RC Helicopter Mechanism 1 Sylvain Marron

1: Mechanism Clutch Main Gear Tail Rotor Drive Swash Plate 2

Clutch 3 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 4 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 5

Tail rotor drive: Comparison test AdvantagesDrawbacks 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 6

Swash Plate 7 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 9 AdvantagesDrawbacks 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 10

Governor The governor automatically maintains constant rotor RPM Operating:  a sensor measures engine speed  the governor controls the throttle servo (and sometimes mixture) Connections: 11 Magnetic sensor Throttle servo Mixture servo Throttle Speed Mixture Receiver Governor

Gyroscope Assists the pilot for rudder control Holds a specific heading regardless of conditions: o torque variations o cross-wind  Without gyroscope:  With head lock gyroscope (or Head Hold): Wind 12

Connecting the gyroscope ReceiverGyroscopeRudder servo Gain Rudder control The gyroscope detects an angular velocity Gain allows to set the gyroscope sensitivity 13

Gyroscope Operating  Gyroscope compensates for unexpected tail drift ReceiverGyroscopeRudder servo Gain Rudder control  Command sent by pilot 14 ReceiverGyroscopeRudder servo Gain Rudder control Transmitter

Flybarless System 15 Flybarless = without flybar Electronic management → 3-axis gyroscope:  controls all functions ! (except throttle) Roll Nick Pitch Rudder Gain Receiver Flybarless ModuleServos Rudder Nick Roll Pitch Cyclic

AdvantagesDrawbacks 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 16  Rotor with flybar  Flybarless rotor

3: Electric Helicopters 17 Nowadays electric helis are as powerful as nitro helis Brushless motors + LiPo batteries = Revolution Light weight (for small and average models)

Equipment 18 1 brushless motor (powerful, high current) 1 ESC Electronic Speed Controller (high current)  built-in governor LiPo batteries (high discharge current)

Classes : 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 20 AdvantagesDrawbacks 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 : 21