Other RC Parts & Components

All RC airplanes and helicopters are controlled by servos - small, electromechanical devices that allow everything from controlled flight to payload releases. So what are servos?  How do they work? And how do you choose the ones that will work best in your model? We’ll answer all these questions, and take you through everything from the basics of servo operation to their technical details.

What is a Servo?

A servo is a device that can rotate to an arbitrary position, as set by the user. Servos usually consist of a small DC (direct current) electric motor, several gears, and a head where an arm or wheel can be attached. When the user tells the servo what angular position to move to, the servo rotates and holds that position until further input is specified. The servo holds position because external forces are always interacting with the aircraft, and would set control surfaces to undesired positions unless stopped. Servos exert a torque on external forces, that prevents them from changing the position of any control surface.

How Servos Work

A servos job is to convert the angular movement of a servo arm to the linear movement of a control surface. This is done by attaching linkages, called control rods to the servo arm and the associated control surface. When the servo head rotates, it pushes the control rod back and forth. The rod is linked to a control surface, and can move it up or down as the servo rotates.
Servos are controlled by three wires: two to provide the DC power that the motor needs, and one that sends the signal, controlling the servo. The signal wire works by sending the servo a series of pulses, which are interpreted by its internal circuitry. By varying the timing of each pulse, the servo knows exactly which position to move to.

RC Servo Motors

The motors that drive RC servos come in several different types. Here’s a list of the most common varieties, and some information on each to help you decide which ones to use:

• Coreless – Conventional motors use copper wires wrapped around metal cores to form electromagnets. In a coreless motor, there is a metal mesh that rotates around the permanent magnets. Coreless motors respond more quickly than conventional motors, because they don’t have to overcome the momentum associated with heavy metal cores.
• Brushless – Servos can be powered by brushless motors, giving them longer life, faster response time, and more torque.
• 3 Pole and 5 Pole – Electric motors have permanent magnets, called poles, that electromagnets are attracted to. Servo motors can have either 3 or 5 poles, with more poles providing better torque. If you’re new to RC or have a regular sport model, you probably won’t notice the difference between 3 pole and 5 pole servos.

Choosing the Right Servo

Servos have a number of defining properties that make them suitable for different applications:

• Torque – This is a measure of the servos strength, or how much “push” it has. More precisely, torque is the product of force and the radius at which it acts. This is shown graphically in the figure on the right. Bigger planes need high torque servos to move their large control surfaces. In general, servo size goes up with rated torque.
• Dimensions – Servos come in many different sizes, which you can choose from depending on your application.
• Weight – The weight of a servo depends on several variables. Most often recorded in grams, the weight of a servo is always reported on the package.
• Bearings – There are two ways to support the output shaft of a servo – bearings and brushes. Brushes are cheaper, but bearings last longer and operate more smoothly. Very small and very cheap servos tend to be brushed, while high end and very large servos generally have bearings. It’s possible to upgrade a brushed servo to bearings, with several upgrade kits being available on the internet.
• Gears – Most hobby grade servos use nylon gears, while higher end servos use metal gears. Metal gears add more weight, but their advantage is that they can’t “strip”, causing an RC helicopter or airplane to crash. Metal gears wear over time, which can cause “slop” in their rotation, but the gears can be replaced somewhat economically. In general, nylon servos are adequate for sport flying. If you’re particularly worried about losing a model in a crash, or are flying intense aerobatics, a metal geared servo is probably the right choice.
• Speed – Speed measures how fast the servo can move from one position to another. Different RC airplanes and helicopters will need servos with different speeds. For example: a trainer doesn’t need to change control surface positions rapidly, but a 3D helicopter or plane does. High speed servos are many times more expensive than standard ones.
• Digital / Standard – Servos can be of two types: digital, or standard. Both digital and standard servos can be used with a normal receiver, the real difference is performance. All servos use a series of short pulses as signals that determine what angular position they should maintain. This series of signals is usually very fast, somewhere around 50 pulses per second maximum. On a standard servo, this rate is so fast that small movements of the control sticks may not have an affect. This means that there’s a small deadband on the control sticks, in which no servo movement takes place. Although it’s not a problem on trainers and most sport class models, the deadband becomes a significant issue with 3D aircraft. Even a small delay with a 3D aircraft could cause a crash.
  Digital servos remove the deadband by speeding up the rate at which it receives      pulses. Usually, this is increased from around 50 to 300 pulses per second. This increase in resolution allows the servo to operate much more precisely.

All RC kits and ARFs will specify the type and brand of servo required. Generally, you should adhere to these recommendations.

Now that you know what servos to get for your model, you can browse the large number of servos available on our website.

Every RC model airplane transmitter has a mode of operation, which defines which sticks control different surfaces. This article will illustrate the differences between them.

