Late February Updates

Well, there's a lot to cover. First off, we've decided on the necessity of a avionics test bed. After looking at a professor's thesis papers on an autonomous plane he worked on and noting that they had a plane dedicated to testing avionics that crashed three times, it seemed natural that we should make one as well. Considering our inexperience and how much we would like it if our competition plane didn't crash, we're going to make a sort bare bones skeleton plane. We're not kidding about the skeleton part too; it'll probably be a carbon fiber tube with a foam wing and tail attached, an electric motor, some batteries, and a box to hold the avionics we're testing. It should be straightforward to design and build. Having that done early will give us extra time to work on our competition plane.

Looking into the camera transmitter part of things, it looks like one of us will need an amateur radio license to legally handle the power that we'll be transmitting. I found this site that talks about the steps to take to get a license. I also found out that this book is apparently the Bible for studying for the test. Hopefully that book will arrive soon and the license not too long after.

On the electronics side of things, I've got a few bits ordered and coming in (hopefully I can pick them up tomorrow). Things include voltage regulators, 16 MHz crystals for Arduino ATmega168's, and an AVR programmer among other things. The programmer is cool because it's a first step towards moving away from the Arduino and programming directly for the microcontroller. Once those IMU units come in I can start testing those integrated with the multiplexing scheme. I also need to test the timing in the multiplexing scheme by doing some pinging.

For the data link, we're reevaluating our options again. Before I was really stuck on the Digi XStream OEM RF Modem at 19200 baud rate. It gave us a range of about 7 miles but the kicker was its $150 price tag. The XBee-PRO 802.15.4 modules sport a range of about 1 mile with a much nicer price tag of $32. However, the trick is we still don't have a concrete maximum flight range. The rules keep talking about staying within the airfield, but the air field is about a mile by mile (square mile). If we're in the center than a 1 mile range will probably do fine. If we're positioned at the edge of the airfield then we're going to need a range of greater than 1 mile. Which is it? Well, I've got an email on it's way to the contest contact point to see if I can get a clearer picture. That's what's holding up the RF modem selection along with antenna selection.

We still don't know what camera we want. Today we were looking at camera transmitters to see if we could find a range. Of course, bad news. The most powerful 2.4 GHz transmitters we've seen so far (of what little we've seen so far) are about 1 Watt with a range of 300 meters (less than a third of a mile). That's making us think we'd want to send the video over 900 MHz to get more range. However, I don't want a 900 MHz camera transmitter and 900 MHz data link on the same plane. The interference might be intolerable. This gives the XBee-PRO data link some more credibility since it operates on a 4.2 GHz frequency instead. Before we start making conclusions though, we haven't actually found a 900 MHz camera transmitter with the range we want yet. Well, time will tell.

As for the camera gimbal? Unfortunately I wasted time on thinking if we could get away with a single-axis gimbal because the contest requires that we be able to see a 60 degree cone from below the plane in all directions. That basically means we need a two-axis gimbal. We've been looking at the Lynxmotion one as a real quick and simple solution to the problem.

We've looked more into the need of a pitot-static system. From what we can tell, if we want airspeed relative to the plane the pitot-state system is unbeatable in its reliability. It'll be costly though with the tube itself already costing $80 already and the pressure transducers another $35 to $65 each (we need two). We considered software methods, anemometers, hot-wire anemometers and turbine meters already. One of my professors says that a pitot-static tube will probably be what we end up with anyway. Finding the pressure transducers has been an uphill battle, but lucky for us Matt found a company named Servoflo that sells them in a beautiful DIP package. The problem is that we haven't figured out how to order from them yet.

Anyway, I think that's a pretty good update for now. Time to crash.

