Choosing the electronics for RC planes By Rachit Aggarwal

Components required Propeller Motor Speed Controller Battery Eliminator Circuit Servos Battery Transmitter & Receiver

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Propeller

Brushless DC Motor Two Types of DC Motor – Brushed and Brushless – Brushed uses slip rings and brushes for commutation – Brushless uses has magnets on rotor and coil on stator. Uses electronic commutation (ESC) Working and Control Advantages: – Precise, higher torque, less electrical noise, less frictional resistance, higher speeds, cooler in temperature, can be used in flammable regions. Distadvantage: – Higher initial cost and complex control mechanism.

Brushless DC Motor Two type: – Outrunner: rotary magnets encloses the stationary coil – Inrunner: rotary magnets are enclosed by stationary coil K v rating: motor velocity constant, measured in RPM per volt. Max motor RPM = 0.8 x 3.7V x Series Cell Count x Motor kV Rating Motor's Output Power (W) = Torque(Nm) x 2  x RPM / 60 Also Power (W) = Voltage x Current So for a higher torque motor choose a higher current and lower K v rating motor.

BLDC Example Specifications. Weight: 38g Dimensions: 22 x 28mm Shaft: 3.17mm Diameter Voltage: 7.2v~11.1v /2s~3s Lipoly Kv: 1450rpm/V Idle Current: 14A Max amp: 22A (10sec burst) Max Watts: 160W Suggested Propeller: 8x6(2s) 7x4.5(3s)

Electronic Speed Controller (ESC) It uses a programmable microcontroller and 3 channels of Power FETs for high speed switching for high current applications. Brushed or Brushless? – If motor has two wires, it is brushed - need a brushed speed control. – If it has three wires, it is brushless motor – need a brushless speed control. Current Rating – Higher the current rating, heavier it is, more expensive – So choose with slightly higher rating than the peak current of the motor. Voltage Rating – ESCs have more than one voltage ratings. Choose with equal or higher voltage. It is wasteful to connect a higher voltage ESC with a lower voltage battery. – The secondary voltage rating is of Battery Eliminator Circuit (BEC). Low Voltage Cutoff – To protect LiPo battery from being discharged too much, most ESCs can shut down when they sense low battery voltage. A very useful feature - it saves LiPo from permanent damage. Programmability – Most ESCs work out of the box. But they can be programmed with throttle profiles, low battery threshold, brakes, etc, though the remote controller or using a programmable card. Price – Price vary with current, voltage ratings and programmable features.

Battery Eliminator Circuit (BEC) Required to eliminate the need of a seperate battery to power the receiver in electric RC planes. Separate voltage regulator circuit is used to distribute power to ESC, receiver and servos. Most modern ESCs come with inbuilt BEC.

ESC Example Example: Constant Current: 18A Burst Current: 22A BEC Mode: Linear BEC : 5v / 2A Lipo Cells: 2-4 NiMH : 5-12

Servo Servo is an automatic device that uses error-sensing negative feedback to correct the performance of a mechanism. How does a servo work? How to communicate the position? Two Types – Standard Servos can be used out of the box with preset specifications. – Digital Servos contains a microprocessor which can be programmed to give better torque profiles and faster response.

Servo Voltage : 3v ~ 6v Weight: 9g Speed : 0.12 sec/60(4.8V) Torque : 1.6 kg-cm

Battery Lithium Polymer (LiPo) Batteries are by far the most long lasting batteries used for RC applications. Deliver twice the capacity in nearly half the weight of conventional cells Safety is most important concern with LiPo packs. 3.0V<V LiPo <4.2V Parameters associated: – Capacity: The max charge stored in a cell (denoted in mAh) – S: Series cell count. E.g. 3S denotes 3x3.7V = 11.1V – P: Parallel cell count to increase the capacity. – C: Denotes current rating. Max constant current = Capacity x C. Cost and Weight: More the current and voltage rating and capacity, more is the cost and weight.

Battery Example Minimum Capacity: 1000mAh Configuration: 3S1P / 11.1v / 3Cell Constant Discharge: 20C Peak Discharge (10sec): 30C Pack Weight: 87g Calculating Flying time For example: Battery is 1000mAh and Motor draw 5A

Charger Is this important?

Transmitter and Receiver Number of Channels = number of controls on the plane (e.g. Throttle, roll, pitch, yaw, flaps, landing gears, etc) Four Modes: – Mode 1: Non-American Convention – have roll and pitch control on different sticks – Mode 2: American Convention (popular in India) – have roll and pitch control on same stick – Mode 3: opposite of Mode 2 – Mode 4: opposite of Mode 1

Wiring it Up