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Information how a radio controlled helicopter is constructed and works


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ABOUT RADIO CONTROLLED (RC) HELICOPTER TECHNOLOGY

New developments in battery and electric motor techology has made it possible to construct model helicopters driven by electricity from batteries and of many sizes. There are small models you can fly inside your opwn house and greater robust models for outdoor flight with a great action radius.

A helicopter must have several mechanisms to controle the flight. The speed of the rotor must be controlled, or alternatively the attach angle of the blades can be controlled instead, in order to controle the power of flight. The tilt angle foreward-backards and right-left of the main rotor must be controlled. And the speed of the tail rotor or alternatively the attack angles of the tail rotor blades must be regulated to controle rotation of the fuselage.

These controles must be directed through the radio units by the pilot and inside the helicopter, and by microprocessors inside the helicopter. The different models have different numbers of controle possiblilities and hence controle channels in the radio controle unit. Advanced helicopter models have many, but are also then more demanding to operate and require more skill from the pilot. Cheaper helicopter models have fewer control grades and therefore fewer contole channels, but they are easier to operate. In many advanced helicopter models several controle grades are also taken care of automatically by the electronics, and therefore require easier stearing controle operations. Most of the helicopters at this page are advanced models with many controle possibilities.

Advanced models with 6 or 7 control grades and the equal amount of channels have the ability to perform acrobatic maneuvers. These are useually called aerobatic helicopter models.

Many of the advanced models can in great extend be customized for the choise of the owner. You can for many models buy different canopies to make the helicopter look as you wish yourself. You can also install special equipment as for example surveillance cameras in many models.

RC helicopter designs

A helicopter must have one or more rotors that give lift and that can be tilted in various direction to make movement in the wanted direction.

These roteors make a screwing force that tries to turn the helicopter around. This torque must be cotrolled so that it is upweighted or just turn the helicopter when this is wanted.

There are many designs that achieve these objective. Most of the designs are also used in real-world work helicopters, but model builders have a greater opportunity to use their fantacy to make fancy constructions.

One is to have a single rotor for lift and movement and a vertical tail rotor that controles the torque. Tis is also the most usual design of real-world helicopters. By varying the force of the tail rotor, the toque can be counteracted wholly or partly, or one can make a torque in the opposite direction.

Another way is to use two main rotors over each other that retate in the opposite direction. By letting the rotors rotate at exaclky the same speed, or by letting them rotate by a somewhat different velocity, the torque can be ounteracted, or one can make a wanted torque in a direction so that the helicopte turns.

Still another way is to have two main rotors after each other, one in the front and one at the tail end that rotate in the opposte direction, so that they counteract the torque of each other. By tilting the rotors differently, one can get the helicopter to turn in a direction wanted.

The engines used are typically methanol-powered two-stroke motors, but gasoline, jet turbine and increasingly electric brushless motors combined with a high-performance lithium ion polymer battery are also used.

There are also possible to make fantacy models of various kinds, for example with many small rotors distributed aound the frame of the vehicle.

RC helicopter motors

Traditionally model helicopters have been made with small two-stroke piston engines. However, by now electric motors driven by rechargeable batteries are steadily more used and are by now the most sold.

For powerful models combustion engines are still used. One can find model helicopters with two-stroke nitro-driven engines , but even turbine-engine driven model helicopters are to be found.

In former days model airplanes often used two-stroke glow-plug-motors driven by methanole. This kind of motor technology is not widely used anymore.

How the mechanical parts produce flight

Exactly how the parts work singly and together to produce flight varies greatly for model helicopters. For advenced model helicopters they work just as in real helicopters or in an even more advanced way. For simple helicopters, the working principles are very simple.

However, advanced technical mechanical solutions are in many models combined with simple controlling actions, so that the helicopter is simple to use also for a beginner.

The power and thus the speed of lift and flight can be controlled in two ways: In simple models it is controlled by the rotational speed of the rotor. In advanced models it is controlled by the attcak angle of the rotor blades, as in a real helicopter. This is called collective pitch.

By this mode of acction the rotor blades are first accelerated up to the working speed. Then the helicopter blades are turned to controle the power for lifting and horisontal motion.

To achieve this power controle that the rotor does, the power of the motor must be set correctly at any time.

It most be controlled whether the helicopter is going upwards, downwards, forewards, sidewise or backwards. This is done by tilting the rotor in the desired direction.

The torque produced by the rotor tend to rotate the fuselage in the opposite direction of the rotor rotation. This rotation can be of opposed by the controlling the power of the tail rotor. But many model helicopters have other means of doing it, such as two contrarotating rotors over each other.

The fuselage must be swung to head in the right direction, usually the direction of the flight. This is also done by the power of the tail rotor. The torque from the

How a RC helicopter is controlled

There are several kinds of contol mechanism that can be applied in a RC helicopter to produce the right flight actions.

Not any RC helicopter have all the controls possible, and often two or more mechanical flight controle actions are linked and controlled together by the controlling electronics and the controle actions of the pilot are thereby made more easy.

RC helicopters having many controls are more demanding to fly, but allows much more modes of flight and maneuvering types than helicopters with fewer controls.

- The throttle or power of the engine must be controlled.

- The rotating speed of the main rotor may be controlled. If the angle of the rotor blades are held constant, the rotating speed will determine the lifting and flight power, and this speed and power is controlled by the throttle.

- In simple RC helicopters the throttle is varied, this varies the speed of the main rotor and hence also he lifting and movement power.

- In more advanced helicopters the main rotor blades may be turned to variate their angle (collective pitch). The power of lift and movement can then be controlled by varing this angle. At start the speed of the main rotor is accelerated to the working speed. Thereafter the speed of the main rotor is held constant by controlling the throttle. This is actually the main way of varying the power in an advanced helicopter.

