Beginners Guide Part 6 - Your First Airplane

Choosing your first airplane

First, do not allow yourself to be easily discouraged. This is a hobby for people with patience and persistence. Flying is something that requires precision, quality and knowledge. Just think how many centuries people have dreamed of ways to fly! And today, every modeler has basic knowledge of the aerodynamics, materials and construction that were secret even for Da Vinci. When you learn to project, create and manage a flying device, you can say that you are in a privileged circle of those who have mastered the "flying secret".

Do not worry if your first model will crash and break - surely it will. Sooner or later. Crashes are also happening to those modelers with 20 years of experience. Sometimes it happens without a "human factor" - radio disturbances (most commonly with cheap Chinese radios), battery downs, etc. The author of these lines has crashed and losed models at all possible ways.Only thing that I've never had is a "mid-air collision", that is, an collision with another model. But there were unsuccessful acrobatics, poor landings, hitting the table and trees, landing on the water, turning off the radio, breaking the wing in the air, losing sight of the model and losing the model in the tall grass after crash.

Choosing the first model will be divided into two categories, purchased models and models you build.

Buying a model

First, take the model that's nice for you. Do not look at aerobatic and 3D models as well as military warbirds (especially scale models from the first or second world war) because they are very demanding for flying.
Avoid symmetrical profiles and focus on high-wing aircraft with dihedral wings that tend to self-stabilize and forgive mistakes of a pilot. The beginners model is not fast, and therefore the speed during approaching and landing is low so you will have more time to react and correct the eventual mistakes.

To begin with, you need a model that is slow enough and stable enough in all weather conditions and that it forgives common beginners mistakes. Also, repairing of the model must be as simple as possible,and the spare parts must be available.

In the early days, the RC models were sold as a wooden balsa kit, which was supposed to be assembled, so the chances for beginner to properly build, setup and fly their first model were quite small. Especially if everything is done without the supervision of a more experienced modeler. Today, beginner models are mostly sold as ARF (Almost Ready to Fly) and RTF (Ready to Fly) models of various foam materials, meaning they can be assembled for only a few hours. RTF models come with all RC components already installed, battery, charger, motor and remote controller(radio).
My advice is to avoid cheap Chinese "all in one" packages with the model, radio and electronics together because they mainly contain the basic 4 channel radios and the most basic (cheapest) electronics.

With each model, the manufacturer will also indicate the number and type of servo motors required for this model. Feel free to buy the recommended/cheapest servos to begin and do not be burdened with servo speed and servo torque. Just look at the mass of the components. If the manufacturer says 9 gram micro servo do not put 40 gram servo "to get tougher".

Before the first flight it is important to check if the center of gravity (CG) and it must be as indicated in the model instructions. The center of gravity can be adjusted by moving the battery or by adding lead to the nose or tail. Beginners, as a rule, neglect the question of the center of gravity, which is just a recipe for disaster. If the center of gravity is not exactly where it should be (plus-minus millimeter or two), there is no chance the model will fly properly. For orientation, the CG, ie the center of gravity, should be at 1/3 of the wings width measured from the front edge of the wing (leading edge). After the first few flights, the position of the CG is usually slightly adjusted, for example, it moves slightly backwards, if the model is not sufficiently movable and noses over or at front if model is unstable and difficult to control.
As a rule, on the first flight, it is better for your model to have a bit of weight on the nose than on the tail, because if it is too big on the tail, the model (any type) is uncontrollable..

Second important thing is that control surfaces have to move perfectly. There is no purpose to go with a model that "does not work properly". You will not achieve anything else except you will crash the model. Therefore, it is necessary to check whether the servo can perform full movement in both directions, that the control rods do not bend, whether the rudder, ailerons and elevator always returns to the neutral position when the stick is released, etc. In some foam models there are no hinges for the control surfaces (ailerons, rudder and the elevator), but just pressed foam - it is therefore necessary to disconnect the control wire and loosen the control surface by moving it several times with your fingers until it is very easy to move. Otherwise, the servo will not have enough strength to move the surface, or it will not return to the neutral position.

Third on what you have to pay attention to are the motor and the propeller - is everything well screwed? They sometimes pack the model in a box with insufficiently screwed propeller and/or engine mount, and the buyer does not even pay attention for it. Do not forget that the RC model is not a harmless toy. Injuries are possible, especially from the propeller.
Never put yourself or others near the propeller or in front of it. When testing a motor, it is best to protect your eyes, for example, with sunglasses, just in case.

So what model would be the best to start with? It is clear that it should be cheap, easy to handle and resistant to crashes. This will certainly be a high-wing airplane, lightweight and stable, or electric glider, and it is desirable that the motor is behind the wings, so it would not be damaged when model lands or crashes at the nose. Today, there are dozens of models in the market that follow this concept.

One of the most popular models is HobbyKing's Bixler in version 1.1.
It's a really good model for beginners, not expensive and easy to fix with  materials that almost anybody has at home.

Scratchbuilding a model

There are two ways for scratch-building the models:

The classic one, constructive design from balsa wood, which requires a lot of patience and time as well as the knowledge and assistance of a more experienced modeler and

Scratch-building from depron (dollar tree foam, foamboard), Styrofoam and similar foam materials.

The second one is much faster and cheaper, so I'll talk about that type  because that can really be done by everyone in a very simple way.

Tools you need: scissors, hobby knife, packing tape, abrasive paper, pen or a pencil.

Best glue for foam materials is UhuPor, and for hard joints (such as the motor mounts and wing spars) use 5 minute Epoxy, some people also use a hot glue.

The material for building is usually 6 mm and 3 mm thick depron, it can be found in most stores selling house needs or hobby shops.

Your first simple construction aircraft may be ready for two afternoons of easy work (without painting the model), so here I will write some recommendations for your first model and how to choose it.

The good thing is that in some stores you can buy these depron boards by piece, not the whole package, which brings the price of the model to very low (you need up to 3 pieces for one airplane).

When you crash your model, the damage is mostly on the depron itself, the electronics in  99% of the cases survive.
So you can use them again in the new model you build within 2 afternoons.

Well, let's go!!

