Transcript RC Helicopter Mechanism Sylvain Marron 1: Mechanism • • • • Clutch Main Gear Tail Rotor Drive Swash Plate Clutch  Purpose: to start the engine without driving the rotor  safety  It.

RC Helicopter Mechanism
Sylvain Marron
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1: Mechanism
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Clutch
Main Gear
Tail Rotor Drive
Swash Plate
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Clutch
 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
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Main Gear
 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
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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
 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
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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)
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Swash plates: Comparison test
Advantages
H1
H2
 1 servo / function
 simple setup
 no need of electronic mixing
?
Drawbacks
• servos have bigger load
• 1 faulty servo = 1 function lost
• mechanical mixing
• 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
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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:
Throttle servo
Magnetic sensor
Mixture servo
Receiver
Throttle
Speed
Mixture
Governor
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Gyroscope
 Assists the pilot for rudder control
 Holds a specific heading regardless of conditions:
o torque variations
o cross-wind
 Without gyroscope:
Wind
 With head lock gyroscope (or Head Hold):
Wind
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Connecting the gyroscope
Gain
Rudder control
Receiver
Gyroscope
Rudder servo
 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
Gain
Rudder control
Receiver
Gyroscope
Rudder servo
Gyroscope
Rudder servo
 Command sent by pilot
Gain
Rudder control
Transmitter Receiver
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Flybarless System
 Flybarless = without flybar
 Electronic management
 → 3-axis gyroscope:
 controls all functions ! (except throttle)
Flybarless Module
Servos
Roll
Nick
Receiver
Gain
Rudder
Pitch
Nick
Roll
Pitch
Cyclic
Rudder
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Comparison test
Advantages
 Rotor with flybar
Flybar
 inexpensive
 simple setup
Flybarless
Drawbacks
 Flybarless rotor
• complex mechanism
• less precise
• drag
• heavier
• fragile in case of crash
 more precise
 fewer mechanical parts
 less drag
 light weight
 less damage in case of crash
 esthetical
• digital servos (speed)
• electricity consumption
• expensive
• complex setup
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3: Electric Helicopters
 Nowadays electric helis are as powerful as nitro helis
 Brushless motors + LiPo batteries = Revolution
 Light weight (for small and average models)
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Equipment
 1 brushless motor (powerful, high current)
 1 ESC Electronic Speed Controller (high current)
 built-in governor
LiPo batteries (high discharge current)
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Classes
• 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
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Electric vs. Nitro
Advantages
Drawbacks
• noisy
• dirty (clean up after each flight)
• expensive fuel
• vibrations
• engine might stop during flight
Nitro
 range (time of flight)
 look more real (noise + smoke)
Electric
 less vibrations
• LiPo batteries are expensive
 quickly ready (plug and fly)
• range (time of flight)
 quiet
 clean
 no engine mixture adjusting
 motor doesn’t stop during flight
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The End
You can find this PowerPoint and other
information on my website :
http://mvlys.free.fr/HelicoRC/index.htm
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