Using the PWM Output with Spark Max

The Canandmag easily integrates with the REV Spark Max motor controller, offering closed loop control feedback. The Canandmag’s PWM output can be read by the Spark Max without the need of any intermediate adapter boards.

Hardware

The Canandmag, by default, ships in Spark MAX compatibility mode. As a result, the 10 pin IDC connector may be directly connected to the Spark MAX data port using the included IDC cable. This will transmit both power and signal with no need for soldering.

If the encoder has had its Spark MAX trace cut (for example, to configure the device in Talon SRX mode), you may bridge the MAX solderpad to re-enable Spark MAX compatibility mode. Make sure not to bridge both the Spark MAX and Talon SRX pads at the same time, as this could damage your motor controller.

Software

The Canandmag acts as a PWM absolute encoder. It can be configured in the Absolute Encoder tab of the REV Hardware Client.

As the output of the Canandmag is similar to that of a REV Through Bore, it may be used in areas where the REV encoder is used (for example, when used in a swerve module, it can be configured and used with similar code to a MaxSwerve module).

Pressing the zero button on the Canandmag will set the currently read position as the new zero point. This can be used to quickly rezero a mechanism such as a swerve module without the use of a computer. If the encoder is connected over CAN, manipulating the absolute position via setAbsPosition() or inverting the direction through either the ReduxLib API or Alchemist will also change the PWM output accordingly, overriding the offset saved by the button press.

Code Example - Java

// Instantiate a Spark MAX and get a handle to a PWM absolute encoder
SparkMax sparkMax = new SparkMax(0, MotorType.kBrushless);
SparkAbsoluteEncoder sparkEncoder = sparkMax.getAbsoluteEncoder();

// Create a config to change the Spark MAX's settings
SparkMaxConfig config = new SparkMaxConfig();

// Below are some configuration options that may be useful when using the
// Canandmag with a Spark MAX. Not all of them are applicable in every use
// case; Read the REVLib documentation for specific details.

// Change this as needed, 8 points to average for velocity measurement is a
// decent starting point
config.absoluteEncoder.averageDepth(8);

// Configure the Spark Max to use the PWM-connected Canandmag for
// closed-loop control
config.closedLoop.feedbackSensor(FeedbackSensor.kAbsoluteEncoder);

// Position wrapping may be useful for swerve pivot applications.
// Wrap the closed loop error within 0 and 1 rotations of the encoder
config.closedLoop.positionWrappingInputRange(0, 1);
config.closedLoop.positionWrappingEnabled(true);

// By default, the Spark Max only transmits position and velocity data
// for duty cycle encoders every 200 ms (5 Hz).
// To increase frequency (e.g. to 20 ms/50 Hz), set the signal periods:

// increase position update frequency to once every 20 ms
config.signals.absoluteEncoderPositionPeriodMs(20);

// increase velocity update frequency to once every 20 ms
config.signals.absoluteEncoderVelocityPeriodMs(20);

// Apply the configuration to the motor controller, resetting to factory
// default and persisting the new parameters
sparkMax.configure(config, ResetMode.kResetSafeParameters, PersistMode.kPersistParameters);

// Reads the PWM Canandmag position (the default unit is rotations)
sparkEncoder.getPosition();
// Read the PWM Canandmag velocity (the default unit is rotations per minute)
sparkEncoder.getVelocity();

Refer to REV’s documentation for more information on using absolute encoders with the Spark Max. The Java API reference for AbsoluteEncoderConfig and ClosedLoopConfig may also be helpful.