OPTO-Isolation and BEC Power

Are KDE Direct ESCs opto-isolated?
Yes, all KDE Direct ESCs are opto-isolated. This means that the power to the ESC via the control lead (white, red, black) is isolated from the battery leads and the signal is transferred via light (photocoupler).

We recommend connecting a 5V UBEC to the ESCs if your flight controller does not supply this voltage. Some flight controllers provide this power to the ESCs while others do not. For example, if you are using a Pixhawk we recommend connecting a 5V UBEC to the MAIN output rail.

🛈 While we recommend using a UBEC, any regulated DC voltage between 3.3V – 12V is acceptable.

Do I need to connect the PWM ground wire to the ESC?
Yes, always connect the PWM ground wire. A shared ground connection is essential for the ESC to reliably detect the PWM signal. Without a common ground, the return path for the signal is incomplete, which can cause unreliable behavior.

🛈 If using a servo tester or signal generator that doesn't provide power, use a Y-harness to combine the PWM (signal and ground) with power from a UBEC (5V and ground). Connect the Y-harness output to the ESC's control lead. This ensures that the ground from the PWM source, UBEC, and ESC are tied together at a single point, providing a stable ground reference.

What is a UBEC?
A UBEC (Universal Battery Elimination Circuit) is a device that steps down your main battery voltage to a lower voltage to supply power to electronics such as ESCs, servos, and gimbals - without needing a separate battery.

There are two types:

• Linear BECs - dissipate excess voltage as heat (less efficient).
• Switching BECs (UBECs) - provide high efficient voltage regulation using MOSFETs

KDE Direct offers two UBECs:

• UBEC-UVC: Supports 4S – 14S batteries
• UBEC22: Supports 2S – 8S batteries

⚠︎ Never connect a UBEC in parallel or series with another UBEC. Only use one UBEC per power rail.

Why do I need to supply 3.3V – 12V to the ESC control lead?
While KDE Direct ESCs will function without external power, if this voltage isn't provided, then the signal received by the ESC is not fully on. For example if you disconnect the red control lead wire, you'll notice a drop in power – this is because the opto-circuit isn't being fully driven.

Providing 3.3V – 12V power ensures:

• The throttle signal is clean and reliable
• Reduced EMI and RF noise
• Proper throttle calibration

Note:

• The ESC will draw less than 50mA through the red control lead wire.
• The opto-circuitry is rated up to 35V max.

How do I connect a UBEC to a Pixhawk?

For a Pixhawk with a traditional setup and single battery (see diagram above). Connect the UBEC in parallel to the battery leads (on the PDB) to power electronics. Use the Power Modules to power the Pixhawk.

For a Pixhawk with a dedicated flight controller battery (see diagram above). Connect the Power Module as follows:

• V_IN -> dedicated flight controller battery.
• V_OUT (pass-through) -> UBEC input -> UBEC output (powers Pixhawk Main Out rail).
• 6-pin connector -> Pixhawk POWER1 or POWER2 port.