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T3

EM406 dynamics: final resolution

Posted by William Premerlani on April 22, 2009 at 4:35am
I have the issue of the latency in the dynamic response of the EM406 GPS in binary mode finally resolved: you have to run at 57,600 baud in binary mode. Apparently there is a large communications buffer in the EM406 that gets flushed by the carriage return/line feeds in NMEA mode, but which does not get flushed in binary mode, unless you run at 57,600 baud. There must have been a memo on this, but I missed it.I will revise the MatrixNav code and release it as soon as I can give it a test flight. The drop in latency from 12 seconds to a few seconds should vastly improve the performance in windy conditions.Thank you all for your help, especially Chris Anderson, Jack Crossfire, and automatik.I should have listened to you, Jack. Next time I will.By the way, the EM-406A performs very well with respect to sensitivity and fast response. Now that I have resolved the binary interface issue, it performs as well as any of the other GPS radios that I tested. I plan to continue using it in future designs. There really is no point to using GPS units with reporting rates that are faster than 1 Hz. As far as I can tell, all they do is interpolate.Bill Premerlani
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Two questions about getting started (FMA sensor, IMU)

Posted by Garry Qualls on April 21, 2009 at 11:55pm
Now that the Ardupilots are back in stock, I am ordering what I need to get one up in the air. The FMA IR sensor is out of stock at FMA Direct until May 15, so does anyone know of another vendor that may have them or if there is an easy replacement I could order or build? It's just three weeks, but I am anxious to get started ;)Question 2, I would like to put a decent IMU onboard to document the vehicle attitude in flight. The three options I've found at SparkFun are the IMU 6DOF - v4, the Atomic IMU 6DOF, and the UAV DevBoard. The "v4" is the only one with magnetometers, so one could expect it to be more accurate at the end of a 30 minute flight, but I've seen similar systems where the magnetometer readings were so noisy that they were useless. Down the road, I might want to use the IMU I purchase to drive a motion compensation system. Has anyone used one of these? All three are within my price range. My main concerns are accuracy and ease of integration. So, does one have a clear advantage? Are there other IMUs on the market that I should consider?
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3D Robotics

A new Arduino library for GPS parsing

Posted by Chris Anderson on April 21, 2009 at 6:30pm
Looks like the Fathers of Arduino have smiled on us UAV guys. David Cuartielles, one of the core Arduino developers, has posted a very welcome set of GPS parsing routines that anyone can use: "I crafted three examples (basic, medium, advanced) featuring the use of different techniques to parse the GPS sentences. If you write something like a data logger, or a GPS toy, post your link here and I will be more than happy to include your code in the next revision of the library. Of course, if you found any errors or made any improvements, do the same thing. This code compiles for Duemilanove and Mega, without any alterations. It works fine with the processors ATmega168 and up. Uses about 300 Bytes of memory space and is documented inside the code. Ah … there is a README.txt you shouldn’t miss; it explains how NOT to use the library."
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EasyStar Mods - Spar Upgrade

Posted by Zach Lovering on April 21, 2009 at 4:59pm
The more equipment that is installed on the plane, the more load the wing will need to take. To prevent the wings from flexing too much, the plastic spar can be replaced with a carbon one.Materials:1. Hacksaw2. Masking tape3. Carbon rod (5/16" OD or 8 mm)4. Original sparProcess:1. Line up the two spars to get an idea of where you will have to cut the carbon spar.

2. Wrap the the location that you are going to cut the carbon spar with masking tape (only a few times around is necessary). The tape will prevent the carbon from fraying when it is cut.

3. Mark the carbon spar where it will be cut, using the plastic spar as a length reference.4. With the hacksaw, cut the carbon spar.

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EasyStar Mods - Spar Hole Reinforcement

Posted by Zach Lovering on April 21, 2009 at 4:59pm
Another simple modification to increase the spar holes strength. I notices that after just a few flights (and a few hard landings) that the spar holes in the wing started to stretch. To fix this problem, I reinforced the holes with fiber washers. (Note that these pictures were taken after I had already done this modification)Materials:1. Hobby knife2. CA3. Two fiber washers (5/16" ID x 3/4" OD)Process:1. Place the spar inside the hole and the washer around the spar so that the washer rest on the root end of the wing. The spar should be fully inserted into the wing so that the washer will be well centered.2. Make a shallow cut around the washer into the wing root to outline where the washer will be installed.

3. Remove foam as needed so that the washer will sit flush to the root end.4. Apply CA on the foam where the washer will be located. Install the washer and let dry.

