Fixing Horizontal Lines at High Throttle on SpeedyBee F405 WING MINI

I. Issue

When using the SpeedyBee F405 WING MINI flight controller, some video transmitters (VTX) may exhibit horizontal band interference at high throttle, affecting FPV picture quality, especially for VTX or cameras sensitive to voltage changes.

II. Root Cause Analysis

1. The SpeedyBee F405 WING MINI uses a different VTX power supply method compared to the SpeedyBee F405 WING APP version. It employs a 5V SERVO BEC or direct battery supply power mode. By default, the VTX is powered directly by the battery.
   
2. Some VTX or cameras are sensitive to voltage fluctuations. When throttle is high, battery load changes cause voltage fluctuations, affecting VTX stability and resulting in horizontal band interference.
3. In testing, we recommend using the SpeedyBee TX ULTRA VTX, which has strong interference resistance and provides clear pictures without horizontal bands. However, other VTX models may still be affected by voltage fluctuations.

III. Solution

Method: Use Parallel Capacitor to Reduce Voltage Fluctuations
The SpeedyBee F405 WING MINI accessory kit comes standard with a 35V 470uF electrolytic capacitor. Testing has shown this capacitor can effectively reduce voltage fluctuations at high throttle, significantly reducing horizontal band generation.

Installation Steps

1. Identify capacitor polarity: Take out the 35V 470uF electrolytic capacitor from its packaging. The long lead is positive, the short lead is negative, and the negative side usually has a "-" mark.
   ※Note: Do not reverse the capacitor polarity, as this will cause the capacitor to explode!!!
   
2. Connect in parallel to the flight controller PDB board: Connect the capacitor's positive lead to the PDB board's positive terminal and the negative lead to the negative terminal.
   ※Recommendation: Try to shorten the capacitor leads as much as possible to reduce signal interference and improve filtering effect.
   
   Supplement: Battery Optimization

• Aged batteries have higher internal resistance, which may cause significant voltage fluctuations at high throttle, making interference more likely to occur.
• Try replacing with high C-value quality lithium batteries to reduce power supply fluctuations.

IV. Verification

After completing the optimization, you can verify if the interference has been eliminated through the following methods:
1) Power on the flight controller and observe the FPV picture

• Observe whether the VTX picture still has horizontal band interference in a stationary state.
  2) Increase throttle and test load conditions
• Increase throttle to over 80% and observe if the FPV picture still has horizontal band issues.
  

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