pxt-ev3/docs/reference/motors/synced/tank.md

tank

Rotate two motors in synchronization.

motors.largeAB.tank(50, 50)

Tanking the brick will drive two motors in synchronization. This means that both motors will start at the same time. Also, each motor uses the same amount of rotation when running at the same speed. You can use different speed values for each motor to perform turns or spins.

Speed and distance

The speed setting is a pecentage of the motor's full speed. Full speed is the speed that the motors run when the brick supplies maximum output voltage to the port.

If you use just the speed number, the motors run continously and won't stop unless you tell them to. You can also give a value for a certain amount of distance you want the motors to rotate for. The value can be an amount of time, a turn angle in degrees, or a number of full rotations.

If you decide to use a value of rotation distance, you need to choose a type of movement unit. Also, if you use a number of milliseconds as movement units, then you don't need to include the unit type. The description in run shows how to use different movement units.

Parameters

• speedLeft: a number that is the percentage of full speed for the motor attached to the left of the brick. A negative value runs the motor in the reverse direction.
• speedRight: a number that is the percentage of full speed for the motor attached to the right of the brick. A negative value runs the motor in the reverse direction.
• value: the number of movement units to rotate for. A value of 0 means run the motor continuously.
• unit: the movement unit of rotation. This can be milliseconds, seconds, degrees, or rotations. If the number for value is 0, this parameter isn't used.

~hint

** Reverse is negative speed**

Tankng the brick in the opposite direction (reverse) is simple. Reverse is just a negative speed setting. To drive the motors in reverse at 75% speed:

motors.largeBC.tank(-75, -75)

~

~ hint

Only one set of synchronized motors will run at the same time. Once you launch tank/steer, it will cancel any existing synchronized speed command.

~

Examples

Tank forward and backward

Move the brick straight ahead and then go backward.

motors.largeAB.tank(75, 75)
pause(10000)
motors.largeAB.tank(-55, -55)
pause(10000)
motors.stopAll()

Slip steer

Run the right motor at 50% and let the left motor spin freely.

motors.largeAB.tank(0, 50)

Skid steer

Set the brake on the right motor. Run the left motor at 60% and let the right motor skid.

motors.largeB.setBrake(true)
motors.largeAB.tank(60, 0)

Spin around

Run both motors in opposite directions to spin the brick around to the left.

motors.largeAB.tank(-30, 30)
pause(5000)
motors.stopAll()

Tank tester

This program lets you change the tank values using the brick buttons

let tankB = 0;
let tankC = 0;

brick.showString(`tank tester`, 1)
brick.showString(`connect motors BC`, 7)
brick.showString(`up/down for tank B`, 8)
brick.showString(`left/right for tank C`, 9)

forever(function () {
    brick.showString(`motor B speed ${motors.largeB.speed()}%`, 4)
    brick.showString(`motor C speed ${motors.largeC.speed()}%`, 5)
    pause(100)
})

function updateTank() {
    brick.showString(`tank A: ${tankB}%`, 2)
    brick.showString(`tank B: ${tankC}%`, 3)
    motors.largeBC.tank(tankB, tankC);
}

brick.buttonUp.onEvent(ButtonEvent.Pressed, function () {
    tankB += 10
    updateTank();
})
brick.buttonDown.onEvent(ButtonEvent.Pressed, function () {
    tankB -= 10
    updateTank();
})
brick.buttonRight.onEvent(ButtonEvent.Pressed, function () {
    tankC += 10
    updateTank();
})
brick.buttonLeft.onEvent(ButtonEvent.Pressed, function () {
    tankC -= 10
    updateTank();
})

updateTank();

See also

steer, run