Simple Auto with Encoder

After the timed-movement challenge, you'll notice the robot can move for 5 seconds at 50% speed. But if you want the robot to travel a specific distance, using time is not reliable — the distance depends on things like battery voltage. If the voltage is lower or higher, the robot won't travel the same distance every time.

To solve this, we use encoder distance instead.

Updating Robot.h

Open the Simple Auto project you created earlier. Everything else is already set up, so go straight to Robot.h. Remove the Timer.h header, and under private: remove this line:

frc::Timer m_timer;

and replace it with:

double targetDistance = 2.0;

Your updated Robot.h should look like this:

Robot.h

#pragma once
#include <frc/TimedRobot.h>
#include <frc2/command/Command.h>
#include "RobotContainer.h"
#include <frc/Encoder.h>
#include "studica/TitanQuad.h"
#include "Constants.h"
class Robot : public frc::TimedRobot {
public:
  void RobotInit() override;
  void RobotPeriodic() override;
  void DisabledInit() override;
  void DisabledPeriodic() override;
  void AutonomousInit() override;
  void AutonomousPeriodic() override;
  void TeleopInit() override;
  void TeleopPeriodic() override;
  void TestPeriodic() override;
private:
  // Motor control object for the wheel
  studica::TitanQuad wheel{constant::TITAN_ID, constant::frequency, constant::Wheel};
  // Encoder object for measuring wheel rotation
  frc::Encoder wheelEncoder{constant::Wheel_VMX[0], constant::Wheel_VMX[1], false, frc::Encoder::k4X};
  // Target distance for autonomous movement
  double targetDistance = 2.0;
};

Updating Robot.cpp

Now go to Robot.cpp. Add the encoder setup inside RobotInit(). RobotPeriodic() stays the same. In AutonomousInit(), reset the encoder. In AutonomousPeriodic(), set the target distance and motor power.

Because this example uses only one motor and the robot isn't driving on the ground, the measured distance won't be fully accurate for real movement. This is just to help you understand how encoder distance works.

Robot.cpp

#include "Robot.h"
#include <frc/smartdashboard/SmartDashboard.h>
void Robot::RobotInit()
{
  // Example: set how much distance each encoder pulse represents
  // You must change this value to match your wheel and encoder setup
  wheelEncoder.SetDistancePerPulse(0.01);
}
void Robot::RobotPeriodic()
{
  frc::SmartDashboard::PutNumber("wheelEncoder", wheelEncoder.GetDistance());
}
void Robot::DisabledInit() {}
void Robot::DisabledPeriodic() {}
void Robot::AutonomousInit()
{
  wheelEncoder.Reset(); // Start measuring from zero
}
void Robot::AutonomousPeriodic()
{
  double targetDistance = 2.0; // Distance you want to travel
  double currentDistance = wheelEncoder.GetDistance();
  if (currentDistance < targetDistance) {
    wheel.Set(0.5); // Move wheel at 50% speed
  } else {
    wheel.Set(0.0); // Stop when target distance is reached
  }
}
void Robot::TeleopInit() {}
void Robot::TeleopPeriodic() {}
void Robot::TestPeriodic() {}
#ifndef RUNNING_FRC_TESTS
int main() { return frc::StartRobot<Robot>(); }
#endif

Challenge. Try this on a 4-wheel robot and make it move a distance you choose. Test different distance values and get used to how encoder-based movement works.