UAV at University of Maryland

[enae100]

Hello all...I am a Graduate Student at the University of Maryland in College Park. I am building a composite UAV that will feature inflatable wings.

My team is primarily composed of 2 grad students and 2 undergraduate "slaves"...but don't tell them that.

Anyway, I am sick of banging my head on some stupid electronics. I favor aircraft design/composite construction/flight testing and Jason is a software powerhouse. As for the electronics - we hurt a little on that side because neither one of us are real experts at it and sometimes stupid things get by us.

So what is my question??? Is there anybody in the vicinity (knowledgeable with electronics and custom circuits) that would like to get a tour of UMD and our Aero Dept and take a look at what we are doing? It is time we get fresh eyes to look at our problem here. The thing on our plate right now is a RPM sensor. We are using a 3W engine and want to pick up the square wave from the ignition box and take it into our counter. There are more details of course but I'll leave it at that.

If can make the time to come on down and put in your two cents in - then you are welcome. Just email me and we can talk on the phone and coordinate things.

Thanks!

[direwolf]

I can put you in touch with Jason Howe, our electronics guru. I will send you a PM with his contact information. He is currently throwing together a full blown sensor package for our SR1-B helicopters, including thermocouple stacks and RPM sensors. I'm sure he'd be happy to help you out in anyway he can.

-- Brian

[danstrider]

University of Kentucky has an inflatable wing project you might want to check out or just email them for more info. Nice guys. If this wasn't my last weekend in DC, I'd volunteer to come take a looksie ... I'm more of an aero anyhow, but it's always fun to have others oogle over your project, right? You'll get lots of ooglers if you post some pics or design concepts!

http://www.engr.uky.edu/bigblue/

Dan

[kd7ost]

I think in the interim, you have to get pulses from your engine to monitor RPM though. I don't know that engine but presume it's got an electronic ignition? If not it at least has a magneto, (My personal preference for small UAS's) and therefore a rotating magnet somewhere on the flywheel in either case. I think it can be a bit dicey trying to get samples from the ignition module back to your electronics. It's an easy way to introduce electrical Noise from your spark ignition into your electronics package. You should have a shielded Spark plug cable. Then using a common Hall effect switch attached so it is in proximity to that rotating magnet on the flywheel, you can feed those pulses into a hex inverter with a schmitt trigger, (common as heck) in fact these are used as servo buffer amps. This will ensure a good clean square wave that can be counted by your circuitry. You might need to feed it through an opto isolator for noise immunity. Keep the hall effect switch as far away from the ignition module as possible. Use shielded cable. Be ready with an O'scope to see if you're getting noise spikes into the hex inverter that will be shaped and counted as pulses on the output.

Alternatively. You can use something like a laser tachometer. http://www.allelectronics.com/cgi-bin/category.cgi?category=search&item=TCH-4&type=store

Something like this can be located farther back from the engine and ignition system. You can hack this for where the reading comes in. You might have to cut the signal in half (two prop blade counts for every revolution) but you can probably deal with that in your software.

Dan

[enae100]

hey guys...thanks a bunch for the responses...and kd7ost....what you describe is exactly what we are using...(the schmitt trigger with the hex inverter on both input and output).

We tried using the Zenoah at first. We wanted to grab the signal out of the magneto and get it into a nice 5v square wave. But we never quite succeeded and the grad student that was doing the work didn't give a crap about it either (he is no longer with us).

So then we went to the 3W engine - with the idea to make use of the output it has from its electronic ignition. Just f10 minutes ago we got it to work....it appears that all of our headache is due to a bad wire that would connect and disconnect randomly. That is why when we thought it was something the next day something else did not work and there was never any logic as to the series of events/tests we ran.

The laser tach is very interesting...

I am going to put up a pic or 2 for you guys...

Evandro

[enae100]

Here are some pics...

Left Fuse being CNC milled.

Both sides of Fuse with bondo...sanded and not sanded...

I'll put up more as I get to them...I may put up a pic of the computer model...I also have a 1/5th scale rapidly prototyped version (but I'd have to take a picture of that for ya.

By the way...I too am working with ILC with inflatable wings. The wings are due to arrive on monday. I have flown a pair of wings that they gave me 2 years ago. We have also conduct wind tunnel test and structural tests with the inflatable wing as well.

Evandro

[kd7ost]

What can you tell us about the inflatable wings? Do they just get blown up with air? Or are they a gas filled with a UV activated epoxy to harden them once inflated?

Dan

[enae100]

well...i've been trying to go to dinner for the last hour...

here is a quick pic of the inflatable wing...when I get something better for ya I'll put it up...

and DAN...I can send you more info on it if you want it.

Evandro

[kd7ost]

Excellent. PM sent, but go eat first. ;)

Dan

[enae100]

ummm....I just confused the two Dans....


I want Dan from NC State to gimme a call...

[enae100]

NC State Dan.... (danstrider)...

did you ever find a solution for your pilot to computer switching mechanism?

