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MARSLib Documentation

Dynamic Power Shedding

Modern FRC hardware—specifically Krakens and Falcons—can physically pull more power than the RoboRIO and a 12V battery can safely provide. If your Swerve Drive engages in a massive pushing match while the Intake is stalled on a stuck Fuel Ball, the battery voltage will dip below 7V, the RoboRIO will reset, and you will lose the match.

1. The Problem with Static Limits

Section titled “1. The Problem with Static Limits”

Most teams solve this by configuring static breaker current limits. This is a compromise. It neuters your robot’s acceleration when the battery is fully charged at 12.8V just to protect it when it drops to 9V.

2. MARSPowerManager: Voltage Scaling

Section titled “2. MARSPowerManager: Voltage Scaling”

In MARSLib, we use the MARSPowerManager to implement Voltage Scaling and Power Shedding. Instead of static stator current bounds, our subsystems dynamically cap their output voltage based on the real-time health of the battery.

// Inside an IO implementation's periodic loop
double currentSystemVoltage = MARSPowerManager.getInstance().getBatteryVoltage();
double maxAllowedVoltage = 12.0;


if (currentSystemVoltage < 9.5) {
  // Battery is sagging heavily, shed power from non-essentials
  maxAllowedVoltage = 3.0; // Throttle intake to prevent brownout
}


motor.setVoltage(MathUtil.clamp(requestedVoltage, -maxAllowedVoltage, maxAllowedVoltage));

3. Subsystem Priority Classes

Section titled “3. Subsystem Priority Classes”

Not all subsystems are created equal. When the MARSPowerManager detects a critical system voltage sag (e.g., < 9.5V), it initiates a lockdown phase. The framework groups mechanisms into three distinct tiers:

  • TIER 1 (Critical): Drivetrain Swerve Modules. These never scale down. Losing traction or evasiveness is unacceptable.

  • TIER 2 (High): Shooter Flywheels & Pivot. Voltage output is slightly scaled to ensure consistent shots, but not eliminated.

  • TIER 3 (Sheddable): Intakes, Feeders, and LEDs. If the voltage drops to 9V, these subsystems are aggressively clamped to a maximum output of 2-3 Volts until the battery recovers.

📖 Further Reading & External Resources

Section titled “📖 Further Reading & External Resources”