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Power

Architecture

One common nominal 5 V rail feeds the robot.

Net Source Loads
+5V Adafruit 5993 VBUS (USB 5V in the wiring PNG) ESP32 5V, PCA9685 5V, MAX98357A Vin; servos from PCA9685 V+
3V3 ESP32 onboard LDO, from the 5 V input ESP32 core/GPIO, PCA9685 VCC, OLED VCC
GND 5993 GND + ESP32 GND Everything

ESP32 internally runs at 3.3 V logic. Servo power does not pass through the ESP32 3.3 V regulator. As drawn: USB 5V → PCA9685 5V; PCA9685 V+ → servo 5V; PCA9685 VCC ← ESP32 3V3.

Warning

Never power the servos from the ESP32 3.3 V regulator.

Waveshare documents the C3-Zero LDO as ME6217C33M5G (hundreds of mA class). That is enough for logic + OLED + PCA9685 digital. It is not a servo supply.

Servo current (worst case)

Datasheet stall currents for HD-1370A:

Voltage Per servo stall × 5 servos
4.8 V ~260 mA ≈ 1.3 A
6.0 V ~320 mA ≈ 1.6 A

Robot rail is nominally 5 V, so expect something between those two if several servos stall or start together.

This excludes:

  • ESP32 (Wi-Fi TX peaks)
  • OLED
  • PCA9685 logic
  • MAX98357A + speaker peaks
  • USB host current shared with programming when flashing over the same cable

USB-C 5993 vs real supply

Adafruit 5993 CC resistors ask the upstream port for 5 V / up to ~1.5 A. Whether 1.5 A actually arrives depends on the charger/port.

Five servos at stall (~1.3 A @ 4.8 V) plus the rest of the robot leaves little safety margin on a 1.5 A USB source.

Recommendation:

  • 5 V / ≥ 2 A, with extra margin if several servos can move while audio plays.
  • 5993 remains a convenient connector; it does not raise the current ceiling above what the source and CC advertisement allow.
  • 5993 is not USB-PD voltage conversion. Feed it 5 V USB, or bypass it with a dedicated 5 V / ≥2 A PSU on the +5V and GND rails.

Insufficient-power symptoms

If the rail sags under servo or audio load:

  • ESP32 resets / brownouts
  • Servo jitter or weak motion
  • OLED glitches or blanking
  • Audio noise / dropouts
  • Unstable I2C (NACKs, PCA9685 or OLED “not found” after motion starts)
  • Resets specifically when multiple servos start moving

Bring-up test turns all five servos together — that is a power-stress moment.

Single USB (5993)

The robot uses one USB-C connector: the Adafruit 5993.

Net 5993 ESP32
+5V VBUS 5V pad (and the shared +5V rail)
GND GND GND
USB D− D− GPIO18 (native USB D−)
USB D+ D+ GPIO19 (native USB D+)

That one cable supplies robot power and programming / serial CDC (ARDUINO_USB_MODE=1, ARDUINO_USB_CDC_ON_BOOT=1, monitor 115200).

Leave the ESP32-C3-Zero onboard USB-C unused when the robot is assembled so two 5 V sources cannot fight on the same rail. For early bare-module flashing before 5993 data is wired, the onboard port is fine.

Related: wiring.md, components.md, interfaces.md.