Multi-Rotor Heli abbreviations, acronyms, secret codes, etc.!


Welcome to!!
Yes, you're right it's confusing and it's ok that you're confused...........there are a lot of perplexing terms and it's worse that the confusing terms are usually made into more confusing abbreviations!! So here, for your continued growth and understanding, is a guide to every abbreviation, acronym, and what must seem like intentional secret codes to help you achieve success with your multi-rotor helicopter. It's going to be a work in progress so there will be a lot of room for improvement until the list fills out, bear with me, we'll get it done.

and a 1, and a 2, and away we go!


AKA, Also Known As, a term used to indicate that there are other ways to refer to the topic or item being discussed
ARF, Almost Ready to Fly, most items needed to complete the build are included, generally speaking the frame, motors, props, tid-bits, landing gear, etc. (varies by manufacturer)
AUW, All Up Weight, the weight of the helicopter as it sits ready to fly, includes everything that would be attached such as batteries and cameras
BEC, Battery Eliminator Circuit, this term is misleading for multi-rotor heli builders, it was used originally with RC planes that would generally have a fueled engine and a separate battery for the receiver, electric motors then came to be and modelers still used a separate battery for the receiver until the ESC's began to have the ability to power the motor and simultaneously power the receiver thus eliminating the receiver battery, this term has come to mean that the ESC has a voltage regulator built into it and that 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
BL, BrushLess Controller, Mikrokopter specific term, see ESC
BNF, Bind And Fly, vehicles delivered with assembly mostly complete so that all that needs to be done is to have the pilot's compatible radio transmitter digitally linked to the receiver to be ready to fly
CAA, Civil Aviation Authority, the name given to the agencies that manage airspace in Australia, Canada, and the UK
CF, Care Free, a mode of flight similar to IOC, CF is a Mikrokopter and Hoverfly term
CH, Come Home, another way of saying RTH, Mikrokopter and others use this term instead of RTH
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 sometimes as viewed from the top looking down at the heli and sometimes as viewed from the cockpit (of a plane) looking out at the propeller in front of you, most multi-rotor helicopters require an equal number of props spinning in each direction, also referred to as Pusher Props (CW usually) and Tractor Props (CCW usually)
DJI, DJI, a manufacturer of multi-rotor and helicopter flight control systems
DOF, Degrees Of Freedom, a term applied to the IMU which is based on the quantity of sensors available to it to determine and maintain its spatial situational awareness (speed, location, heading, altitude, etc.), it typically includes a number that is a multiple of three (e.g., a 9DOF will incorporate a triple axis accelerometer + a triple access gyro + a triple access magnetometer), the higher the DOF prefix number, the more precise will be the IMU measurement
ESC, Electronic Speed Control, enables the brushless motor to spin, enables control, two power wires in, three wires to the motor, one 3-wire servo connection for control via your RC receiver or flight control system
FAA, Federal Aviation Administration, United States government agency that manages regulations and responsibilities related to airspace usage
FC, Flight Control (flight controller, flight control system), uses a computer processor, software, gyro's, accelerometers and a mysterious supply of magic smoke to maintain control of the helicopter according to your commands as sent to it via a wireless control system
FHSS, Frequency Hopping Spread Spectrum, 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
FOD, Flip Of Death, a result of system failure not pilot error despite what the pilot said about how it happened, can happen for a variety of reasons, more typical for quadcopters due to the (mostly) unrecoverable imbalance that occurs when one motor or prop fails, a rapid, sudden and spastic flip that usually results in a crash and damage, may be one flip or many depending on the level of panic the pilot is experiencing at the time of the "maneuver"
FOD (2), Foreign Object Damage or Foreign Objects/Debris, miscellaneous items that may be drawn into the helicopter (usually close to the ground) due to air circulation around the helicopter often having a negative effect on props, airframe parts, etc., may also occur in flight
FPV, First Person View, piloting your heli or plane via the use of a forward facing camera using the view from the camera as if you were sitting in the vehicle
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
FWIW, For What It's Worth
GPS, Global Postioning System, a collection of satellites that together enable a receiver to calculate its position in space (location over the ground and altitude), this equipment is usually separate from the flight controller but integrated to work with it
GUI, Graphical User Interface, an interactive, visually-dependent software presentation
HF, Hoverfly, a manufacturer of multi-rotor flight control systems
