JAVA RobotDrive Motors Signal Out of Sync

During programming of our test stand in JAVA, we found that regardless of control channel for the move speed value, the motors start rotating at different points. This will cause a robot to turn at low speeds with no turning inputs.

This issue was confirmed with multiple channel changes of the motors, and the problem switching motors if the channel for motor signal is switched.

Is there an inherent problem in the RobotDrive or other library files that may be causing this problem?

We are using the arcadeDrive function to feed outputs to the robot.

Regardless of the changes made to the control scheme the problem persists. Resolution of this issue appears to require a PID controller to ensure constant direction without turning input. While this would be one way to solve a built in turn, this should not be required to make an aligned robot move straight forward.

Anyone with information on this issue would be much appreciated.

Post your code?

Here is the current code we are using, for a controller we are using the Logitech X30 flight stick.

package org.usfirst.frc.team5837.robot;

import edu.wpi.first.wpilibj.CameraServer;
import edu.wpi.first.wpilibj.IterativeRobot;
import edu.wpi.first.wpilibj.Joystick;
import edu.wpi.first.wpilibj.RobotDrive;
import edu.wpi.first.wpilibj.Victor;

public class Robot extends IterativeRobot {
	Victor R_Motor = new Victor(1);
	Victor L_Motor = new Victor(0);
	RobotDrive chassis = new RobotDrive(R_Motor ,L_Motor);
	Joystick drive = new Joystick(0);
	int autoLoopCounter;
	double yAxis = drive.getY();
	double xAxis = drive.getX();
	double slider = drive.getRawAxis(3);
	double yMath;
	double xMath;
	double sliderMath;
     * This function is run when the robot is first started up and should be
     * used for any initialization code.
    public void robotInit() {
    	CameraServer server = CameraServer.getInstance();
     * This function is called once each time the robot enters Disabled mode.
     * You can use it to reset any subsystem information you want to clear when
	 * the robot is disabled.
    public void disabledInit(){

	public void disabledPeriodic() {

    public void autonomousInit() {
    	autoLoopCounter = 0;

     * This function is called periodically during autonomous
    public void autonomousPeriodic() {

    public void teleopInit() {

     * This function is called periodically during operator control
    public void teleopPeriodic() {
    	xAxis = drive.getX();
    	yAxis = drive.getY();
    	slider = drive.getRawAxis(3);
    	sliderMath = Math.abs((slider-1)/2);
    	if (Math.abs(xAxis) < 0.25) {
    		xMath = 0;
    	else {
    		xMath = Math.signum(xAxis)*(Math.abs(xAxis) - .25)*1.333*sliderMath;
    	if (Math.abs(yAxis) < 0.25){
    		yMath = 0;
    	else {
    		yMath = Math.signum(yAxis)*(Math.abs(yAxis) - .25)*1.333*sliderMath;
    	if (drive.getRawButton(2)){
       chassis.arcadeDrive(yMath, xMath);
    public void testPeriodic() {

You can calibrate your speed controllers to fix this. If you look online, you can find a manual for your speed controller that should explain how.

But when I go into reverse the motor that starts first switches to the other motor; it isn’t motor specific or even controller specific. More so which virtual motor it correlates to. Would calibrating the motors still fix this?

That makes sense if the controllers aren’t calibrated.

The PWM controllers have a small deadband where they will give no power. If one controller considers the zero point to be slightly ahead of where it should be, it will be late to start when going forward and early to start when going backward.

Even if when I change motor controllers, meaning the on that previously started before and the one that started later are switched, the problem still happens with the same virtual motor.

Try calibrating the joystick?

We have used the slider Axis on the front bottom in order to have no side to side input and the problem still occurred. Also we have a dead zone and using the control panel to have it as centered as possible it still happened. I’m wondering if the error is inside the RobotDrive function provided by FIRST that one motor doesn’t start as soon. Thank you for helping, all ideas help; We will definitely calibrate them first thing tomorrow as well.

Sounds like something is lagging. I would try disabling the camera stuff.

What type of speed controller are you using?

Victor SP controllers, and the camera isn’t currently being used but I’ll definitely comment it out for now.

Well, there’s your problem. You created Victor objects, not VictorSP objects. Try changing them to VictorSP.

I’ll change that, would that cause the motors to be set different values?

Yes, the PWM timing is different.

I’ve changed it to VictorSP and the error is smaller but it is still there.

Watch the LEDs on the motor controllers. Is one motor controller’s throttle LEDs activating before the other ones? If so you may need to calibrate all the Victor SPs, or factory-default all the Victor SPs. Either will ensure identical throttle response.

If the observation is just the motor beginning to spin differently, that can happen since no two motors are truly identical (and have identical loads).

Also be sure you are applying the same throttle to all Victor SPs(i.e. make sure there isn’t something going on in your math).

Our team had a similar problem last season. At first, we though it was an electrical problem and we tried various methods such as calibrating our Talons several times. We finally determined the problem was with the joystick (Logitech X30 Flight Stick) and it was off-center slightly when no one was touching it. This issue made it to look as if some of the speed controllers were lagging. We tried to recalibrate the joystick through Windows but it didn’t seem to help. We got another joystick of the same model and seemed to work fine for several months but recently it’s giving us the same issue.

I would suggest for you to look to see if all the axis are at the same values in Driver Station. Even a minor difference will produce drastic incorrect movement. If the values aren’t equal, try calibrating the joystick (through Devices and Printers in Windows) or you could try completely opening the joystick and centering it again. Another alternative would be to try QDriverStation which allows using the keyboard as input. If you absolutely have to get another joystick, I’d recommend going for a 360 controller or going for a higher-priced joystick.