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Predator by your own hands! Some help needed :)

Posted by Justas on April 21, 2009 at 12:00pm

Hi, my name is Justas, i am from Lithuania (a small country near Baltic sea), i am 19 years old, i am studying Informatics in Mykolas Romeris university. So, after a few years of flying in flight simulators i decided that i need to go to something more serious, and i found myself in RC. I have been flying with helicopters, gliders and planes. I never had one, so i decided to make one by myself. I could buy it, but for me, building something is even more interesting than using it! I didn't need long to decide what should it look like, for sure it's predator! I decided it because i am in Lithuanian volunteers army (not professional army, more for young people who associate their future with military), so it took my eye from first shot.Firstly it should be controlled manually (because of lack of money, hard time for non working student...), and in a few months after that it should be upgraded with ArduPilot, CoPilot and GPS to become a real UAV!For a while i am not going to annoy you with questions about ArduPilot, CoPilot and GPS (i'm a newbie in that).The first thing i am going to do is to build the main Predator, it's wingspan should be about 160cm or less. (what i want is to be enough to cary about 1kg, it would be a high resolution photo camera and a video camera).After long searches all i found that could be useful was this (didn't found a good quality scheme with V tail up):

predator-diagram.gif

So what i need is help from people who already did this, i'd have some questions like:1. What the material should be?2. What about measurements?3. What about wings construction?4. How to attach wings?Ant i would be wery hapy if someone who did this could share theyr experience, any photos and sketches(most important to me).I'm not very good sketcher, but i tried to show the construction of the main body that i'm thinking about, what do you think about that(just a sample, form isn't very similar to predators):

Impatiently waiting for any help! Thanks and see you soon ;)
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3D Robotics

ArduPilot 2.1 released + setup utility and ground station

Posted by Chris Anderson on April 21, 2009 at 12:30am

A big code release tonight--this is the full setup that won the Sparkfun autonomous vehicle competition. Along with general improvements to the code, this is the entire package of autopilot, setup utility and ground station code. It's a full Unmanned Aerial System, not just a UAV! ArduPilot 2.1
  • All the features of ArduPilot 2.0 plus...
  • Supports XY sensor in diagonal postion
  • Requires Z sensor [UPDATE: FMA is no longer carrying those. While we sort out alternative sources, you can buy them from Dean Goedde for $40 (scroll down for price list)
  • Controls throttle if airspeed sensor is attached via the ArduPilot expansion board.
  • Supports desktop setup utility for waypoints and autopilot settings. (Waypoints are no longer manually entered in the code. They can only be entered with this utility.)
  • Last version of the code to support the original ATMega168-based board. Future versions will require the new ATMega328-based board.
  • Field setup procedures are here
  • Get it here
If you are using the expansion board and airspeed sensor, to control the throttle you must solder a wire from digital pin 8 to "MUX IN 3" Desktop setup utility

  • Add waypoints manually; utility displays them on Google Maps
  • Set max altitude, speed, circle radius
  • Set elevator, aileron/rudder trim
  • More features coming
  • Get it here ("ArduPilotConfigUtility")
When using this utility for the first time with ArduPilot, click Write before anything else in order to format the EEPROM. Also, ensure that the "Set RTS on close" box is checked in your serial port's advanced properties (control panel/device manager), as described in our Arduino debugging tips) Ground station

  • Requires free Labview runtime engine and serial drivers (install both. Note: if you've already installed Lego's Mindstorms NXT software you may find you've got a driver conflict, because it's based on LabView, too. Uninstall the Mindstorms software first.)
  • Works with Xbee wireless modules
  • Displays real-time attitude, speed, altitude, current waypoint, heading, distance to next waypoint, etc
  • Displays real time position on Google Earth
  • Get it here
  • Source code is here
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ArduPilot modification, running on Arduino Pro Mini board

Posted by Michal B on April 20, 2009 at 12:22pm

Here's a modification of original ArduPilot, running on Arduino Pro Mini.I'm just posting photos for now, since there's still lots of things to do for my planes to fly. Maybe when things are tuned, I'll post also modified code.My first testing or original ArduPilot few weeks ago was disaster, I tried to see my plane to see directly follow path, so I skipped slow testing of everything in small steps. Result was plane out of control, flying away to distance. Later I found it using bike, 1.5 km away. I had luck that time, I could have some $350 flown away, or maybe breaking someone's roof. Anyway, my previous plane was not flying nice, so this one is replacement, and it flies good in manual mode.

See the Arduino Pro Mini, compared to ArduPilot. It's smaller, and it lacks mux and failsafe chips. So great care must be done for switching between autopilot/manual modes on main cpu. Luckily tests show that it can be done relatively nicely using interrupts, so if main program control locks, interrupts still keep running, providing the possibility to gain control over plane.

