MultiCopter Acronyms

[firey1]

ACC = accelerometer used to measure angular velocity or acceleration on a given axis
AIL   = ailerons also known as roll
AH    = altitude hold will help maintain height uses "BARO"
AL    = auto leveling means the flight controller can stay level once tuned uses "ACC"
ALT = altitude as in how high you are
ATT = attitude as in what angle the multi is currently in
APM= Arducopter flight board
Arducopter = a form of flight program software
AUW = all up weight or max weight with lipo ready to fly
AVP = Ariel video photography possibly what you will want to do
BARO = barometric altimeter use to measure altitude by using barometric pressure
BEC = BEC allows such a model to carry only one battery (the motive power battery) instead of two (motive power, and a separate battery to operate the R/C equipment)
BOB = break out board normally a sensor board that can be connected to the "FC" via the i2c port
BS    = bulls**t used to explain "some" of what you will read
CA    = Cyrano adhesive also known as superglue bonds in seconds watch you fingers
CCPM = cyclic collective pitch mixing more for heli fliers but helps explain how we fly
Crius = make of flight board for multi wii and mega pirates
DD    = direct drive prop designed to go straight on a motor shaft without a gear reduction
DOF = degree of freedom so 6DOF (gyro and acc) and 9DOF (gyro acc and baro or mag) give clues as to whats on the "IMU"
ELEV = elevator also known as pitch
ESC = escape better known as speed controller we use this to speed up and slow down motor "RPM"
FC    =  flight controller
FHSS = frequency hopping spread spectrum a way to transmit radio signals
FOV   = field of view from the multi wider the FOV the less chance of seeing props with a gopro
FP    = fixed pitch normally associated with rc helicopters
FPV   = first person veiw basically this setup lets you see where you are going LIVE and in real time
F W = flightWare another name for what flight program your using
GPS   = global positioning system used to track movement or hold position at predefined coordinates
GYRO = gyroscope measures or help maintain orientation
HEXA   = hexacopter 6 motors no servos all motors on same level
I2C   = inter-IC I2C is a multi-master bus meaning many devices can be connected to the same port each acting as his own master
IMU    = inertial measurement unit which is a "BOB" containing sensors that send data to the flight controller
LIPO = should be Li Po lithium-ion polymer battery our preferred power source right now
MAG   = Magnetometer/compass used to let our "FC" know which direction it is pointed in compared to the Earths Magnetic field
MegaPirates= a form of flight program software that copies Arducopter
Multi Wii = A form of flight program software
OCTO = octocopter 8 motors no servos all motors on same level
OP    = original poster
OSD = on screen display
OT    = off topic
PDM =  Pulse Density Modulation
PCM = pulse code modulation used to digitally represent sampled analog signals
PH    = position hold normaly uses "GPS" to figure out where we are and maintain position
PPM SUM = pulse position modulation i,e instead of 5 servo leads sending 5 signal we send 8 signals down one wire (signal)
PWM = pulse width modulation a way of controlling power to inertial electrical devices
PROP = propeller a critical item in multi rotor design, motor choice battery selection
QUAD = quadcopter 4 motors no servos yaw achieved by varying speeds of motors
RPM = revolutions per minute or how many time a motor shaft will rotate 360deg in 60 seconds
RTF = ready to fly but thats not always the case
RTH = same as "RTL" but is return to home, home being any giving starting position
RTL = return to launch a very handy GPS function that 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"
SF    = slow fly prop designed to go on a motor using a gear reduction to lower prop speed
SimonK = An ESC flash software optomised for multirotors
SONAR = ultrsonic range finder horizontally it can be used to avoid objects from below verically it can avoid objects from any side it faces
THRL = throttle used to control motor "RPM"
TRI   = tricopter 3 motors and one servo for yaw
TX    = transmitter sends our commands to the "RX"
UBEC = Universal Battery Elimination Circuit (UBEC) is a ';switch mode'; DC regulator
VTOL = vertical take off and landing
W,TF = hey what just happened?
WOT = wide open throttle or throttle stick at max up

[firey1]

PID is an acronym for "Proportional, Integral, Derivative". These are in fact 3 algorithms that work together to form a basic "control system".

