3D Robotics

FAQ: Confusing terms explained

This is a glossary of some of the terms you may read on DIY Drones. Please feel free to suggest others in the comments below!

  • 2.4 GhzThe 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.
  • AHRSAttitude and Heading Reference System. See explanation here.
  • AMAAcademy of Model Aeronautics. The main US model aircraft association. Generally hostile to amateur UAVs, which are banned on AMA fields. But each AMA chapter and field may have slightly different policies, and it's possible to test airframes and some technology on AMA fields without violating the association's rules.
  • ArduCopterRotary-wing autopilot software for the APM and Pixhawk electronics
  • ArduPlaneFixed-wing autopilot software for the APM and Pixhawk electronics.
  • ArduPilot: The overall autopilot project that ArduCopter, ArduPlane, and ArduRover live within
  • ArduRover: Ground and water autopilot software for the APM and Pixhawk electronics
  • ArduinoAn open source embedded processor project. Includes a hardware standard originally based on the Atmel Atmega (and other 8-bit) microprocessor microcontroller and necessary supporting hardware, and a software programming environment based on the C-like Processing language. Official site is here.
  • 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.
  • BASIC StampA simple embedded processor controller and programming environment created and sold by Parallax. Often used to teach basic embedded computing and the basis of our autopilot tutorial project. Parallax also makes the very capable Propeller chip.
  • Bluetooth: A wireless technology standard for exchanging data over short distances (using UHF radio waves in the ISM band from 2.4 to 2.485 GHz) from fixed and mobile devices, and building Personal AreaNetworks (PANs). Originally conceived as a wireless alternative to RS-232 data cables. It can connect several concurrent devices.
  • Bootloader Special code stored in non-volatile memory in a microprocessor that can interface with a PC to download a user's program.
  • COA Certificate oAuthorization. A FAA approval for a UAV flight. See this for more.
  • Eagle file The schematic and PCB design files (and related files that tell PCB fabricators 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.
  • DCM Direction Cosine Matrix. A algorithm that is a less processing intensive equivalent of the Kalman Filter. See this for more.
  • DSM / DSM2 / DSMX: Spektrum, an RC equipment maker, refers to their proprietary technology as "Digital Spectrum Modulation." Each transmitter has a globally unique identifier (GUID), to which receivers can be bound, ensuring that no transmitter will interfere with other nearby Spektrum DSM systems. DSM uses Direct-Sequence Spread Spectrum (DSSS) technology.
  • DSSS: Direct-Sequence Spread Spectrum is a modulation technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that modulates the carrier or broadcast frequency. The name 'spread spectrum' comes from the fact that the carrier signals occur over the full bandwidth (spectrum) of a device's transmitting frequency..
  • EEPROM:  Electonically Erasable Programmable Read Only Memory. A type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g.,static calibration/reference tables.  Unlike bytes in most other kinds of non-volatile memory, individual bytes in a traditional EEPROM can be independently read, erased, and re-written.
  • 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 (BEC), which provides power for the RC system and other onboard electronics, such as an autopilot.
  • FHSS  Frequency-Hopping Spread Spectrum is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver.advantages over a fixed-frequency transmission: Advantages: 1. Spread-spectrum signals are highly resistant to narrowband interference. The process of re-collecting a spread signal spreads out the interfering signal, causing it to recede into the background. 2. Spread-spectrum signals are difficult to intercept. A spread-spectrum signal may simply appear as an increase in the background noise to a narrowband receiver. An eavesdropper may have difficulty intercepting a transmission in real time if the pseudorandom sequence is not known. 3. Spread-spectrum transmissions can share a frequency band with many types of conventional transmissions with minimal interference. The spread-spectrum signals add minimal noise to the narrow-frequency communications, and vice versa. As a result,bandwidth can be used more efficiently.
  • FPVFirst-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.
  • FTDIFuture Technology Devices International, which is the name of the company that makes the chips. A standard to convert USB to serial communications. Available as a chip for boards that have a USB connector, or in a cable to connected to breakout pins. 
  • GCSGround 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.
  • GIT: A version control system for software developers. The DIY Drones team use a Git-based service called GitHub.