HK, Hong Kong or
IMHO, In My Humble Opinion, may also mean In My Honest Opinion
IMU, Internal Measurement Unit, usually refers to the collection of sensors either on the flight control board or a separate circuit board, typically consists of three triple axis sensors (three gyros, three magnetometers and three accelerometers), other sensors may also be included such as a pressure sensor for altitude sensing control
IOC, Intelligent Orientation Control, DJI's term for this feature, a control mode where Yaw, Pitch, and Roll revert to only left/right/forward/back, heading of the heli no longer factors into control, dependent on magnetometers for control
KF, Kalman Filtering, a software algorithm within FC's firmware used to improve the FC's ability to control the helicopter, developed by Dr. Kalman at NASA in the mid 60s making IMU functioning possible
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
LG, Landing Gear
LiPo, Lithium Polymer, a type of battery commonly used to power multi-rotor helicopters and many other devices, see our LiPo tutorial HERE
LOS, Line of Sight, piloting your plane or heli by keeping it within view from your position on the ground
MK, Mikrokopter, a manufacturer of multi-rotor flight control systems
MR or MRC, Multi-Rotor Copter, one of many ways to refer to a heli that flies on multiple rotors/props instead of one main rotor
MRF,, the world-wide multi-rotor community!
MTOW, Maximum TakeOff Weight, aka MGTOW (Maximum Gross TakeOff 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, inop aids to navigation, closed runways, temporary obstacles near airports or elsewhere, etc.)
OP, OpenPilot, a manufacturer of multi-rotor flight control systems
OS, Operating System, usually refers to a Microsoft or Apple product, can also be Android
OSD, On Screen Display, 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
PBKC, Problem Between Keyboard and Chair, not related specifically to multi-rotor heli's, not to be taken personally it's a less flattering way way of saying "user error"
PDB, Power Distribution Board, a centralised circuit board that is used to distribute power from the main source like a battery or flux capacitor to the multiple ESC's/motors, may also have additional power taps for accessories
PH, Position Hold, requires GPS, a feature that enables the heli to maintain position over a fixed point, "dynamic" position hold means you can move the heli around while in PH and when you let go of the sticks it will maintain that new position
PID, Proportional Integral Derivative, a control system whereby the difference between a desired position is compared to the actual position and responses are calculated so that the response commands are optimized and flight performance is without wobbles or undue drifting
POI, Point of Interest, a term used by DJI and MK, a function of the FC and GPS that can keep a camera mount pointed at a point on the ground while the helicopter flies around it or by it
POS, Piece of Sh**, a subjective claim regarding quality or value, usually after significant personal expense and effort has been wasted, doesn't necessarily keep others from wanting to buy one too (strange)
PWM, Pulse Width Modulation, the method of signal carry by which individual radio channels are controlled, pulses are sent at set intervals using either a high or low, the duration of the high within the fixed pulse length determines the control command, once the high is sent the signal returns to a low for the remainder of the fixed pulse duration
RC, Radio Control or Remote Control, use of a wireless system for control of your heli or plane, consists of a Transmitter and Receiver, may also have additional sensors/features depending on the manufacturer and model
RTF, Ready To Fly, heli or plane is delivered with all assembly and configuration steps completed and ready for you to put it into service with a minimum of additional effort, varies widely by shop and manufacturer
RTH, Return to Home, requires GPS for navigational guidance, a feature that enables the heli to fly autonomously back to the point from which it took off
Rx, Receiver, the part of the radio control system that flies on the helicopter and relays control commands to the FC
SPW, Skew Planar Wheel, a type of antenna used in some FPV wireless video systems
SRH, Single-Rotor Helicopter, a helicopter which relies on a single, large span rotor for lift and a very talented pilot for control
sUAS, small Unmanned Aerial System, the FAA's official designation for remotely piloted vehicles below a certain size and weight
TBH, To Be Honest
TL, Tau Labs, a manufacturer of multi-rotor flight control systems
Tx, Transmitter, the part of the radio control system that you use to remotely manipulate the flight path and functions of the helicopter
UAS or UAV, Unmanned Aerial System (or Vehicle), an airborne system that operates without an onboard pilot/crew
vRx, Video Receiver, the part of the wireless video system that enables remote monitoring/viewing of a live video stream from helicopter, 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 from the helicopter
WKM, WooKong(Multi-Rotor), DJI brand flight control system
XA, Xaircraft, a manufacturer of multi-rotor flight control systems

