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Multirotor Abbreviations & Acronyms.

By admin, 01/01/2014 - 23:29
Multirotor, drone, UAV abbreviations, acronyms and confusion

Welcome to the first article in the Multirotor Beginner's Guide.

The drone world is full of abbreviations, acronyms and confusion. We can’t even decide what to call the flying things; Drones, multirotors, multicopters, quadcopters, UAVs (unmanned aerial vehicle) and UAS (Unmanned Aerial Systems) are the main ones, but there are plenty more. While the pros understand these terms like their own language, beginners can be left feeling baffled.

My aim here to is to provide a useful reference to help beginners get to grips with the subject. I’ve highlighted the key ones.

  • ACC: Accelerometer - used to measure angular velocity or acceleration on a given axis.
  • AIL: Ailerons also known as roll.
  • AH: Altitude hold - a function provided by a good flight controller, which helps to maintain height using the Barometric Altimeter (BARO) or a Sonar module. 
  • AL: Auto leveling - a feature that the flight controller employs to stay level once tuned, uses the Accelerometer (ACC).
  • ALT: Refers to the height of the vehicle.
  • AP: Aerial photography.
  • ARTF: Almost ready to fly - these types of kits usually require a battery and radio control.
  • ATT: Attitude - angle of the vehicle (front to back relationship).
  • AUW: All up weight or max weight, the weight of the craft as it sits ready to fly, includes everything that would be attached such as batteries and cameras.
  • BARO: Barometric altimeter - used to measure altitude by sensing barometric pressure. Local pressure variations will therefore result in a change of the inferred altitude. This is an important consideration if you conduct automated landings; subtle pressure variations during the course of a flight will in affect invalidate the pre-take off home altitude datum. For instance if pressure decreases during the flight, the FC will think it’s higher than it actually is (remember atmospheric pressure decreases with height). 1mb (millibars) = 30 ft. While 1mb of pressure change is very unlikely during the course of a short flight, a precise BARO will detect and therefore reflect subtle variations pressure/height.
  • BEC: Battery Elimination Circuit - An electronic circuit designed to drop down and regulate the main supply voltage (i.e. 11.1v for a 3S Lipo). Typically employed to supply power at the correct voltage (typically 5V) to the receiver other auxiliary devices. Many ESC's have a voltage regulator built into it and the red wire of the 3-wire "servo" lead will have some reduced voltage (usually 5V although some ESC's allow you to select the accessory voltage), a non-BEC ESC will have no voltage in the red wire.
  • BOB: Break out Board - normally a sensor board that can be connected to the Flight Controller (FC), for instance a sonar.
  • CA: Cyrano adhesive - also known as superglue - be careful not to stick your fingers together with it!
  • CAA: Civil Aviation Authority, the name given to the agency that manages airspace in the UK.
  • CG or CoG: Center of gravity - a single point on your Vehicle where if suspended, there would result in full balance in all Axis. This is important consideration when building a multirotor, for optimum performance the CG should be in the center of the vehicle.
  • CL: CloverLeaf, another name for CP antennae.
  • CP: Circular Polarized, a type of antenna used in some FPV wireless video systems.
  • CW/CCW: ClockWise or Counter ClockWise, refers to the rotation of the propellers as viewed from the top looking down at the multirotor. Most multirotors require an equal number of props spinning in each direction, also referred to as Pusher Props (CW usually) and Tractor Props (CCW usually).
  • Diversity Tracking: An FPV setup that uses a dual receiver system that monitors the RSSI signal strength and picks between multiple antennas to display the best picture possible.
  • DJI: DJI, is one of the leading manufacturers of multi-rotor flight control systems, frames and accessories. 
  • eCalc: A handy tool to help design multirotor setups. It can calculate and evaluate motor/prop efficiencies to predict flight times (http://www.ecalc.ch/xcoptercalc.htm?ecalc&lang=en).
  • ELEV: elevator also known as pitch.
  • EPA: End Point Adjustment - a setting that defines how much the servo moves at full stick input.
  • ESC: Electronic Speed Control. An ESC is an electronic device that controls the speed of electronic motors (speeds up and slow down motor "RPM"). It’s the link between the receiver, the battery and the electronic motor, because the receiver’s signal output is to weak to power the motor. Many ESCs are programmable using either your RC transmitter or a special ESC programming card.