Definitely for the first model to choose from is one that has no motor and propeller on the nose, just because of the first flights and possible crashes (same as the recommendations for buying models) and which is so called profile construction, in short, with very few parts without closed surfaces (such as fuselage).

From my personal experience, the two models have proven to be excellent for getting started:
F-16 Falcon and F-22 Raptor.

The F-16 is easier and quicker to build and not so "reactive" in flight, meaning it flies nicely and not too fast, it is flying even when the motor is turned off, almost like a small glider, which is convenient for landing.

The F-22 has similar characteristics, but it can be much faster and "more responsive" to the commands from the sticks, so it is possible to perform all types of aerobatics in the air.

How do I make my first airplane, where are the plans, how to put it all together?

It is enough to download PDF file for a particular model, print the template on a plain printer in a ratio of 1: 1 (choose the "Posterize" and "Cut Marks" prints in the PDF reader to mark the cut-offs), cut those printed pages where marked with Cut Marks and arrange it in a unique template. Then cut out all the pieces, copy those pieces on depron board and finally cut them out.
Picture of a cut-out model:

Next step is adding the wing spar to the wing.
Why is that necessary?
Let's say that the plane wing span is e.g. 1m. Model wing made from that material (depron), can not withstand strains in flight, and the wing will be torn apart. This is why the wing spar is needed, you glue it in with epoxy glue..
First, make a V shaped groove in the designated position with the entire length where the wing spar goes, and then glue the wing spar it into the groove and let it dry.
As a wing spar material, the best are carbon tubes 5-6 mm thick. They are sufficiently firm and light.

If you can not find carbon tubes in the store near you, there is an alternative solution.
Just find fishing and hunting shop, and there, buy a single arrow. Some of them are made of carbon, and if they are not, you can use the plastic ones as a wing spar.

The control surfaces are hinged if you bought hinges.
If not, that is not a problem at all.
You can use packing tape as a hinge (personally, I use tape hinges in 90% of my builds).

It is very important that those parts of the control surfaces that attach to the rest of the wing, are tilted by 45 degrees with hobby knife or abrasive paper. The same should be done from the wing point of attachment..

Everything is written in the instruction manual for making a plane (the links are below), and here are the pictures how it's done.
It is important to say that the packing tape should go from both sides, and make sure that the control surfaces move well.

For connecting the control surfaces to servo arms, carbon or metal rods are used, and horns with multiple holes with stoppers and clevises.

Now, this all can be bought ... but it does not have to.

The horns can be made  of old credit cards , the rods can be made from old depleted umbrella, and the stoppers from electric connectors.

It should be noted that the place of installation of the horn is such that the joint of the rod and the horn is exactly above the rim of the control surface.

Make the motor mount from 3 mm plywood, and glue it with 5-min epoxy glue.
You can mount the servo with a hot glue, it holds firmly, and later if you need to replace it, it can easily be unglued (use hair drier  around the servo to melt the glue).

The finished model looks like this:

Model Setup:

As I have mentioned before, stick on what the model manufacturer or its designer recommends.
For both these beginner models, the setup is the same, so when you decide which one you are going to build, you need 2 servos, propeller, motor, ESC and battery.

Clicking on shop name will take you to the mentioned part:

Motor: 2200KV
from HobbyKing
from RCTimer

ESC (any 30A ESC will do):
from HobbyKing
from RcTimer

Servo (any 9 gram servo will do):
from Gearbest
from HobbyKing

Propeller 6x4:
from HobbyKing type 1
from HobbyKing type 2
from HobbyKing type 3

Battery: (any 2200 mAh 3S 30C and up to 45C):
from HobbyKing

And that's it.

You can paint the model with any water based paint.

And finally, where to download the designs for these two beginner models?

F-16:
http://rc.tomhe.net/f-16
http://www.rcgroups.com/forums/showthread.php?t=964249

F-22:
http://rc.tomhe.net/f-22
http://www.rcgroups.com/forums/showthread.php?t=723890

In each archive you also have instructions and build guide, so I think there will be no problems with building them.

And when you become a bit experienced in building models from depron, here you have free designs for over 700 airplane models:

http://rcflug.ch/plans/

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Beginners Guide Part 5 - Batteries And Chargers

LiPo (lithium polymer) batteries

Please, read this topic carefully, LiPo batteries are highly flammable and can explode. They even burn in the water because they do not need oxygen for burning.

Nowadays, this type of battery suppressed NiCd (Nickel-Cadmium) and NiMH (nickel-metal hydride) batteries because they have lower weight and low voltage drop compared to Nickel type batteries. The NiCd is still used to power the RC components in the glider (receiver and servo) as well as in the radio transmitters, but it is very likely that your new electric model will be driven just with LiPo batteries.

While NiCd and NiMH batteries for RC models typically consist of 4 to 8 cells, LiPo comes in 1 and up to 12 cells, although batteries over 6 cells are rarely used for beginner models.
The nominal voltage of a LiPo cell is 3.7V.
When the single cell is full charged voltage is 4.2 Volts.
Battery labels tell us how many cells a battery has, and the letter S is used for this label.

So in the specifications we have that 2S battery voltage is 7.4V, 3S battery 11.1V ...and so on.

The second label on the battery that is important is its capacity, expressed in mAh (milliamper hours).
The higher the capacity of your battery, the longer flight time will be.
Of course, batteries with higher capacity are much heavier, so you have to be careful not to overweight the overall weight of the model because the over-weighted model does not fly at all.

The third label that is very important for the battery is the C rating label.
We will discuss this a bit longer because it is a pretty confusing for the beginner.
The C-rating tells us how much current battery can constantly deliver.
The power of the battery that can be constantly supplied also depends on the capacity of the battery itself.
So we come up with the formula capacity (in Ah) times C-rating = max. electric current that battery can provide.

Let's take an example of 2200mAh battery labeled 20C:

2200mAh is 2.2 Ah (amper-hours) times 20 = 44A
Therefore, this battery is designed for a maximum constant discharge of 44A.
The same kind of battery, but with 40C label, can be constantly discharged with electric current of 88A.