There are several keywords that I have to introduce before we go on to tuning.

Plant - the thing that you control. In our case, it';s an aeroplane or multicopter.
Plant Output - normally it would be just plain fun  but for the purpose of this tutorial, it';s things like pitch, roll and yaw.
Output rate - how quickly, in a unit of time, the output changes. So yaw rate is how fast does your aircraft spin.
Setpoint : the intended value of the output. Let';s say, that you want your multicopter not to spin - just keep the current heading. This means that your setpoint for the yaw rate is zero.
Error. This is the important one. It';s not that your quadcopter makes errors. Well it kind of does, but who doesn';t? For this tutorial, error is the difference between setpoint and actual plant output.
Control Action. This is also the plant input. Basically it is what the control algorithm calculates the plant has to do. For example, if you were to control the multicopter yourself, you would apply rudder to correct for the yaw rate.
To have any kind of control over the plant, one has to be able to measure plant output (yaw rate), estimate the error, apply a "control algorithm", to the error signal, and eventually, apply the Control Action to the plant.


Tuning
Ok, the above terms are clear, but how do I tune the PID?

There is a number of scientific methods to do that, but here I will present a very simple "do it yourself" method - no maths! With a bit of practice, it should give satisfactory results. Remember, read first, then do.

OpenPilot uses a ';dual loop'; controller, with internal PI loop and outer PI loop. the "D" part is not used by default.

Start by switching to the "rate" mode in the Input Configuration - Flight Mode Switch tab. In this mode, attitude stabilisation is not used and you can safely ignore it';s settings.
Set the settings to default. If they don';t work for you, set the Proportional setting to a low value like 10, and Integral value to zero.
Set Proportional gain to a small value. Try to fly. It will not feel well - it will feel ';unstabilised'; and uncontrollable.
P is "proportional". The control action will be proportional to the error. This simple method gives suprisingly good results for many plants.
Increase the P by 15%. Increasing by less will probably not make much difference, and increasing more risks you to overdo it. If the P gain is at appropriate value, the plant will begin to feel "responsive" to your setpoint.
Continue with point 4 until given output begins to "oscillate". If it feels like oscillating, or the motors yell too much, reduce P by 10% and save the result.
If you find yourself stepping by less then 5% it is probably not worth it - better to have the "P" term a bit low rather than too high.This applies to other terms too.
The goal should be to obtain as ';stiff'; or ';responsive'; response to the setpoint as possible, but without introducing oscillations. Oscillations are bad.
Then goes the "I" gain. I stands for integral. I trust that it was zero for you while tuning "P". It';s a parameter that corresponds to a kind of memory of error over time. Let';s say, that error is, eg. 5 degrees, and it does not decrease despite corrective action from Proportional algorithm. This error gets accumulated in a special accumulator - and as this accumulator fills up, the Integral algorithm will add more and more to the corrective action. This way some imperfections of balance of your airframe can be corrected, for example if the battery is not central, or something has landed on one of the arms  It might also help to fly straight in windy conditions. Be the more carefull with this parameter though. When set too high, it can introduce strange, slow (low frequency) oscillations that will be annoying for you to compensate with your sticks.
By this point you probably know what to do - start with a small value, and increase slowly. 20% steps are OK. Do more testing this time - as the effects of I parameter are rather subtle, unless you overdo it, in which case it becomes annoying.
When you are happy with the response of the multicopter in the rate mode, you can start to tune outer control loop - Attitude stabilisation. However, remember that it will not work correctly if the inner loop is not tuned well.
Start by setting the Integral term to zero and Proportional to a small value. Note that in the Attitude stabilisation mode, the effect of the control sticks is very different from the rate mode - as you are now controlling the attitude and not the rate. Kind of obvious but might be surprising to newcomers.
As before, increase the proportional term by 10-15% and try flying. The multicopter will become responsive and eventually controllable. Again, if the propotional gain is too high, you will get oscillations but they will be kind of slower this time. In such case back off the Proportional term a step back.
Same as before goes for the Integral parameter in the Attitude stabilisation mode. You should generally need less or zero of it in the outer loop.
Finally, if you feel like an expert, you can try the D (derivative) parameter.
D is for "derivative" over time. Some people call it the accelerator parameter, because it will try to predict what the plant (or you) is trying to do and magnify the Control Action. In other words, if the error is increasing, it will add more to the Control Action. If the error is decreasing fast, it will reduce the Control action, to make the error approach zero more carefully. This parameter can have positive effect on overall stability of the plant, eg. by helping to overcome the inertia of ESC and motor/propeller faster. But a bit of warning here. D parameter makes the plant more sensitive - if your multirotor oscillates, "D" will make oscillations worse. "D" can amplify the measurement noise (eg. when the gyro is not measuring the pitch accurately enough). It can also get into a complicated interaction with P and I terms. If use D, you might need to re-tune P and I to keep the plant well stabilised. So, all in all - use carefully. In any case, remember to start in the "rate" mode (inner loop only), as the Attitude mode (outer loop) cannot correct for incorrect operation of the inner loop.

