What am I doing wrong?

Discussions on low powered model rockets using E powered motors and below.

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baq
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What am I doing wrong?

Postby baq » Sun Jul 31, 2016 5:42 pm

Hi Guys,

Finally got my bum into gear and went to play with the little Estes Silver Arrow.

Checked wind direction and positioned ourselves accordingly.

Launch briefing for the button pusher.

Fresh 9v in the B6-4 in, recovery wadding in, chute packed.
Put the starter in, touching propellant, plug, stuck to side, hooked up launch wires. Retreated to safe distance.

Then this happened.
[youtube]https://www.youtube.com/watch?v=-axEA26H324[/youtube]

https://www.youtube.com/watch?v=-axEA26H324
What you don't get to see because I was too busy watching and forgot to video was the rocket fly up, and back over our heads - which is what I wanted it to do, got some good height, then the 'chute deployed and the wind blew it back over us and about 160m downrange. It was all pretty good.

We retrieved it, repacked everything, new engine in, tried to relaunch and... couldn't.

The starters didn't seem to be working. I thought it might have been a dead short at the starter end. Fixed that, no. Pulled it out pushed the button with the starter out of the engine and it started smoking so it was getting current. Put it back in, tried a new starter. Nada. LED was lighting when pressing in the key, just no movement.

I'm yet to put a multimeter on it, but my guess is either the dead short stuffed the battery or some other battery failure that's causing not enough juice to get to the starter.

Is this common? How many launches do you normally get out of a 9v? Am I missing something obvious?

Thanks!

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Re: What am I doing wrong?

Postby Viking » Sun Jul 31, 2016 6:47 pm

Hi baq,

You're doing nothing wrong, it's just a poor controller design using a 9v battery.
They're great for very low current devices like multimeters and smoke alarms etc where they will last for years, but no good for much more than that.

Problem is, 9v batteries are actually 6 really small 1.5v cells in series and because these cells are so small they have a low capacity and a high internal resistance, this resistance means they can't deliver much current and not for long. If you did have a short then yeah that would've pretty much drained it.
Replace with a nice new alkaline and you should be good to go again for a little while, also best to go with a brand-name battery instead of a cheapie.

What controller is it?
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Re: What am I doing wrong?

Postby Happy Heyoka » Sun Jul 31, 2016 9:12 pm

Assuming that since you have a multimeter and know how to drive it, you could check out the battery and maybe even (in a safe place) try and fire one of the igniters that failed. Depending on the kind of igniter sometimes it's hard to tell if the igniter failed or the motor just failed to be ignited by it (both things can happen).

It is not that unusual for igniters to fail. On a really bad day, you can get a few in a row... some people are legendary for that. Have a few spares in your box.

You could try replacing the 9v with one of the 6xAA holders (about $2 from somewhere like Jaycar) or even a 12v SLA if you have the means to recharge it. I use one from an old UPS that no longer meets spec but is fine for firing igniters.
Keep in mind if you add more current into the mix you might want to consider adding a fuse so you don't accidentally melt your controller leads via a dead short :roll:
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Re: What am I doing wrong?

Postby OverTheTop » Sun Jul 31, 2016 9:17 pm

The igniters are very fragile. Handle very carefully. I try to keep my fingers on the tape to avoid bending the wires.

+1 for the suggestions from the other guys.
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Re: What am I doing wrong?

Postby kopius » Mon Aug 01, 2016 10:33 am

It really comes down to one thing... Estes.

as mentioned above, the Estes igniters (aka starters) are very delicate and commonly break. They are also have a high resistance and therefore are harder to ignite (probably the issue you faced and need to hold the button down long enough to burn the composition).

Additionally, many of the Estes controllers don't have true safety circuits in them and use the high resistance of the igniter as their 'resistor' on the continuity circuit. This is very dangerous if you later try and use a better quality igniter.

If you want to resolve your issues, instead of swapping batteries etc. just get better quality igniters which are low resistance and not delicate. SCR igniters are exactly that: http://ausrocketry.com.au/igniters-e-matches.html
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Re: What am I doing wrong?

Postby SpaceManMat » Mon Aug 01, 2016 12:35 pm

kopius wrote:Additionally, many of the Estes controllers don't have true safety circuits in them and use the high resistance of the igniter as their 'resistor' on the continuity circuit. This is very dangerous if you later try and use a better quality igniter.


Found that out during one to do duel deployment testing. Just as well I was taking other precautions ie I was out of the way. Beware anyone that uses one of the Estes controllers they can easily cause an uncomanded launch or other issues.
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Re: What am I doing wrong?