Some battery series have two C-rating labels, for example the Turnigy Nano-Tech series, which are labeled as at 25-50C.
What does this mean?
This means that the battery is nominally rated as 25C and supports a constant discharge of 25C, but it also supports the so-called Burst (short duration about 1-2 seconds) discharge, when the current can jump up to 50C in very short time, without damaging the battery.

It should be noted that the batteries with a higher C-rating are more expensive than those with smaller rating and a few grams are heavier.
Also, if you buy battery from well known manufacturers (Gensace ..), you can be sure that the C-rating is exactly what it is written on the battery. Such batteries are sometimes several times more expensive than Chinese ones with the same cell count,capacity and C-rating.

If you try to buy cheapest battery do not be surprised to come up with a low-cost, high-C battery, which, after 2 charhing cycles, becomes unusable. This is because they often write that the battery is 25C, and in fact, it is barely 10 or 15C.
From my personal experience, I recommend always getting a battery of at least 30C, as good enough and not so expensive I recommend the Zippy Flightmax battery series from HobbyKing.

Each battery has 2 wire extensions. The one with thick wires and various types of connectors (the connector depends on the capacity and current that the battery can deliver - small connectors for small currents, bigger for large currents), that is the main output of the battery and connects to the ESC.

The second wire extension (3 wires upwards - depends on the number of cells in the battery) is called the balancing output, and is essentially the output from each cell in the battery, and is used when charging the battery to monitor the state of each cell in battery.

The disadvantages of LiPo cells are their high sensitivity, both on physical damage and on voltage. If the voltage of a particular cell falls down below a 3V per cell, battery can be permanently destroyed.
Also a damaged (deformed) battery can be a great risk of using or charging, as it may cause a fire or explosion.

Generally, a few basic rules should be taken when using the LiPo battery:

• Use only special chargers for LiPo
• Always monitor the battery while charging . Periodically check that it does not overheat.
• Do not charge the battery in the vehicle.
• Do not overload the battery with an inadequate motor / propeller (to pull more current than it can)
•  Use only those ESCs designed for LiPo batteries.
• Make sure there is no short circuit.
• Never puncture, drill, distort or break the battery.
• Do not leave the LiPo battery in the model connected to the ESC

Storage of the batteries

Batteries, when not used for a long time, should be placed in the so-called Storage Mode. Every quality charger for the LiPo battery has this option, and it is about putting every cell in a battery to cell voltage of 3.8V.
This voltage allows the battery not to lose its properties when they are not in use for longer period.

Let's sum up everything we need to pay attention to:

Battery killers:

• voltage below 3.2V per cell in use
• voltage below 3.6V per cell in standstill or storage
• charging over 4.2V per cell
• temperature above 60 degrees Celsius
• fast >0.5C charge at a temperature below 10 degrees Celsius
• draining more than 80% of battery capacity
• storage of fully charged battery (4,2V per cell)

Chargers

Using a balanced charger is highly recommended. Almost all new batteries  on the market are sold with an additional charging connector, which connects to the chargers balance port.

Always read instructions provided with the battery and charger before charging your first battery.

Why is this important?

Because of all things mention above about the batteries. The battery charger is in fact a little computer that constantly monitors the voltage of each cell during charging and does not allow one cell to higher voltage over the others or to exceed the maximum voltage of 4.2V per cell.

Also, these chargers have different operating modes, from the above-mentioned Storage Mode for battery storage, up to cycle recharging and battery discharge.

Also, with these chargers you can charge other types of batteries (LiFe, LiIo, NiMh, NiCd, Pb ...).

Some purchased RTF(ready to fly) models come with small chargers for 2S and 3S batteries, which have low charging current (max 500mA).

These chargers are OK for you to start, but are not recommended for longer use because you can not put your batteries in storage with these chargers and they do not balance the cells well during charge, so it may damage the battery.

In addition, due to the low charge current, with such a charger you will charge a battery of 2200mAh almost 4-5 hours. Now imagine that you have 3 batteries that you plan on one nice day to use for your models for flight, how much time will it take for you to charge all of them?

An example of cheap charger and charging the battery is shown in the picture.

Minimum for your first charger I would recommend IMAX B6 or Turnigy Accucell that can charge 1S batteries up to 6S with maximum current of 5A, which is quite enough for you to start with.Of course, for this charger you need an adequate power supply, you can use old power supply from the laptop that can deliver 5A current at 12-18V voltage.

All these chargers can be found at HobbyKing, eBay, GearBest and similar web shops.

There are also a lot of expensive chargers that can charge multiple batteries at once, have higher charging current and cost a lot, but this doesn't belong to this topic for beginners, so I will not even write about it now.

Again, be very careful when using LiPo batteries, as mentioned at the beginning of this topic, these batteries are highly flammable. Always monitor the battery while charging, check for its temperature, don't overcharge or over dischage.If the battery is inflated or bloated, don't use it any more!!!!

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Beginners Guide Part 4 - Electric Motors

Choosing the motor

We have come to one of the most important parts of every RC model, which is a main engine drive.
About this topic it can be written very much , because, indeed, there is a lot of details about the main drive, I will try to keep as much on the most basics that can satisfy the absolute beginner without being overwhelmed with the amount of data and options choosing a motor.

We divide the engine drives into two categories: internal combustion engines and electric engines.

Nowadays, electric motors with their efficiency and price are mostly the first choice for beginners, so I'll base this topic onto them.

Electric motors

Electric motors are divided into several categories:

The basic division is based on brushed and brushless motors. Brushed motors are of the older generation they wear and have the need to replace the brushes from time to time. Also they have less efficiency than brushless motors. By choosing the type of motor also depends choice of ESC (the brushed ESC has only two wire leads toward motor, opposite to brushless ESC which has 3 wires).
Brushless motors entered through the small door into modelling with CD drives, which included a motor and a ESC. For many, this has been the way to avoid the high cost of the modeling brushless motors at that time. Today, a solid motor can be bought for 10$, so brushed motors are not recommended anymore.
The main advantage of brushless motor is efficiency, which is typically higher by about 20% compared to the corresponding brushed motor. This is easy to understand because there is no friction on the brushes, sparking, and similar losses during operation. Brushless motors are generally simpler and have better construction. Hence their long life.

