Limiting Power Consumption

Current limits

There are two types of currents involved in a SmartMotorController, the Supply current and the Stator current.

• The current input of the motor controller is the Supply current.

• The current output of the motor controller is the Stator current.

Some motor controllers, like SparkMax and SparkFlex do not let you set these separately

CTRE has excellent documentation explaining the relationship between the supply and stator currents.

Improving Performance with Current LimitsPhoenix 6

If your mechanism interacts with a game element or has a chance of getting stuck a current limit WILL cause the mechanism to stutter until the current is back below the limit. This can cause strains on the mechanism as it constantly starts then stops but it could save your motor controller and prevent brownouts because your mechanism will not be able to pull more power than necessary.

Setting Current Limits in YAMS

SmartMotorControllerConfig motorConfig = new SmartMotorControllerConfig(this)
      .withStatorCurrentLimit(Amps.of(200)) // Current to the motor
      .withSupplyCurrentLimit(Amps.of(40)) // Current to the motor controller

Ramp Rates

Ramp rates is the minimum time it takes for a motor to go from 0% to 100% power to the motor.

If the ramp rate is omitted from configurations you will commonly see mechanisms taking up a majority of power whenever they go from rest to moving with a closed loop controller.

Whenever possible use current limits instead of ramp rates. Ramp rates delay input response and make the robot seem "slow" or "delayed".

There are two ramp rates defined in motor controllers.

• Closed loop ramp rate

• Open loop ramp rate

These ramp rates are applied whenever the motor controller is in the appropriate mode. So the closed loop ramp rate is used when the motor controller PID is used. The open loop ramp rate is used when the dutycycle or voltage control is used.

Setting Ramp Rates in YAMS

SmartMotorControllerConfig motorConfig = new SmartMotorControllerConfig(this)
      .withClosedLoopRampRate(Seconds.of(0.25)) // 0.25 seconds minimum 
      .withOpenLoopRampRate(Seconds.of(0.25)) // 0.25 seconds minimum