Mode 4 Transmitter

On a mode 4 transmitter, ailerons and throttle are controlled with the left stick and rudder and elevator are controlled with the right stick.

Mode 3 Transmitter

On a mode three transmitter, ailerons and elevator are controlled with the left stick and rudder and throttle are controlled with the right stick.

Mode 2 Transmitter

On a mode two transmitter, throttle and rudder are controlled with the left stick, and ailerons and elevator are controlled with the right stick.

Mode 1 Transmitter

On a mode one transmitter, elevator and rudder are controlled with the left stick, and throttle and ailerons are controlled with the right stick.

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Phone: 1-800-979-9794 / 306-955-9907
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Spread spectrum technology represents the latest advancement in RC radio control systems. This article will show you how spread spectrum technology works, and introduce you to some of the technical terms which you may encounter.

Unlike conventional PPM (pulse position modulation) and PCM (pulse code modulation) radio systems which operate on distinct frequencies, spread spectrum radios broadcast over a large range of frequencies simultaneously. These frequencies are all members of the 2.4 Ghz band, which removes them from the frequencies often used by other communication devices. Because of this, spread spectrum radio systems are already immune to interference caused by non RC radio systems.

Spread Spectrum technology has another advantage though: there is no need for frequency control.
Spread spectrum radio systems broadcast over a multitude of radio frequencies, and the user is never aware of what they are. This works because:

1. The transmitter is assigned a unique identification code when it is manufactured.
2. The receiver is programmed to seek and lock to this same code.
3. After the transmitter is powered on, it encodes the signals it sends with its identification code.
4. The receiver scans for this code, and locks to the frequencies that the transmitter is operating on.

Each identification code is globally unique, meaning that no other radio system is using it. Because of this, the individual frequencies that the radio is operating on are irrelevant, so as a result an unlimited number of spread spectrum radios can operate simultaneously.

The most noticeable consequence of this technology is that spread spectrum radios are immune to radio interference. Spread spectrum radios also allow an extremely fast servo response time, because the entire encoding, decoding, and execution of radio commands happens in milliseconds.

Spread spectrum technology is becoming more prevelant in RC radio systems, and will shortly replace conventional FM radio systems entirely.

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Phone: 1-800-979-9794 / 306-955-9907
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You should always balance your RC model airplane propellers before using them. Running your RC model airplanes with properly balanced propellers will increase motor or engine lifespan, prevent fuel from foaming, and even extend the life of your electronic components. This article will show you how to balance your RC model airplane propellers using simple and inexpensive equipment.

The best way to balance your RC model airplane propellers is to use one of the many prebuilt balancers available. Blade balancers usually come in two varieties:

1. finger prop balancers – sufficient for most modelers, you can get good results using a simple blade balancer for 5 to 10 dollars depending on the supplier. Great Hobbies has a balancer which works sufficiently well to balance most model airplane props.
2. magnetic prop balancers – produce highly accurate results and are usually more expensive than finger balances.

Use the blade balancer by unscrewing the two metal rings and then placing your propeller in between them. Tighten the metal rings so that the prop doesn’t move and support the entire apparatus with one finger tip on each hand. The prop is balanced if it remains motionless. If it tips forward or backward then you will have to adjust it according to the following procedure:

1. Mark the heavy side (which tips downwards) with a felt tip pen.
2. Sand one side of the propellers heavy end with medium to fine grit sandpaper. Do not sand the propeller tip – this will cause a dynamic imbalance when the engine is running.
3. After removing a very small amount of material from the heavy side of the propeller, test it again using your blade balancer.
4. Repeat steps 2 and 3 until the propeller remains motionless while held in the blade balancer.

This procedure will balance your propeller accurately enough to eliminate the most severe vibration during flight. 3D aerobatics, racing, or other demanding flying requires propellers to be balanced more precisely. You can get a higher end magnetic balancer for 20 to 30 dollars. It’s usage is about the same as the finger balancer except that the propeller is held between two magnets.

Check your propeller’s balance using the above method and be sure to follow the manufacturers instructions when putting the propeller in the balancer.

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Phone: 1-800-979-9794 / 306-955-9907
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There are many fun games that you can play using RC model airplanes. This article shows you how to set up and play some of the most interesting ones.

Aerial Combat

You can simulate aerial combat with your RC model airplanes without excessive risk to your models. Here’s how:

1. Find as many friends with RC model airplanes as possible.
2. Divide the available RC model airplanes into teams
3. Attach different colored streamers to each RC model airplanes tail, depending on which team that it’s on.
4. Have all the RC planes take off at once
5. The object of the game is to use your RC model airplanes propeller to cut the streamer off of our opponents.
6. After a set amount of time all of the planes land and the length of their streamers are measured. The team with the most streamer remaining wins.

