Continuity & short checks on three cluster rocket

The Rocketry Forum

Help Support The Rocketry Forum:

Switch

Well-Known Member
Joined
Nov 5, 2016
Messages
65
Reaction score
52
Is there a smarter way to check continuity on a three cluster rocket than to check each igniter separately? Also, is there a way to know if there is a short? I want to be able to ignite three low power motors reliably & these issues have caused several failures. I also had a problem with insufficient current which I fixed by using a relay. So what I'm looking for is a fail safe circuit to check continuity and detect shorts on a three cluster rocket after I have all of the igniters connected to the relay. Ideally a Green LED means the rocket is ready to fly and a Red LED means there's a short or a lack of continuity & will prevent ignition if triggered by the relay.
 

Sandy H.

Lifetime Supporter
TRF Lifetime Supporter
Joined
Mar 20, 2009
Messages
970
Reaction score
386
Not impossible, but not sure if it is worth the effort. At the end of the day, if you have good igniters, good technique and a relay launcher that has a good battery, your success will be pretty high, IMO.

Personally, when launching clusters at a club (or with your own high current controller), the igniters are the weak link. Hooking everything up and going back to to launch control to only find it isn't green is better than red, but it would be better to have confidence in the cluster launch before you walk away from the rod.

Back when Q2G2's were easily available, I tossed all the Estes igniters and just used those. 100% success with a 7 motor cluster, multiple flights. The 'new' clear Estes igniters are less reliable than Q2G2's for any launch, IMO. I suspect everyone would agree.

Now, when I launch clusters, they are home built igniters. If I could get Q2G2's for $1 each, that's what I would use, but that isn't the case.

Now that my diatribe is done, you absolutely can create a controller that gives a green/red with a specified igniter combination. Since the igniters are run in parallel, you can figure out the resistance that is good. A short or open circuit would change that answer. Having said that, if you design and build a controller that is good for 3 Estes igniters in parallel, it won't be good for 2, 4, 7 (etc.) Estes igniters in parallel unless you do something programmable. Heaven forbid you get your hands on some Q2G2's, build your own, etc.

You can use a DMM to check each igniter and do the math for the parallel igniters and be fairly certain it will work as well. If you see something that is outside of logical parameters, you bail out and do it over. A go/no-go solution would be tedious unless it was just for a specific case or was programmable, IMO.

Sandy.
 

Voyager1

Well-Known Member
TRF Supporter
Joined
Oct 23, 2015
Messages
730
Reaction score
243
Location
ACT, Australia
If you have 3 igniters in parallel then your combined resistance is about 0.3 - 0.5 Ohms, assuming a single igniter resistance of 1 - 1.5 Ohms, typically. You would need a DMM to measure the resistance to detect whether any are open circuit. If any go short circuit, then the whole parallel combination is shorted.

Trouble is, if you’re measuring the combined igniter resistance over a long cable, you need to account for the cable resistance too, otherwise your measurements are erroneous. This is particularly important if you’re using thin cable with a relatively high resistance.

If you want a fail safe method of detecting shorted or open circuit igniters in a cluster, then you really need to be able to check continuity on each igniter.
 

cerving

Owner, Eggtimer Rocketry
TRF Sponsor
TRF Supporter
Joined
Feb 3, 2012
Messages
4,613
Reaction score
2,084
I've seen people use Wilson wireless launch controllers in drag race mode, one output for each igniter. Then they can check continuity on each output separately. Of course, bad things can still happen, like lighting one motor short if there's a bad igniter, but at least the continuity side can be checked before hitting the button.
 

UhClem

Well-Known Member
Joined
Feb 6, 2009
Messages
1,884
Reaction score
318
I use a 4 wire (aka Kelvin) Ohm meter designed specifically for measuring igniter resistance. Check them one by one and then once wired in parallel.

I also like the Q2G2 igniters, especially the long wires. For Estes Solar igniters I soldered color coded (one red and one blue) extension wires onto them.
 

Steve Shannon

Well-Known Member
TRF Supporter
Joined
Jul 23, 2011
Messages
7,135
Reaction score
4,212
Location
Butte, Montana
If your club has a system that supports drag races and displays continuity for each channel just hook your rocket motors up to three different channels as if they are each a different rocket in the drag race.
 

Switch

Well-Known Member
Joined
Nov 5, 2016
Messages
65
Reaction score
52
So it sounds like I'm looking for a solution to a problem I shouldn't have. I appreciate the feedback!
 

RocketRev

Lifetime Supporter
TRF Lifetime Supporter
Joined
Jul 25, 2012
Messages
349
Reaction score
215
Yes, any Wilson F/X system can report the continuity status of any particular individual igniter lead. Any WFX multi-pad pad-box can be used to do a drag race or a cluster. Each igniter lead has its own relay or FET (we're finishing up the beta testing on FETs right now. QCRC my guinea pigs, can't tell any difference in performance between relays and FETs in my WFX tech). But available battery power at the pad for your drag race or cluster can be a problem. Not much WFX can do about that other than we have a voltage report at the pad on the pad-box and at the controller on the LCO table.

Every Wilson F/X controller can report individual continuity status from each separate igniter lead, but an individual continuity status report is pretty much the industry standard for launch systems. If you can build one ignition circuit with Green and Red led continuity status reporting, then you can build as many separate/parallel circuits as you need for your own cluster system.

If you really need ("need" being a relative term) a red or green LED visual report for each igniter lead then a Wilson F/X custom controller could work for you. I've attached a pic of an LCU128x controller with all 8 pads selected on bank C. If you look, closely, only pads 1 and 2 have continuity as they are GREEN. Pads 3-8 have no continuity so they are showing RED. And yes, this pic was taken in direct sunlight about 5 in the afternoon as you can see from the shadows.

LCU-128x showing continuity.JPG
 
Top