Watch here the F.A.C. V2 teaser

Abstract

The Floppy Ant Controller (FAC V2) is a compact and highly configurable control board designed for antweight (150g) combat robots. Developed as an advanced alternative to commonly used controllers, the FAC focuses on flexibility, safety, and openness, while maintaining a competitive cost and extremely small form factor.

FAC V2 introduces a completely redesigned hardware and firmware architecture, enabling advanced control logic, extensive configuration via USB, and future expansion through onboard sensors such as an integrated IMU.

Motivation and Design Philosophy

Combat robots, especially in small weight classes, often require unconventional control schemes: mixed drive systems, kinetic weapons, custom actuators, and strict safety constraints. Many existing controllers are either too limited in configurability or too complex and expensive for small robots.

The FAC was designed with the following goals:

• Maximum configurability without sacrificing usability
• Strong safety mechanisms, suitable for competition environments
• Hardware flexibility, supporting multiple motors, servos, and receiver types
• Open-source philosophy, allowing users to inspect, modify, and extend both hardware and firmware

FAC V2 represents a significant evolution over previous versions, with a complete redesign aimed at advanced users who still value simplicity and reliability.

Hardware Overview

Despite its compact size, the FAC V2 integrates multiple features typically found only in larger controllers.

Key Specifications:

• DC Motor Outputs (3x)
• Up to 1.8 A per channel
• 1000-step resolution per direction
• Adjustable PWM frequency from 100 Hz to 10 kHz
• Servo / ESC Outputs (2x)
• High-voltage (battery powered)
• 1000-step resolution
• Adjustable pulse width and frequency (20–300 Hz)
• Inputs
• 2 digital auxiliary inputs (3.3 V max)
• 1 analog auxiliary input (3.3 V max), designed for potentiometers
• Battery Support
• 1S–2S Li-Po / Li-ion
• Configurable low-voltage warning and CUT-OFF protection
• Receiver Compatibility
• PWM (up to 4 channels)
• PPM (up to 8 channels)
• ELRS (planned, firmware support in development)
• Physical Characteristics
• Dimensions: 21 × 31 mm
• Weight: 2.4 g (without receiver), 3.6 g with FS2A receiver

Integrated IMU and Future Control Logic

One of the most important new features of FAC V2 is the integration of an Inertial Measurement Unit (IMU), combining a gyroscope and accelerometer.

This sensor enables the development of advanced control algorithms, such as:

• Automatic drive inversion when the robot is upside down
• Orientation-aware movement control
• Future stabilization or feedback-based behaviors

The IMU is already supported at firmware level and will be increasingly used as new MIXes and Special Functions are introduced.

Safety-Oriented Architecture

Safety is a critical aspect in combat robotics, and FAC V2 implements multiple independent protection mechanisms.

Activation Logic

The firmware does not start until a valid receiver signal is detected. This prevents accidental activation if the robot is powered on without the remote control.

Arming and Fail-Safe

FAC relies on the receiver’s fail-safe configuration to ensure that, in case of signal loss, the robot is automatically disarmed. An optional arming channel allows explicit remote arming and disarming.

Watchdog Protection

A hardware watchdog continuously monitors firmware execution. If the firmware becomes unresponsive for more than 500 ms, the controller is automatically reset, preventing uncontrolled behavior.

Battery CUT-OFF

To protect lithium batteries from deep discharge, FAC continuously monitors battery voltage. If the voltage remains below a configurable threshold for a set time, the controller enters an irreversible CUT-OFF state, requiring a power cycle to recover.

Operating States

FAC operates as a finite-state system, clearly indicated through LED patterns and motor sound signals:

• Start – Initialization, EEPROM check, IMU calibration
• Disarmed – Outputs disabled, safe idle state
• Armed – Full operation, motors and servos active
• CUT-OFF – Emergency battery protection state

This explicit state machine improves both usability and competition safety compliance.

Configuration via FAC Tool

All configuration is performed through the FAC Tool, a browser-based application available at:

👉 https://factool.floppylab.it

Key features of the FAC Tool:

• USB-C connection (no drivers required)
• Offline use as a Progressive Web App
• Full configuration of:
• Receiver settings
• Battery thresholds
• Channel mapping
• MIXes and Special Functions
• Motor and servo behavior
• Real-time telemetry:
• Receiver channel values
• Battery voltage and cell detection
• FAC operating state
• IMU data (visualization planned)

Settings can be tested temporarily before being permanently saved to the controller.

MIXes and Special Functions

FAC separates control logic from physical outputs.

• MIXes generate multiple coordinated outputs (e.g. differential drive)
• Special Functions generate single outputs for direct or automated control

Currently available features include:

• Simple Tank MIX for differential drive robots
• Direct Link to Channel for direct motor, servo, or ESC control
• DC servo (planned)

This architecture allows the same control logic to be reused across different robot layouts simply by changing the mapping.

Open-Source and Extensibility

FAC is an open-source project, both in hardware and firmware. Users are encouraged to:

• Modify the firmware
• Develop new MIXes and control algorithms
• Experiment with IMU-based behaviors
• Adapt the controller to non-standard robotic applications

All usage and redistribution conditions are defined in the project LICENSE file.

Conclusion

The Floppy Ant Controller V2 is not just a motor controller, but a flexible control platform for small combat robots. By combining compact hardware, strong safety features, advanced configuration, and an open-source ecosystem, FAC enables builders to push beyond standard designs and experiment with smarter, more capable robots.

Thanks to PCBWay for supporting version 2.0 of this project. The boards produced are always excellent and the assembly service is fast and accurate. The boards were initially produced in green and then in matt black, and I must say that both are very attractive, although matt black always has its charm. 

Order suggestions and settings

Set your PCB order like that:

The maximum number of FACs that can be ordered is 14 if you want to stay within the PCBWay $29 PCBA offer. With this quantity, each individual piece will cost approximately $15/$16 including shipping.

If you have any questions or require further information, please contact me by email.

thefloppylab@gmail.com