Another important advantage is that they can run large propellers without the use of gears, ie. they can have a large torque and a small number of revolutions, but also vice versa, a very high speed and a smaller torque required for the EDF (electric ducted fan) drive.

With this basic division, there is also a stator-based division ofelectric motors:

Outrunner motors have the magnets mounted on the outer casing and the outer casing is spun around the fixed coils in the center of the motor casing, hence the term "Outrunner"

Inrunner motors have the fixed coils mounted to the outer casing and the magnets are mounted to the armature shaft and this spins inside the casing, hence the term "Inrunner"

The inrunner motors are narrower and longer and generally have higher rotation speeds than outrunner designs which have a higher torque because of the chassis that acts as a flywheel and can spin to a larger propeller. The outrunner can be also recognized as a bell motor. The inrunners are most often used with additional gears to keep the tips of propeller blades remain at subsonic speed. The number of revolutions relative to the voltage is marked with KV and the inrunners can have up to 5000 KV, while for outrunners can be less than 200 KV. Thus, for example, the Inrunner with 4000 KV at 11 volts turns 4000 x 11 = 44 000 rpm. Most of the ESCs support inrunner and outrunner motor types. There are 10 times more manufacturers of electric motore than manufacturers who make combustion internal motors for modelers. Every other factory in China has its own brand. The most famous and the most expensive are Hacker, Kontronik, Neo, Scorpion.

A little about "the numbers" (we all hate them):

Dimensions of the electric motor, what do all of those numbers mean in name of outrunner motor?
let's say, you build an kit airplane, and manual says to use the 2826-6 2200 KV motor.

The first part (2826) is the dimensions of the motor. So 28 means that the diameter of the motor itself (bell) is 28 mm.
The second part (26) is the length of the motor itself without a fastening bracket.
That mark 6 sometimes indicates the number of motor poles, or something else, depends on manufacturer, I would not go into details about that now.

It means that 2200 KV (though the naming has no logic) indicates, as I have already mentioned, the speed of the motor revolution per voltage: Rpm/V

So, if such a motor is supplied with a 1V of voltage, it will turn in idle (meaning no propellers) 2200 times per minute.
Consequently, if powered by a 10V voltage, it will turn 22000 rpm, which is very fast.
This is one of the most important things about selecting a motor for your model, because the bad choice of motor can result in motor or ESC burn.
It is recommended that you always hold onto manual, what the manufacturer recommends, most often in the motors description stays ehat is the maximum current that motor can sustain (with this data you can choose how "big" the ESC you need) and which propeller at the specified battery voltage has the highest usability.
Engine power data is presented in Watts, and you can even get maximum power by simply calculating by yourself.
Let's say that motor pulls max 25A on a 3S battery with 6x4 propeller, then the calculation is simple:
Battery voltage x current = Power, or 11.1x30 = 277.5 Watts. For such "setup" you need a 30A ESC (It's always recommended tu use bigger ESC by 10%).
Quite a lot of power for a small, 50-gram motor. This is one of the reasons why more and more modelers use the electric motors. For those large models, internal combustion engines are still being used.

Selecting the propeller

Let's go further on the propeller selection, which is also a very important item in every "setup".
If you do not know which propeller to select, look at the motor datasheet.
For this specific example data says that a 2S-3S battery is recommended for the motor, 2S is recommended for propeller 7x4 and 3S for propeller 6x4.

The propeller number tags refer to propeller diameter and propulsion (pitch). To shorten and not confuse beginners, the diameter indicates a thrust or how strong the propeller is, or how much weight it can pull.
The pitch indicates how much air flow velocity can be achieved, therefore, higher airflow rate means higher air velocity of the model in the air.

Now many beginners, as I have been, think, this is great. I'm going to take motor as fast as possible and a bigger propeller, with a big pitch, the plane will take off like a joke because it can pull well, and it will be a fast in the air like a rocket.
It does not go that way.
If I put a bigger propeller on the mentioned 2200 KV motor, say 9x6, yes, I would get a thrust of at least 2 kg and speed over 100 km/h. Theoretically.
But the engine with such a propeller, due to its size and components that create motor load, would pull up to 80A of electric current with full throttle. And what would happen?
After one second or two, motor or ESC would burn, but in my experience ... probably both.

In short, it is very important to select a good "setup", ie. a ESC-motor-propeller combination for certain types of aircraft.

Please note again:

USE SETUP AS MANUFACTURER OR DESIGNER OF THE MODEL RECOMMENDS IF YOU ARE BUILDING YOUR OWN MODEL.

For your own calculations you have a lot of On-Line calculators where you enter or choose the motor you have, add the propeller to him, and it calculates the load, thrust, max speed, flight length and everything you might be interested in.

One of these is at:

http://www.ecalc.ch/motorcalc.php?ecalc&lang=en

There are also off-line programs that are regularly updated with new models of motors, propellers and ESCs, and which I personally use and can be downloaded at:

www.drivecalc.de


Please note that all these programs give you approximate values, but again good enough to avoid burning of your equipment and model.



Why  are there motors with lower KVs and higher KVs anyway?

This depends on the type of aircraft, for example, a modern military aircraft model or what's called JETs, due to its small wingspan and narrow profile, will require higher flight speeds. In such models, high speed motors with small propellers and large pitch or EDFs are used.




Models of classic airplanes, such as Cessna, Piper,WWI Warbirds ... use slower motors with larger propellers because they are not fast flying models, but they need power, good towing, keeping them in the air at low speeds.




Propellers are also classified as electric propellers and gasoline/nitro propellers.

When choosing an electric propeller,again, you have more sub types:

SF propellers, or so called Slow Flyer. These are propellers that run at small revolutions and, as the name suggests, serve for slow flying models. Mostly often they are made of noticeably soft and elastic plastic and have a limited maximum rotation speed (up to about 9000 rpm).They do not tolerate larger RPMs (revolutions per minute) and can easily break, with result in severe injuries.




Standard and sports propellers. These are propellers that can withstand high rotation speeds, they are made of solid plastic or reinforced with fiberglass. They are used on high speed motors ( with bigger KVs).






Wooden propellers. If you are building scale models from the First World War, one of the cool detail is a wooden propeller that "beautifies" the whole model because at that time, all propellers were made of wood.