  • Hardware-in-the-loop simulationDoing 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.
  • I2CInter-Integrated Circuit. A serial bus that allows multiple low speed peripherals, such as sensors, to be connected to a microprocessor. See this for more.
  • IDEAn integrated Integrated development Development Environment, such as the Arduino editor/downloader/serial monitor software. Often includes a debugger.
  • IMUAn inertial Inertial measurement Measurement Unit. 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. One technique for doing this is the Kalman filter (see below).
  • Inner loop/Outer loopUsually 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).
  • INSInertial Navigation System. A way to calculate position based on an initial GPS reading followed by readings from motion and speed sensors. Useful when GPS is not available or has temporarily lost its signal.
  • ICSPICircuit Serial Progammer. A way to load code to a microprocessormicrocontoller. 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 FilterA 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.
  • LOSLine oSight. Refers to a FAA requirement that UAVs stay within a pilot's direct visual control if they are flying under the recreational exemption to COA approval.
  • LiPo Lithium Polymer battery, aka LiPoly. Varients include Lithium Ion (Li-Ion) battery. This battery chemistry offers more power and lighter weight than NiMh and NiCad batteries.
  • MAVMicro Air Vehicle. A small UAV. More here.
  • MAVLink: The Micro Air Vehicle communications Link protocol used by the ArduCopter and ArduPlane line of autopilots. See this for more info on MAVLink.
  • Microprocessor: A microprocessor incorporates the functions of a computer's central processing unit (CPU) on a single integrated circuit or at most, a few integrated circuits (system clock, memory, peripheral device drivers).
  • Microcontroller: A microcontroller (sometimes abbreviated µC, uC or MCU) is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form flash or EEPROM is included on the chip, as well as a typically small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications.
  • 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
  • OSDOn-screen Screen Display. A way to integrate data (often telemetry information) into the real-time video stream the aircraft is sending to the ground.
  • PCBPrinted Circuit Board. In our use, a specialized board designed and "fabricated" for a dedicated purpose, as opposed to a breadboard or prototype board, which can be used and resused re-used for many projects.
  • PCM: Pulse Coded Modulation. A method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, Compact Discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps. Primarily useful for optical communications systems, where there tends to be little or no multipath interference
  • PICPilot ICommand. 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.
  • PID Proportional/Integral/Deriviative control method. A machine control algorithm that allows for more accurate sensor-motion control loops and less over-control. See this for more.
  • Pixhawk: The next-gen 32-bit autopilot, which succeeded APM. A collaboration between 3D Robotics and the PX4 team at ETH, the technical university in Zurich
  • POIPoint of OInterest, also known as Region of Interest. Designates a spot that a UAV should keep a camera pointed towards.
  • PPM: Pulse Position Modulation. Signal modulation in which a set number of message bits are encoded by transmitting a single pulse in one of possible 2(number if message bits) time-shifts.
  • PWMPulse Width Modulation. The square-wave signals used in RC control to drive servos and speed controllers.
  • ROI: Region of Interest. Also known as Point of Interest (see above)
  • RTLReturn TLaunch. Return the aircraft to the "home" position where it took off.
  • Shield: a specialized board that fits on top of an Arduino to add a specific function, such as wireless data or GPS
  • SiRF IIIThe SiRF is a technology company that has developed a standard used by most modern GPS modules. Includes SiRF III binary mode, which is an alternative to the ASCII-based NMEA standard described above.
  • SketchThe program files, drivers and other code generated by the Arduinio IDE for a single project.
  • SVNShort for the Subversion Version-control Number repository used by the DIY Drones (in the past) and other teams for source code.
  • ThermopileAn 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.
  • UAVUnmanned 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).
  • WAASWide 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.
  • ZigBee (related: Xbee): A wireless communications standard, which has longer range than bluetooth but lower power consumption than WiFi.
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  • What confused me was reading on the different sites Pixhawk, PX4, APM, PX4FMU and then needing some modules to make things work.

