The glossary is not indexed. It is in alphabetical order so just scroll down to find the topic of interest.

2.4 Ghz: The frequency used by digital (spread spectrum) radio communications in our applications, including 2.4Ghz RC, Bluetooth and some video transmission equipment. This is a different band than the older 72 Mhz band that is used for analog RC communications. To avoid radio frequency conflict is it often a good idea to use 72 Mhz radio equipment when you are using 2.4 Ghz onboard video transmitters, or use 900 Mhz video when using 2.4 Ghz RC equipment.

AGL: Altitude above ground level

AHRS: Attitude Heading Reference System. An IMU (see below) plus the code to interpret the output from its sensors to establish a plane’s XYZ and heading orientation.

APM: ArduPilotMega.

AMA: Academy of Model Aeronautics. The main US model aircraft association. The AMA works closely with the Federal Aviation Administration (FAA) to establishreasonable rulesfor the use of amateur UAVs. Each AMA chapter and field may have slightly different policies, but it’s possible to fly and test air frames and some technology on AMA fields without violating the association’s (or FAA/NAS) rules.

Arduino: An open source embedded processor project. Includes a hardware standard currently based on the Atmel Atmega168 microprocessor and necessary supporting hardware, and a software programming environment based on the C-like Processing language. Official site is here.

APM (AutoPilot Mega): Autopilot providing capabilities for stabilized flight, position maintenance and automated mission (waypoint) path following.

ATC: This could be the Atitude Control library in Copter with params starting with “ATC_” or it could mean Air Traffic Control. Usually located at an airport control tower but can also be an app or service such as AirMap or Altitude Angel.

Copter: Rotary-wing autopilot software variant of the ArduPilot project.

Plane: Fixed-wing autopilot software variant of the ArduPilot project.

Rover: Ground and water autopilot software variant of the ArduPilot project.

BEC: Battery Elimination Circuit. A voltage regulator found in ESCs (see below) and as a stand-alone product. Designed to provide constant 5v voltage for RC equipment, autopilots and other onboard electronics.

Bootloader: Special software code stored in non-volatile memory in a microprocessor that can interface with a PC to download a user’s program. Also see Firmware.

COA: Certificate of Authorization. A FAA approval for a UAV flight. See the web site for more details and the DIY Drones Regulatory FAQ.

DCM: Direction Cosine Matrix. A algorithm that is a less processing intensive equivalent of the Kalman Filter. See this for more.

Eagle file: The schematic and PCB design files (and related files that tell PCB fabs how to create the boards) generated by the free Cadsoft Eagle program. This is the most common standard used in the open source hardware world, although, ironically, it’s not open source software itself. Needless to say, this is not optimal, and the Eagle software is clumsy and hard to learn. One hopes that an open source alternative will someday emerge.

ESC: Electronic Speed Control. Device to control the motor in an electric aircraft. Serves as the connection between the main battery and the RC receiver. Usually includes a BEC, or Battery Elimination Circuit, which provides power for the RC system and other onboard electronics, such as an autopilot.

Firmware: The software or sketch that is loaded into the non-volatile memory of microprocessor based products. It is called ‘firmware’ because it stays in the non-volatile memory even if power is removed - thus ‘non’ - volatile. In the case of the autopilots, it is the ‘program’ or application (App to smart phone users) that determines what the auto pilot does, and how.

FPV: First-person view. A technique that uses an onboard video camera and wireless connection to the ground allow a pilot on the ground with video goggles to fly with a cockpit view.

FTDI: A standard to convert USB to serial communications. Available as a chip for boards that have a USB connector, or as an adapter to connected to breakout pins. FTDI stands for Future Technology Devices International, which is the name of the company that makes the chips.

GCS: Ground Control Station. Software running on a computer on the ground that receives telemetry information from an airborne UAV and displays its progress and status, often including video and other sensor data. Can also be used to transmit in-flight commands to the UAV.

Hard Iron magnetic distortion: distortions that arise from magnets or magnetized metals on the airframe that affect the compass. These distortions remain in the same location relative to the compass for all heading orientations. These distortions can be mostly compensated for by adding constant offsets to the values returned from the 3d magnetometer (compass).

HIL (Hardware-in-the-loop simulation): Doing a simulation where software running on another computer generates data that simulates the data that would be coming from an autopilot’s sensors. The autopilot is running and doesn’t “know” that the data is simulated, so it responds just as it would to real sensor data. Hardware-in-the-loop uses the physical autopilot hardware connected to a simulator, as opposed to simulating the autopilot in software, too. In an “open loop” simulation, the software simulator feeds data to the hardware autopilot; in a “closed loop” simulation, the hardware feeds data back to the software simulator, too.

I2C: A serial bus that allows multiple low speed peripherals, such as sensors, to be connected to a microprocessor. See this for more.

IDE: An integrated development environment, such as the Arduino editor/downloader/serial monitor software. Often includes a debugger.

IMU: An inertial measurement unit such as the ArduPilot OilPan. Usually has at least three accelerometers (measuring the gravity vector in the x,y and z dimensions) and two gyros (measuring rotation around the tilt and pitch axis). Neither are sufficient by themselves, since accelerometers are thrown off by movement (ie, they are “noisy” over short periods of time), while gyros drift over time. The data from both types of sensors must be combined in software to determine true aircraft attitude and movement to create an AHRS (see above). One technique for doing this is the Kalman filter (see below). Now superseded by Autopilots which include CPU and sensors in one unit.

