CTRE Controllor with Sensors

The CTRE TalonSRX and TalonFX controllers can be assigned sensors. The sensor can be attached directly to the talon, or it can be a remote sensor (attached somewhere else).

Each motor gets assigned ONE configured "selected sensor" for EACH of the 2 PID loops. The sensor can be

• an attached sensor
• a remote sensor,
• the sum or difference of two sensors

The "selected sensor" are assigned to one of two possible PID loops on each controller. PID loop 0 is the primary loop and PID loop 1 is the secondary loop. More about the 2 PID loops later.

1. Assign a Connected Sensor

One connected sensor can be assigned for each PID loop .

Assign a sensor with configSelectedFeedbackSensor:

• You can choose from a variety of feedback devices.
• The second argument is the PID loop this sensor is assigned to (0 or 1)
• The third argument is the timeout time in ms (how long to wait for the controller to respond)

This stamement assigns a QuadEncoder to motor 1, PID loop 0. The encoder must be attached to the motor.

motor1.configSelectedFeedbackSensor(FeedbackDevice.QuadEncoder, 

    0, 20); 

For talonFX's use FeedbackDevice.IntegratedSensor

2. Assign a Remotely Connected Sensor

Before assigning a remotely connected sensor, you need to configure a remote sensor filter, which tells where to find the sensor and what type it is:

• the first argument is the device CAN ID. Here, a Pigeon gyro was previously created, and we use the .getDeviceID method to get it's CAN ID
• the second argument is the type of sensor source signal to expect. Here it is the yaw angle of the gyro.
• The third argument is the remote sensor number. Up to two remote sensors can be defined, numbered 0 and 1.
• The fourth argument is the timeout time in ms.

motor1.configRemoteFeedbackFilter( gyro.getDeviceID(),   

     RemoteSensorSource.Pigeon_Yaw,  0, 20;

A remote sensor can also be the selected connected sensor of another motor. This line assigns the connected encoder of motor 2 to be a remote sensor #1 of motor 1.

 motor1.configRemoteFeedbackFilter( motor2.getDeviceID(),   

     RemoteSensorSource.TalonSRXSelectedSensor,  1, 20;

Once the remote filter is configured, we can assign the remote sensor. This line assigns the gyro to be the sensor for PID loop 1 on motor 1.

motor1.configSelectedFeedbackSensor( FeedbackDevice.RemoteSensor0,

      1, 20);

3. Sensor Sums and Differences

We can use the sum of difference of two different sensors to be a remote sensor. Why would you do this? One reason would be to average the right and left side encoders.

To set up a sum, we need to configure two sensors to be the first term (Sum0) and second term (Sum 1). The sum will be Sum0 + Sum1. The sum is then assigned to be the selected sensor for motor 1.

 motor1.configRemoteFeedbackFilter( motor2.getDeviceID(),   

     RemoteSensorSource.TalonSRXSelectedSensor,  0, 20;

motor1.configSensorTerm(SensorTerm.Sum0,    

   FeedbackDevice.RemoteSensor0, 0) 

motor1.configSensorTerm(SensorTerm.Sum1, 

    FeedbackDevice.FeedbackDevice.QuadEncoder , 0) 

motor1.configSelectedFeedbackSensor( FeedbackDevice.SensorSum, 

       0, 20,);

To get the average, assign a sensor coefficient of 1/2 to the sum. This assigns a coefficient of 0.5 to the sensor assigned to PID0. The first argument is the coefficient, the second is the PID loop, and the third is the timeout.

motor1.configSelectedFeedbackCoefficient( 0.5, 0, 20)

4. PID Loops and Putting it All Together

One way to make use of the two available PID loops is to use the primary (PID0) for controlling either distance or velocity, and the a auxiliary (PID1) for control angle.

For position, you could use the average of the two encoders, see section 3, for PID 0, and the gyro for PID1.