Drivetrain#

Introduction#

The drivetrain class controls how a robot drives and turns. A drivetrain is made of motors and wheels that work together to move the robot.

A drivetrain does not use a Gyro Sensor or Inertial Sensor for heading-based or rotation-based turns. It can drive forward or reverse and turn left or right, but it cannot turn to a specific heading or rotation. For heading-based and rotation-based turns, use the smartdrive class.

This page uses myDrivetrain as the example drivetrain name. Replace it with your own configured name as needed.

Derived Classes#

The drivetrain class serves as a base class for the following derived class:

smartdrive — Creates a drivetrain with Gyro Sensor or Inertial Sensor support.

Class Constructors#

1 — Creates a drivetrain using existing motor_group objects for the left and right sides.

drivetrain(
    motor_group      &l,
    motor_group      &r,
    double           wheelTravel = 320,
    double           trackWidth = 320,
    double           wheelBase = 130,
    distanceUnits    unit = mm,
    double           externalGearRatio = 1.0 );

2 — Creates a drivetrain using existing motor objects for the left and right sides.

drivetrain(
    motor            &l,
    motor            &r,
    double           wheelTravel = 320,
    double           trackWidth = 320,
    double           wheelBase = 130,
    distanceUnits    unit = mm,
    double           externalGearRatio = 1.0 );

Class Destructor#

Destroys the drivetrain object and releases associated resources.

virtual ~drivetrain();

Parameters#

Parameter	Type	Description
`&l` / `&r`	`motor_group` / `motor`	The left and right motors or motor groups. Both parameters must use the same type: either two `motor_group` objects or two `motor` objects.
`wheelTravel`	`double`	The circumference of the drivetrain wheels. The default is `320`.
`trackWidth`	`double`	The distance between the left and right wheels. The default is `320`.
`wheelBase`	`double`	The distance between the front and back wheels. The default is `130`.
`unit`	`distanceUnits`	The unit for `wheelTravel`, `trackWidth`, and `wheelBase`: `mm` (default) or `inches`.
`externalGearRatio`	`double`	The gear ratio used to adjust drive distances if gears are used. The default is `1.0`.

Example#

// Create the left and right motor objects.
motor leftMotor = motor(PORT1, false);
motor rightMotor = motor(PORT9, true);

// Create the drivetrain object.
drivetrain myDrivetrain = drivetrain(
    leftMotor,  // left motor
    rightMotor, // right motor
    259.34,     // wheelTravel
    320,        // trackWidth
    40,         // wheelBase
    mm,         // unit
    1.0 );      // externalGearRatio

Member Functions#

The drivetrain class includes the following member functions:

Actions — Move and turn the robot.

drive — Moves the robot forward or reverse forever.
driveFor — Moves the robot forward or reverse for a specific distance.
turn — Turns the robot left or right forever.
turnFor — Turns the robot left or right for a specific number of degrees or revolutions.
stop — Stops the robot’s movement.

Settings — Adjust drivetrain settings.

setDriveVelocity — Tells the robot how fast to drive.
setTurnVelocity — Tells the robot how fast to turn.
setStopping — Tells how the robot will stop moving: by braking, coasting, or holding.
setTimeout — Sets how long the robot will try to finish a movement.

Values — Check movement status.

isDone — Returns whether the robot is finished moving, as a Boolean value.
isMoving — Returns whether the robot is moving, as a Boolean value.
velocity — Returns how fast the robot is driving.
current — Returns how much electrical current the drivetrain is using.
power — Returns how quickly the drivetrain is using energy.
torque — Returns how much torque the drivetrain is using.
efficiency — Returns how efficiently the drivetrain is using power.
temperature — Returns how warm the drivetrain is.
voltage — Returns the electrical voltage of the drivetrain.

Before calling any drivetrain member functions, a drivetrain object must be created.

/* This constructor is required when using VS Code.
Drivetrain configuration is generated automatically
in VEXcode using the Device Menu. Replace the values
as needed. */

// Create the left and right motor objects.
motor leftMotor = motor(PORT1, false);
motor rightMotor = motor(PORT9, true);

// Create the drivetrain object.
drivetrain myDrivetrain = drivetrain(
    leftMotor,  // left motor
    rightMotor, // right motor
    259.34,     // wheelTravel
    320,        // trackWidth
    40,         // wheelBase
    mm,         // unit
    1.0 );      // externalGearRatio

Actions#

drive#

drive moves the robot forward or reverse forever. The robot will continue to move until it is given another action, like turning or stopping.

