniters has good continuity. With one good and three bad I would still get the same continuity signal.

I'm trying to figure out how I can solve this, and it's really an electrical engineering problem. An "obvious" solution would be to put an LED in series with each lead, but a) LEDs have a forward voltage drop, and b) the current used for the igniters would fry the LEDs after a few uses. Putting a resistor in defeats the purpose of giving the igniters as much current as possible.

Putting LEDs in parallel to each lead also doesn't do much, since the continuity current will mostly bypass the LED and it won't light up.

Any ideas?
 

Steve Shannon

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Either switch your ignition current around the LEDs or actually measure resistance of the igniters and calculate whether the resistance makes sense. Or hook up your igniters in series. It works too.
 

UhClem

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Hm. How would the resistance be tested?
Apply a known (small) current and measure the voltage.

Complicated by the long wire to the pad and I don't think anyone is willing to add the complexity of a four wire connection (test current in one pair and the measured voltage (zero current) in the other pair) at the pad just to get good resistance readings.
 

Joshua F Thomas

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Yeah, I had the same misgivings.
I guess one possible solution would be to run four (or whatever number) of separate wires to the pad, one return ground, and put a continuity check on each line. Or one check with a rotary switch to pick a line...

That is an annoying amount of extra work.
 

Steve Shannon

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Yeah, I had the same misgivings.
I guess one possible solution would be to run four (or whatever number) of separate wires to the pad, one return ground, and put a continuity check on each line. Or one check with a rotary switch to pick a line...

That is an annoying amount of extra work.
Or use four pad boxes and light all four as if it were a drag race.
But really connecting all four in series is the easiest way.
 

Joshua F Thomas

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In series? You don’t mean the igniters, do you? Because that would be a terrible idea for cluster launches...
 

rharshberger

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In series? You don’t mean the igniters, do you? Because that would be a terrible idea for cluster launches...
Generally the pyrogen on the igniter lights well before the nichrome burns through opening the circuit. The igniters currently made by Estes are an exception ascthey have no pyrogen.
 

Steve Shannon

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In series? You don’t mean the igniters, do you? Because that would be a terrible idea for cluster launches...
Everyone always says that. :D Once a guy said that that first igniter would burn through before the later ones get energized. In a series with only resistive elements every igniter gets the same current at the same time.
Look on the forum here to see how the world record cluster was wired. It was a combination of series and parallel igniters.
Here:
 
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Joshua F Thomas

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Everyone always says that. :D Once a guy said that that first igniter would burn through before the later ones get energized. In a series with only resistive elements every igniter gets the same current at the same time.
Look on the forum here to see how the world record cluster was wired. It was a combination of series and parallel igniters.
Here:
No, the resistance should be the same (assuming all the igniters are the same), but if one of the earlier igniters burns through before the others light, you're going to lose all the rest.

That means I have to trust the igniters are all going to behave the same, and all can ignite the motors before any of them burn through. Too many things to trust, imo.
 

Rocketjunkie

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Series works for e-matches but not for the typical starters that come with the motors. Run them in parallel. You can use an ohmmeter to check the resistance if each starter before connecting them together. (I use the term starter here since it's not regulated. Igniters require a LEUP and ATF compliant storage.)
 

JoePfeiffer

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I built a box with four switches and four sets of clips. I can turn one on at a time for continuity checks, then all four for launch.
 

ksaves2

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Generally the pyrogen on the igniter lights well before the nichrome burns through opening the circuit. The igniters currently made by Estes are an exception ascthey have no pyrogen.
Hey Rich, Easy enough to dip ‘em in ones own pyrogen. Can lookup some recipes or easy enough to buy some commercial dip (or doctor certain forth of July celebratory articles for the same purpose.)
 

Steve Shannon

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Series works for e-matches but not for the typical starters that come with the motors. Run them in parallel. You can use an ohmmeter to check the resistance if each starter before connecting them together. (I use the term starter here since it's not regulated. Igniters require a LEUP and ATF compliant storage.)
I agree it’s easier with electric matches, and they should be nearly the same resistance. The average launch controller doesn’t supply enough voltage to light a series of high current starters.
I’ve been assured by the lawyer who accompanied me to our most recent meeting with ATF that if someone does something stupid with a starter the ATF will pay no attention to what it’s called. Function is all that matters to them. But what we call them can help them pay less attention to us. Thank you for the reminder.
 

rharshberger

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Hey Rich, Easy enough to dip ‘em in ones own pyrogen. Can lookup some recipes or easy enough to buy some commercial dip (or doctor certain forth of July celebratory articles for the same purpose.)
I do Kurt, I keep a small pill bottle of mixed BKNO3-V dip in my range box and if its slow dip igniters, I also trade my dipped ones for undipped ones to help ensure the kiddies rockets actually ignite.
 

RocketRev

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To the curious,

You are correct that "lighters" of the same kind, OUGHT to all function the same, but then reality sets in and reality is that all "lighters" even if them are from the exact same batch from the exact same Manufacturer, are NOT always the same. There are so many ways in which they can be slightly different from each other that it would be a waste of time to try and list them all. And slight differences from one "lighter" to the next can make for larger functionality differences.

Then there's the problem of your "launch system" itself. It is clearly designed as a single motor "lighter"system. It has one continuity circuit, because there is only one ignition circuit. If you were to test the resistance of say 10 different "sets of 4 lighters" with the same clip-whip and igniter lead not connected to the rest of your launch system(of course), you will get a pretty good idea of what a "set of 4 lighters" resistance should be. The difficulty is that if you mark each set very carefully and "retest" all ten sets resistance again, that you will probably get slightly different readings. Again, reality is setting in. How well the clip whip is currently connected to the current set-of-four will change slightly each time that you hook it up. You will eventually get a pretty good average resistance reading that you could use to determine as close as is possible with a clip whip and four lighters, what the resistance ought to be.