This game can be played with any number of RC model airplanes, but keep in mind that the risk of a collision increases with the number of RC model airplanes flying.

Flying the Limbo

This is one of the easiest games to play, but it’s also the most risky. To play,simply find a large football or soccer field and fly your models through the goal posts. Make sure that you are allowed to fly your models in the field that you’re using, and that there are no people in the field that could get hurt -should the airplane crash.You can also construct a makeshift goal post out of PVC pipe, found in most hardware stores. Cut the pipe to a decent length, and then friction fit it together using PVC fittings.

Bomb Dropping

RC pilots frequently modify their aircraft to carry and drop payloads. If you would like to add this ability to your RC model airplane, follow this procedure to construct a launching apparatus:

1. Find a rectangle of balsa wood, at least as long and wide as the payload that you intend to carry on your RC model airplane.
2. Horizontally mount a spare servo to the end of balsa wood. Make sure that the servo arm points upwards and rotates 90 degrees when activated.
3. Stretch a rubber band over the two corners of the balsa rectangle opposite the servo, and then loop the rubber band over the servo horn.
4. Mount the whole apparatus on your RC model airplanes fuselage, and connect the servo to your receiver.

After the servo moves, the rubber band slips off the horn. If you place your intended payload under the rubber band, you can drop it from your RC model airplane at the flick of a switch. Take a look at this picture, which shows one such design completed and loaded with plastic parachute toys.

You can make bombs to drop out of Styrofoam cups, rubber cement, and talcum powder. Here’s how:

1. Place one Styrofoam cup on a flat work surface, and fill it with a few tablespoons of talcum powder. Take a small paint brush, and coat the Styrofoam cups rim with a small amount of rubber cement.
2. Place another Styrofoam cup on top of the first, lining up the rims.
3. Let the cups dry
4. Take a hobby knife and cut a cross section into one of the cups.
5. If you like, spray paint the bomb and add cardboard fins.

After the bomb hits the ground, the cross section that you cut into the nose will cause it to shatter, releasing the talcum powder it contains. When it works, this looks a lot like the cloud of smoke and debris that real bombs leave after exploding. After you drop the bomb, be sure to watch your airplane and not the resulting cloud of powder.We hope that you enjoy playing these games with your RC model airplane. Be safe,and have fun.

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Phone: 1-800-979-9794 / 306-955-9907
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Introduction

RC jet engines represent some of the most impressive technology that the RC industry has ever created. RC jets are always an amazing sight at the flying field, because they look and sound just like the real jets you find at airports and military airfields. In this article, we will take a look at how model jet engines work, and show you the differences from full scale jet engines.

Before you go out an buy a jet, be warned that RC jets are some of the most complicated, expensive, and difficult RC model airplanes available. You will need both many hours of flying experience and a huge budget to successfully own and fly an RC jet.

This article is about real jet engines which burn kerosene (or jet A1), not the electric ducted fan models frequently found in hobby stores. EDF jets are great models to fly, and some are capable of advanced aerobatics, but they are not to be confused with real RC jets using real jet engines.

How Full Scale Jet Engines Work

In order to understand how model jet engines work, it is helpful to examine the full scale engines used by airliners and other jet aircraft. A jet engine is a device which operates inside a fluid (in most cases air), and expels it at high speed achieving a propulsive effect. The mechanics of jet engines are best represented by Newton’s laws of motion, specifically: “For every action, there is an equal and opposite reaction.” This means that the reason jets go forward is because they expel air backwards, faster than it came in. This basic principle applies for all types of jet engines.

But how do we achieve the movement of air needed to propel an aircraft? We know from high school chemistry that the volume and the temperature of any gas are proportional. Because of this, when air is heated, the volume increases. If the air is held in a container (the combustion chamber of a jet engine), then the pressure will also increase. Releasing the heated gas will result in an exit speed greater than the speed at which the air entered, creating the backwards flow of air needed to travel forward.

Interestingly enough, rockets are considered to be a type of jet engine. The only difference between a rocket and a conventional jet engine is that the rocket operates in a vacuum, and thus needs to take both fuel and an oxidizing chemical with it. The discussion of rockets and other exotic jet engines is beyond the scope of this article, so we will limit our investigation to three of the most common designs. These jet engines are listed in order of complexity, and all were used in full scale aircraft at some point in time.

