How to power flight controller servos when BEC supply is insufficient

I. Symptoms

When using a flight controller (FC), if the servo load is too high, a servo BEC power supply insufficiency issue may occur, leading to:

• Servos stalling, jittering, or responding sluggishly
• FC restarting due to insufficient power supply
• Other equipment such as VTX (video transmitter), ESCs, etc. being affected
  This situation typically occurs with large fixed-wing aircraft, especially when using multiple servos, landing gear, flaps, gimbals, and other equipment.

II. Cause Analysis

The power supply for servos is provided by the BEC (Battery Eliminator Circuit) on the flight controller:

• F405 WING APP Servo BEC: Continuous 4.5A, Peak 5.5A
• F405 WING MINI Servo BEC: Continuous 4A, Peak 5A
• F405 WING APP V2 Servo BEC: Continuous 7.5 A, Peak 14A
  If the total current of the servos exceeds the power supply capacity of the BEC, it may lead to insufficient power supply.
  For example:
  
  For a 90mm EDF Viper using 9x 13g servos, in extreme stall conditions:
  
• Total servo current = 9 × 1A = 9A (exceeding the power supply capacity of some FC BECs)
• This may cause insufficient servo power supply and FC restart

III. Solutions

Method 1: Partially use ESC-built-in BEC for power supply
1. Power Supply Analysis
Use the flight controller BEC for some servos and the ESC-built-in BEC for others, taking the 90mm EDF Viper as an example:

• Flight Controller BEC Power Supply:
• Ailerons (2 units), connected using a Y-splitter cable, occupying one PWM channel.
• Elevator (1 unit), occupying one PWM channel.
• Rudder (1 unit), occupying one PWM channel.
  (Total 4x1A=4A, below the peak current of the servo BEC, safe)
• ESC BEC Power Supply:
  (Assuming the ESC BEC has a 5A power supply capacity)
• Flaps (2 units), connected using a Y-splitter cable, occupying one PWM channel.
• Retracts (3 units), connected using a Y-splitter cable, occupying one PWM channel.
  (Total 5x1A=5A, not exceeding the BEC peak current 5A, safe)
  This effectively distributes the current load and prevents flight controller BEC power insufficiency.
  2. Specific Method
  Use the Y-cable modification method for wiring, as shown in the schematic below:
  
  3. Specific Wiring
  Steps:
  1. Prepare Y-cables
  
  2. Power a single servo using ESC BEC
• One end to flight controller (remove positive wire)
• One end to ESC (remove signal wire)
• One end to servo
  
  3. Power multiple servos using ESC BEC
• Add more Y-cables
• Connect positive to ESC positive
• Connect negative to ESC negative
  
  4. Important Notes
  Flight controller, servos, and ESCs must share a common ground, otherwise signal distortion may occur!
  It is recommended to use flight controller BEC for critical servos (ailerons, elevator, rudder) and ESC BEC for non-critical servos (flaps, landing gear)!
  Ensure servo current is less than the BEC rated power supply capacity, otherwise power insufficiency may still occur!
  Method 2: Completely use ESC-built-in BEC for power supply
  1. Applicable Scenarios
  If your ESC has a high-current built-in BEC (8A or higher), you can completely use the ESC BEC for power supply, for example:
  
  9x 13g servos, total current 9A
  ESC BEC power supply capacity 10A
  Can completely use ESC BEC for power supply
  2. Specific Operations
  For WING APP flight controller
• Use Y-cable modification method
  For WING MINI flight controller
• No wiring modification needed
• Directly disconnect the flight controller Servo BEC power jumper
• Servos can be directly powered by the ESC
  
  
  3. Important Notes
  If using multiple ESCs, only one ESC's BEC should be used for power supply, otherwise it will cause the ESC BEC to burn out!!!

IV. Verification

How to check if the power supply is normal?
1. Observe servo operation

• No stuttering, no jittering, no abnormal resets
  2. Check flight controller power supply stability
• Whether the flight controller restarts
  3. Use a multimeter to measure BEC output
• Whether it maintains 5V / 6V
• Whether there is significant voltage drop at high throttle

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