Postby SL666 » Tue Aug 02, 2016 12:15 pm

I actually came here to post this -

I've had 1? fail until Saturday - where i had all 3 in a row fail.. on a fresh battery...

after removing from the rocket - the composition has smouldered off the filament, but not actually burnt.. 'feels' like this has only been an issue since the ignitors went to clear goop on the filament, not the black composition?

eg - this -
Image
(old pic replaced)

L- R
Old style ignitor compound completely consumed, New style unused, old style (only fail I've had - presumably dead battery)

Checking the voltage on my controller - 8.65V vs new out of pack 9.05v - from only 3? successful launches and then the further 3 failed (which did indeed have some extened button mashing).

I notice that the filament is not consumed - just supposed to glow?.. (hooking them up to a bench power supply results in a very short flash :) unless you have it cranked right down...)

if i was to build a replacement with a lipo - post likely it would pop that sucker in no time at all.. so whats a scientician to do?

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Re: What am I doing wrong?

Postby SpaceManMat » Tue Aug 02, 2016 2:43 pm

There's something wrong with the image you posted SL6
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Re: What am I doing wrong?

Postby SL666 » Tue Aug 02, 2016 8:01 pm

aaand i can no longer edit?

Image


maybe?

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Re: What am I doing wrong?

Postby Viking » Tue Aug 02, 2016 11:44 pm

Strange, I can see the first pic just fine on my tablet, but not on a Windows machine.

The voltage may seem fine with no load, but as soon as you load it up with an igniter the voltage will drop considerably due to the battery's internal resistance and little current will flow, that's why your igniters are burning the coating but not the wire.
A lipo will work fine, even a tiny 3 cell one that can be retrofited into a 9v battery compartment.
I've never had an issue with the 'new' Estes igniters and a little 12v 1.2Ah lead-acid battery.
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Re: What am I doing wrong?

Postby Lamp » Thu Aug 04, 2016 12:04 am

I think others have answered your problem, I just don't think the igniter is getting enough current. The wire "should" glow white hot under the current, but it does not matter if it lights the pyrogen and that lights the motor.

Back in the early 70's we just used a short length of fine NiChrome wire, without any pyrogen and we used a little ball of cotton wool (jammed into the clay nozzle with a dead match) to hold it in place. We almost never had ignition failures using this system...but we did use a motorbike battery to power the launch controller too. :wink:
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SL666
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Re: What am I doing wrong?

Postby SL666 » Thu Aug 04, 2016 11:39 am

"hmm"

anyone have a gut feel on if temp makes a difference to a rockets likelyhood to light?

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Re: What am I doing wrong?

Postby SpaceManMat » Thu Aug 04, 2016 5:18 pm

SL666 wrote:"hmm"

anyone have a gut feel on if temp makes a difference to a rockets likelyhood to light?


I know Canadian fly in the snow some times. Extreme cold can cause propellant grains to crack. Once the igniter material is lit the chances of lighting the motor should be fairly close to the same.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 10,849 feet
Largest Motor: CTI 1115J530 IM
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baq
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Re: What am I doing wrong?

Postby baq » Sun Aug 07, 2016 11:16 am

kopius wrote:It really comes down to one thing... Estes.

as mentioned above, the Estes igniters (aka starters) are very delicate and commonly break. They are also have a high resistance and therefore are harder to ignite (probably the issue you faced and need to hold the button down long enough to burn the composition).

Additionally, many of the Estes controllers don't have true safety circuits in them and use the high resistance of the igniter as their 'resistor' on the continuity circuit. This is very dangerous if you later try and use a better quality igniter.

If you want to resolve your issues, instead of swapping batteries etc. just get better quality igniters which are low resistance and not delicate. SCR igniters are exactly that: http://ausrocketry.com.au/igniters-e-matches.html


A couple of good leads - thanks.

Your comment about the Estes controllers makes me nervous. I'm sharing this new hobby with my 6yo. Now, he'll always be under strict supervision, but I'd rather address risks like this.

What's the controller of choice in the "cheap and cheerful" range?

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Re: What am I doing wrong?

Postby kopius » Sun Aug 07, 2016 7:35 pm

The SCR controller has a resistor on the continuity circuit so it won't accidentally fire an igniter when you simply want to test the circuit: http://ausrocketry.com.au/hardware/launch-hardware/lpr-launch-pad-and-controller.html
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