Micro-UAV's & propulsion

[Arkangel]

Here's a little cutie (http://news.bbc.co.uk/1/hi/sci/tech/1270306.stm) , a bit on the clumsy side, and not with much lift, but with LOTS of potential.

It seems that the power supply with these things is always the problem. There was another thread along these lines a while ago (the little multi motor hovering thing), but this thread is more to do with motive power than anything else.

If it's completely electrically powered, then the battery for anything like this is going to be the main weight and a major limitation. On some of the missiles I worked on, they have a pyrotechnic "thermal battery" as well as pyrotechnic charges to provide power to the guidance gyro's (now superceded) and the control fins.

What do we reckon about a pyrotechnic semi-internal combustion engine for this type of device? It could be as simple as a single turbine engine (quieter), or you could have multi engines driven from a central combustion chamber, with individual power controlled by a central servo system.

Whatever, one difficulty is going to be varying the power produced by your pyrotechnic comp. Most such compositions have an increased rate of burn along with pressure. I think you'd need some kind of dump valve in case of overpressure, as well as a way of increasing the area of combustion if you needed more power.

An advantage though, is that your craft would get substantially lighter as the mission went on, unlike the battery, which stays the same weight.

Anyone got ideas as to the relative efficiency of an electric system versus something like this?

[vulture]

If you can use thermal energy:

Metal + Acid --> H2 + salt

H2 greatly decreases the density of the battery and could even be used for floating.
If not, just burn the stuff!;)

[knowledgehungry]

Using Acid plus a metal will not decrease the density of the battery, unless the salt is somehow removed as it is formed, because the mass stays the samein side the battery while the volume stays the same.

[vulture]

What I meant to say is that the H2 would be vented off to fill a chamber or balloon. That will decrease density.

[Tuatara]

Electric motors can be very efficient, but power to weight ratio is the problem. Piezo-electric motors could be used to drive a micro-UAV.

For a power source, if you are going thermal then it will always be best to use air as the oxidiser, since you don't have to carry it on board. Maybe a zinc-air battery or a methanol fuel cell would be good. Li-ion batteries have a pretty good energy / weight ratio. Best I've heard of is the sodium/sulphur battery - but it only operates at 300C :(

For a heat engine you could use a Stirling cycle engine - quiet, efficient, can use a continuous external heat source

[knowledgehungry]

I always thought that stirling engines would be too heavy for use in aviation... The ones i've seen are always pretty big, plus an external heat source would make it even more bulky.

[Jager]

attach a balloon of hydrogen to that gizmo, and instead of using a battery, use a gas turbine or a tesla turbine that runs on the hydrogen, then turbine would then be conected to a magneto, that way you wouldn't have to have a battery.

[Tuatara]

And the whole thing would weigh far more than the equivalent Lithium primary battery.

[vulture]

Jager:
attach a balloon of hydrogen to that gizmo, and instead of using a battery, use a gas turbine or a tesla turbine that runs on the hydrogen, then turbine would then be conected to a magneto, that way you wouldn't have to have a battery.

Me:
H2 greatly decreases the density of the battery and could even be used for floating.
If not, just burn the stuff!

Really inventive of you! :rolleyes:
Fucking read posts before posting.

[Jager]

quote:
--------------------------------------------------------------------------------
H2 greatly decreases the density of the battery and could even be used for floating.
If not, just burn the stuff!
--------------------------------------------------------------------------------

you caught me...hot damn, I bet the police chief will promote you to detective after this big bust




I think Tuatara is right, it was a bad idea

[Tuatara]

No, not a bad idea, just an inappropriate one in this instance. All ideas have merit - thats how new stuff gets invented.

[vulture]

you caught me...hot damn, I bet the police chief will promote you to detective after this big bust

You don't want to run into the police chief, so you better lay low. :mad:

[zaibatsu]

End this line of discussion quickly Vulture and Jager, I don't want to have to ban anyone. Jager, there is no point repeating things already discussed in the topic, it isn't useful.

[Arkangel]

Now THIS (http://news.bbc.co.uk/1/hi/world/middle_east/3262557.stm) is more practical!

Looks a sexy little beast, which I'd had one for my action man when I was a kid.

And the link also includes a STUPID remark from some idiot journalist - Its new helicopter features vertical take-off and the ability to hover

Which would be impressive if we were talking about a submarine, but isn't that what helicopters DO? What a fucking moron:rolleyes:

[Jacks Complete]

Indeed it is what they do. Otherwise it would be a plane! Of course, if journo's were all the human race had, we would still be sitting in our caves, too scared to leave without army back-up. We would have scared and starved ourselves to death...

I think the idea of building a micro-UAV is nice, but to be realistic, there are lots of companies throwing lots of money at this problem, so it is unlikely anyone on the forum is going to have a major success at home.