Carbon fiber propellers. The most expensive and lightest of all, exceptionally strong and lightweight, there are also SF versions that is used with drones (multirotors). If you can afford this for yourself that's great. They have excellent performance and can withstand great rotation speeds.







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Beginners Guide Part 3 - Servos and controls

Servos and controls

Servo motors receive signals from the receiver and turn them into work. They are in RC models similar to what the muscles are in your body. The servo is most often used for controlling aerodynamic surfaces that then change the air flow on airplane wing or tail and thus the flight direction of the model itself. By aerodynamic surfaces, we mean the steering and directional control surfaces like ailerons, elevator, rudder, flaps, air brakes, etc.

For models with internal combustion engines, one of the servo should be assigned for throttle control. It is clear that some smaller and lighter servo can be used for this purpose since its strength is not the most important, but it is precision. The servo and the carburetor on the engine are adjusted so that the full throttle on the stick makes the engine reach its maximum speed, while with the stick at the opposite end, holds motor at idle.

Servos can also be used to control the wheels on the model in order to control the direction of movement during taxiing. Usually the same servo is used to run the steering wheel combined with rudder control.
Some other applications for the servo in the flying models are servos for big towing gliders, who have the task of unlocking the glider from the model of the aircraft that pulls them up and raises with them.

There are a large number of servo types in the market, which differ in size, strength, quality and price,but almost all of the servos have the same design. There is a miniature electric motor that triggers a reduction mechanism, which ends with a control arm. There is also a potentiometer or similar electronics that controls the arms range of motion.

The servo connects to the receiver via cable with 3 wires. In the past, various manufacturers have used different connectors but today it is mostly standardized. Beginners in RC modeling usually come up with this question: Can I use one manufacturer's servo with the receiver of another manufacturer? Answer: Today, in 99% of cases, yes. The next question is: Is it good to mix the servos of different manufacturers in the same model? Answer: There is nothing particularly bad about this, you can see in the models of more experienced modelers mixed types of servos. The servo is a servo. Possible problems may arise around energy consumption in larger models with more than 4 servos. Such models are not for beginners, so there is no need to discuss about that now.

Today , servos are mostly  categorized in these three categories: standard, mini and micro.

Standard servos are often supplied with the RC transmitter and receiver. These are robust servos with a typical weight of 40-50 grams and a power (ie. torque) of 3 to 4 kg/cm. Some of the known models are Hitec HS-311, Futaba S3003, etc. Four such servos will suit eg.. a trainer model with full flying weight of about 2 kg, powered by an internal combustion engine of 6.5 cubic centimeters.

For slightly smaller models, typically about one kilogram of flying weight, optimal are "mini" servos, weighing 15-20 grams and have a power of about 2.5kg/cm such as Hitec HS-81.

For small models, so-called park-flyers,which are most often powered by an electric motor,"micro" and "sub-micro" servos are suitable. Their weight is about 10 grams, and the power is 1.2 kg/cm (Hitec HS-55). A few decades ago, these small servos were quite expensive due to the delicate mechanism, but today it is no longer the case. The most popular micro-servos mentioned are Hitec HS-55, HITEC HXT900 and its derivatives (Towerpro TG9, various Turnigy and HobbyKing 9 gram servos ...)

The servo connection with the model itself is fitted with two or four screws and servo tabs. In some cases the screws may be impractical, such as with foam models. It is not uncommon for servo to glue it in model with foam safe glue (hot glue, 5 min epoxy). But - what if the servo breaks down and needs replacement? Servo glued with hot glue is easiest to remove, use a hair dryer (for glue to soften a little bit) around the servo, and just pull it out. Servos does not break often but it does happen. The more servos and other components you have in the model, the higher the chances of something breaks down.

With some models you should also consider motor vibration. These vibrations can, in some cases, lead to improper operation of the servo mechanism or its damage. That is why the servo is mounted with the help of the rubber pads, so the servo body does not directly touch the fuselage of the model and does not receive vibration from it.

Control links

Finally, let's talk about control links and rods. This should be given maximum attention because if the control connection release or fail during flight it will lead to damage or loss of the model.

Generally, control links can be divided into rods and cables. In the case of the cables, usually seen in larger models, two are required on both sides of the servo arms ("closed loop control"). If you use rods, only one is enough.

The control connection between the servo and control surfaces usually consists of two clevises and one lever. If it is a metal rod, then the clevises can be omitted - the rod is bent at the ends in the shape of the letter Z (Z-bend) and such insert in one of the holes of the servo arm.

In the early days of RC modeling, the control rods and clevises were regularly metal and soldered together. One or both clevises  would have a screw and nut for fine tuning of the control link length. For example, the connection could be shortened or extended by some 5 mm.

Nowadays, a large number of modelers, use nylon clevises and carbon rods, which are then combined with some adhesive. Such a control link is not flexible in length but is light and inexpensive. Another way to connect is by using stoppers at the ends of the control rods. They have much greater flexibility to adjust the control link length.
I usually use a combination of 2 methods, on the one hand I use the Z-bend and the other stopper.

Types of Servos

The basic question is what are the proper servos for my model?
What is the difference between them?
Can every servo be connected to any type of receiver?

1. METAL GEAR vs. PLASTIC GEAR servo

The most important difference is that those servos with metal gears are often stronger and can withstand shocks more than plastic ones. Most commonly these servos are marked with "MG" (Metal Gear) in their names.
However, they also occasionally cause harmful interference when connected to certain receivers.
Also, those "MG" servos have an additional problem , some cheap manufacturers cheat by pointing that they are metal geared and very often they put one or two plastic gears between the metal ones, so it is some kind of a mixture, and not full MG servos.

2. BALL BEARING vs. BUSHING servo

Each servo has an output shaft that passes through the servo housing. The servo works much more accurately and easier if it has ball bearing.
If not, over time, the casing will be worn out and some scratches appear on the casing, and that can lead to problems in servo arm movements. It's a recommendation to buy servo motors with bearings. Most commonly these servos are marked with "BB" (Ball bearing) in their names.

3. DIGITAL vs. ANALOG servo

Can I connect a digital servo on my receiver?

Both digital and analog servo can be programmed on each receiver.

