Very, very clever. I'm surprised that altitude activated switches aren't available off the shelf.
Followers of our Paper Aircraft Released Into Space (PARIS) project will be aware that our first attempt to put together a pressure-operated Vulture 1 release mechanism didn't exactly go according to plan. For those of you who're not up to speed on this vital mission component, we should explain that it's the device which will …
Very, very clever. I'm surprised that altitude activated switches aren't available off the shelf.
And where's the fun in that?
...but where's the fun in that?
A real boffin would have tapped his own rod.
Note: Any pedantic bugger who points out a tap is for holes and a die for rods can go get a sense of humour.
You're saying that real boffins are wankers?
That is classic british "garden shed" engineering!
It's bigger than I thought it would be though. What dimensions will P.A.R.I.S have?
<---Beer because there isn't a cup of tea (the engineering drink) icon
The epoxy holding the threaded bush to the underside of the rubber bung may be a weak spot; if it fails then there's no force applied to the rod. Maybe mount the bush at the top of the bung instead?
With such a subject line I believe the traditional response is "hehehehehe".
Hairy badgers because, uhm..
Use a low-temperature oil instead - but be aware that it could damage the rubber bung, so you may need to use a non-rubber bung instead.
Umm, to paraphrase, "Use low-temp oil instead. But then, you'll need to change the bungs".
Err, how about stick with the current design and change nothing!
Lovely stuff Reg. It's great to read of some proper boffinry. Boffinry with bits and bobs from the "bits of string" drawer.
Indeed, I was particularly impressed to see that old rubber bungs have been used, rather than shiney new ones!
So if the tube is only for structural purposes and not to act as a pressure vessle why not get the big drill out and perforate it? should save many grams doing that. Additonally why not use a carbon/glass fibre push rod? An Angleing store or a Kite shop will have what you need.
Carbon Arrow shafts from any decent archery store.
Hmm. I'm guessing the reason that you didn't go with the condom-inside-syringe idea that a lot of commenters suggested on the last post was that the rubber would perish above -20 degC or so?
I'm hoping that rubbers perish *below* -20C or so, not above. I'm fairly sure my normal amorous activities raise the temperature regularly above -20.
Isn't this thing going to be GPS tracked? Can't you run a signal off that to check that altitude and then just use a simple solenoid?
Anyway, do like the mechanical way of solving things, all good fun!
Look at Julianh's post, third from the top:
While GPS in principle can do the trick, the civilian GPS units that will be used are limited to about the altitude PARIS will need... and that would be sketchy.
Besides, as has been noted, this is way more garden-shed and therefore much much cooler.
...coil the tube up into a spring shape for space savings? It'll still expand inside whatever drum or coiled tube you put it in. Also I'll second Parax; that PVC tube can probably have more than 50% of its mass drilled out and still retain enough shape and strength to function. That's if you don't decide to go posh and use a glass or carbon fibre tube (or old fishing rod).
If you want something super-light and you think you can form it around something (dowel and some grease paper possibly), model shops will sell a kit of thin glass fibre sheets and resin that's designed for constructing helicopter bodies and suchlike. It'd take a bit of work and sandpaper, but you would end up with a very lightweight fibreglass tube that can be as thin as its task allows. It probably wouldn't blow the budget either - I think I remember it being a tenner or so for about 4 1m/sq sheets plus bottles of thin adhesive/hardener.
Last but not least, I hope you can get a couple of nice telescopes to film this thing through. That or let any commentards know where and when with enough notice that they can bring theirs. This is daftness on a scale of painting a Robin Reliant up as a radio-controlled space shuttle and sending it heavenward on the most powerful non-commercial rocket built in Europe. It'd be a shame to not have a video of the fun.
"This is daftness on a scale of painting a Robin Reliant up as a radio-controlled space shuttle..."
You'll be giving Lester ideas. I could handle a paper plane landing on the roof if things go tits up. Not so sure about a three wheeled car.
The rubber tube is a stroke of sheer mechanical genius and much is to be applauded for the solution but the idea of using the GPS or even a reading from a barometric pressure sensor to determine altitude does have some useful advantages in a contingency situation.
Say for example, the balloon bursts for some reason without getting to the planned altitude, the onboard CPU will detect the sudden drop in altitude and release the payload before falling too far.
I would say it's better to release at a lower altitude, than to watch it fall and crash.
The boiling point of water at 20,000m is 14C, if you've heavily insulated the mechanism then are you sure it won't start to boil and release prematurely?
But not a drop in PARIS
Where did they mention "water"? Not sure it's mentioned anywhere. The word you're looking for is "liquid", specifically antifreeze.
Even ignoring that, if they were to use water, it's boiling point at 20,000m is about 30C by my reckoning. But this is dependent on the PRESSURE, not the height. The tube the water is in is coincidentally, sealed, effectively keeping it at ground level pressure, meaning the boiling point stays at a steamy (pun intended) 100C.
It's the pressure differential that causes the mechanism to work.
You really are an idiot.
It expands as the pressure INSIDE drops
This is not a constant Volume Pressure Vessle.
Yes the boiling point drops. BUT the outside temp drops to too...
You can use termoretractile plastic to smooth the threaded rod, and also to help seal it against the rubber.
a layer or two.
Its all well and good that you've unit tested the oxygen tube, but you must test the full assembly!
Otherwise, solid engineering.
... isn't that rather big?
What about using the insides of an aeneroid barometer and a microswitch?