Available Functions

1 — Drives using the current drive velocity.
void drive(
    directionType dir );

2 — Drives at the specified velocity.

void drive(
    directionType dir,
    double        velocity,
    velocityUnits units );

Parameters

Parameter	Type	Description
`dir`	`directionType`	The direction the robot moves: `forward` or `reverse`.
`velocity`	`double`	The velocity to drive with from 0% to 100% when using `velocityUnits::pct`, from 0 to 120 rpm when using `rpm`, or from 0 to 720 degrees per second when using `dps`. If no velocity is provided, the robot drives at the current drive velocity.
`units`	`velocityUnits`	The velocity unit: `velocityUnits::pct` (percent), `rpm` (rotations per minute), or `dps` (degrees per second).

Return Values

This function does not return a value.

Notes

drive is non-waiting. The project will run the next line of code right away.
The robot will continue to move until stop is called or another drivetrain movement function runs.
isDone and isMoving are not used with drive because drive does not have a target distance.

Examples

// Drive forward and back.
myDrivetrain.drive(forward);
wait(2, seconds);
myDrivetrain.drive(reverse, 25, rpm);
wait(2, seconds);
myDrivetrain.stop();

driveFor#

driveFor moves the robot forward or reverse for a specific distance. The project will wait until the robot is done moving before the next line of code runs.

Available Functions

1 — Drives in the specified direction for a distance using the current drive velocity.
bool driveFor(
    directionType dir,
    double        distance,
    distanceUnits units,
    bool          waitForCompletion = true );

2 — Drives in a direction based on the distance value using the current drive velocity.
bool driveFor(
    double        distance,
    distanceUnits units,
    bool          waitForCompletion = true );

3 — Drives in a direction based on the distance value at the specified velocity.
bool driveFor(
    double        distance,
    distanceUnits units,
    double        velocity,
    velocityUnits units_v,
    bool          waitForCompletion = true );

4 — Drives in the specified direction for a distance at the specified velocity.

bool driveFor(
    directionType dir,
    double        distance,
    distanceUnits units,
    double        velocity,
    velocityUnits units_v,
    bool          waitForCompletion = true );

Parameters

Parameter	Type	Description
`dir`	`directionType`	The direction the robot moves: `forward` or `reverse`.
`distance`	`double`	The distance the robot drives.
`units`	`distanceUnits`	The distance unit: `mm` (millimeters), `inches`, or `cm` (centimeters).
`velocity`	`double`	The velocity to drive with from 0% to 100% when using `velocityUnits::pct`, from 0 to 120 rpm when using `rpm`, or from 0 to 720 degrees per second when using `dps`. If no velocity is provided, the robot drives at the current drive velocity.
`units_v`	`velocityUnits`	The velocity unit: `velocityUnits::pct` (percent), `rpm` (rotations per minute), or `dps` (degrees per second).
`waitForCompletion`	`bool`	`true` (default) makes the project wait until the robot is done moving before the next line of code runs. `false` makes the next line of code run right away.

Return Values

Returns whether the robot reached the target distance, as a Boolean value.

true — The robot reached the target distance.
false — The robot did not finish the movement, or the function returned before the movement completed because waitForCompletion was set to false.

Notes

Running another drivetrain movement function while driveFor is running will interrupt the current movement.
driveFor uses a target distance, so isDone and isMoving can be used with it.

Examples

// Drive 200 mm, then back 200 mm.
myDrivetrain.driveFor(forward, 200, mm);
myDrivetrain.driveFor(reverse, 200, mm);

turn#

turn turns the robot left or right forever. The robot will continue to turn until it is given another action, like driving or stopping.

Available Functions

1 — Turns using the current turn velocity.
void turn(
    turnType dir );

2 — Turns at the specified velocity.

void turn(
    turnType     dir,
    double       velocity,
    velocityUnits units );

Parameters

Parameter	Type	Description
`dir`	`turnType`	The direction the robot turns: `left` or `right`.
`velocity`	`double`	The velocity to turn with from 0% to 100% when using `velocityUnits::pct`, from 0 to 120 rpm when using `rpm`, or from 0 to 720 degrees per second when using `dps`. If no velocity is provided, the robot turns at the current turn velocity.
`units`	`velocityUnits`	The velocity unit: `velocityUnits::pct` (percent), `rpm` (rotations per minute), or `dps` (degrees per second).

Return Values

This function does not return a value.

Notes

turn is non-waiting. The project will run the next line of code right away.
The robot will continue turning until stop is called or another drivetrain movement function runs.
isDone and isMoving are not used with turn because turn does not have a target angle.