Arduino Pro Mini on left, ArduPilot board on right.So far I play with FMA copilot replacement, implementing just stabilization. 6 RC channels are read, and 4 are written, the code can pass 4 channels through unmodified, or read them and mix with other values.
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EasyStar Mods - Wing Root Magnets

Posted by Zach Lovering on April 20, 2009 at 12:00pm
In this modification, magnets are installed into the wing root. This modification was inspired by the tendency for the wings to vibrate themselves apart during flight. Since simply pinning the wings in place (either mechanically or with adhesive) would not allow the wings to be compliant during a hard landing, magnets seemed like a good substitution. The process for installing the magnets in the wing root is very similar to the process for installing magnets in the canopy (see my previous post, "EasyStar Mods - Magnetic Canopy"). (Note that these pictures were taken after I had already done this modification)Materials:1. EasyStar RC plane2. Hobby knife3. Epoxy or CA4. Four neodymium magnets (I used 0.25" diameter, 0.125" thick; in retrospect, going one size up to 0.375" might be better)Process:1. In one wing, cut two small holes using the hobby knife for the magnets to fit into. The holes should be located near the forward and aft part of the root. The hole depth should be sufficiently deep to allow the magnets to be flush to the surface.2. Install the magnets by bonding them in place with either CA or epoxy. I used CA and have had no problem with them coming out.

3. After the adhesive has dried, cover the magnets with a piece of wax paper and snap 2 new magnets on top of them. Insert the spar into the wing (breaking through the wax paper). Slide the other wing over the spar and push down so that the magnets leave an impression in the wing. This will ensure proper placement of the magnets in the second wing.

4. Cut small holes in the second wing where the impressions were made and put adhesive in the holes.5. Replace the wing so that the magnets fit into the holes. I feel that this method is better than dropping the magnets into the holes since it guarantees that the magnets have the correct orientation.6. Once the adhesive has dried, separate the wings and peel off the wax paper.
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Possible useful UAV programming codes

Posted by Tom in NOVA on April 20, 2009 at 8:32am
UAV codes.pdfI am only about 4 hours into my "self-induced" C++ tutorial course starting from "what is a programming language?" So I cannot determine with great certainty how useful the included codes in the attached project may be. I hope that it would help some of you way ahead of me in the programming department.Would appreciate any feedback on the usability of these codes...
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T3

EM406 dynamic response is fine: mystery solved

Posted by William Premerlani on April 20, 2009 at 4:47am
The mystery of the 12 second latency in the dynamic response of the EM406 GPS is solved.Recently, I stirred up a debate about whether or not the EM406 has a 12 second latency or not. A few of us were seeing a 12 second latency. The majority of EM406 users were not seeing it.It turns out that the dynamic performance of the EM406 depends on which interface you use, NMEA or binary. If you use binary, there is a 12 second latency, then a 3 second "smoothing" transient.If you use NMEA, there is a smoothing transient only. The NMEA interface to the EM406 provides dynamic performance as good as the LOCOSYS or the ET312.It is my speculation that "track smoothing" is turned on in the EM406 for the binary interface, and either it is always on, or I have not figured out how to turn it off. If anyone knows how to turn track smoothing off in the binary interface for the EM406, please let me know so that I do not have to scrap my binary interface and start over on a NMEA interface.
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3D Robotics

At least three of the rovers in the Sparkfun contest used ArduPilot, too

Posted by Chris Anderson on April 18, 2009 at 1:30pm

ArduPilot isn't just for planes--it's a great board for robot cars, too. At least three of the rovers in the Sparkfun Autonomous Vehicle Competition used our board for their vehicles, where it was just acting as a 2D autopilot. Nathan Siedle, the CEO of Sparkfun, used a modified ArduPilot board for his rover and others used the board stock. Like almost all the rovers, regardless of what board they used, they went awry at one corner or another, due to waypoint, software or sensor errors or just wild out of controlness (see above). The one rover that finished the course used a custom Atmega32 board. Next year I'd expect more rovers to finish the course, just like DARPA road race. I also expect more of them to use ArduPilot: it's the easiest way to add RC and GPS to Arduino. You just need to program them right! (photo from Makezine)
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EasyStar Mods - Magnetic Canopy

Posted by Zach Lovering on April 17, 2009 at 10:30pm
This is a pretty simply modification to the canopy to replace the plastic tabs with magnets. Once done, it is quick and simple to get the canopy on and off and, as a bonus, it makes a neat snapping sound when you put the canopy back on. The process is straightforward. (Note that these pictures were taken after I had already done this modification)Materials:1. EasyStar RC plane2. Hobby knife3. Epoxy or CA4. Four neodymium magnets (I used 0.25" diameter, 0.125" thick; in retrospect, going one size up to 0.375" might be better)Process:1. Remove the plastic tabs by cutting around them with a hobby knife and then pulling them out.2. Cut small holes in the canopy area of the fuselage to fit the magnets into. Install the magnets (I installed mine near the front, as shown) by bonding them in place with either CA or epoxy. I used CA and have had no problem with them coming out.

3. After the adhesive has dried, cover the magnets with a piece of wax paper and snap 2 new magnets on top of them. Replace the canopy and push down so that the magnets leave an impression in the canopy. This will ensure proper placement of the magnets in the canopy.

4. Cut small holes in the canopy where the impressions were made and put adhesive in the holes.5. Replace the canopy on the fuselage so that the magnets fit into the holes. I feel that this method is better than dropping the magnets into the holes since it guarantees that the magnets have the correct orientation.

6. Once the adhesive has dried, remove the canopy and peel off the wax paper.

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