TERMS (that have stubbornly resisted our attempts to abbreviate them)

Accelerometer, a type of sensor that can detect lateral movement, three used together can detect lateral movements (accelerations) in all three axis
Carefree Mode, see IOC above
Gyro, a type of sensor that can detect rotational movement, three used together can detect rotational movements in all three axis

Feel free to post requests/suggestions for additions to the lists above.


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A few more: PPM, Atti, FASST, S-BUS, T8FG/8FG, PAL, NTSC, HDMI, Alexmos, eCalc
All configs: Octo, Hex, Y6, X8, etc
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DESST - A DJI term related to RC radio technology but I have no idea what it stands for!!!

Maybe someone reading this will know and/or id the source for this new acronym!


DOF (which you already have) are also used in Photography and because a lot of people in here are into Aerial Photography it would maybe bee a good idea to have that also just to clarify.

DOF=Depth Of Field


This is great Bart, there's definitely a learning curve to catch up on these! Here's a few more I had to look up the first time I saw them... please correct anything I got wrong.

OLED - Organic Light-Emitting Diode (tiny screen that allows programming without laptop)
CAN - type of connection port
RS232 - pinned Serial data port
UART - chip that converts RS232 to USB
SBG - Simple Brushless Gimbal
PMU - Power Management Unit (?)
INS - Inertial Navigation System
PU Gel - Polyurethane Gel Elastomers (isolates vibration)
EMI Zone - Electromagnetic Interference Zone
BVR - Beyond Visual Range

great.... just one minor correction.

UART = A universal asynchronous receiver/transmitter. It converts data between parallel and serial forms....and was common well before USB.


Whoops - PPM not PPW
Please add "PPW" as in "You'll be presented with a window featuring a column on the right labelled 'Select Device', there you select the EzUHF 8ch. Rx and in the configure tab you can configure PPM out on CH1 using Mikrokopter mode (other channels will remain working normally)."


"RSSI" as in 12 bit digital to analog converter (DAC) used to convert pwm signal that come from Immersion EZUHF receiver to 0v-3.3v analog output so it can be used on any OSD as analog RSSI (Receiver Signal Strength Indicator). You just plug it in EZUHF receiver where you configure RSSI out channel (usually it is CH8), on other side you plug it in your OSD. Configure your osd that 0v is minimum or 0% RSSI and 3.3V is full or 100% RSSI. If OSD doesn't have that option, you can plug it in second battery voltage input so RSSI is shown as volatege. 0v to 3.3v (0v = 0%, 3.3v = 100%)."

The abbreviation table has come a long way since November!

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This is really useful, thanks!

Would love to see a similar thread (or part of this one) with the names of different electrical connections & maybe example images... If I need something, I often know what it looks like but have no idea what it's called so finding them can be difficult!


Eugene Dean

New Member
Thank you so much for explaining what all these secret acronyms mean. Drones have become my new obsession, but I have been a little discouraged by all the jargon. Researching information is difficult when one of these terms is used in almost every sentence. With this list, I will sound like a professional drone operator in no time.


@Bartman under CP coupd you add RH (right hand) and LH (left hand) - thanks.

As in:"Because 1.3 has far superior range and penetration. I run 1.3 on everything. And I also run it on the ALTA. I use RHCP and LHCP on adjacent channels and it works great."