Multiplexing Scheme Works

Well, apparently that multiplexing scheme I was merely hoping would work actually does work. It manages to pick up data from two ATmega168's acting as buffers to other sensor data. One buffers the GPS data and the other buffers ADC conversions of soon to be accelerometer and rate gyro data (just ordered an ADXL330 and three ADXRS300's today). A sensor collector ATmega168 queries each buffer for data. If data is unavailable then it simply moves on to the next sensor. If data is available it will read it and echo it back to the computer for debugging purposes. Eventually the sensor collector will filter the signal and pre-process it for the flight computer in another ATmega168. Why so many ATmega168's? Well, the Arduino makes it so easy to work with the ATmega168 already so I figured it'd be better to just go with what we know works. Anyway, check out the pictures:

Updated Components Diagram

This is still preliminary, but it's been updated to show more detail and some new decisions. Instead of the IMU package it looks like we're going to go for the raw components: one triple-axis accelerometer (the one used in Wiimotes actually) and three rate gyros. We'll have to write our own firmware to integrate the gyro rates and come up with actual position and orientation in conjunction with the GPS module. This came up after a discussion with our advisor Damian Toohey. It'll be more work and a bit riskier, but it's also probably more fun and we'll get a lot more from it. I also detailed how I plan on using multiple microcontrollers. This still needs to be proven out since there are concerns about communication speed involving both the multiplexers and controller to controller communication.

Components Diagram (Preliminary)

Hey guys, I couldn't sleep so I updated the components diagram a bit. It's still preliminary, but it's very close to being complete. I'll be proving out the multiplexing scheme for the UART soon. If that works, we might very well be able to pull this off with just an ATmega168 microcontroller. Will we want to? Not quite sure yet. It'll be interesting, that's for sure!


Things that need more design and/or selection: fail-safe system (hard line? relay?), main board selection, camera w/ transceivers, pitot-static system, RC receiver mixing with controller

Things that need proof of concept: UART multiplexing scheme (includes data buffering with microcontroller), range finder (sonic Maxbotix LV-EZ1), magnetic compass, IMU package, servo controller

Things that need research: video capture directly in ground station (possibly using DirectShow)

Well, the above is an incomplete list; it's just all I can think of for now. Great progress has been made in computer to electronics communication, GPS interfacing, and command-query programming. Details to follow, hopefully.

GPS Logger Works!

Hey everyone,

So despite not have any sleep the night before and it being about 10:42 pm, I managed to get my programming on. I spruced up the ground station interface a bit and added the ability to log received GPS coordinates. The program then plots the GPS coordinate history on top of a satellite view that I took screenshots of from Google Maps. If you can tell in that bottom-left window there, that's Engineering IV (practically my current residence). The red and blue +'s are calibration marks. They are actually off for some reason; the math is right but the image scaling is wrong. Anyway, those green +'s are recorded GPS positions. It was basically me standing out there in the 50 degree cold walking around. I'm actually pretty happy with the precision from this EM-406A GPS module. It's probably a perfectly fine candidate for use in the plane. Anyway, there's more feature building to be done on the ground station program. However, I think it might be time to move onto some controls stuff... Either way, pics of the progress below.

Initial Tasks Detail

Here's info from my earlier email on the individual tasks.

Plane Structures and Aerodynamics
Plane design isn't my forte, but Jerry and Gerard are extremely good at it. Jerry has already completed an initial iteration, and it's up to where he is to determine where you guys start. For now, I have a lot of online resources that I'd like for everyone to read. Please spend some time familiarizing yourself with general RC plane construction and design.
Airfield Models - Model Builder's Information Source
Airfield Models - Formulas Used with Flying Model Aircraft
Airfield Models - Designing Radio Control Model Aircraft
Styles of Model Aircraft Wing Construction
Aircraft Design, Synthesis and Analysis
MIT OpenCourseWare on Aeronautical Engineering

Plane Propulsion
Gaurav and Ben, I think both of you have things under control. I'd like to see a motor selection in about two weeks. That should give you enough time for the plane to get into a state where motor selection is more realistic. Just keep in mind that understanding how to maintain one is just as important as understanding how to select one. The only online resource I have for you is one you've probably already seen.
Airfield Models - Starting, Running, and Breaking In Model Airplane Engines

