Choosing the electronics for RC planes

ByRachit Aggarwal

Components required

• Propeller• Motor• Speed Controller• Battery Eliminator Circuit• Servos• Battery• Transmitter & Receiver

Lift to Thrust Ratio

• @Ankit: please make this slide. I don’t have these fundae.

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

• Kv 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 Kv rating motor.

BLDC ExampleSpecifications.Weight: 38gDimensions: 22 x 28mmShaft: 3.17mm DiameterVoltage: 7.2v~11.1v /2s~3s LipolyKv: 1450rpm/VIdle Current: 14AMax amp: 22A (10sec burst)Max Watts: 160WSuggested 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: 18ABurst Current: 22ABEC Mode: LinearBEC : 5v / 2ALipo Cells: 2-4NiMH : 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: 9gSpeed : 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<VLiPo<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: 1000mAhConfiguration: 3S1P / 11.1v / 3CellConstant Discharge: 20CPeak Discharge (10sec): 30CPack 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