Error with the RobotDrive

[e10]

The robot is moving in the opposite direction from how we move the joystick. It moves forwards and backwards correctly, but it turns left when we turn it right and it turns right when we turn it left. We are using windriver and we are coding in c++. How can i change the direction of the x axis?

[Alan Anderson]

You have several options for correcting your problem. The easiest one is simply to swap the left and right motor controls.

Are you using tank drive or arcade drive? If tank, you might have your joysticks swapped. Press a button on the left one and make sure the indicator on the Driver Station display shows that to be the joystick you expect it to be. If they're reversed, just drag them to the proper place in the Setup list.

You could negate the X axis in the code if you're using Arcade drive.

However, the correct thing to do is to go through the motors one by one and make sure the wiring matches the programming. If you run one motor at a time, is it the motor you expect to run? Does it run in the direction you expect it to? There are several places both in hardware and software where things can get swapped.

[mikets]

If you are using ArcadeDrive, there is a bug in WPILib in my opinion. I have reported it last year and I am surprise to see it not fixed for this year. See code excerpt below:
If both moveValue and rotateValue are positive, I am expecting the robot to go forward and turn to the right by convention. But as you can see, when both values are positive and for demonstration purpose, let's say moveValue equals to rotateValue. leftMotorOutput will be zero and rightMotorOutput will be some positive number. This will make the robot to turn left, not right!
If you want to argue that my understanding of the convention is wrong, then please look at MecanumDrive_Cartesian and apply the same values (both Y and rotation being positive and equal and X is 0). You will see the left motor powers will be the sum of Y and rotation which are both positive and the right motor powers will be zero. So the robot is turning right. So the convention in mecanum drive is different from the arcade drive! So my conclusion is that ArcadeDrive is wrong.

WPILib\RobotDrive.cpp line 439:
if (moveValue > 0.0)
{
        if (rotateValue > 0.0)
        {
                leftMotorOutput = moveValue - rotateValue;
                rightMotorOutput = max(moveValue, rotateValue);
        }
        else
        {
                leftMotorOutput = max(moveValue, -rotateValue);
                rightMotorOutput = moveValue + rotateValue;
        }
}

WPILib\RobotDrive.cpp line 501:
    wheelSpeeds[kFrontLeftMotor] = xIn + yIn + rotation;
    wheelSpeeds[kFrontRightMotor] = -xIn + yIn - rotation;
    wheelSpeeds[kRearLeftMotor] = -xIn + yIn + rotation;
    wheelSpeeds[kRearRightMotor] = xIn + yIn - rotation;

BTW, the way we fixed it was to have our own DriveBase class that inherits the RobotDrive class. We then override the ArcadeDrive method that negates the rotation argument.