Examples

// Turn right, then left, then stop.
myDrivetrain.turn(right);
wait(2, seconds);
myDrivetrain.turn(left);
wait(2, seconds);
myDrivetrain.stop();

turnFor#

turnFor turns the robot left or right for a specific number of degrees, revolutions, or raw units. The turn is relative to the current position of the robot. The project will wait until the robot is done turning before the next line of code runs.

Available Functions

1 — Turns for the specified angle using the current turn velocity.
bool turnFor(
    double        angle,
    rotationUnits units,
    bool          waitForCompletion = true );

2 — Turns in the specified direction for an angle using the current turn velocity.
bool turnFor(
    turnType      dir,
    double        angle,
    rotationUnits units,
    bool          waitForCompletion = true );

3 — Turns for the specified angle at the specified velocity.

bool turnFor(
    double        angle,
    rotationUnits units,
    double        velocity,
    velocityUnits units_v,
    bool          waitForCompletion = true );

4 — Turns in the specified direction for an angle at the specified velocity.

bool turnFor(
    turnType      dir,
    double        angle,
    rotationUnits units,
    double        velocity,
    velocityUnits units_v,
    bool          waitForCompletion = true );

Parameters

Parameter	Type	Description
`dir`	`turnType`	The direction the robot turns: `left` or `right`.
`angle`	`double`	The amount the robot turns.
`units`	`rotationUnits`	The turn unit: `deg` (degrees), `rev` (revolutions), or `raw` (raw units). One revolution is equal to 360 degrees.
`velocity`	`double`	The velocity to turn with from 0% to 100% when using `velocityUnits::pct`, from 0 to 120 rpm when using `rpm`, or from 0 to 720 degrees per second when using `dps`. If no velocity is provided, the robot turns at the current turn velocity.
`units_v`	`velocityUnits`	The velocity unit: `velocityUnits::pct` (percent), `rpm` (rotations per minute), or `dps` (degrees per second).
`waitForCompletion`	`bool`	`true` (default) makes the project wait until the robot is done turning before the next line of code runs. `false` makes the next line of code run right away.

Return Values

Returns whether the robot reached the target angle, as a Boolean value.

true — The robot reached the target angle.
false — The robot did not finish the turn, or the function returned before the turn completed because waitForCompletion was set to false.

Notes

Running another drivetrain movement function while turnFor is running will interrupt the current movement.
turnFor uses a target angle, so isDone and isMoving can be used with it.

Examples

// Turn right, then left.
myDrivetrain.turnFor(right, 90, degrees);
wait(1, seconds);
myDrivetrain.turnFor(left, 90, degrees);

stop#

stop stops the robot’s movement. If a stopping mode is provided, it controls how the robot stops for this function call.

Available Functions

1 — Stops the drivetrain using the current stopping mode.
void stop();

2 — Stops the drivetrain using the specified stopping mode.
void stop(
    brakeType mode );

Parameters

Parameter	Type	Description
`mode`	`brakeType`	How the robot will stop: `brake` — Stops immediately. `coast` — Slows to a stop. `hold` — Stops immediately and holds the wheels’ position.

Parameter

Type

Description

mode

brakeType

How the robot will stop:

brake — Stops immediately.
coast — Slows to a stop.
hold — Stops immediately and holds the wheels’ position.

Return Values

This function does not return a value.

Examples

// Drive forward, then coast to a stop.
myDrivetrain.setDriveVelocity(100, percent);
myDrivetrain.drive(forward);
wait(2, seconds);
myDrivetrain.stop(coast);

Mutators#

setDriveVelocity#

setDriveVelocity tells the robot how fast to drive. A higher percentage makes the robot drive faster and a lower percentage makes the robot drive slower.

Every project begins with the robot driving at 50% velocity by default.

Note: A higher velocity makes the robot drive faster, but it may be less precise. A lower velocity makes the robot drive slower, but it can be more precise.

Available Functions

void setDriveVelocity(
  double velocity,
  velocityUnits units );

Parameters

Parameter	Type	Description
`velocity`	`double`	The velocity to drive with from 0% to 100% when using `velocityUnits::pct`, from 0 to 120 rpm when using `rpm`, or from 0 to 720 degrees per second when using `dps`.
`units`	`velocityUnits`	The velocity unit: `velocityUnits::pct` (percent), `rpm` (rotations per minute), or `dps` (degrees per second).

Return Values

This function does not return a value.

Notes

The drive velocity is used by later drivetrain movement functions unless a specific velocity is provided in the function call.