  • FC: Flight controller - the brain of the drone, it will stabilize and control the vehicle based on signals from the gyro, acc, GPS etc, mixing them with inputs from the transmitter provided by the pilot.
  • FHSS: Frequency hopping spread spectrum - It allows multiple radio systems to share the same frequency band without the individual radio transmitters interfering with each other, Tx and Rx have the ability to change the discreet sub-frequencies being used when signal quality drops below a set value, generally in the 900 Mhz and 2.4Ghz bands.
  • FOV: Field of view - usually measured in degrees. Wider field of views will allow you to see more, however you may get the props coming into shot.
  • FPV: First person view - Its the closest thing to flying, without actually flying! It requires a setup involving a forward facing camera and transmitter located on the drone, and a groundstation including a receiver and monitor to receive the downlink. It's a technique that allows you to see where you are flying in real time. Use video goggles and it's like you a sitting in the thing, pretty cool, huh?
  • FW: Firmware, software designed specifically for the piece of equipment it's being loaded into, use caution when upgrading to new firmware as quality control amongst vendors can be inadequate.
  • GCS: Ground Control Station - software/hardware used to remotely monitor/control your drone. Some platforms allow you direct GPS enabled drones using waypoints.
  • GND: Ground - mostly referring to the minus of the battery / power supply. Ground should always have electrical potential of 0V.
  • GPS: Global positioning system - a collection of satellites that together enable a receiver to calculate its position in space. Used to track movement or hold position at predefined coordinates. This system becomes less reliable in built up areas.
  • GYRO: Gyroscope measures - employed by the FC to help maintain craft orientation.
  • HAM: Amateur Radio Operator - a person who is licensed to use special frequencies by his country's government. Not all frequencies in all countries are allowed for RC and/or FPV. Improper use of radio allocations can disrupt licensed services and may pose a risk to military, emergency and commercial communication networks. All operators are responsible for knowing their local regulations.
  • IMU: Internal Measurement Unit, usually refers to the collection of sensors either on the flight control board or a separate circuit board.
  • JST: Type of power/battery connector.
  • LED: Light Emitting Diode, a small electrical component which can emit light at very low voltages and while using very small amounts of electricity, they come in a variety of intensities and colors and can be dimmed, flashed, pulsed, etc. via a digital controller.
  • LIPO: Lithium-ion polymer battery - most commonly used battery type in multirotors due to it’s high energy storage to density ratio. They have the potential to be dangerous and pose a serious fire risk if they are overcharged or damage. Ensure that you understand how to maintain them before using them.
  • LOS: Line of Sight - piloting your drone by keeping it within view from your position on the ground. Important with respect to safety and operating drones for commercial use. Flying beyond line of sight without aids is irresponsible; an out of control drone has the potential to do a lot of damage.
  • MAG: Magnetometer/compass used to let our "FC" know which direction it is pointed in compared to the Earths Magnetic field. They are badly affected by interference so ensure that they are located away from flight electronics, motors, ESC etc which generate a lot of electrical noise.
  • Mode 1: Tx throttle position - stick on the right.
  • Mode 2: Tx throttle position - stick on the left (the more widely used configuration).
  • MTOW: Maximum Take Off Weight, the highest weight possible for your helicopter or plane to safely launch for flight.
  • NOTAM: Notice to Airmen, a formal, time sensitive bulletin from a government aviation authority used to make operators within a defined area aware of potential hazards or non-standard conditions (i.e. parachuting, closed runways, temporary obstacles near airports or elsewhere, etc).
  • OSD: On Screen Display. Hardware that facilitates mixing data in a text or graphical form over an existing video feed. Used with FPV systems to generate an overlay of vehicle navigation (altitude, speed, position, attitude, etc.) and systems (battery voltage, current, mah consumed, etc.) info which will appear over the image generated by the FPV camera, looks similar to a cockpit heads up display, features dependent on brand of OSD used.
