Conductive rubber - or even just copper tape contacts on top of the rubber?
Why does this prevent the contact based approach?
Over the past couple of weeks, the Low Orbit Helium Assisted Navigator (LOHAN) team has been chewing the fat with readers over just how to hook up the Vulture 2 spaceplane's rocket motor heater. Click here for a bigger version of the LOHAN graphic There's more on the current state of play with the heater right here, and a …
Why does this prevent the contact based approach?
conductive rubber isn't all that conductive.. and the more resistive it is, the more heat it will dissipate.
Copper tape also corrodes very quickly, I wouldn't want to rely on it. (connectors are always flashed with gold for a reason ;-)
Can you not split the titanium rod, and then use the two sliders as the electrical contacts?
Like my toothbrush. No contact, sealable, nothing to prevent release.
Just need to use AC not DC power, surely this is within the weight budget of the truss?
There are off the shelf solutions for wireless charging, e.g;
However, these are limited in wattage (5W), and their range is limited. Using anything else requires some serious engineering.. which I suspect el reg don't have time for without sacrificing valuable pub time :-p
It might be do-able, with the wireless modules, you would have to give it a go and see
If you're going to be shunting energy around as EM radiation, why not just use a microwave transmitter and keep the electronics etc. warm just by zapping them with microwaves?
glad that was only semi serious lol :-p
before I mention the weight of a magnetron.. or its power supply.. or the fact it would need more power than you can get out of a wee little battery (magnetrons aren't particularly efficient) or the effect concentrated microwaves will have on the electronics.. or metallic components.. in fact I'll stop there :-p
inductive heating might be slighty more efficient than the wireless power stuff.. however I think wireless power would allow you to have a lot more control over the heating. Not entirely happy with the thought of heating explosive compounds to begin with, but if you have to, then make sure its consistent, monitored and controllable :-p
I still favour a spring pin arrangement.. maybe combined with the magets to provide the coupling force.. hmmm
I promise I'm not a contact plate junkie but...
In your closeup diagram of the Lohan mounting interface, the Aluminium plate from the truss is shown very close to the top of Lohan's fuselage.
So build into the surface of Lohan, just behind the rear-most Teflon guide, two copper contact patches. Then run two electrical tracks down the Aluminium plate which would terminate in, you've guessed it, spring loaded contacts. These contacts would then hang below the aluminium plate, and rest atop the contact patches on Lohan's fuselage.
The springs should be of a very low resistance, so Lohan can rock about and keep free of the ice on her rod, so don't think of these springs doing any stabilisation of the plane, they are merely there to keep the contacts touching.
Anyway at launch the toasty warm motor fires and Lohan streaks away, pulling her smooth contact patches away from the spring loaded contacts like a tablecloth out from under a plate. The truss-mounted contacts then either fall away under gravity or simply dangle from their power wire which is still soldered to the aluminium plate.
This system doesn't actually need to be attached to the aluminium plate as wires would be used to supply the current to the spring contacts, so the contact patches could easily be mounted elsewhere on the fuselage - the top of the guidance loops, for example. The trick would be to find a place on the Truss that is sufficiently close to Lohan's fuselage for short, weak springs to maintain contact, and that won't foul any 'trailing' fuselage, that is bodywork to the rear (motor end) of the contact patches that will pass the spring contacts when the motor fires...
How about inductively coupled charging, like on an electric toothbrush? I’m not sure if this would allow enough current, anybody with experience in the area?
Get a couple of wooden or bamboo clothespins. Place a strip of copper tape around the insides of the jaws; attach feed wires to the tape outside the jaws. The pins clamp onto a connector — perhaps even part of the plane with similar metal-tape contacts — to supply power. When launch-time comes, they will separate quite easily. All you have to do is secure the pins reasonably well to the truss.
When I suggested clothespegs my idea was officially branded as "tomfoolery" but I still think it's a goer.
I don't see this in the round up summary so, here goes:
Two strips of aluminium foil with a small notch in the middle at the edge of each. One end of each mounted on the truss, the other end of each on the plane. Foil strips should be slack so that they can tolerate reasonable wobble and movement of the plane on the way up. They should be clamped with the ends of the strips slightly off parallel so that as the strip pulls taught the initial tension passes through the edge with the notch. Then you should get a nice tear straight across each strip which shouldn't require much tension along the strip (i.e. holding back the plane) to achieve.
I'm not sure I can diagram this with ascii art though - hopefully the description is clear! I guess it's a bit like tearing a sheet of paper by putting a good sharp crease in it, starting the tear at one end of the crease then pulling from the corners that are on the edge where you put the tear.
Might well be some better materials than kitchen foil but I'm not sure what the materials science description of the relevant properties would be. Needs to be flexible, can be cut to take a good sharp notch and have a very low resistance to the notch propogation when perpendicular tension is applied.