Examples

// Drive forward, then coast to a stop.
myDrivetrain.setDriveVelocity(100, percent);
myDrivetrain.drive(forward);
wait(2, seconds);
myDrivetrain.stop(coast);

setTurnVelocity#

setTurnVelocity tells the robot how fast to turn. A higher percentage makes the robot turn faster and a lower percentage makes the robot turn slower.

Every project begins with the robot turning at 50% velocity by default.

Note: A higher velocity makes the robot turn faster, but it may be less precise. A lower velocity makes the robot turn slower, but it can be more precise.

Available Functions

void setTurnVelocity(
  double velocity,
  velocityUnits units );

Parameters

Parameter	Type	Description
`velocity`	`double`	The velocity to turn with from 0% to 100% when using `velocityUnits::pct`, from 0 to 120 rpm when using `rpm`, or from 0 to 720 degrees per second when using `dps`.
`units`	`velocityUnits`	The velocity unit: `velocityUnits::pct` (percent), `rpm` (rotations per minute), or `dps` (degrees per second).

Return Values

This function does not return a value.

Notes

The turn velocity is used by later drivetrain turning functions unless a specific velocity is provided in the function call.

Examples

// Try default, slow, then fast.
myDrivetrain.turnFor(right, 360, degrees);
wait(1, seconds);
myDrivetrain.setTurnVelocity(20, percent);
myDrivetrain.turnFor(right, 360, degrees);
wait(1, seconds);
myDrivetrain.setTurnVelocity(100, percent);
myDrivetrain.turnFor(right, 360, degrees);

setStopping#

setStopping sets how the robot will stop moving: by braking, coasting, or holding.

Available Functions

void setStopping(
  brakeType mode );

Parameters

Parameter	Type	Description
`mode`	`brakeType`	How the robot will stop: `brake` — Stops immediately. `coast` — Slows to a stop. `hold` — Stops immediately and holds the wheels’ position.

Parameter

Type

Description

mode

brakeType

How the robot will stop:

brake — Stops immediately.
coast — Slows to a stop.
hold — Stops immediately and holds the wheels’ position.

Return Values

This function does not return a value.

Notes

The stopping mode is used by later stop calls unless a specific stopping mode is provided in the function call.
If this function is not used, the robot will use brake when stopping.

setTimeout#

setTimeout sets how long the robot will try to finish a movement. If the robot cannot finish in that time, it will stop trying and move on to the next line of code. This keeps the robot from getting stuck on a movement.

Available Functions

void setTimeout(
  int32_t time,
  timeUnits units );

Parameters

Parameter	Type	Description
`time`	`int32_t`	The amount of time the robot can try to finish a movement. This should be a positive whole number.
`units`	`timeUnits`	The unit of time: `sec` (seconds) or `msec` (milliseconds).

Return Values

This function does not return a value.

Notes

The timeout only applies to drivetrain functions that move to a target, such as driveFor and turnFor.

Examples

// Turn right after driving forward.
myDrivetrain.setTimeout(1, seconds);
myDrivetrain.driveFor(forward, 25, inches);
myDrivetrain.turnFor(right, 90, degrees);

Getters#

isDone#

isDone returns whether the robot is finished moving, as a Boolean value. This can be used to control the timing of other behaviors based on the robot’s movement.

Available Functions

bool isDone( void );

Parameters

This function does not accept any parameters.

Return Values

true — The robot is finished moving.
false — The robot is still moving.

Notes

isDone works with target-based drivetrain movement functions, such as driveFor and turnFor.
isDone is not used with drive or turn, since those functions do not move to a target.

isMoving#

isMoving returns whether the robot is moving, as a Boolean value. This can be used to control the timing of other behaviors based on the robot’s movement.

Available Functions

virtual bool isMoving( void );

Parameters

This function does not accept any parameters.

Return Values

true — The robot is moving.
false — The robot is not moving.

Notes

isMoving works with target-based drivetrain movement functions, such as driveFor and turnFor.
isMoving is not used with drive or turn, since those functions do not move to a target.

velocity#

velocity returns how fast the robot is driving.

It can return velocity as a percentage, in rpm, or in dps. A positive value means the robot is driving forward. A negative value means the robot is driving in reverse.

Available Functions

double velocity(
  velocityUnits units );

Parameters

Parameter	Type	Description
`units`	`velocityUnits`	The unit to return velocity in: `percent`, `pct`, `rpm`, or `dps`.

Return Values

Returns the drivetrain velocity as a double in the selected unit.

