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back to article Pyrotechnic boffin poised to light LOHAN's fire

Cometh the hour, cometh the man, as the old saying goes, and we're delighted to report that a Reg reader has stepped forward to resolve the thorny problem of just how to get our Low Orbit Helium Assisted Navigator (LOHAN) mighty thruster to fire at altitude. Click here for a bigger version of the LOHAN graphic The first rocket …

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"The solution? A more potent igniter"

True to the spirit of Real Engineering:

- if it doesn't fit, force it

- If it can't be forced, use a bigger hammer

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Anonymous Coward

Re: "The solution? A more potent igniter"

As the great philosopher Tim "The Toolman" Taylor rendered it: MORE POWER

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Happy

Re: "The solution? A more potent igniter"

....and if it still won't go in, spray it with WD40 and then hit it again.

Heating with an oxyacetylene torch until a brightly glowing cherry red colour is achieved and then belting the living daylights out of it with a sledgehammer is the nuclear option[1].

[1] If you happen to be a nuclear physicist with access to a decent amount of high-grade fissile material, your opinion may differ here. However, it should be pointed out that reducing your trivial engineering problem and a wide surrounding area to radioactive slag in a fit of pique counts as admitting defeat.

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Mushroom

Re: "The solution? A more potent igniter"

and if it breaks, it needed replacement anyway

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Re: "The solution? A more potent igniter"

- If it breaks, you probably needed a new one anyway.

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Re: "The solution? A more potent igniter" - admitting defeat.?

"Reducing your trivial engineering problem ... to radioactive slag ... counts as admitting defeat."

Not if it's a rogue asteroid it doesn't.

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Coffee/keyboard

Re: "The solution? A more potent igniter"

> True to the spirit of Real Engineering:

> - if it doesn't fit, force it

> - If it can't be forced, use a bigger hammer

That's not engineering, that's proper British Bodging - a proud tradition.

Going by my experience as a 'software engineer' an engineering solution would be:

1. Try it again to see if it happens every time

2. Have lots of meetings in which nothing concrete is agreed but lots of managers tell you how important it is to fix it quickly

3. Under management pressure come up with some half assed bodge

4. Implement half-assed bodge

5. Spend the next 4 weeks explaining to various managers why the half-assed bodge doesn't work properly

Like you, I used to think that engineering was about making things. But eventually I came to realise that it's about dodging blame, writing powerpoint slides, and guessing how long things will take before you do them.

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Re: "The solution? A more potent igniter"

You forgot 6. spend another 4 weeks getting the bodge to actually do what it needs to.

7. Spend 8 weeks on some other bodge

8. "Upgrade" your programming to do more, including tasks it was never intended to do

8.1 using protocols and designs chosen at 3 for their simplicity which are now woefully inadequate for the much more complex demans.

9. Start at 1.

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Re: "The solution? A more potent igniter"

Forgot to add at 8:

This is ofcourse under severe pressure from previously mentioned managers who understood crap about the troubles at step 5 and promised some big-wig client they could deliver next week.

And at step 8.1

Also under pressure of said managers, "because that's what you are already using, so it will be easier".

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Burn baby

Burn baby, burn!

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Pint

<- Obligatory

You should set up a proper "Buy our contributors a pint" donations page though - I'm sure I'm not alone in wanting to treat them to something stronger than a jpg beer!

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(Written by Reg staff) Bronze badge

Re: <- Obligatory

That's not a bad idea. I'm sure we'll be buying them a few real pints at some stage.

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FAIL

Re: <- Obligatory

*views image information*

It's a PNG. Bother.

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Vic
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Re: <- Obligatory

> I'm sure we'll be buying them a few real pints at some stage.

I was about to suggest that SPB articles should run "Beernotes" instead of "Bootnotes"...

Vic.

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igniter box

"12V igniter box - with its eight AA batteries - will provide the necessary electrical poke to get the ball rolling"

Why waste so much weight on ignition batteries? Stack a few coin cells to get to your desired voltage and use a capacitor to ensure a decent current density. Make sure you test the whole set-up at cold temperatures.

OTOH, you might want to carry one battery to run everything (camera?!). A continuous discharge should keep the battery warm.

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Re: igniter box

separate and dedicated battery systems provide much better reliability and better tuning to the needs of the particular battery.

I would see about using a Li-ion or Li-Po battery. AA batteries provide a manageable power to weight ratio. Avoid 9 volt blocks like the plague. Very underpowered and drain very fast.

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(Written by Reg staff) Bronze badge

Re: igniter box

I take your point about weight. We certainly don't want to run everything off one battery, though. All systems, cameras, etc, should have independent power supplies. SPB rule 2: Put not your faith in a single source of power.