- In some advanced helicopters, the rotating speed of the main rotor is automatically controlled, and the throttle is controled together with the tilting angle of the main rotor blades.

- Tilting of the top rotor to left or right (roll) can be controlled.

- Tilting of the top rotor foreward or backward (pitch) can be controlled.

- The rotating speed of the tail rotor may be controlled. In this way the helicopter can be turned.

- The angle of the tail rotor blades may be controlled. If the rotating speed of the tail rotor is hold constant, the power of he tail rotor, and hence the power to turn the helicopter can be varied by controlling this angle.

The various helicopter controls are effected by means of small servo motors. A piezoelectric gyroscope is typically used on the tail rotor (yaw) control to counter wind- and torque-reaction-induced tail movement. This "gyro" does not apply a mechanical force, but rather, electronically adjusts the control signal to the tail rotor servo.

The controls must have signals from the pilot. This is achieved by a tranmittor held by the pilot and a resceiver installed in the helicopter. The transmittor t have as many channels as there are mechanical controls in the helicopter. The number of controls and hence the channels vary between 2 and 6, where the most advanced, but also the must difficult to fly helicopters have 6 channels.

Four controls is a very usual configuration: Aileron (Roll - Cyclic Pitch), Elevator (Fore-Aft Cyclic Pitch), Rudder (Yaw) and Pitch/Throttle (Collective Pitch/Power).

For a non-3D helicopter, the Pitch will range from about -1 degree at 0% throttle to about 11 degrees at 100% throttle.

Nitro RC helicopters

Nitro helicopters come in different sizes: 15, 30, 50, 60 and 90 size. These numbers originated from the size of nitro engine used in the different models (0.30 cu in, 0.50 cu in and so on). The bigger and more powerful the engine, the larger the main rotor blade that it can turn and hence the bigger the aircraft overall.

Electric RC helicopters

The smallest radio-controlled helicopter made (Guinness World Records 2006) is the Picoo Z sold at many toy stores, electronics stores and internet stores, costing about $40/�30. The next smallest is the Micron FP helicopter, which is also a battery-operated R/C helicopter.

Recent advancements in battery technology make electric flying more feasible in terms of flying time. However, these lithium polymer batteries can explode upon overheating. U.S. Consumer Product Safety Commission Recall Alert.

In the past electric helicopters were used mainly indoors due to the small size and lack of fumes. Larger electric helicopters suitable for outdoor flight and advanced aerobatics have become a reality over the last few years and have become very popular. Their quietness has made them very popular for flying sites close to residential areas and in places such as Germany where there are strict noise restrictions. Nitro helicopters have also been converted to electric power by commercial and home made kits.

Radio transmitters and resceiver for remote controle helicopters

Brands: Spektrum, Futaba, JR, Hitec, Airtronics, Sanwa, Multiplex

Small fixed-pitch helicopters need a 4-channel radio (throttle, elevator, aileron, rudder) while collective-pitch models need a minimum of 5 channels with 6 being most common (throttle, collective pitch, elevator, aileron, rudder and gyro gain). Because of the normal interaction of the various control mechanisms, advanced radios include adjustable mixing functions, such as throttle/collective and throttle/rudder. Radio prices vary from $199-$3,000 USD.

Modulation

Radios emit the FM signal in two types of modulation.

PPM is cheaper than PCM and is generally used in low-end helicopters. The lack of a failsafe in PPM makes it more suited to small, less dangerous models. Higher-end radios offer PCM and PPM modulation for better compatibility with all radio receivers.

PCM - Pulse Code Modulation: A scheme in which the commanded position for each servo is transmitted as an encoded number. Manufacturers use their own proprietary system to encode this number with various bits of precision. JR use Z-PCM (10 bits, 512 values) then S-PCM (11 bits, 1024 values). Futaba use PCM-1024 and G3 PCM (12 bits, 2048 values). PCM also includes a feature called Fail Safe to set servo positions to a predefined position, or to hold them at the last valid position, should a valid radio signal be lost.

PPM - Pulse-position modulation: A scheme in which the commanded position for each servo is transmitted as the duty-cycle of the transmitted pulses 1 per servo position.

Construction

Construction is typically of plastic, glass-reinforced plastic, aluminium or carbon fibre. Rotor blades are typically made of wood, fibreglass or carbon fibre. Models are typically purchased in kit form from one of about a dozen popular manufacturers and take 5 to 20 hours to completely assemble.

These model helicopters contain many moving parts, from the swashplate to the mechanical linkages that allow the rotor to be tilted thus controlling direction.

The construction of helicopters has to be more precise than for fixed-wing model aircraft, because helicopters are susceptible to even the smallest of vibrations, which can cause problems when the helicopter is at flight.

How to individualize RC helicopters

Some helicopters are sold as scale models of real life helicopters. Others are however sold with only a minimal fusledge canopy. They can of course be used as is, but you can shift out the dummy canopy with some canopy made to resamble the fuslage of some real life or historical helicopter.

Advanced Rc helicopters can also be furnished with spy or surveillance cameras, so that you also can use the helicopter as a surveillance tool.

It is also possible to buy helicopter scheletons without motor, but with rotors and all controlling mechanics. Then one can buy motos, vanopy and radiocontrolling units afte one's own whish and this way indibidualize the helicopter.



INFORMATION ABOUT VEHICLES TECHNOLOGY - Especially RC vehicles

- The working principles of an aircraft

- About radio-controlled aircrafts im professional life

- About the F-35 lightning all purpose combat plane

- Motor technologies for RC aircrafts and vehicles

- About remote controle transmitters and resceivers

- About helicopter history

- Battery technology for RC vehicles