RC Helicopter Mechanism Sylvain Marron 1 1 Mechanism

RC Helicopter Mechanism Sylvain Marron 1

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

Clutch ü Purpose: to start the engine without driving the rotor Ø safety ü It is a centrifugal clutch: Ø main rotor is driven when engine accelerates Ø main rotor is not driven when engine idles 3

Main Gear ü Purpose: to drive the main rotor ü A tail drive pulley is mounted just below ü This assembly is mounted on a one way bearing: Ø when the engine runs it drives the rotor Ø when the engine idles or stops, the main rotor turns freely 4

Tail rotor drive ü Belt drive ü Torque tube drive 5

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 6

Swash Plate ü Purpose: to transmit orders to main rotor Ø moves Up/Down → collective pitch control Ø tilts → cyclic pitch control ü There are many swash plate types: Ø swash plate type defines the layout and the number of servos which operate the collective pitch function Ø swash plate type may differ according to the model and the manufacturer 7

Swash plate types ü H 1 → 1 servo for collective pitch ü H 2 → 2 servos for collective pitch ü H 3 → 3 servos (2 nick) üH 3 → 3 servos (2 roll) Ø named 120° CCPM, widespread üH 4 → 4 servos 90° (2 nick / 2 roll) 8

Swash plates: Comparison test Advantages H 1 H 2 § 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 H 3 § no mechanical mixing § load is shared by three servos • same servos for identical speed and torque • electronic mixing H 4 § safety : 2 servos per function • same servos for identical speed and torque • electronic mixing • some servos might bind 9

2: Electronics • Governor • Gyroscope • Flybarless system 10

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

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

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

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

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

Comparison test Advantages Ø Rotor with flybar Flybar § inexpensive § simple setup Flybarless Drawbacks Ø 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 16

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

Equipment ü 1 brushless motor (powerful, high current) ü 1 ESC Electronic Speed Controller (high current) Ø built-in governor üLi. Po batteries (high discharge current) 18

Classes • 700 : 700 mm blades (= 90 -size nitro model) • 600 : 600 mm blades (= 50 -size nitro model) • 550 : 550 mm blades (= 30 -size nitro model) • 500 : 425 mm blades • 450 : 325 mm blades • 250 : 205 mm blades 19

Electric vs. Nitro 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 • Li. Po batteries are expensive § quickly ready (plug and fly) • range (time of flight) § quiet § clean § no engine mixture adjusting § motor doesn’t stop during flight 20

The End You can find this Power. Point and other information on my website : http: //mvlys. free. fr/Helico. RC/index. htm 21