Camera Gimbal Design
Tom and Eric, I'd like for both of you to work together on the camera gimbal. Tom was at the meeting so he pretty much knows what this is all about. I need you both to decided on how much gimbal control we need. Some teams can pull it off with a single wide angle camera at the bottom, fixed. For more view we could put the camera on a single gimbal have it do a side to side sweep as it moves along. Actually, if our camera has large zoom on it the field of view would be so small that we would have to gimbal it. Also do a trade study on whether or not a two-axis gimbal would work nicely. Some things to consider are if we want the camera center to coincide with the center of rotation. Figure out the details. This one is a bit long term as it'll probably take about a weeks worth of "looking up" and another two weeks of designing. Remember that we're optimizing for weight, cost, and stability. You'll have to stay in contact with the plane structures team to figure out where the camera ball will go and how it will fit with the rest of the plane.

Camera Selection
Matt's got this down I think, but a little more thought needs to go into it. Literally I'd like to see a camera selection in a week or two if it gets difficult. Just do a quick field of view study on what kind of resolution we want and if we need a zoom lens to augment that. The worst case scenarios is a 2 ft x 2 ft target 250 ft off center and a 2 ft x 2 ft target 500 ft up. We're probably limited to a resolution of about 640x480 max so see what kind of field of view will get us a target screen size large enough to achieve identification. On that note, see what screen size would be large enough. Maybe about 40 pixels by 40 pixels, just eyeballing it. Work with the camera gimbal design group so that they'll have the information to perform selection as well. The field of view kind of determines whether or not we have to gimbal the camera.

Wireless RF Communication
Although we've made a lot of progress on the electronics side, we still need to select a radio frequency module. I'd like for both of you to get extremely familiar with RF communication. There are a lot of things we don't know such as antenna design, antenna types, blocking materials, etc. I think the best way to start is by looking at the two RF modules that I've been looking at. Read the data sheets on them and try to understand every part of the data sheet. One thing to note is that we want one with a really simple TTL serial interface. Basically one with RX (receive) and TX (transmit) pins. It also has to be two way (transceivers) so that we can upload new GPS waypoints. The range we're looking for is at least 1.5 miles. The two below satisfy the requirements with my personal preference towards the XStream OEM RF Module. This has a steep learning curve so please contact me often with questions.

XStream OEM RF Module
http://www.digi.com/products/wireless/long-range-multipoint/xtend-module.jsp

AeroComm 4790-200
http://www.aerocomm.com/rf_transceiver_modules/ac4790_mesh-ready_transceiver.htm

Target GPS Coordinate Acquisition
I've already talked to Ian and I know he has a good idea of what I'm looking for. We basically have to figure out the target position in GPS coordinates from the target's screen coordinates. This can be evaluated given plane GPS position, plane orientation, camera offset, camera orientation, camera field of view, etc. There's probably a lot of information you'll need so keep in touch with me and other team members. You can probably find a nice general solution and fit in the details afterwards. Try to get a good methodology in a week and possibly a full solution in two. Thanks.

Initial Teams

Remember that these are only initial assignments. As tasks get done people will be reassigned with new ones.

Plane Structures
Matt Wong
David Tuman
Scott Larson
Sam Goljahi
Sung Park

Plane Aerodynamics
Jerry Huang
Gerard Toribio
Sharon Querido
Charles Jaikumar
Clarence Gan

Plane Propulsion
Gaurav Bansal
Ben Farahmand

Camera Gimbal Design
Tom Wiltse
Eric Huang

Camera Selection
Matt Wong
Jeffrey Duh

Wireless RF Communication
Jon Nguyen
Marcel Nations
Song Zheng

Target GPS Coordinate Acquisition
Ian Schultz
James Umali