2-3Earning Your Driver's License: Driving

Up to this point, you have learned the various components of the robot, how they are represented by software, and how to use some of those components. Now, you will learn how to program one of the essential functions of any robot: driving.

• RobotDrive
  • Arcade Drive
  • Tank Drive
• Activity

RobotDrive

You may remember the RobotDrive object from lesson 1-3. This object provides various functions to make managing the drive system simpler. There are two functions that you will see most often: ArcadeDrive() and TankDrive().

For all of the following examples, assume the following have all been declared:

//Declarations
Talon* m_lDrive;
Talon* m_rDrive;

RobotDrive* m_robotDrive;

Timer* m_timer;

//Initialization
m_lDrive = new Talon (1);
m_rDrive = new Talon (2);
 
m_robotDrive = new RobotDrive (m_lDrive, m_rDrive);

m_timer = new Timer;

Arcade Drive

This is the drive method that we most commonly use.

void RobotDrive::ArcadeDrive(float velocity, float rotation)

ArcadeDrive() parameters

float velocity

the desired relative velocity of the robot (forwards/backwards)

float rotation

the relative velocity at which the robot rotates (left/right)

ArcadeDrive() use

How you use ArcadeDrive() depends on which routine you are programming. If you are programming in Teleop, you give it the opposite of the left Y axis and the right X axis (so that the robot doesn't drift sideways if the left Y is being used), like so:

m_robotDrive->ArcadeDrive(-m_gamepad->GetRawAxis(2), -m_gamepad->GetRawAxis(4));

However, in autonomous, you would feed ArcadeDrive() either set or calculated values. If you are using set values, you would use it in conjunction with a Timer or an encoder.

if (!m_timer->Get() < 2.0)
   m_robotDrive->ArcadeDrive(0.75,0.75);
else
   m_robotDrive->ArcadeDrive(0.0,0.0);

The above code will run the robot in a curve to the right for two seconds, and then stop.

Tank Drive

The other driving function can achieve essentially the same effect as the ArcadeDrive(), but the mechanism it uses is different.

void RobotDrive::TankDrive(float left_power, float right_power)

TankDrive() parameters

float left_power

the relative power (-1.0 to 1.0) going to the left drive

float right_power

the relative power going to the right drive

TankDrive() use

How you use TankDrive() is determined in the same way as ArcadeDrive(). However, the game controllers do not lend themselves to this driving method. Instead, TankDrive() is actually the preferred method for driving in autonomous (since it is generally easier to control the heading of the robot that way).

if (m_timer->Get() < 2.0)
   m_robotDrive->TankDrive(0.5,1.0);
else
   m_robotDrive(0.0,0.0);

The above code will run the robot in a left turn, moving forward, for two seconds, and then stop.

Activity

Program the robot to do the following:

• Drive forward and backward with the left stick.
• Move left and right with the right stick.
• When the start button pressed, toggle between the above mode and the following:
  • Drive forward when Y is held.
  • Rotate the robot counterclockwise (to the left) when the X button is held
  • Rotate the robot clockwise (to the right) when the B button is held.
  • Drive backwards when the A button is held.
  • Run everything at half power in this drive mode!

The joystick drive and the button drive cannot be enabled at the same time!