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Version: 3.2.1

Swing Movements

pid_swing_set() has many ways of calling it with many default values you can configure and override in specific motions.

How does it work?​

pid_swing_set() turns the robot by moving one side of the drive with PID and the other side to a fixed amount. This is called a swing turn because the robot "swings" around a point.

Clockwise is positive and counter-clockwise is negative by default:

  • going to 90 degree is clockwise
  • going to -90 degrees is counter-clockwise

PID is an algorithm that tries to damp momentum. PID is very good at dampening a consistent amount of momentum, but every angle a robot turns to produces a pretty different amount of momentum. EZ-Template tries to help this by having a kI set in the default constants, but what EZ-Template takes this a step further. If there is a kI set, and there is a start_i set, and the turn distance is larger than start_i, the robot will limit its max speed once it's within start_i. This helps dampen excess momentum on larger turns.

In EZ-Template, you decide what side of the drive you'd like to move the robot to the desired target. You can also decide at what speed the opposite side of the drives moves at.

By default this is 0. When that side if set to not move, it will use your drive PID constants to lock itself in place and ensure it stays still. You can also set this to any number between -127 and 127. By setting this you change the size of the arc that the robot takes to get to your target angle.

Absolute Swing Turns​

All of the normal swing turn functions use absolute heading. This means turning to 0 degrees will always turn to face the direction the robot initially started in.

Simplest Swing​

At minimum, you need to give the robot an angle to go to and a speed limit (0-127). You can do this with and without okapi units.

// Turn to 45deg with the left side of the drive
chassis.pid_swing_set(ez::LEFT_SWING, 45_deg, 90);
chassis.pid_wait();

// Turn to 0deg with the left side of the drive
chassis.pid_swing_set(ez::LEFT_SWING, 0, 90);
chassis.pid_wait();

// Turn to 45deg with the right side of the drive
chassis.pid_swing_set(ez::RIGHT_SWING, 45_deg, 90);
chassis.pid_wait();

// Turn to 0deg with the right side of the drive
chassis.pid_swing_set(ez::RIGHT_SWING, 0, 90);
chassis.pid_wait();

Starting Angle​

You can change the starting angle of the robot with drive_angle_set(). This is nice when your robot is facing a strange angle to start the autonomous routine, and you can align your angles with the field.

chassis.drive_angle_set(45_deg);  // Start the robot facing 45 degrees

// Swing to 0deg
chassis.pid_swing_set(ez::LEFT_SWING, 0_deg, 90);
chassis.pid_wait();

// Swing to 45deg
chassis.pid_swing_set(ez::LEFT_SWING, 45_deg, 90);
chassis.pid_wait();

Arcs​

// Turn to 45deg with the left side of the drive, and the right side going 30
chassis.pid_swing_set(ez::LEFT_SWING, 45_deg, 90, 30);
chassis.pid_wait();

// Turn to 0deg with the left side of the drive, and the right side going 30
chassis.pid_swing_set(ez::LEFT_SWING, 0, 90);
chassis.pid_wait();

// Turn to 45deg with the right side of the drive, and the left side going 30
chassis.pid_swing_set(ez::RIGHT_SWING, 45_deg, 90, 30);
chassis.pid_wait();

// Turn to 0deg with the right side of the drive, and the left side going 30
chassis.pid_swing_set(ez::RIGHT_SWING, 0, 90, 30);
chassis.pid_wait();

Swing Paths​

You can set the robot to always turn a specific direction.

chassis.pid_swing_behavior_set(ez::shortest);

// This will turn 1 degree to the right with the left side of the drive
chassis.pid_swing_set(ez::LEFT_SWING, 361_deg, 90);
chassis.pid_wait();

But you can override these defaults in each motion.

chassis.pid_swing_behavior_set(ez::shortest);

// This will turn 361 degrees to the left
chassis.pid_swing_set(ez::LEFT_SWING, 361_deg, 90, ez::longest);
chassis.pid_wait();

You can also pick between turning clockwise and counterclockwise.

chassis.pid_swing_behavior_set(ez::shortest);

// This will turn to 180deg counter clockwise
chassis.pid_swing_set(ez::LEFT_SWING, 180_deg, 90, ez::ccw);
chassis.pid_wait();

// This will turn to 0 deg clockwise
chassis.pid_swing_set(ez::LEFT_SWING, 0_deg, 90, ez::cw);
chassis.pid_wait();

Slew​

Slew ramps up the speed limit of the robot to give smoother accelerations.

chassis.slew_swing_set(true);  // Enables global slew
chassis.slew_swing_constants_set(5_deg, 50);

// Over the first 5 degrees, the robot will ramp the speed limit from 50 to 110 
chassis.pid_swing_set(ez::LEFT_SWING, 90_deg, 110);
chassis.pid_wait();

You can change the behavior of slew for each motion. In the example below, slew is disabled globally but is enabled in one of the motions.

chassis.slew_swing_set(false);  // Disables global slew
chassis.slew_swing_constants_set(5_deg, 50);

// Over the first 5 degrees, the robot will ramp the speed limit from 50 to 110 
chassis.pid_swing_set(ez::LEFT_SWING, 90_deg, 110, true);  // Slew will be enabled for this motion
chassis.pid_wait();

