Combat Robot ESP32 Controller

Competition robowar firmware — differential drive mixing, weapon arming and hard failsafe

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Overview

Control firmware for the RC robowar bots campaigned across the 8 kg, 15 kg and 30 kg classes. One control architecture serves all three weight classes — only the drive motors, ESC current rating and battery scale up with the robot.

This is combat hardware, so the engineering priority is not features but deterministic failure behaviour. A 15 kg robot with a spinning weapon that loses radio link is a safety problem, and the failsafe path below is the part of this firmware that matters most.

Rebuilt after the original project files were lost to a hard disk failure.

Domain & Techniques

Layer	Implementation
Signal Capture	Interrupt-driven pulse-width measurement of the RC receiver's steering, throttle and weapon channels — no blocking pulseIn() in the control loop
Drive Mixing	Steering and throttle mixed into differential left/right velocities, emitted as PWM + DIR pairs to the motor driver
Weapon Arming	The spinner ESC arms only above a 1700 µs threshold on a dedicated channel, never sharing a channel with drive
Failsafe	Loss of a valid RC pulse for 300 ms — out of range, transmitter off, wiring fault — cuts drive and disarms the weapon automatically
Status Feedback	A single LED distinguishes healthy link (solid) from failsafe (blinking), readable from outside the arena

Pipeline

RC receiver
   |  steering / throttle / weapon channels
   v
[ interrupt-driven pulse width capture ]
   |
   +--> valid pulse within 300 ms? ---- NO ----> FAILSAFE
   |                                             - drive motors cut
   |                                             - weapon disarmed
   YES                                           - status LED blinks
   |
   +--> [ differential mixing ] --> L/R PWM + DIR --> motor driver
   |
   +--> [ weapon channel > 1700 us ] --> ESC arm --> spinner

Hardware

Signal	ESP32 Pin	Notes
Steering channel (RC in)	GPIO 34	Input-only pin
Throttle channel (RC in)	GPIO 35	Input-only pin
Weapon arm channel (RC in)	GPIO 32	Input-only pin
Left motor PWM	GPIO 25	To motor driver
Left motor DIR	GPIO 26	To motor driver
Right motor PWM	GPIO 27	To motor driver
Right motor DIR	GPIO 14	To motor driver
Weapon ESC signal	GPIO 33	Standard 1000-2000us servo pulse
Status LED	GPIO 2	Solid = signal OK, blinking = failsafe

Drive motor driver: any PWM+DIR style dual motor driver rated for the weight class (e.g. Cytron MDD10A for 8kg, higher-current driver for 15kg/30kg).

Dependencies

• ESP32Servo library (for weapon ESC control)

Safety

• Weapon only arms above a clear RC pulse threshold (1700us) on a dedicated channel — never on the same channel as drive.
• Failsafe disarms the weapon and stops drive on any signal loss.
• Always test with the weapon motor disconnected first when bringing up a new build.

Repository Layout

Path	Purpose
CombatRobotController.ino	Full firmware — capture, mixing, arming, failsafe state machine

Project Status

Implemented: interrupt-driven RC capture, differential drive mixing, dedicated-channel weapon arming, 300 ms link-loss failsafe, status indication.

Competition record: this control architecture placed across Robowars events at IIT Delhi, IIT Madras, DTU, MNIT, COEP, PEC and others — see the full competition record.

Roadmap: current-sense telemetry on the weapon ESC to detect stall/jam conditions, and a brownout-aware restart path.

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_{Part of the AI + Robotics engineering portfolio of Divyansh Sachdev
90+ national & international competition wins · IIT / NIT / IIIT podiums}