Inner loop/Outer loop: Usually used to refer to the stabilization and navigation functions of an autopilot. The stabilization function must run in real-time and as often as 100 times a second (“inner loop”), while the navigation function can run as infrequently as once per second and can tolerate delays and interruptions (“outer loop”).

INS: Inertial Navigation System. A way to calculate position based on an initial GPS reading followed by readings from motion and speed sensors using dead reckoning. Useful when GPS is not available or has temporarily lost its signal.

ICSP: In Circuit Serial Programmer. A way to load code to a microprocessor. Usually seen as a six-pin (two rows of three) connector on a PCB. To use this, you need a programmer, such as this one, that uses the SPI (Serial Peripheral Interface) standard.

Kalman Filter: A relatively complicated algorithm that, in our applications, is primarily used to combine accelerometer and gyro data to provide an accurate description of aircraft attitude and movement in real time. See this for more.

LOS: Line of Sight. See VLOS below.

LiPo: Lithium Polymer battery, aka LiPoly. Variants include Lithium Ion (Li-Ion) battery. This battery chemistry offers more power and lighter weight than NiMh and NiCad batteries.

MAVLink. The Micro Air Vehicle communications protocol used by the Copter and Plane line of autopilots. See here for more info on MAVLink.

MAV: Micro Air Vehicle. A small UAV. More here.

NMEA: National Marine Electronics Association standard for GPS information. When we refer to “NMEA sentences”, we’re talking about ASCII strings from a GPS module that look like this: $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,47

Oilpan: An arduino style shield meant to be paired with the ArduPilotMega. Contained the majority of the sensors (gyos, accelerometers, barometer, etc) that allow the ArduPilotMega to function as an autopilot, now superseded by subsequent Autopilots that incorporate CPU and sensors in one board.

OSD: On-screen display. A way to integrate data (often telemetry information) into the real-time video stream the aircraft is sending to the ground.

PCB: Printed circuit board. In our use, a specialized board designed and “fabbed” for a dedicated purpose, as opposed to a breadboard or prototype board, which can be used and resused for many projects.

PCM: Pulse Code Modulation: The technique some modern RC transmitters/receivers communicate the RC channels information. It is transmitted digitally using a digital code to represent the channel number, position of the transmitter stick or switch, and sometimes other information. Some modern RC systems also provide digital signals to control digital servos - typically specific to each manufacturer.

PDB: Power Distribution Board. A board used in multicopters to distribute power to multiple ESCs.

PIC: Pilot in Command. Refers to a FAA requirement that UAVs stay under a pilot’s direct control if they are flying under the recreational exemption to COA approval. See Line of Sight above. (Not to be confused with the PIC processor series by Microchip)

PID: Proportional/Integral/Derivative control method. A machine control algorithm that allows for more accurate sensor-motion control loops and less overcontrol. See this for more.

POI: Point of Interest. Designates a spot that a UAV should keep a camera pointed towards.

PPM: Pulse Position Modulation. The square-wave pulse train used to transmit multiple channels of information between some RC transmitters and receivers. Some RC receivers provide a PPM output (sometimes referred to as the PPM Sum) which can be used on Pixhawk-series boards. Other receivers convert the PPM signal and only provide PWM signals for each channel.

PWM: Pulse Width Modulation. The square-wave signals used in RC control to drive servos and speed controllers. There is one PWM signal for each channel. The width varies from 1000 to 2000 microseconds, depending on the RC manufacturer.

PX4FMU/PX4IO: First version of Pixhawk-series autopilots (FMUv1). Discontinued.

RTL: Return to Launch. Fly back to the “home” location where the aircraft took off.

SiRF III: The standard used by most modern GPS modules. Includes !SiRF III binary mode, which is an alternative to the ASCII-based NMEA standard described above.

Sketch: The program files, drivers and other code generated by the Arduinio IDE for a single project.

SVN: Short for the Subversion version-control repository used by the DIY Drones and other teams for source code.

Telemetry System: A two way radio system to allow flight data to be sent from your aircraft and also to allow control or adjustment information to be sent back to it from a “ground station”, commonly a laptop computer. See the telemetry landing page for options.

Thermopile: An infrared detector. Often used in pairs in UAVs to measure tilt and pitch by looking at differences in the infrared signature of the horizon fore and aft and on both sides. This is based on the fact that there is always an infrared gradient between earth and sky, and that you can keep a plane flying level by ensuring that the readings are the same from both sensors in each pair, each looking in opposite directions. These have been largely displaced by electronic gyros and are no longer in common use.

UAV: Unmanned Aerial Vehicle. In the military, these are increasingly called Unmanned Aerial Systems (UAS), to reflect that the aircraft is just part of a complex system in the air and on the ground. Ground-based autonomous robots are called Unmanned Ground Vehicles (UGVs) and robot submersibles are called Autonomous Underwater Vehicles (AUVs). Robot boats are called Unmanned Surface Vehicles (USVs).

VLOS: Visual Line of Sight. The pilot’s ability to see an aircraft from the ground well enough to control it, without the use of artificial visual aids (aside from glasses). Required by FAA regs.

WAAS: Wide Area Augmentation System. A system of satellites and ground stations that provide GPS signal corrections, giving up to five times better position accuracy than uncorrected GPS. See this for more.

Xbee: The commercial name of the recommend ZigBee-compatible radio modems commonly used by amateur UAVs. They can be found at sparkfun although remember you also need a board to mount it on like this one from sparkfun.

ZigBee: A wireless communications standard, which has longer range than Bluetooth but lower power consumption than WiFi.