With your current system that's probably your best bet.

Your other current option is to quadruple your current "launch system" from 1 circuit to 4 circuits. If you're doing a lot of clusters, that's probably the way to go. As you said, it would be a major annoyance when it comes to how much work it would take, but it is your system.

I do have to ask, your "continuity circuit" is it a simple "power can go thru - with a light-bulb to keep from firing the lighter" ' or is it something more complicated?

Brad
 

Joshua F Thomas

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I do have to ask, your "continuity circuit" is it a simple "power can go thru - with a light-bulb to keep from firing the lighter" ' or is it something more complicated?

Brad
I posted the circuit diagram in the other thread which shows the whole build. It just checks for current low enough to light an LED (around 5-10 mA).
 

Joshua F Thomas

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I do Kurt, I keep a small pill bottle of mixed BKNO3-V dip in my range box and if its slow dip igniters, I also trade my dipped ones for undipped ones to help ensure the kiddies rockets actually ignite.
I use the QuickDip pyrogen to improve the Estes igniters and they've worked 100% of the time for me. I just bought some nichrome wire so I'm going to start making my own.
 

FredA

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Curious : What do you know about your "lighters?"
- What is their nominal resistance?
- What is the "all fire" current?
Let's figure this out instead of guessing.....
 

ksaves2

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I do Kurt, I keep a small pill bottle of mixed BKNO3-V dip in my range box and if its slow dip igniters, I also trade my dipped ones for undipped ones to help ensure the kiddies rockets actually ignite.
I’ve kept some around too and like the green color with open air testing. MTV is good for ground launching motors too! I’ve used several different types of recipes for starters and they all work. Kurt
 

JohnCoker

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When I launched the Crayon Pack, I used a conventional clip whip and just tested the igniters with a multimeter right at the pad before attaching the alligator clips.

 

jderimig

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As Steve said, best practice is to use high quality commerical ematches in series and a dip or ignition pellet (pyrodex) in the motor. The resistance variance between them doesn't matter because the identical current flows through each and everyone. If that current is a well above the all-fire current then they will ALL Fire. Rule of the thumb the pyro guys use is your voltage across the ematch string should be 2V x number of matches.

If your igniters are anything else then all bets are off and you should measure each one and not depend on a the launch controller to determine if each igniter will get any current.
 

jrap330

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Yeah, I had the same misgivings.
I guess one possible solution would be to run four (or whatever number) of separate wires to the pad, one return ground, and put a continuity check on each line. Or one check with a rotary switch to pick a line...

That is an annoying amount of extra work.
I never cluster and this comment is just base on the Estes controller. The continuity check is not 100% foolproof anyway. You can have dirty contacts, slightly deformed clips and even poor battery connection and still get a light. It helps indicate an issue when clip falls off and maybe shorts on the deflector plate or against each other. So I am not sure why everyone cares about it..excerpt for looks. Otherwise either series connection or as you stated multiple LEDs for each wire through a rotary switch.
 

FredA

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+1 John -- I just said to measure the resistance so you don't have to guess if you're able to dump enough current using Ohms law for the SERIES circuit. Somebody might be reading this and using Nichrome or other heating element that is higher than an Ohm or two.
 

Joshua F Thomas

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I never cluster and this comment is just base on the Estes controller. The continuity check is not 100% foolproof anyway. You can have dirty contacts, slightly deformed clips and even poor battery connection and still get a light. It helps indicate an issue when clip falls off and maybe shorts on the deflector plate or against each other. So I am not sure why everyone cares about it..excerpt for looks. Otherwise either series connection or as you stated multiple LEDs for each wire through a rotary switch.
Those kind of issues should fall under “taking good care of your equipment”, at least imo...
 

jrap330

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Those kind of issues should fall under “taking good care of your equipment”, at least imo...
Yes, but he (OP) is worried about continuity light fort cluster ignitions. The whole purpose of the continuity light is to tell you if everything is OK and a go for launch.....but as I pointed out you can get a good light..it looks good and bright and still get no ignition so since it is not 100% fool proof...I think it is really unnecessary especially if you are having trouble designing a controller.

Am I incorrect about the "usage" of continuity light?
 

Joshua F Thomas

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I am the OP :D

Continuity means no more and no less than having a good electrical circuit with the igniter - it can pass current.

The issue on clusters comes from having multiple igniters and trying to confirm *all* of them have a good electrical connection.

My launch controller - which I had no issues building - fits my needs but lacks the ability to distinguish between valid continuity on only one igniter versus all igniters. There are multiple ways to solve this problem and most of the have been mentioned here. It would be convenient if I could find a low-effort solution using my existing setup.
 

Joshua F Thomas

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+1 John -- I just said to measure the resistance so you don't have to guess if you're able to dump enough current using Ohms law for the SERIES circuit. Somebody might be reading this and using Nichrome or other heating element that is higher than an Ohm or two.
The main problem I have with the “measured resistance in series” solution is that it both limits me to specific igniters (or whatever you want to call them), and requires me to trust that they always have the same resistance regardless of manufacturing and environmental conditions. I don’t like to design things where I have to trust someone else got their end right. I *could* literally check the resistance of every igniter I use... but that’s too much work, and what if I forget the meter? No thanks.
 
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