swerve-drive-drift.md

description
Drift can be caused by anything and everything in a swerve drive...

Swerve Drive Drift

Swerve drive drift has been a persistent problem for many years and there have been many discussions as to why it happens. This page will guide you through 3 categories of common causes of swerve drive drift. It is important to keep in mind that SEVERAL of these issues could be present in your robot.

Hardware

Wiring

Incorrect wiring can be further broken down into 3 categories for the swerve drive. These are the symptoms if the wiring is worn down, incorrectly routed, or broken some where (especially in connectors!)

Encoder

• Telemetry readings will be erratic and nonsensicle.
• Motor could spin out of control.
• Errors in the driver station console may appear.

Motor Controller

• Telemetry may be slow to update.
• Motors may suddenly stop or spin out of control.
• Motors may not respond to commands.
• Errors in the driver station console may appear.

Gyroscope/IMU

• Telemetry may be slow to update.
• Field Relative robot control may be unusable.
• Autonomous drifts uncontrollably.
• Errors in the driver station may appear.

Physical Components

Magnetic Encoder

• Magnet not secured to the swerve module and slips while in motion.
  • Absolute encoder offsets would constantly need to be readjusted until magnet is secured.
• Magnetic encoder is not secured to the swerve module.

Motor

• Motor may not have firm connection to swerve module shaft.
  • Motor would "twitch" while running if a amperage limit is set.
• Motor is dying.
  • Motor may be pulling more amperage to get the same speeds.

Swerve Module

• Modules are inconsistent with the same PID.
  • Grease may need to be applied to the gears.

Robot

• Robot center of gravity is not ideal.

Software

• Constant Command Scheduler loop overruns because of other parts of your code.
• Maximum physical velocity is not set correctly.
• If using open loop, modules run at different speeds.
• Controller input filtering.
• Use of SwerveDrive.setCosineCompensator
• Use of SwerveDrive.setHeadingCorrection
• Use of SwerveModule.setAntiJitter
• Use of SwerveDrive.chassisVelocityCorrection
• Use of SwerveDrive.setMaximumSpeeds
• Use of SwerveDrive.replaceSwerveModuleFeedforward
• Use of SwerveDrive.setGyroOffset
• Use of SwerveDrive.updateCacheValidityPeriods
• Use of SwerveDrive.setOdometryPeriod
• Use of SwerveDrive.addVisionMeasurement
• Use of SwerveDrive.setChassisDiscretization

PathPlanner

• PathPlanner AutoBuilder PID's are not tuned well.
• Maximum module velocity is too high or too low.
• Testing path is curved.
• PathPlanner auto doesn't define preset pose.
• PathPlanner path doesnt reset odometry on start.

Configuration

• Module locations are not correctly defined.
  • Remember these are from the center of the robot to the center of the module!
• Swerve Module configurations do not have the correct definitions for the Absolute Encoder, Angle Motor, or Drive motor.
• The conversion factor is defined inside of swerve module configuration files is different from the one in physicalproperties.json
  • The conversion factors in the swerve module files are completely OPTIONAL and do not need to be defined unless you have a reason. You should only define them in the code or use physicalproperties.json to avoid redundancy.
• The conversion factor is not correct.
  • If you see your swerve drive constantly going further than it should with pathplanner this is probably the case.
  • If your angle motors never align the module correctly this may also be a cause of it.
• Drive and steering/azimuth/angle motor PIDs are not tuned well enough.
• The amperage limit is too low.
• Translational axis changes with robot orientation.