Failsafe SPOC
Is it wise to have a failsafe system using the same battery pack as the primary ignition system?
LOHAN cranks up old-school clockwork failsafe
We're obliged to Low Orbit Helium Assisted Navigator (LOHAN) fans for answering our call for suggestions as to just how a back-up ignition system for our Vulture 2 spaceplane's rocket motor might work. Click here for a bigger version of the LOHAN graphic Our primary system is the Special Project Electronic Altitude Release …
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Thursday 27th June 2013 18:26 GMT graeme leggett
Re: Failsafe SPOC
battery size/weight - do you need voltage or capacity?
If only the former, then how about a stack of the tiniest button cells (hearing aid batteries?) to give the 9 volts
It would fit inside the casing.
You could also save some grammage but soldering the wires directly to the terminals instead of using the Lucar (spade) connectors.
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Thursday 27th June 2013 18:41 GMT graeme leggett
Re: Regarding accuracy, it's pretty good. Here are the results:
To counter the cold, you could put a tube of dessicant (say Magnesium percholorate) in the casing and leave it deliberately open to the exterior at one end but initially capped
the inner end would remove water vapour from the interior so that if it did get cold there would be no icing up of the works. Remove the outer cap before launch and the exothermic reaction of the MgClO-whatever with the moisture in the air would produce heat.
In my experience about 20ml of granular MgPerc can make a glass tube uncomfortably hot to the touch.
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Friday 28th June 2013 14:05 GMT phuzz
Re: Regarding accuracy, it's pretty good. Here are the results:
I'd be more worried about the cold causing shrinkage, er, I mean parts of the clockwork shrinking at different rates which might affect the timing of the clockwork.
Of course, this particular model is designed to go in an oven, so might have some features to avoid temperature differentials, but testing it in a freezer would be a good first step.
tl/dr cold causes shrinkage, shrinkage bad!
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This post has been deleted by its author
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Thursday 27th June 2013 13:43 GMT Magnus_Pym
Parachute?
Rather than the tricky parachute wouldn't it be better to use the tension on the support line (or sudden lack thereof) to trigger the mechanism. The balloon tether pulls upwards (along as the balloon has lift) this holds a firing mechanism in the 'off' position. A weaker spring is rigged to pull against it . When the balloon bursts lift fails, the spring 'wins' and pulls the switch into the fire position.
This then doesn't rely on the untested low-air-density parachute so (in theory) will definitely fire very soon after burst. The downside is the chance of turbulence setting it off early but this is also an argument against the parachute. Some sort of timer would be required to make sure the upper atmosphere has been reached before it is fully armed.
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Thursday 27th June 2013 16:42 GMT Anomalous Cowturd
Re: don't forget to grease the locking pin
A foolproof switch is easily made with two drawing pins pressed into either jaw of a sprung wooden clothes peg. Strip of credit card for insulator / firing pin.
Probably less than 10g total weight. 9v battery for back up power, say another 40g. Sorted.
Mine's a pint. Cheers.
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Friday 28th June 2013 00:50 GMT Don Jefe
Suspicious Object
"Bomb disposal and anti-terrorism teams were dispatched to the countryside today. There an armed drone, containing what authorities are describing as an explosive device wired to a kitchen timer was recovered. A sophisticated electronics and imaging system was also contained in the drone. Local authorities are now working with INTERPOL to arrange extradition of the suspects."
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Friday 28th June 2013 12:14 GMT Anonymous Coward
careful with the parachute opening
https://en.wikipedia.org/wiki/Parachute#Parachute_malfunctions
With respect, I'd worry that the 'signal line' running under the fringe of the canopy, may actually act to keep the canopy closed, especially in the thin air at altitude, or lead to an 'inversion' or 'line over' kind of malfunction. IMVHO, the best thing to do with the canopy edge is leave it alone ! I realise I don't immediately have a solution for the original problem, but I don't think this is it ....
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Friday 28th June 2013 14:21 GMT imanidiot
I have doubts
I've voiced my doubt before, especially about the line getting entangled around the chute. With a bit of experimenting and fiddeling to choose just the right amount of slack it could work, but it'll still be pretty error prone IMHO. If you do go with the hollow bearing idea, keep in mind you will also have to add a swivel to the pull line, spin of the chute would otherwise still wind up the string, causing it to bunch up and pull in.
As for the oven timer, I agree it would be a good idea to redo the tests after a good trip through the freezer. There is a good chance the cold would alter the properties of the clockspring enough to seriously throw off the timing.
I know mechanical FEELS more reliable over electronics (With things like flat batteries and such) but "the industry" has long since moved just about everything to electrical systems as far as I see. I simple 5v electronic timer with a single solid state relay, fed by a volt scavenger circuit (ala minty boost or similar) from a pair of penlites has a lifetime measured in years, while being pretty darn reliable.
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Friday 28th June 2013 14:32 GMT imanidiot
Addendum
I'd also like to add the following: Well before launch, stick all parts and payloads in a low vacuum chamber to dehydrate. If at all possible, keep the chamber nice and warm. Keep it there for as long as you can. An atmospheric pressure box with a good amount of dessicants would also work. Transfer it all to a thermo/cooler box with a load of dessicant bags (Silicagel would probably work best) and keep it all at a nice warm temperature. Don't take anything out until it is needed.
This way all parts will be bone dry. Thus much less chance of lenses developing condensation and such.
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Monday 1st July 2013 00:50 GMT Martin Budden
It will still twist!
Even if you pass the line through the centre of a bearing (great idea by the way) the line itself may still twist, which means you also need a small swivel in the line itself. Fishing supplies shops sell very cheap small ones which will be ideal, they look like this:
https://www.google.com.au/search?q=fishing+line+barrel+swivel&safe=off&source=lnms&tbm=isch&sa=X&ei=y9HQUdLcHOPSiwKb5IHADg&ved=0CAkQ_AUoAQ&biw=1083&bih=904
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