As something that might be more realistic, has anyone tried doing the Estes (or other model rocketry) thing with the camera, and taking a photo, and parachuting it down?

With a small wireless camera, you wouldn't need to develop the film, you would have a constant feed which you could capture into your PC, then review. Once the camera is floating back down, it is still streaming you live footage, and the signal from the camera means that, for tests, etc. you can find it a bit more easily (important with a £200 camera!)

Wouldn't this be the perfect way to do a sit. rep. if the SWAT team were sat outside?

A development from that would be to make the camera into a little self-righting turret that you could then "pop-up" and have a look around with.

I could start talking about my idea for a knife missile, a la Iain M. Banks, but the rules say not too! (and it involves Hydrogen :p )

[Jacks Complete]

Since more than 24 hours has passed, I can't edit my post. However, there have been substantial advances!

Check out http://www.otherlandtoys.co.uk/product397/product_info.html. This little beastie will fly around under your control, indoors. I bought one the other day, shown here (http://www.gadgetshop.com/eshop/product.asp?pf_id=16748&SITE=1&VID=&S_ID=187B0171DFE44AB68DB2BAD0F192C322&REFID=0&SESSID=&BRAND=1&S_TYPE=U&AV=F&QB=F&CAMID=0&BV=0) but it doesn't have steering, and cost less than half as much.

If you are loaded, try http://www.hobbytron.net/Dragan-Fly-4-deal.html for a camera mounted version! Damned expensive, though.

Also, there are some available on eBay for thirty quid as featured items, which are helicopter type devices, with a greater range, which are styled as proper helicopters Here (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=3155032148&category=1185).


p.s. where is everyone? In this area it so looks like I am post whoring! On October 23rd there were 61 people... Is it something I said?

[TRUTHSEEKER]

You can buy thermo-electric modules that convert heat to electricity from surplus electronics stores. They can also be purchased from manufacturers. Some small refrigerators use them ( one side gets cold and one side gets hot when electricity is applied to them).

This may allow you to use the heat of the motor to generate electricity for the electronics.

[Jacks Complete]

TRUTHSEEKER,

using the heat energy from the motor to power the motor is perpetual motion - it cannot work!

You would need some kind of heat source that provided heat continuously. The problem is, if you get the junction too hot, it will destroy the semiconductor. It would be better to take a higher quality heat source, such as petrol, and just use that in an engine.

[Wild Catmage]

Originally posted by Jack's Complete

As something that might be more realistic, has anyone tried doing the Estes (or other model rocketry) thing with the camera, and taking a photo, and parachuting it down?

There is a good collection of videos shot with various cameras at: http://www.dph.com/vidroc/vidroc_1.htm

"For less than $100.00, you can purchase a wireless 2.4GHz video system that will transmit video and audio back to the ground for recording. Several companies sell a suitable downlink system -- X10's XCam (www.X10.com), Spy Eagle's SpyCam (www.SpyEagle.com), Plantraco's Color ATV and RF-Video.com, to name a few."

The only problem I can percieve is that there would not be much footage, as the rocket's flight time is farily short, and a rocket is not as controllable as a helicopter. However, a rocket is much faster and would be extremely difficult for the cops/feds/whatever to shoot at, unlike a helicopter.

A rocket could also be coupled with a flare for use at night, but the image would probably be pretty crap due to the poor light.

[Blackhawk]

As for the camera in a rocket thing, I have dont that, granted in a rocket that was 2.2m tall, but the actual camera unit was only around 15cm long. The camera was a dolphin digital pencam I got for $50 AUD from DSE on special, it will take 26pics at 640:480 or 76 at 325:240 or crappy little avi vids at around 3fps (Really not worth it). The rocket flew to 935ft AGL (Onboard altimiter reading) and the camera was internally hotwired to a DSE pulse timer to take one picture every second. The timer was activated when two plates touched together under the G forces of liftoff, which latched an SCR on so the timer didn't turn off after the rocket had stopped accelerating. All in All I got 26 good shots, the camera worked much better than I thought it would, unfortunately I have nowhere to put them on the internet so if you want them email me and I'll send the best ones.

The camera: http://www.dolphinfast.com/products/007.html
The timer: http://www.dse.com.au/cgi-bin/dse.storefront/3fbb43bb0b0b52e0273fc0a87f9c0722/Product/View/K1331
The rocket (Mine is Heavily modded): http://www.aerotech-rocketry.com/customersite/products/kits/mirage.html
The motor: http://www.thrustcurve.org/AEH128.shtml

[Anthony]

A peltier needs to get damn hot to generate a significant voltage/current, a motor that hot would be long dead.

Also, the power generated by the peltier would probably be less than the power required to lift the extra weight of the peltier.