RC Helicopter Mechanism

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Sylvain Marron

1: Mechanism

• Clutch• Main Gear• Tail Rotor Drive• Swash Plate

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Clutch

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Purpose: to start the engine without driving the rotor safety

It is a centrifugal clutch: main rotor is driven when engine accelerates main rotor is not driven when engine idles

Main Gear

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Purpose: to drive the main rotor

A tail drive pulley is mounted just below

This assembly is mounted on a one way bearing: when the engine runs it drives the rotor when the engine idles or stops, the main rotor turns freely

Tail rotor drive Belt drive

Torque tube drive

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Tail rotor drive: Comparison test

Advantages Drawbacks

Belt fewer mechanical parts inexpensive less damage in case of crash

• less accurate rudder• regularly check the tension of belt

Torque tube precise rudder no maintenance

• expensive• fragile in case of crash

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Swash Plate

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Purpose: to transmit orders to main rotor moves Up/Down → collective pitch control tilts → cyclic pitch control

There are many swash plate types: swash plate type defines the layout and the number of servos which operate the collective pitch function swash plate type may differ according to the model and the manufacturer

Swash plate types H1 → 1 servo for collective pitch

H2 → 2 servos for collective pitch

H3 → 3 servos (2 nick)

H3 → 3 servos (2 roll) named 120° CCPM, widespread

H4 → 4 servos 90° (2 nick / 2 roll)8

Swash plates: Comparison test

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Advantages Drawbacks

H1 1 servo / function simple setup no need of electronic mixing

• servos have bigger load• 1 faulty servo = 1 function lost• mechanical mixing

H2 ? • same servos for identical speed and torque• mechanical mixing + electronic mixing

H3 no mechanical mixing load is shared by three servos

• same servos for identical speed and torque• electronic mixing

H4 safety : 2 servos per function • same servos for identical speed and torque• electronic mixing• some servos might bind

2: Electronics

• Governor• Gyroscope• Flybarless system

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Governor The governor automatically maintains constant rotor RPM

Operating: a sensor measures engine speed the governor controls the throttle servo (and sometimes mixture)

Connections:

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Magnetic sensorThrottle servo

Mixture servo

Thro

ttle

Spee

dM

ixtu

re

Receiver

Governor

Gyroscope Assists the pilot for rudder control Holds a specific heading regardless of conditions:

o torque variationso cross-wind

Without gyroscope:

With head lock gyroscope (or Head Hold):

Wind

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Connecting the gyroscope

Receiver Gyroscope Rudder servo

Gain

Rudder control

The gyroscope detects an angular velocity

Gain allows to set the gyroscope sensitivity

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Gyroscope Operating Gyroscope compensates for unexpected tail drift

Receiver Gyroscope Rudder servo

Gain

Rudder control

Command sent by pilot

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Receiver Gyroscope Rudder servo

Gain

Rudder controlTransmitter

Flybarless System

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Flybarless = without flybar Electronic management → 3-axis gyroscope:

controls all functions ! (except throttle)

RollNick

PitchRudder

Gain

Receiver

Flybarless Module Servos

Rudder

Nick

Roll

Pitch

Cyclic

Advantages Drawbacks

Flybar inexpensive simple setup

• complex mechanism• less precise• drag• heavier• fragile in case of crash

Flybarless more precise fewer mechanical parts less drag light weight less damage in case of crash esthetical

• digital servos (speed)• electricity consumption• expensive• complex setup

Comparison test

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Rotor with flybar Flybarless rotor

3: Electric Helicopters

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Nowadays electric helis are as powerful as nitro helis

Brushless motors + LiPo batteries = Revolution

Light weight (for small and average models)

Equipment

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1 brushless motor (powerful, high current)

1 ESC Electronic Speed Controller (high current) built-in governor

LiPo batteries (high discharge current)

Classes

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• 700 : 700mm blades (= 90-size nitro model) • 600 : 600mm blades (= 50-size nitro model)

• 550 : 550mm blades (= 30-size nitro model)

• 500 : 425mm blades

• 450 : 325mm blades

• 250 : 205mm blades

Electric vs. Nitro

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Advantages Drawbacks

Nitro range (time of flight) look more real (noise + smoke)

• noisy• dirty (clean up after each flight)• expensive fuel• vibrations• engine might stop during flight

Electric less vibrations quickly ready (plug and fly) quiet clean no engine mixture adjusting motor doesn’t stop during flight

• LiPo batteries are expensive• range (time of flight)

The End

You can find this PowerPoint and other information on my website :

http://mvlys.free.fr/HelicoRC/index.htm

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