So where's the difference?

Similarities:
Both digital and analog servo motors have majority of components same. This means both of them can have the same electric motor, same gears and the same potentiometer. There are no differences there.

Differences:
What is different is how to process the incoming signal (servo move commands).
The analog servo motor has a specially designed motor control chip and the digital servo has a microprocessor and control amplifier.
When the signal is given, the analog servo sends the motor pulses (50 impulses per second). At digital servo, the microprocessor sends 300 impulses per second to the motor and the motor moves faster.

Both types have its good and bad sides.

Digital servo centers servo arm perfectly, keeps its position and responds faster. Unfortunately, some digital servos will not last longer than analog ones because they constantly "push" the electric power to the servo motor regardless the position of servo arm and its load, so they easier malfunction or burn the motor.
Analog servos are less accurate, more accessible and more durable than digital ones.

Digital servo motors spend much more electricity and if you have several of them in your model, be sure to supply them with enough battery power.

Digital servos require an electronic power switch for good micro-processor performance, as well as cable protection in the form of ferrite rings to reduce interference.
Digital servos give us a full torque at all angles while the analog does not.

4. STANDARD MOTORS vs. CORELESS MOTORS in servos

Common electric motors have a stator and rotor. The rotor is wound to the metal core. Because of this, the rotors are heavy and inert. The rotor is secured on both sides.
Coreless motors are designed on the same principles as common ones, but they are assembled differently. The rotor is lightweight. The threads are made in a metal-free cylinder and are attached only at one end of the rotor.
Because they are much lighter (no metal in the middle) they react much faster on commands from stick, they are less inert, and slow down much faster, also they are more precise, and can generate more torque for the same size of servo as one with common motor.

HIGH SPEED vs. HIGH TORQUE servos

For most of the people, faster and more powerful servo is better. In fact, high-speed servo motors are as good as one can react quickly.
Large torque is important for larger models or models with large control surfaces where large forces (such as 3D models) are created.
The speed of the servomotor is expressed in seconds to move servo arm for 60 degrees. There are servos of 0.05s - 0.2s and maybe more for 60 degrees of movement. Here it should be noted that not all manufacturers give exactly at what voltage on the servo is claimed speed. It is not the same whether it is 0.12s for 4.8V or for 6V voltage.

Almost all servo sizes are roughly the same speed as they are loaded, while their power is different. Therefore, servos with lower power are slower and servos with higher power are faster at the same load.

Also, the torque depends on the voltage supplied. The motor is more powerful at higher voltages.
The torque is measured in kg/cm or oz/in . The ratio is as follows: 1 kg = 35.27 ounces, 1 inch = 25.4 mm.

How to measure the torque of the servo?

The servo must be fixed and 1 cm long servo arm attached to shaft . Then you can check how much weight this servo can hold without bending or breaking the gears. So if it can withstand 2.63 kg then it's a 2.63 kg/cm servo or 36.1 oz/in.

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Beginners Guide Part 2 - ESC and BEC

ESC

ESC means Electronic Speed Controller.
Every electric RC vehicle has its power system which consists of motor, ESC and LiPo battery.

ESCs connects between the motor and the battery. They have more important functions.
First, the ESC gives impulses to the motor without which the motor could not operate. Second, it controls the motor speed, according to the throttle position. Thirdly, it powers the other RC devices in the model (receiver and servos) so that no special battery is needed. Fourth, monitors that the voltage in the LiPo battery does not fall below 3 volts per cell, which would cause problems with the power of other RC components and may even destroy the battery.
ESCs today are a small computers and allows programming of a large number of parameters, ranging from impulse length to minimum battery voltage.

They generally come in 2 versions, with built-in BEC (Battery Eliminating Circuit) for powering the receiver and without the BEC (OPTO ESC).
In addition, two values are important for each ESC.

Maximum continuous current in A and maximum burst current in A that you should not exceed if you do not want to "burn" the ESC. Thus, the ESCs come in values of 5A, 8A, 10A, 25A, 35A, etc., which indicate the maximum continuous current, the maximum burst current usually stands in a bracket eg. 25A (30A burst). Additionally, the maximum voltage at which the ESC can work is also important, usually marked by the number of cells (10-14 NiMH / 2-4S Lipo).

ESC usually has three groups of wires:

• Three wires for the motor
• Two thick wires for the battery
• Three twisted wires for the receiver, similar to cables on servos and other RC devices.

The two wires for the battery are usually red and black, and there is a need to be careful that the ESC and the battery do not connect vice versa because of short circuit where ESC will burn and be destroyed.

It is best to use connectors that do not allow incorrect connection. In this regard, a beginner should avoid the so-called "Bullet" gold connectors for connecting the battery.

The three wires for the motor can be connected with identical connectors to the motor wires (best to use bullet connectors, but also you can weld them and insulate with shrink tube if you do not intend to move the ESC to other model). Through these three wires, the ESC supplies power to the motor but also controls the motor's performance. The information flow is bi-directional - not just from the ESC to the motor but vice versa, because the ESC must know at any time the position of the rotor relative to the stator. A detailed explanation of how this is done is quite complicated for beginners and not necessary. The first brushless motors had special sensors that informed the ESC about the current position of the rotor. Today's modelling motors are "sensorless", meaning they do not have special sensors, but ESC receives feedback thanks to magnetic induction in the windings.

Some ESCs, especially those of higher power, still have two or three wire strands with a RC switch at the end. This is nice for security reasons, so that the receiver would not drain the battery until the model is prepared for flying. Of course, the battery should always be unplugged from the model when the flight ends, because of danger for the battery, that itdoes not consume too much battery power, after which it may become unusable. Of course we are talking about LiPo batteries.

Another thing that most newer ESCs and even some of the cheapest ones have, is the protective mechanism against the accidental starting of the motor.

What does this mean l?

This means that when you connect the battery to your model, if you leave the throttle stick on radio in a position that is not neutral (the lowest), the motor will not start,it will produce a range of sounds to alert you that something is wrong.

Otherwise,if that's not the case, the motor might start to spin the propeller while your fingers are near, which can lead to wounding and even loss of some extremities.

Many better and more expensive radios and their receivers have this mechanism built into the receiver as well.