My first thought was to wonder if you could get a light enough solar panel but the best I could find was 115g which is pretty similar to the weight of battery you're going to use anyway. Therefore just stick the battery in the plane.
stick the connections separately on each wing and use the spring idea coming off of the teflon strips, a pity the springs would be perpendicular to the flight path but it might be alright? OK maybe springs wouldn't be the right idea but there were other ideas which were discarded due to danging wires, which would be less of a problem if the wires were separated on the wings. Of course I've probably only had that idea because I've already read it on here somewhere and forgot about it.
Let's try again:
Take one of the wires, cut it in two, strip wire-ends back 1cm, overlay exposed wires, don't twist together.
Take lightly oiled paper and apply to 1 side on the wire covering and heat-shrink the whole, but not exceeding the oiled paper.
The connection is made and enforced by the heat-shrink and the oiled paper allows the heat-shrink to easily slip off the wire covering. A little tinkering with the heat-shrink maybe required to validate tensions.
For safety, to avoid exposed wires touching post separation, repeat the process for the other wire, but place the oiled paper on the opposite covering and ensure the 2 wire cuts are offset by 2 or 3 cm.
For each side of the junction, you are left with 1 exposed wire end and 1 covered end offset from it and the weight added to the whole is neglible (gms).
I've mentioned it before, but I'll repeat it again. How are you going to mount teflon to the rubber backing, or to the truss for that matter. Teflon is very nice and slippery, but this also means there's no known sticky substance that will adhere to it properly. (Glueing foam is already a pain in the neck for that matter)
The products I work with every day contain a lot of teflon parts. NONE of them are glued, even though for several of these parts, my employer would love to.
How about this? http://www.techbelt.co.uk/ptfe_adhesive_tapes.html
We could stick it to a thin strip of, say, plastic, and then glue that to the foam...
It would be worth a try for sure. The question is, can you obtain it in a small enough amount for a decent price? (The big challenge for any garden shed tinkerer for sure. Lots of stuff is out there. Getting just a bit of it is a challenge) I have no experience with that tape other than the mentioned application of proctecting the heating element on a sealing machine.
Come to think of it, from an engineering standpoint: Do you really need the Teflon strips? Would perhaps thin carbon or aluminium rods perform the same function adequately. Perhaps with a tiny patch of teflon on the wing of LOHAN at the contact point. 2 long teflon strips, with backing, etc is going add quite a lot of weight to the truss, something that is already at a premium i'd imagine.
Reading back, I feel I need to clarify the last bit:
The only function the guides perform is to stop LOHANs wings from contacting the truss, so anything smooth enough not to dent or heavily scour LOHANs wings while she slides her curvacious surfaces over it could perform this function. No need to stare blindly at Teflon for being the only solution. I don't know the material composition of whatever LOHAN will be built out off, but it might even be softer than normal Teflon, meaning any rough edge would still scour the wing as it moves past.
Bootnote: I'm not trying to diss the idea or be a smartass, just trying to think along. It's sort of not really what I do for a living ;-)
I'll go on the blag if I can't get a small amount at a reasonable price. I reckon the thing is to get a bit and see if the idea floats.
Point taken about weight. It's always a major factor in any design decision.
Not sure of the details, but surely the titanium rod can be used as a conductor?
Looking at the schematics, the following seems reasonable to propose:
- Attach foil strips on top of each wing with spacing to match the teflon-covered rails above.
- Attach wire brushes (just some multi-thread wire with insulation stripped off at the end) to the teflon rails in places where they would touch the foil strips on the lorbiter wings in its resting, pre-launch position.
- Lubricate the brushes-strips contacts with something like this.
The added benefit is that the brushes would stop the lorbiter from wobbling on the titanium rod during ascent. On launch the lorbiter will just slip from under the brushes and any further contact with the rails will be in the teflon-covered area...
But, really - it's a spaceship, so it needs explosive bolts for "umbilical separation", right? :-)
Flexi-PCB: Comes in standard 0.1'' pitch and you can get connectors with REALLY low insertion / removal force.
Alternative would be a strip of tinfoil with a notch cut as an aid to predictable failure.
Keep It Simple Stupid! 2 wires that run from the battery (via a fuse!) to 2 separate connectors at the rear of spaceplane. When the rocket fire the thrust will blast them out way before the spaceplane starts to move. You could even tape the bare ends of the wires to the plane with conductive tape as you only need the connection functional up to launch.
Titanium is paramagnetic and if my ancient memory serves, then the rod could function as the core of an isolation transformer. This assumes that the heater would work acceptably using AC instead of DC and as it is a plain resistance load this is likely true. Batteries stay on the truss, DC run through small inverter to get AC, then wind some magnet wire around the titanium rod. From the spaceplane, make a few turns around the teflon plug and run the resulting AC to the heater pad.
Feel free to laugh at and ridicule me if this is an insane idea. If it works, just knowing I had a small part in helping this magnificent effort will be reward enough for me.