The Pulse Jet

The pulse jet is one of the simplest jet engines, consisting of little more than a pipe and a fuel source. Pulse jets were used by Germany during World War II to propel primitive cruise missiles (V1 flying bombs). A pulse jet works by igniting a fuel air mixture in high frequency bursts. A typical pulse jet cycle operates as follows:

1. Air is allowed to enter the combustion chamber, and fuel is simultaneously added.
2. The intake valve is closed.
3. Ignition is triggered, resulting in an outward flow of air and low pressure inside the combustion chamber.
4. The valve is opened, and new air rushes in due to the low pressure in the combustion chamber.

This cycle repeats during the entire operation of the engine.

Pulse jets are not very efficient, and are extremely loud. Because of this they are not often used in full scale aircraft, but hobbiests often build them due to their design simplicity and lack of moving parts. In some cases, pulse jets are built to small dimensions and used on RC model airplanes.

Turbojet Engines

More sophisticated jet engines use turbines to compress the air fuel mixture before igniting it. A turbine is a device which consists of sets of moving blades attached to an axle. If the turbine blades are spinning, they will move air through themselves and towards the back of the vehicle. This figure shows a moving turbine, spinning on an axle.

The operation of a turbojet is represented in this figure.

Unlike pulse jets, turbojets lack a repeating cycle (the engine operates continuously). There is a sequence of events that occurs during the engines operation though, so we list them here in chronological order.

1. Air enters the turbine and becomes compressed.
2. The compressed air is routed to the combustion chamber, where is is mixed with fuel.
3. Ignition occurs, and the resulting hot air is allowed to exit the jet engine.
4. Before leaving the engine, the hot air is forced through a gas turbine, which drives the compressor used in step 1.

Turbojets are far more efficient than pulse jets, because some of the energy produced by the combustion process is reused

Turbofan Engines

Even though turbojet engines are more efficient than pulse jets, they are not often used in subsonic aircraft because of the noise they produce. Turbojet engines are well suited to high speed operations, exceeding the speed of sound. They become less efficient at the subsonic speeds which airliners and other commercial jet aircraft operate at.

The turbofan design operates on exactly the same principle as the turbojet engine, but instead of routing all of the intake air through the combustion chamber a small amount is allowed to exit unburned. Instead of being mixed with fuel and burned, some of the cool air is mixed with the exhaust, reducing the exhaust speed and increasing fuel efficiency. This figure illustrates the operation of a turbofan jet engine:

How Model Jet Engines Work

RC Model airplane jet engines work in exactly the same way as the full scale ones discussed above, with the exception of the air compression. Instead of using an axial turbine compressor, RC jet engines use a centrifugal compressor. A centrifugal compressor propels air outwards after it enters the engine, causing it to hit the engine case and be compressed. Centrifugal compressors need fewer moving parts than axial turbine compressors, and are more efficient for small applications. Many small full scale jets use centrifugal compressors for the same reasons.

Here is a picture of a typical RC model airplane jet engine, mounted on top of an RC model airplane.

RC jet engines operate on kerosene, exactly the same fuel that full scale jet engines use. Ignition is achieved with a small glow plug, like those found on two and four stroke RC model airplane engines.

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Phone: 1-800-979-9794 / 306-955-9907
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All of the APC RC Airplane Propellers include a set of motor shaft adapter bushings, so that they can be used on a variety of different RC airplane motor shafts. It is important to use the correct adapter bushing so your propeller fits snugly on the motor shaft.

Which Motor Shaft Adapter Bushing Do I Use?

To determine which adapter you should use you have to know the shaft diameter the motor you’re using. For example, if your motor has a shaft diameter of 0.313in (7.95mm) then you need to use the APC adapter bushing with an inside diameter of 0.313in.

Inside Diameters of the Motor Shaft Adapter Bushings

* All the APC adapter bushings have the same outside diameter.

Precision Motor Shaft Mounting Procedure

1. Each APC propeller’s hub may be precisely adapted to motor shaft diameters of 0.128in, 0.158in, 0.197in and 0.313in by using bushings 1 through 5.
2. Remove the desired locating ring by twisting.
3. Insert the ring with draft angle as shown.
4. The propeller hubs may be adapted to other shaft diameters by reaming the non-precision 0.250in (1/4in, 6.35mm) hole to the size you need.

Never Drill a Propeller, Use a Reamer Instead

In the instructions that come with each propeller, APC tells customers to “drill to desired diameter”. Never drill a propeller. A drill will make an asymmetrical hole and ruin the propeller’s balance. A reamer will make a perfectly centered hole.

Where to Buy APC Electric RC Airplane Propellers

Draganfly Innovations Inc. has a huge selection of APC Electric RC Airplane Propellers. The three types are Slow Flyer, Wide Electric and Electric and range in size from 6 to 24in.
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© Draganfly Innovations Inc.
Phone: 1-800-979-9794 / 306-955-9907
Email: info@rctoys.com
Web: www.rctoys.com
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