Therefore, it is very important before turning off the radio to disconnect the battery (disconnect it from the ESC), so that it does not repeat the above written scenario and have undesirable consequences.

Connection diagram is presented with the following picture:

High quality ESCs (Jeti, Kontronic, Himax ...) come with a whole list of additional functions that can be programmed. Programming is performed either by the throttle stick on radio, or, more comfortably and safely, by a special programming card. One of the most important functions of the ESC is to give a warning before the first motor start. Usually, one or more "beeps" are heard a second or two, after which the propeller starts to spin. So you have enough time, for example, to pull your fingers away if you unintentionally launched the motor.

There are also a braking functions (essential for electric gliders with folding propellers), motor start-up (quick start, softer or faster) and much more that I would not go into because a novice with a simple model will not need it at the very beginning.

Is it possible to reverse the direction of rotation of the motor and the propeller? 

If the ESC does not have this function, the wires must be reconnected. Most brushless motors currently on the market are of outrunner type. When you connect the motor to the ESC and the battery and notice that the propeller is turning in the wrong direction, all you have to do is switch any 2 wires (of three) between ESC and motor. And that's it.

One of the frequent questions about the brushless power systems is whether it is enough to have one ESC for two motors?

No - each motor must have its own ESC. So if you are building twin engine plane, both motors must have their own ESC, although both ESCs can then be connected to the same battery.

Also, something that is very confusing to beginners is when you connect the battery for the first time. ESC releases only sound "beeps" and motor does not respond to throttle.

This is because the new ESC first needs to "learn" how much is the throttle range of your radio and receiver.

The "learning" procedure is extremely simple and is the same in most cheap Chinese ESCs. Those more expensive come with instructions, so it is recommended to stick to the instructions.

Before you continue, remove propeller from motor, just in case.

In short, it is necessary as always, first turn on the radio, and push the throttle to the maximum.

Then connect the battery to the ESC(which is connected to motor) and wait for the first "beep" or two to be heard. After that (the same second), lower the throttle stick to the lowest position.

Now the ESC makes one or several "beeps" (it depends on the ESC), which indicates that it has remembered the highest and lowest throttle and the entire range of it, and no other sound warnings from it anymore. If this does not work, check the instructions of the ESC itself.

This procedure doesn't need to be repeated if everything went well.

As i have mentioned before, many today's ESCs have BEC installed.

So let's explain, what BEC is and what it is used for.

BEC is an abbreviation for the Battery Eliminator Circuit.

The receiver as well as the servos used to run the control surfaces, the flaps, the retractable landing gear, bomb drops and more, use some voltage and current for their work.

But that voltage and current are not as good as it is needed to run the motors.

All receivers work at 4-6 V voltage and they power everything that is connected to them, so each servo is powered by the receiver, with the same voltage as the receiver.

In order to get the required 5 or 6V rated voltage with battery rated voltage of 11.1V, the battery voltage must be "lowered" to the one that is intended for the receiver and servo operation. The higher the voltage would burn both the receiver and the servo, which can lead to significant cost.

That's why there is a BEC, it can be embedded in a ESC, or can be purchased separately.

Another important item in BEC is the maximum current in the amperes that can be given at rated voltage (5V or 6V). What does this mean now?

So every RC component, of course, consumes electricity. So the receiver consumes a certain amount of current, say 100mA, each idle servo consumes some (say) 100mA, but when it is under load, the current rise up to 400mA or more, it depends on the servo. Small servos consume less, but they also have less power. Bigger servos consume more acordingly.

And now, if you have a model with 2 small servos and receiver built in, you will need a BEC of 1A.

But if there are more servos (4-6), and even more like the retractable landing gears and some LED lighting , such a BEC will not be sufficient, it will be necessary to use a BEC that can supply the receiver with a current of 3-5A or more. Again, it all depends on how large components (servos) are built into the model.

There are several types of BECs:

Linear BEC - regulates the voltage by an analog circuit using an active element, never using just a resistor.

Except for a large loss (heating) regulating only with the resistor is not actually a regulator, as sevros consume more current , voltage on resistor drops down and ultimately the servos get less voltage. The main problem of Linear BECs is the cost of manufacturing. For high currents they need expensive parts and compacted circuits.Switching BEC is now appearing in the form of a single chip and costs are very low.

Linear BEC is predominant for small currents and small voltage differences, and in that it does not emit any radio pulse disturbances.

UBEC - stands for Universal BEC and it signifies a BEC that is not embedded in ESC, ie. a self-powered electronic power supply. The type may be linear or switching. SBEC - stands for the Switching Battery Eliminator Circuit

SBEC is an improved version of BEC that uses switching technology as a circuit, and can therefore provide more current in amps. Many SBECs can also be used with much higher input voltages than standard BECs (batteries above 6 cells).

Switching BEC, due to its contouring and mode of operation, emits small but noticeable radio impulse disturbances.

Thus, the recommendation to any ESC with or without built-in SBEC, or SBEC only in your model,is to put away from the receiver as far as possible to be less disruptive to the receiving signal from your radio.

Connecting an ESC with an external BEC is shown in the illustration. If you have an ESC with a built-in BEC that is too weak and you want to add an external BEC, you need to disable the middle wire (from the 3 color) on the connector to the receiver by removing it from the connector.

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Beginners Guide Part 1 - Radio

Enter into the Hobby!

Before we begin, you must decide how much you are interested in modeling. This hobby asks a lot of free time, but also money. I say this in order to immediately be able to skip the toys from  a variety of different Chinese stores.

Choosing the Radio (transmitter)

Let us start from the transmitter as a crucial element.
As a minimum you need transmitter with 4 channels (throttle, aileron, elevator and rudder ).
Every RC modeler will recommend that you don't save money on transmitter. Once purchased, the transmitter will rarely be changed, so I recommend a minimum of a six channel transmitter with which you still have room for improvement. The transmitter will be used for all of your models.
All newer transmitters use 2.4 GHz spectrum (instead of 35/40/72 MHz) as well as Wi-Fi networks, and do not need be paired with crystal quartz to use a specific channel. Transmitters at 2.4 GHz themselves paired with receivers, are more resistant to interference and there can not happen for two modelers to use the same frequency and interfere with each other.

