Hobbyking Swamp Dawg build – #1


I couldn't resist the Hobbyking Swap Dawg as an opportunity to play with SimonK ESC firmware with forward / reverse enabled.

ESC selection and implementation

I selected a Hobbyking F-30A ESC, which might seem a bit of overkill but it is a closed air space which reduces its dissipation capacity. The F-30A have proven themselves reliable with SimonK on a range of BLDC motors.

If water gets into the ESC electronics, it is usually fatal as the high impedance FET gate circuits can be turned on in an uncontrolled way and destruction of some FETs and possibly the motor is a likely outcome.

The F-30A was prepared for this application by:

  • unwrapping it;
  • cleaning the MCU pins to ensure reliable adapter contact;
  • building a custom version of bs_nfet.hex with RC_PULSE_REVERSE and symmetric throttle limits;
  • installing and testing the firmware;
  • wrapping the ESC with heatshrink with a little hot melt adhesive lining the ends to seal them when complete.


Above the water resistant F-30A. It has been turned over for the photograph, it normally sits heat sink upwards for best cooling. Subsequent upgrades and configuration changes to the firmware are done throught the servo cable interface.

Extract from the sed script to create the custom firmware.

/^\.equ    RC_PULS_REVERSE/c\
.equ    RC_PULS_REVERSE    = 1
/^\.equ    RC_STOP_RC_PULS/c\
.equ    STOP_RC_PULS    = 1060
/^\.equ    FULL_RC_PULS/c\
.equ    FULL_RC_PULS    = 1500+(1500-STOP_RC_PULS)

Radio configuration

The 9XR Mode 2 radio was configured to use left vertical stick for throttle, TRN switch (momentary) for reverse, and right horizontal stick for rudder.

Screenshot - 16_03_2015 , 08_14_26

Above is an OpenTx Companion screen shot of the mixes.