[direwolf]

I talked to Jason Howe about his RPM sensor today. He has simply tied a PIC to the govenor, so he gets the same count that the govenor gets. But, I'm going to guess you guys aren't using a govenor. Sounds like you got your circuit working, anyway. :)


<Wave to Dan Strider>
Hey buddy! Good to see you made it out alive. I think we had fourteen people on the verge of heat-stroke down there. :)

-- Brian Stone

[enae100]

Direwolf -
We did get things to work...things got bad before they got good. I went over all of my connection and redid somethings. It turns out that not having the spark plug in make s a huge difference. I took the spark plug out so I could free spin the prop and generate the signal through the electronic ignition...that way I could run the test indoors without the engine actually running. The spark plug needed to be in the spark plug housing otherwise nothing works. I didn't think it mattered and it seemed like a last ditch long shot but not having the spark plug in the spark plug cap was screwing things up. All I have to do is run the whole thing outside and check if everything works when the engine is on.

kd7ost -
I should have more stuff on the inflatable wing in my office. I'll yet send them to you.
But in the meantime here is a picture of a trainer I converted. This aircraft was flown 2 years ago. You can see what the original trainer looks like. I also converted it into a taildragger and put into it a nice OS 90 4 stroke!

Question for anyone...
I am curious to know what you guys use for a pitot tube. I use a small pressure transducer made by Omega. Cna some of you tell me what you use and if you've had good luck with them...I am curious.

[enae100]

Does anybody know how to get a vibration damper like the ones in this picture? Or does anybody use dampers on their softmounts????
All I know is that these are german...

[danstrider]

Whoa! That inflatable wing on the trainer looks awesome!

*glad to be finally moved back to Raleigh, thus the day's response delay*

Lots of questions, let's see if I can hit them all....
* I'll give you a call enae100 a bit later tonight

* for a pitot-static probe, you have many options:
-- you can use two seperate probes (pitot is just open tube pointed into the freestream, static is a similar tube, but the end is filled and rounded and at least 7 diameter lengths downstream 4 holes are drilled through the tube at 90 deg apart)
-- you can buy a nifty premade pitot-static probe that has the two pressure taps in the same probe (what I've always used, heritage part though, no idea where it came from)
-- you can build a combined pitot-static probe (I'll let you search around, I seem to recall a thread about that specifically somewhere)

* I've always used some kind of engine vibration damping. I found some old Sullivan soft-mounts that have a square rubber foot which slips over the mounting lugs and then a metal "cage" is mounted to the engine mount which keeps the engine and rubber feet from slipping out. The Dubro soft-mount are okay too, but seem to not dampen enough. Hyde soft-mounts are also excellent. You can find Lord Mounts from McMaster to be used in a manner similar to the German soft mount pictured. Try McMaster page 1218 and beyond.

* Switching circuit: yes, I did find a solution. JayFrancis gave me his prototype and is cooking up a new rev hopefully to be around in the near future (though I have no idea of his schedule). Alternately, now that the circuit and parts are proven, it wouldn't be that difficult to whip up a custom circuit using the parts listed in the mux-switch thread. I'd kinda like to see someone else take a stab at it anyhow...

Did I miss anything?
Dan (the danstrider one :-)

[kd7ost]

Does anybody know how to get a vibration damper like the ones in this picture? Or does anybody use dampers on their softmounts????
All I know is that these are german...

http://www.estcoenterprises.com/index.php
http://www.estcoenterprises.com/display_items.php?cat_id=9&line_id=47

[Bernd Brunner]

Look at http://www.toni-clark.com/ for the hydro-mount system. That´s a vibration damping system!

Bernd

[JustinONE]

what is the main idea behind having inflatable wingskins? Is this for de-icing in flight, or to just change the lift of the airfoil?

[shedao]

Good question, I assumed it was for transport. I know that large wings can be a pain to pack up and move to another location.

[kd7ost]

That’s probably the biggest reason on terra firma. I've read bits and pieces of articles though where testing is being done to send these types of craft to Mars for example. A College tested a drop from 100,000 feet agl or so with a glider that had inflatable wings. The interior of the largely translucent wings were smeared with an epoxy resin that quickly polymerized when exposed to UV radiation. The theory is you can use a small bottle of a compressed inert gas to inflate the wings initially. Once inflated and the epoxy is exposed to sunlight it hardens the wings in shape so the gas doesn’t have to be contained for a long period of time.

http://pdf.aiaa.org/preview/CDReadyMASM04_665/PV2004_1373.pdf

Added this link. Glider was lofted by High altitude Amatuer Radio group "EOSS, Edge of Space Sciences" in Colorado. Some details and links are here.

http://www.eoss.org/ansrecap/ar_100/recap66.htm
http://science.nasa.gov/headlines/y2003/02may_bigblue.htm

Dan

[JustinONE]

Oh, OKAY! this is for Mars exploration, I got yah now.

[davidfee]

Those dampers on the soft-mount look like the oil-filled dampers that are used in R/C cars and trucks. Just go to a hobby shop and you will find them. You should be able to fabricate the required brackets pretty easily.

-David