Minimum specifications for transmitter:

- operates on a frequency of 2.4 GHz
- min. 6 channels with all standard mixers
- the ability to memorize at least ten models
- availability of various types of receivers
- quality radio link protocol (DSMX, FAAST, FAASTEST, hott ...)

Speaking of 6 channels, there is little chance that you will initially fly model that will need all six channels, but it's not impossible.
But in almost every model you will use mixes. Mixes combine the movement of two or more servos into a single command. These are the most common mixes, with many transmitters already have pre-configured for ease of use:
- mixer for ailerons (if each aileron has its own servo)
- elevon mixer (models with delta wings, flying wings, and other miscellaneous tailless airplanes)
- the V-tail mix (usually seen in gliders)

Among other functions that every transmitter should have, the most important are: reverse, dual rate and expo. These functions are related to each channel, it means that they do not mix several channels.

Reverse means that you want your servo to change the direction of rotation relative to the transmitter stick. (This allows you to, among other things, don't  care how you position the servo when installing it in the model).
Dual Rate (D/R) is particularly important with high speed and 'nervous' models, where you want to reduce the maximum deflection of the control surface (aileron, elevator, rudder) relative to movement of the stick. Eg. Dual Rate of 50% means that if you move the stick to the end, servo will turn only half as much as it usually can.

Expo is very similar to the Dual Rates but the ratio of moving sticks and servos is not linear, instead it is in the form of a parabola. How can that be useful ? Well, you want to eg. soften servo arm movement with a gentle stick motion, but you still want that the servo horn comes to it's maximum when you move the stick to the end. These 'fast and nervous' models can then be easy to fly with moderate movements of the sticks while the model is flying under a higher speed, and when the engine stops and the model becomes slower and sluggish, you can land using the full swing of the control surfaces.

Possibility of transmitter to store the settings for more than one model is an important feature. Let's suppose that you have two models, a glider and a helicopter. Adjustments on the transmitter for two different models like this will be quite different. When you take into account that adjustment commands for each of the models may require considerable time (and nerves), it is clear that through this process you do not want to go every time you change the model. If transmitter can store a 10 models, that's fine, but today's transmitters can store a much more. With the more expensive transmitters there are memory cards  that can be removed and inserted into a computer, and setup model on your transmitter .
Also, I should mention  not only every model can have their settings, but also the same model can have multiple "flight modes". For example, expensive and sophisticated competition gliders in F3J category use one mode for start on the winch, the other while flying in thermals, the third as they are landing with flaps, etc.

MODE description

When buying a new radio, salesman will probably confuse you by asking which MODE of the transmitter do you want to buy. There are 4 modes defined 1,2,3 and 4: They are most commonly sold as Mode 1/3 or Mode 2/4. Modes determine the function (command) of the sticks. If you select MODE 1 you will have aileron command and the throttle on the right stick, and the left stick controls the Rudder and Elevator. If you select MODE 2 you will have aileron and elevator controls on the right stick, and the throttle and rudder on the left stick.
This is all because that on throttle stick there is no control that would  return the stich to the neutral position (center), as is the case with all other movement sticks. If this wouldn't be necessary,  there would be no difference between the MODEs on transmitter because the commands on the sticks can be assigned independently.
A better transmitters have the possibility of mechanical switching between MODEs. And those top, expensive transmitters, have software switching, without opening the radio itself.





Control surfaces for the height or depth  (ELE- elevator), tilt (AIL - aileron), direction (RUD - rudder or yaw on the helicopters) and throttle (THR - throttle) are shown below:















The cheapest radio(transmitter) that will meet the needs of every beginner is Turnigy-i6, which also has telemetry data.
It is a 6-channel radio which proved to be quite good for beginner models.
The range of radio is solid 500m, which is quite enough to fly airplanes and helicopters, and even small gliders and quads.
For the price of 50$, it really offers more than enough. With the radio you also get one 6 channel receiver , and the radio has memory for 10 different models.






One of the most popular (and cheap) computerized radio is Turnigy 9x.
For the price of 77$ this 8-channel radio will offer each newcomer  much more than what he will initially need.
Also, the receivers for this radio are quite cheap, so every your model can have its own receiver, and when you decide to fly, it is enough to charge the battery, put it in the desired model and pleasure can begin.


Many people will say that there are cheaper 6 channel radios on the market, that can be bought for 20-30$, but in my personal experience, such radios often lack the delta mix necessary for beginner's model (type ZAGI), and the range is quite questionable. There are cases when a range is hardly up to 50 meters,they are susceptible to interference, and ultimately flying with a such radio can end quite fatal for the model.

Best Buy radio currently is FrSky Taranis.

It is a 16/32-channel radio with all possible options that exist in the market, therefore, telemetry, voice notification, any number of settings, memory for 250 models ....  everything. It uses well-known and extremely resistant ACSST protocol in communication between radio and the receiver, which is quite resistant to all external influences and  that radio swept most expencive radios from renowned manufacturers such as Futaba, Graupner, Spektrum. With this radio and the receiver, you can be sure that the range will be at least 1.5 km minimum. If the conditions are good, range can go up to 2.5 km with this combination.
A nice thing is that the radio has a slot for an additional module if by any chance you already have receivers and models from other manufacturers (different protocols). Just prick the module to the station (such as Spektrum for DSMX or DSM2 protocol) and use it instead of the internal.
Using internal and external module together, you can get 32 ​​channels , which will rarely be needed.

There are many radios from other manufacturers, one that I prefer because ease of use and high quality is Spektrum (by Horizon Hobby).
A 6 channel radio from Spektrum has telemetry, voice and intuitive and easy setup procedure that every beginner will understand, unlike other cheaper radios.

Another benefit (again in the case of the Spektrum) is a pile of finished BNF (Bind And Fly) model airplanes, helicopters and gliders that you can buy, ranging from micro planes and gliders up to large motor planes. BNF models for Spektrum have in themselves already installed Spektrum compatible receiver, such models come complete, and some fully assembled, with batteries and a charger. It is only necessary to charge the supplied battery, connect (BIND) radio with model and flight can start in less than half an hour of opening the box.

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