Correcting Mecanum Wheels with Encoders (Ether, We Summon You!)

[goldenguy00]

We have the mecanum wheels set up to properly move in the Y (forwards and back) direction and to turn without any problems, but when attempting to strafe, the robot veers off to one side instead of going straight to the side. To fix this, we are using encoders, but we are running into some severe difficulties. Through a bit of troubleshooting, I found that this works...

public class TalonCan {

    CANTalon talon;

    public TalonCan(int canID){
	talon = new CANTalon(canID);
        talon.changeControlMode(ControlMode.PercentVbus);
    }
}

And this doesn't...

public class TalonCan {
    
    CANTalon talon;
    
    public TalonCan(int canID){
        talon = new CANTalon(canID);
	talon.changeControlMode(ControlMode.Speed);
	talon.setPID(0.1, 0.001, 1, 0.0001, 100, 36, 0);
	talon.set(0);
	talon.setFeedbackDevice(FeedbackDevice.QuadEncoder);
    }
}

I believe it's from not using the encoders, so my question is, what am I doing wrong in the second example? The robot does not move in autonomous, nor in teleop.

[EDIT]
We have already put the robot on blocks and the wheels are moving in the correct direction and correct speed. It's only on the floor that we have problems, hence the need for encoders.