You know, that's just crazy enough to work!
Certainly easy to test, just take the rod and wind a pair of coils.
There's no need for an inverter, just rapid switching (kHz) of the DC output with a mosfet. The inductance of the coil will smooth it out and reduce EMI (which would be bad for the radio) - this is how isolating DC-DC units work.
Won't be very efficient, the
iron titanium losses will be fairly high as it's the wrong shape and the coils are necessarily quite far apart - at least the width of the rubber.
So you'd want the rubber to be as thin as possible for maximum
1. Fuse wire could be a very thin strand of copper out a good audio lead or whatever
2. Fit a crowbar circuit (see Wiki) on board Lohan - this will blow the fuse wire on demand
3. Fit a DC/DC convertor on the truss to supply a higher voltage to the heater, say 15V
4. At the right moment a relay can swap from battery supply to 15V and the crowbar blows the fuse
It might work and if there's some spare inputs on a processor you could even log the whole process;
In my youth, I used quick disconnect sockets at the ends of wires all the time. The type I used had a round cylinder female end. I'd just bare a length of wire and fold it over and stick it in the quick disconnect. As long as the end of my wire was outside of the socket, the only thing that kept my wire in the socket was friction. It never took much to pull the wire out of the socket. I used to use this as part of an alarm system in my room, and later as part of the wiring I did for a key switch for my garage door opener. If someone pried the key switch off to try to open the door by shorting the wires, they would fail due to the wires not being long enough to allow movement and due to pulling out of the quick disconnect socket.
Just my two cents...
not hard, and of course will allow the thing to still rock in the breeze the magents are small enough not to impede take off.
Okay, how about this?
Two sockets on either side of the motor UNDER the heat blanket, so they will be nice and toasty.
Two rods (pick your material) that slide up into these sockets, connected via wires to the battery and properly secured to the base plate.
INSIDE those heated sockets, pack them with conductive grease, then insert your rods.
That's right, some double penetration action going on here...
The rods are your means of applying charge to the heating blanket.
That blanket heats those rods in their nice, snug sockets.
The conductive grease gives you a 100% rod-to-socket contact for your electrical connection.
Because the whole thing is inside LOHAN (the innuendos going on here are rather thick on the ground) you reduce the chance of anything icing up. Use some decently insulated wires and the heat from that blanket will propagate along the wire, ensuring where it goes into LOHAN won't ice up either.
And when the rocket fires the rods simply slip free of their nice, warm, and well lubed sockets.
Find some conductive grease which is non-flammable, btw.
I made a picture!
So, you're suggesting pulling out just at the climactic moment?
Always leave them wanting more. :P
Granted, there has to be wires for setting off the rocket, but I'm not so convinced of the elegance of wrapping LOHAN's motor in a heating blanket + its trailing wires, and somehow contriving to have the blanket+wire not get in the way of launch.
Think outside the box for a moment. Actually, within the box:
Put LOHAN and her rail within a styrofoam box, just like the electronics. Keep the interior nicely warm with a heater blanket glued to the walls of the box: no worries about wire and such. A side benefit is that it should protect LOHAN somewhat from the wind buffeting.
The tricky part is: how does LOHAN get out of the box come launch time?
Perhaps put a hinged door at the exit end of the box , with a motor that opens it a minute or so before the ignition signal is sent to get LOHAN on her way.
Alternately, have the door hinged on the bottom side, and a solenoid that releases a latch, to allow the door to swing down by gravity.
One could also include crafty, purely mechanical capture latches to ensure that the door stays open once it is opened.
Another possible advantage of an insulated box is that LOHAN can now ride on top of her rail, instead of hanging her there. Further, the rail need not be so protected from icing, etc..
Let's take a step back and consider whether it is a good design to place the heat source in LOHAN herself. Yeah, yeah, you have that nice heating pad and it would be a shame for it to be cast aside. However, if the truss-mounted electronics enclosure also enclosed a small heat source and a very small fan, then simple plastic soda straw duct-work could deliver heated air to LOHAN's innards. For the connection itself, consider two straws of different diameter with one fitting inside the other, perhaps gently sealed with a little bit of that Molykote 33.
The resulting weight reduction of LOHAN would mean that the mighty rocket thrust at the exquisite climactic moment would push her to heretofore unimaginable heights of ecstasy.
Mount a solenoid on the base plate and mount a connector to the end of the rod.
Connector plugs into socket on the ship.
Right before launch, switch the battery power from the heater to the solenoid, pulling the plug from the ship.
After ignition and launch, power off the solenoid. neat, clean no dangling wires to short.
There are a variety of solenoids with a plunger range of .5 to two centimeters, which should be enough travel to disconnect the plug before launch.
A sample of solenoids here: http://www.surplussales.com/relays/resoleof-1.html
Couple of small paperclips gripping two bits of copper. Dunno why all the complexity.