  • Pal / NTSC: Both are video formats. In the UK we use Pal format, but what’s the different? Pal has a resolution of 720×576 but lower frame rate 25 fps. NTSC on the other hand has a resolution of 720×480 but higher frame rate of 29.97 fps. Most equipment is compatible with both systems but we tend to choose Pal for its better resolution.
  • PCB: Printed circuit board - electronic components typically incorporate a PCB, the FC and PDB are examples.
  • PCM: pulse code modulation used to digitally represent sampled analog signals.
  • PDB: Power Distribution Board -  It's a centralised circuit board which is used to distribute power from the flight battery to the speed controllers and other auxiliaries. High wattage motors can draw a large current, so ensure that your PDB has an appropriate rating. 
  • PH: Position hold, in effect a hover. The system is normally reliant on "GPS" to figure out the vehicles location to enable it to maintain that position.
  • PID: Proportional Integral Derivative - a control loop, that attempts to minimize the difference between a measured process value and its desired value by adjusting the control input of a process. A PID based system is used tune flight characteristics.
  • PNP: Plug and Play - great if you don't want to solder.
  • Polarization: A subject related to FPV antennas. A matched polarized signal has both the transmitter and receiver signals matching in pattern having a large cross section of the signal returning to receiver and providing a great picture. Once a plane backs and / or polarization of the signals don’t match very well the intersecting cross section is small and gives a low quality or no picture.
    A matched polarized signal has both the transmitter and receiver signals matching in pattern having a large cross section of the signal returning to receiver and providing a great picture. Once a plane backs and / or polarization of the signals don’t match very well the intersecting cross section is small and gives a low quality or no picture.
  • PPMPulse Position Modulation - a way of sending (servo position) data. Data is defined by time spans between pulses. 
  • PWM: Pulse width modulation - a way of controlling power to inertial electrical devices, for instance motors.
  • RPM: Revolutions per minute or how many time a motor shaft will rotate 360deg in 60 seconds.
  • RF Radio Frequency: A circuit design that operates in a range of electromagnetic frequencies above the audio range and below visible light. Common frequency bands in use are 5.8gHz, 2.4gHz, 1.2gHz, 433mHz, 900mHz. Not all bands are available in all countries, and some require a HAM (Amateur Radio Operator) license.
  • RSSI: Received signal strength indication - a system to enable signal strength monitoring. Many receivers both radio and video have a RSSI pin on their board, this can be exploited and used to indicate signal strength normally displayed in a percentage to indicate strength or packets of data lost. The higher the packets lost the high the chance control or picture degradation will occur.
  • RTF: Ready to fly - Vehicle should be delivered with all assembly and configuration steps completed and ready for you to put it into service with a minimum of additional effort, however not always the case. Check for included items, a "Required to Fly" list, and Reviews and Comments; and the phrase "Some Assembly Required".
  • RTH: Same as "RTL" but is return to home - home being any giving starting position.
  • RTL: Return to launch - when enabled auto returns the multi to the place where it started or where GPS was activated.
  • RUDD: Rudder also known as yaw.
  • RX: Receiver which takes our "TX" commands and sends them to the "FC".
  • SPW: Skew Planar Wheel, a type of antenna used in some FPV wireless video systems.
  • THRL: throttle used to control motor "RPM".
  • TX: transmitter sends our commands to the "RX".
  • UAS/UAVUnmanned Aerial Vehicle - an aircraft without a human pilot onboard. Control is provided by an onboard computer, remote control or combination of both.
  • vRx: Video Receiver, the part of the wireless video system that enables remote monitoring/viewing of a live video stream from onboard camera. Up until now the video stream has had to be analog although digital high definition systems are beginning to become more affordable.
    vTx:  Video Transmitter, the part of the wireless video system that enables remote monitoring/viewing of a live video stream. European regulations place a limit of 25mW on 5.8GHz video transmitters. More powerful transmitters are used to boast range but require a HAM license.
  • VTOL: Vertical take off and landing.

If I have missed any, please add a comment below and I'll update my list.

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