[Gaza07]

Excellent post Mike I have made it sticky 

[Marty McFly]

A lot of good work there Mike,well done,Marty. :scotland:

[Augerin]

Bravo! Just what I was looking for. Loads of info in one place. Fantastic! 

Could there be a sticky/link from the newbies thread - Just so us novices don';t miss it?

[Oakie]

TX    = transmitter sends our commands to the "TX"

Correction needed
TX    = transmitter sends our commands to the "RX"

[kilby]

Actually Tx should be more along the lines of Transmit, can be applied to Radio transmitter or serial transmission data pin/pad ....

Considering I';m not unusual in having a telemetry radio and serial pins on the fat quad

Something similar for Rx

[mosstrooper]

Just starting out and I came here to learn about Acronyms used to baffle us beginners. I read them all but didn';t see BEC - UBEC - VCC - PDB - comp PWM, or what exactly this is. 3x #F-20A/15202 Hobby King 20A ESC 3A UBEC = $20.91
all of which (and more) appear in these forums.

I have viewed a lot of Tricopter builds on the Tube, some use a Power Distribution Board some don';t, is there any reason for this?

Hoping to get started.
Mosstrooper.

[firey1]

power distribution boards there was a feeling that they created a strong interference under the flight controller so some use direct lines to the esc and join close to the connector plug

I have tried both and not noticed any difference between the two methods

[firey1]

TX    = transmitter sends our commands to the "TX"

Correction needed
TX    = transmitter sends our commands to the "RX"


DONE

[darren]

A very informative post no doubt. Thank you for the time and effort you have put into it. 

[Calomile]

1D10T - A common error that typically manifests in the configuration and operation of UAS.
PEBQAC/PEBQAT - Problem Exists Between Quad And Controller/Transmitter. Substitute quad for drone where appropriate.

[atomiclama]

RTFM Read the F*&^&%^ Manual  ::)

[yorkiejeff]

what is acro? think it involves the handling but not sure what it is.

[Calomile]

Acro is short for acrobatic mode, it means that the quad will maintain whatever angle you put it at without self levelling. So if you want to fly directly at the ground upside down the quad will do nothing to stop you. Fortune favours the brave...

[yorkiejeff]

rrriiiiiiight, might leave mine of that till i canactually fly it properly then  ::)

[nub]

Acro is short for acrobatic mode, it means that the quad will maintain whatever angle you put it at without self levelling. So if you want to fly directly at the ground upside down the quad will do nothing to stop you. Fortune favours the brave...

hehe nice way to explain it ::)

[Slayer23]

could I add a couple I think as a noob I will become familiar with

FUBAR = F*!$ed up beyond recognition (my first or second crash will result in this I just know it)

SNAFU = situation normal another F*!? up (as I know I am bound to wire something wrong and allow the magic smoke to escape !!!)

[hoverfly]

My favourite. NORWICH.  ::)

[Slayer23]

Is that in Norwich way did that go ????

[Bad Raven]

My favourite. NORWICH.  ::)

Which technically should be KORWICH...................

[hoverfly]

Which technically should be KORWICH...................

Pickey  ...

[rchobby]

wow these are so complete terms
thanks mate,