// This will not use slew to return to 0 degrees
chassis.pid_swing_set(ez::LEFT_SWING, 0_deg, 110, true);  
chassis.pid_wait();

Arcs and Swing Paths​

You can use slew in conjunction with different turn behavior.

chassis.pid_swing_behavior_set(ez::shortest);
chassis.slew_swing_constants_set(5_deg, 50);

// This will turn to 270 deg clockwise, with the right side going 30
chassis.pid_swing_set(ez::LEFT_SWING, 270_deg, 90, 30, ez::cw);
chassis.pid_wait();

// This will take the shortest path to 0 degrees, with the right side going 30
chassis.pid_swing_set(ez::LEFT_SWING, 360_deg, 90, 30);
chassis.pid_wait();

Arcs and Slew​

You can use slew in conjunction with different turn behavior.

chassis.slew_swing_set(false);  // Enables global slew
chassis.slew_swing_constants_set(5_deg, 50);

// This will turn to 270deg while slewing, with the right side going 30
chassis.pid_swing_set(ez::LEFT_SWING, 270_deg, 90, 30, true);
chassis.pid_wait();

// This will turn to 270deg without slew, with the right side going 30
chassis.pid_swing_set(ez::LEFT_SWING, 360_deg, 90, 30);
chassis.pid_wait();

Arcs, Turn Paths, and Slew​

You can use slew in conjunction with different turn behavior.

chassis.pid_swing_behavior_set(ez::shortest);
chassis.slew_swing_set(false);  // Enables global slew
chassis.slew_swing_constants_set(5_deg, 50);

// This will turn to 270 deg clockwise while slewing, with the right side going 30
chassis.pid_swing_set(ez::LEFT_SWING, 270_deg, 90, 30, ez::cw, true);
chassis.pid_wait();

// This will take the shortest path to 0 degrees without slew, with the right side going 30
chassis.pid_swing_set(ez::LEFT_SWING, 3600_deg, 90, 30);
chassis.pid_wait();

Relative Swing Turns​

All of the syntax for absolute swing turns above applies to relative turns, use pid_swing_relative_set() instead.

"Relative" means the robot will swing turn X degrees relative to where it is before it starts the swing turn. The two code blocks below do the same thing.

note

Relative swing turns are based on target heading and not current heading. If you relative swing turn +90deg, but the robot actually goes to 89deg, your next relative swing turn will be based off of 90 and not 89.

// Turn to Heading + 45deg
chassis.pid_swing_relative_set(ez::LEFT_SWING, 45_deg, 90);
chassis.pid_wait();

// Turn to Heading - 45deg
chassis.pid_swing_relative_set(ez::LEFT_SWING,-45, 90);
chassis.pid_wait();

You can also change your starting angle from 0 to whatever you want. Here are two examples that do the same thing with absolute and relative turning, but with a starting angle of 10 degrees.

// Set the starting angle to 10deg
chassis.drive_angle_set(10_deg);

// Turn to Heading + 35deg
chassis.pid_turn_relative_set(ez::LEFT_SWING, 35_deg, 90);
chassis.pid_wait();

// Turn to Heading - 35deg
chassis.pid_turn_relative_set(ez::LEFT_SWING, -35, 90);
chassis.pid_wait();

Absolute vs Relative​

At the end of the day, this is fully preference. But, I'm still going to give an argument for why I think absolute turns should be used.

While tuning your autonomous routine, if you decide to change the very first turn here, no other turn will be affected.

chassis.pid_drive_set(24_in, 110);
chassis.pid_wait();

chassis.pid_swing_set(ez::LEFT_SWING, 90_deg, 110);
chassis.pid_wait();

chassis.pid_drive_set(24_in, 110);
chassis.pid_wait();

chassis.pid_swing_set(ez::LEFT_SWING, 180_deg, 110);
chassis.pid_wait();

chassis.pid_drive_set(24_in, 110);
chassis.pid_wait();

chassis.pid_swing_set(ez::LEFT_SWING, 270_deg, 110);
chassis.pid_wait();

chassis.pid_drive_set(24_in, 110);
chassis.pid_wait();

chassis.pid_swing_set(ez::LEFT_SWING, 360_deg, 110);
chassis.pid_wait();

In order to make the Tuned auton below do the same thing as the Tuned auton above, an additional line of code is needs modifying. This isn't a huge deal, but I don't want to add another thing to remember to do while tuning an autonomous under the stress of a tournament.

chassis.pid_drive_set(24_in, 110);
chassis.pid_wait();

chassis.pid_swing_relative_set(ez::LEFT_SWING, 90_deg, 90);  
chassis.pid_wait();

chassis.pid_drive_set(24_in, 110);
chassis.pid_wait();

chassis.pid_swing_relative_set(ez::LEFT_SWING, 90_deg, 90);
chassis.pid_wait();

chassis.pid_drive_set(24_in, 110);
chassis.pid_wait();

chassis.pid_swing_relative_set(ez::LEFT_SWING, 90_deg, 90);
chassis.pid_wait();

chassis.pid_drive_set(24_in, 110);
chassis.pid_wait();

chassis.pid_swing_relative_set(ez::LEFT_SWING, 90_deg, 90);
chassis.pid_wait();

chassis.pid_drive_set(24_in, 110);
chassis.pid_wait();