Examples

// Show velocity before and during motion.
Brain.Screen.print("Resting: %f", myDrivetrain.velocity(percent));
myDrivetrain.drive(forward, 100, velocityUnits::pct);
wait(1, seconds);
Brain.Screen.newLine();
Brain.Screen.print("Moving: %f", myDrivetrain.velocity(percent));
myDrivetrain.stop();

current#

current returns how much electrical current the drivetrain is using. Current is the amount of electricity flowing through the drivetrain. It can be returned in amps (amperes) or as a percentage, depending on the unit.

A higher current value means the drivetrain is using more electrical current. This can happen when the robot is pushing against an object or trying to move when it is stuck.

This can be used to check if the drivetrain is struggling during a movement. If current stays high, the drivetrain may get warmer or use power less efficiently.

Available Functions

1 — Returns the drivetrain’s electrical current in amps.
double current(
    currentUnits units = currentUnits::amp );

2 — Returns the drivetrain’s electrical current as a percentage.
double current(
    percentUnits units );

Parameters

Parameter	Type	Description
`units`	`currentUnits`	The unit to return current in: `amp`.
`units`	`percentUnits`	The unit to return current in: `percent` or `pct`.

Return Values

Returns the drivetrain current as a double in the selected unit.

power#

power returns how much power the drivetrain is using, measured in watts. Power shows how quickly the drivetrain is using energy.

A higher power value means the drivetrain is using energy faster. This can happen when the robot is pushing against an object or trying to move when it is stuck.

This can be used to compare movements or check if the drivetrain is struggling. If power stays high, the drivetrain may get warmer or use energy less efficiently.

Available Functions

double power(
  powerUnits units = powerUnits::watt );

Parameters

Parameter	Type	Description
`units`	`powerUnits`	The power unit: `watt`.

Return Values

Returns drivetrain power as a double in watts.

torque#

Torque shows how hard the drivetrain can push or pull while the wheels spin.

torque returns how much torque the drivetrain is using, measured in Newton-meters (Nm) or inch-pounds (InLb).

A higher torque value means the drivetrain is pushing or pulling harder. This can happen when the robot is pushing against an object or trying to move when it is stuck.

This can be used to check if the drivetrain is struggling or to compare how much push different movements need.

Available Functions

double torque(
  torqueUnits units = torqueUnits::nm );

Parameters

Parameter	Type	Description
`units`	`torqueUnits`	The unit to return torque in: `Nm` (newton meters, default) or `InLb` (inch pounds).

Return Values

Returns drivetrain torque as a double in the selected unit.

efficiency#

efficiency returns how efficiently the drivetrain is using power, as a percentage from 0% to 100%.

Efficiency shows how much of the drivetrain’s power is being used for movement. A higher efficiency value means more of the drivetrain’s power is being used to move. A lower efficiency value can happen when the drivetrain is working hard but not moving much, like when the robot is stuck or pushing against an object.

This can be used to compare movements or check if the drivetrain is wasting power instead of using it for movement.

Available Functions

double efficiency(
  percentUnits units = percentUnits::pct );

Parameters

Parameter	Type	Description
`units`	`percentUnits`	The unit to return efficiency in: `percent` or `pct`.

Return Values

Returns drivetrain efficiency as a double in the selected unit.

temperature#

temperature returns the average temperature of the drivetrain as a percentage from 0% to 100%.

Temperature shows how warm the drivetrain motors are. A higher temperature means the motors are getting warmer while they work. The motors should stay below 55°C to keep working at full performance.

If the motors get too hot, they will lower their maximum current to protect themselves. At 70°C, the motors will stop running until they cool down.

This can be used to check if the drivetrain is getting too hot during repeated movements, long runs, or when it is pushing against an object.

Available Functions

double temperature(
  percentUnits units );

Parameters

Parameter	Type	Description
`units`	`percentUnits`	The unit to return temperature in: `percent` or `pct`.

Return Values

Returns the average drivetrain temperature as a double in the selected unit.

Notes

A returned value of 50% means the average motor temperature is about 45°C (113°F).
The typical operating temperature range for the drivetrain is about 20°C (68°F) to 70°C (158°F).

voltage#

voltage returns the electrical voltage of the drivetrain.

Voltage is the electrical pressure supplied to the drivetrain motors. This can be used with current and power values to understand how the drivetrain is using electrical energy.

Available Functions

double voltage(
  voltageUnits units = voltageUnits::volt );

Parameters

Parameter	Type	Description
`units`	`voltageUnits`	The unit to return voltage in: `volt` (default) or `voltageUnits::mV`. `voltageUnits::mV` means millivolts.

Return Values

Returns drivetrain voltage as a double in the selected unit.