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.