It is good that you thought of freezing, I would suggest using 100% antifreeze as the liquid. But there is one other problem you probably overlooked: rubber solidifies and becomes less flexible at extremely low temperatures. The expanding hose might crack instead of expanding. I suggest you test this apparatus in a hyperbaric chamber, AND at low temps.
Last I heard it's not too pricey for a breeze-block-sized lump of the stuff. The problem is finding enough insulation that you still have enough dry ice left to cool the apparatus by the time it gets to the test chamber. Polystyrene foam would probably work.
First Antifreeze! Ethylene Glycol 100% solution frezes at -12C! when mixed with water (70%EG) you can achieve -60C (is that cold enough?) Anyway DO NOT USE 100% !
Anyway in this situation pure 100% methanol (-95C) would probably be the best Solution (pun intended no coat) alternativly use solid unexpandable granuals (6mm Plastic Airsoft BB balls? - make sure they are VERY dry) with the required airspace.(this only needs to expand once, and not contract.)
Second Rubber! This is a military grade Oxygen Hose! the same as those you would find in U2 - the reason this thing is so big is because they ARE using the correct Rubber!
*Nobody* knew enough to take some smooth nickel plated brass rod and a die and make a suitable threaded piece?
What the hell is on the school curricula these days? (Latin wasn't on mine, but over the years the basic engineering they taught me in metalwork has proved of more use than a dead language).
Christ on a bike, so much for England, the cradle of engineering. This is what a "point, click, ship" culture gets you.
What the hell are you on about?
The earliest known engineer was Imhotep of Egypt, ca. 2700 BCE. After that, Chinese, Indian, Egyptian, Greek and Roman, Aztec, Mayan and Incan engineering works are well documented; and after the fall of Rome, Abū al-’Iz Ibn Ismā’īl ibn al-Razāz al-Jazarī, an Arab engineer, created a wide variety of devices, many still in use today — including a catchment device used in clocks, and a reciprocating water pump for irrigation purposes.
So, um, *England* the cradle of engineering? Are you on crack?
Whilst others have tinkered only one really succeded. A cradle is for nuturing growth after the birth not for conception.
oh and perhaps you mean escapement not catchment.
Education these days really is piss poor. (as I beleive the OP was suggesting) Threading a brass rod by hand would only take 10 minutes but they don't sell Taps and Dies in B&Q!
Remember antifreeze etc are hygroscopic (is that the right word? Water magnets, anyway) which may behave unpredictably at altitude - I'd look at an oil-based substance of some kind which at least should be less likely to trap water. Just a thought.
Pure genius. IKB would be proud.
I was expecting something a little less SFW :(
Do you even need the release mechanism to be inside the aircraft? That's a lot of weight saved if you were to, say, use an eye-hook or something on the back to pass a loop of thread through. Use some kind of double tubing to stop the string from tangling with itself as it goes down from the release mechanism, through the eye-hook and back up. On release, one end of the string is released/cut/burned through/whatever. You'd lose the release mechanism but have an aircraft that's a lot lighter.
Or alternately, attach a parachute and transponder to the release mechanism as well and have it find its own way down. Rubber Tubing Released Into Space doesn't have quite the same ring to it though.
... for the glass syringe idea then. I thought it was really elegant, simple, robust, light and small, and some vacuum grease would have solved both the leak and stiction problems (the one you used here would most probably have worked, did you test that?).
But at least with with this latter design you can use duct tape! So please, do.
this is a paper aeroplane fcs. whilst this kit works as an actuator, on this scale it could be used to drop a humvee lands sakes it must weigh round a pound. what about a simple trip operated by a squash ball ( or sim ) housed in a cardboard tube/chamber. ounces instead of lbs.
if the caf at the lab was any good ?.....
otherwise PARIS is a jolly good job that's needed doing forever and can't wait for the telemetric files
-- And you're worried about freezing?
That El Reg has not adopted an IT solution to this problem. A simple GPS + computer hooked up to your release mechanism could do this instead of the Heath Robinson system proposed. On top of that you could probably use the waste heat from the CPU to keep the release mechanism defrosted if needed.
If you really wanted to demonstrate ingenuity, how about jailbreaking an iPhone or Android phone, getting it to report its location periodically or on demand, and then accepting/generating a release command through its USB connector?
"A simple GPS + computer hooked up to your release mechanism could do this"
No, it very much couldn't.
"how about jailbreaking an iPhone or Android phone"
How about NO? That wouldn't be ingenuity, that would be LOLkiddie showoff. Plus, it wouldn't work anyway.
What's wrong with releasing it by tether? A few tends of thousands of feet of monofilament attached to a simple pin-and-loop and Bob's your mother's bother.
Talk about overthinking a problem.
A small target mechanically triggering the release. Shoot it with a pellet gun when desired altitude is reached.
Bear in mind that the balloon won't go straight up. If you've ever played with or made your own sky lanterns, you'll know that the balloon could quickly find itself ten miles along the horizontal for every thousand feet of altitude, and that's before it gets to jetstream altitudes. Now think of how much a couple of hundred miles of wire will weigh and the probability of part of it snapping. Also, what's going to happen to a couple of hundred miles of released monofilament under the influence of gravity and wind?
Though the idea of holding a balloon and paper aeroplane on the end of a fantastically long fishing line like a perverse high-altitude kite does amuse.
Fun project, but why not use that bicycle pump?.... just grease up the inner plunger and block the valve hole.
You can buy even smaller ones, but they'd cost more than the £3 that one's worth.
Scheader valves have a rubber washer inside which might get screwed up by the cold or the antifreeze. the other kind of valve "presta", or sometimes called "high pressure" uses a plastic washer instead, and can hold more pressure.