    Still most of the documentation that I am able to find has to do with APM and not Pixhawk so for someone new that doesn't know they run the same software it makes things difficult.

    Also doesn't help that the Pixhawk site (http://pixhawk.org/users/tutorials) has "PX4 autopilot" logo on it with a different board than what the Pixhawk actually looks like.

  • "Fly-By-Wire" is an archaic, aviation term from the 1980's.
    But, it is still useful in describing the difference between
    the direct control of a conventional, RC aircraft and a
    RC aircraft that is computer-controlled, with direction
    from a pilot.

    Another term from the 1980's is "Glass Cockpit," which describes
    the change-over from standard, mechanical avionic instrumentation,
    to LCD display and touchscreen control, like using an iPAD to control
    the Parrot AR Drone and Parrot BeBop.

  • thank u sir:)...i a now quite clear with the concepts..When i went through the construction of drones i found that that ATmega is being used..Why specifically ATmega..Why not 8051 or other controllers?What is the  main purpose of this controller in construction of drone? What does this controller do?

    Thanks in advance

  • Admin


    As explained in other Newbie blog,  reading the wiki will make it easier for your get better picture.  Explaining you here would involve repeating the wiki again.

    As to your question

    1. the GPS in the airframe connects to autopilot and supplies its location info to the micro-processer for further process inside the airframe MC.

    The GPS in groundstation supports/supplies its location in/to the mission planner  or GCS software to point it's location on the map. So you will see your location( GCS- ground control software/station) and your UAV location's at the same time on the map in GCS. Hope this clears your doubt.

    2.  There is not such "tool" to develop entire UAV in single plateform.  A UAV involves many components but fundamentally it is software/s and lot of hardware devices put together. You cannot develop all of them your self.  You will probably buy most of the subcomponents like motors, servos, battery,  RC control system ( remote controller and receiver) etc. Developing/designing/fabrication of these components are beyond 95% of enthusiasts abilities. Buying them and integrating them is easier first steps, testing and flying them is what most of us do. Some of these that we buy from others( vendors, manufacturers like 3DR, sparkfunhobby king , RCtimer& many more ) are

    1. Motor for propulsion

    2. Airframe of your choice but you can make them from kit or from scratch if you have little patience and experience.

    3.  Servos for controlling the control surfaces.

    4.  Radio controller and its receiver.

    5. Batteries and power modules( ESC , BESC etc),   fuel for gas motor.

    6.  Open or closed auto pilot

    7.  Cameras and video Tx/Rx system,  antennas for them

    Micro controller programming software depending on MC , this can be free or paid ver from manufacturer.

    There are some things that you can do, some things you can't due to complexities involved.

    Good luck and happy flying.

    DiyDrones Support

  • A lot of questions arises sir kindly help out..

    1)what is the main purpose of APM planner 2.0? i have installed in my system ...now how should i proceed and what should i do?I am controlling the UAV at safe altitude with the help of GPS.If so a GPS module is seen connected with the ATmega168 microprocessor in the UAV and  another GPS module at the sender side is the APM planner 2.0? Is it so..how the GPS of my UAV is located...

    2)Is there any software tool available to develop my entire UAV vehicle...if so please provide me the link

  • A lot of questions arises sir kindly help out..

    1)what is the main purpose of APM planner 2.0? i have installed in my system ...now how should i proceed and what should i do?I am controlling the UAV at safe altitude with the help of GPS.If so a GPS module is seen connected with the ATmega168 microprocessor in the UAV and  another GPS module at the sender side is the APM planner 2.0? Is it so..how the GPS of my UAV is located...

  • Please correct it, PID: proportional-integral-derivative instead of Proportional/Integral/Derviative

  • I would add Telemetry.

  • On the mission planner application:



    Both are options for connecting I think...

  • 3D Robotics

    rik: thanks for the typo catch. Fixed!

This reply was deleted.