Wall-E's wiring is pretty simple actually.
The ESP32-Cam is connected to the power rail only.
The Wemos D1 ESP8266 controls a single I²C bus, where it commands:
* an OLED screen (actually I replaced the Wemos OLED shield with a slightly bigger .96" model)
* a Wemos Motor shield, to interface geared motors for the tank tracks,
* a PCA9685-based 16-channel PWM controller, to interface all servos,
* a GY-80 IMU, to measure Wall-E's orientation (Madgwick orientation filter is not functional yet).
The same 5V power rail, derived from a 2x18650 battery + controller pack (not shown below), powers the actuators (servos, geared motors) as well as the sensor and both microcontrollers. The ESP8266 and ESP32-Cam both have onboard 3.3V regulators, I count on that to compensate for the voltage drop that probably occur when motors & servomotors draw too much current. I initially powered it all from a single 18650 battery, and experienced spurrious resets (probably from brown-out detector). With a 2x18650 module, the system is way more stable.
The unused servo headers of the PWM controller make for a handy power rail connector, where I plug in the battery module, ESP32-Cam, motor shield power input, etc.