Introduction to Simulation

Many CTR Electronics devices support high-fidelity simulation, allowing the simulated robot to match the behavior of the real robot hardware as closely as possible. This makes simulation a powerful tool to quickly diagnose and fix bugs in robot code without relying on access to hardware.

Supported Devices

Currently, all Phoenix 6 devices are supported in simulation.

Warning

Multiple CAN buses using the CANivore API is not supported at this time. All CAN devices will appear on the same CAN bus. If you wish to run your robot code in simulation, ensure devices have unique IDs across CAN buses.

Simulation API

Each supported device has a device-specific SimState object that can be used to manage I/O with the simulated device. The object can be retrieved by calling getSimState() on an instance of a device.

Java

var talonFXSim = m_talonFX.getSimState();

C++

auto& talonFXSim = m_talonFX.GetSimState();

Note

Phoenix 6 utilizes the C++ units library when applicable.

Orientation

The SimState API ignores typical device invert settings, as the user may change invert for any reason (such as flipping which direction is forward for a drivebase). As a result, for some devices, the SimState object supports specifying the orientation of the device relative to the robot chassis (Java, C++).

This orientation represents the mechanical linkage between the device and the robot chassis. It should not be changed with runtime invert, as runtime invert specifies the logical orientation of the device. Rather, the orientation should only be modified when the mechanical linkage itself changes, such as when switching between two gearboxes inverted from each other.

Java

var leftTalonFXSim = m_leftTalonFX.getSimState();
var rightTalonFXSim = m_rightTalonFX.getSimState();

// left drivetrain motors are typically CCW+
leftTalonFXSim.Orientation = ChassisReference.CounterClockwise_Positive;

// right drivetrain motors are typically CW+
rightTalonFXSim.Orientation = ChassisReference.Clockwise_Positive;

C++

auto& leftTalonFXSim = m_leftTalonFX.GetSimState();
auto& rightTalonFXSim = m_rightTalonFX.GetSimState();

// left drivetrain motors are typically CCW+
leftTalonFXSim.Orientation = sim::ChassisReference::CounterClockwise_Positive;

// right drivetrain motors are typically CW+
rightTalonFXSim.Orientation = sim::ChassisReference::Clockwise_Positive;

Inputs and Outputs

All SimState objects contain multiple inputs to manipulate the state of the device based on simulation physics calculations. For example, all device SimState objects have a supply voltage input:

Important

Non-FRC platforms are required to set supply voltage, as it affects simulation calculations. It’s recommended that FRC users set supply voltage to RobotController.getBatteryVoltage() (Java, C++) to take advantage of WPILib’s BatterySim (Java, C++) API.

Java

// set the supply voltage of the TalonFX to 12 V
m_talonFXSim.setSupplyVoltage(12);

C++

// set the supply voltage of the TalonFX to 12 V
m_talonFXSim.SetSupplyVoltage(12_V);

Some device SimState objects also contain outputs that can be used in simulation physics calculations. For example, the TalonFXSimState (Java, C++) object has a motor voltage output that can be used to calculate position and velocity:

Java

private final DCMotorSim m_motorSimModel =
   new DCMotorSim(DCMotor.getKrakenX60Foc(1), 1.0, 0.001);

public void simulationPeriodic() {
   var talonFXSim = m_talonFX.getSimState();

   // get the motor voltage of the TalonFX
   var motorVoltage = talonFXSim.getMotorVoltage();

   // use the motor voltage to calculate new position and velocity
   // using WPILib's DCMotorSim class for physics simulation
   m_motorSimModel.setInputVoltage(motorVoltage);
   m_motorSimModel.update(0.020); // assume 20 ms loop time

   // apply the new rotor position and velocity to the TalonFX;
   // note that this is rotor position/velocity (before gear ratios)
   talonFXSim.setRawRotorPosition(m_motorSimModel.getAngularPositionRotations());
   talonFXSim.setRotorVelocity(
      Units.radiansToRotations(m_motorSimModel.getAngularVelocityRadPerSec())
   );
}

C++

frc::sim::DCMotorSim m_motorSimModel{
   frc::DCMotor::KrakenX60FOC(1), 1.0, 0.001_kg_sq_m
};

void SimulationPeriodic()
{
   auto& talonFXSim = m_talonFX.GetSimState();

   // get the motor voltage of the TalonFX
   auto motorVoltage = talonFXSim.GetMotorVoltage();

   // use the motor voltage to calculate new position and velocity
   // using WPILib's DCMotorSim class for physics simulation
   m_motorSimModel.SetInputVoltage(motorVoltage);
   m_motorSimModel.Update(20_ms); // assume 20 ms loop time

   // apply the new rotor position and velocity to the TalonFX;
   // note that this is rotor position/velocity (before gear ratios)
   talonFXSim.SetRawRotorPosition(m_motorSimModel.GetAngularPosition());
   talonFXSim.SetRotorVelocity(m_motorSimModel.GetAngularVelocity());
}

High Fidelity CAN Bus Simulation

As a part of high-fidelity simulation, the influence of the CAN bus is simulated at a level similar to what happens on a real robot. This means that the timing behavior of control and status signals in simulation will align to the same framing intervals seen on a real CAN bus. In simulation, this may appear as a delay between setting a signal and getting its real value, or between setting its real value and getting it in API.

In unit tests, it may be useful to increase the update rate of status signals to avoid erroneous failures and minimize delays. The update rate can be modified for simulation by wrapping the signal update frequency in a Utils.isSimulation() (Java, C++) condition.

Java

if (Utils.isSimulation()) {
   // set update rate to 1ms for unit tests
   m_velocitySignal.setUpdateFrequency(1000);
}

C++

if (IsSimulation()) {
   // set update rate to 1ms for unit tests
   m_velocitySignal.SetUpdateFrequency(1000_Hz);
}