Rule 1, btw, is: Let there be beer.

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Re: igniter box

Li-Po?

Must be the chemist in me - but I wondered if a Lithium Polonium battery was a spot of overkill (in every sense). Then I did some googling - bitterly disappointed now.

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Stop

Re: igniter box

Lipo? Forget it, it has serious issues when getting cold. Ask any electric model plane flyer.

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Re: igniter box

Well, It can't be true that LOHAN needs liposuction, can it?

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Boffin

Re: igniter box

I'm not sure how far you are in the design process for the battery/igniter box, but you might want to consider to at least test its performance at the designated temperature:

I'm already assuming that you are not using alkaline batteries as their current output is basically zilch at -60°C. If you want to stick with AA batteries, lithium batteries (e.g. Energizer L91) will perform way better than alkalines.

Also, I'd want to be really sure that the mechanical stress in/on the box due to the freezing temperatures does not introduce extra electrical resistance due to a bad mechanical contact -- that's 8 battery-to-battery connections of which only one has to fail sufficiently to result in a no go. Other than that, 8 batteries weigh quite a bit (without the enclosure 8 AA alkaline batteries will be about 200 grams, 8 AA lithium around 120 grams), which is lifting capacity you'd rather use to get your balloon to a higher launch altitude.

For a relatively short trip, you can try insulating your battery box with styrofoam and maybe add an exothermic heater (hand heater pads) to keep the temperature of the batteries acceptable, but this also adds more weight.

Personally, I'd try going with 4 smaller 3V lithium photo batteries (eg Energizer 123); you don't need a lot of charge, but you do need peak current which they should be able to provide even at ungodly temperatures. Stuff four of these in a styrofoam box with a small sodium acetate handheater and Bob's your uncle. For extra NASA-points, replace the styrofoam with aerogel :-).

cheers,

Bram

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Facepalm

Re: igniter box

Forget about the hand warmer and just keep the battery box in a sealed styrofoam/aerogel container -- I just looked up some data on the lapse rate and this should buffer the internal temperature of the battery box quite nicely during the ascend and keep it within operating range for Lithium batteries.

I'd still go for less batteries though: there are 3V lithium batteries in AA form factor with high enough peak current output if you want to use an existing battery box design. It will save precious weight.

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Re: igniter box

Can the batteries be pre-heated before launch so they have more heat to lose before they fail? If they're specced for operation at +50, launch them as that temperature.

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Facepalm

Why such a bulky battery pack ?

Why such a bulky battery pack to provide redundancy at low temperatures?

.

An elegant solution is to insulate the battery and short it with an embedded PTC thermistor / Posistor.

With good insulation, very little current is required for temperature maintenance.

Alternatively, use a separate piggy-back battery for temperature maintenance.

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Mushroom

Re: igniter box

LOl. I'm disappointed too :)

If it was Polonium, the radioactive decay would have solved the warming issue.

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Totally lovin the SPB work - thanks Lester and Team for keeping me sane(ish) at work!

Just wish I could contribute, but I only specialise in drinking coffee and telling my end users NO

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Anonymous Coward

now there's a thought...

sounds like the battery/electronics might have to go inside the rehab too!

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Re: now there's a thought...

LOHAN's REHAB stay extended to determine which mix of chemicals provides maximum power?

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Happy

How about having a resistor connected across the battery (from launch time)? Choose a value so it and the battery together generate just enough heat to keep them and their container cosy.

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You're going to need Energiser Lithium batteries.

To fire that lot off, I'd suggest Energiser Lithium AA's. They work down to -44 degrees C

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Facepalm

Two into one does not go

You'll probably manage to get one strand of PIC through the nozzle and slot, but no chance of getting both strands. If you find/make ematches with finer wire than you generally see, you could thread two matches into the motor, one higher than the other, for redundancy, with a scrap of blackmatch and a scrap of PIC. You'll want to be pretty sure there's enough room for all the wire to be spat out past the nozzle when the thing lights though, else it'll be much more spectacular than intended.

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Anonymous Coward

Glad someone picked up on my suggestion of pyro igniters and match, but I wonder if the pic is the best terminal fuse, I suppose you could spiral it into the motor throat, pic will give a longer burn time,although match would give more energy.

However, this device is more than simple fusing, the maker would need a manufacturing license which the vast majority of pyro's don't have and it would certainly be illegal for you, as a member of the public, to use, as the pyrotechnic device has not been tested and is certainly not classified.

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Chill Factor

Sorry to put a damper on this solution but won't the silicon harden in the cold ( remember the 'O' rings on the shuttle) and form a solid barrier leading to a compression chamber and resulting blowout. This seems to be an OTT solution that will cause more problems than it solves. KISS.

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