Chief Delphi - Programming Mecanum?

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- - Programming Mecanum? (http://www.chiefdelphi.com/forums/showthread.php?t=90422)

iNiLz

29-01-2011 15:00

Programming Mecanum?

Our team decided to use mecanum wheels this year and we've used java last year. I'm a bit familiar with java but I can't seem to find a way to approach programming mecanum. I checked out the library but I can't seem to understand. Does anyone have a simple or pseudo program for mecanum they can share?

Ether

29-01-2011 15:08

Re: Programming Mecanum?

Quote:

Originally Posted by iNiLz (Post 1011111)

I checked out the library but I can't seem to understand.

Could you articulate in a bit more detail what you don't understand about the library support for mecanum? You'll get better-targeted answers if you do that.

FirebearBenD

29-01-2011 15:50

Re: Programming Mecanum?

Under public class RobotMain extends IterativeRobot,
RobotDrive m_drive;
Under public void RobotInit
m_drive = new RobotDrive(m_frontLeft, m_rearLeft, m_frontRight, m_rearRight); // those reference the motors declared in another section of the code
Under public void TeleoperatedPeriodic
m_drive.mecanumDrive_Cartesian(-1 * m_rstick.getX(),-1 * m_rstick.getY(), -1 * m_lstick.getX(), 0); //m_rstick and m_lstick are just joysticks

That's the code we're using right now. Cartesian is much simpler than Polar, because then you don't have to deal with the annoying trigonometry with polar coordinates. m_rstick and m_lstick are just joysticks. So, based on what we get for input from our joysticks, we can control forward/backward, strafe left/right, and turn clock/counter-clockwise. The rest of the code has been done by the WPI. Sorry if this doesn't help.

Patrick Chiang

01-02-2011 00:13

Re: Programming Mecanum?

You COULD do this:

Code:

/* Simulated tank drive controls for mecanum wheels */

magnitude = (leftStick.getMagnitude() + rightStick.getMagnitude()) / 2;

direction = (leftStick.getDirectionDegrees()+rightStick.getDirectionDegrees()) / 2;

rotation = (leftStick.getY() + rightStick.getY()) / 2;

driveRobot.mecanumDrive_Polar(magnitude, direction, rotation);

^ We did it like this because our driver specifically asked for these controls. He has driven tank drive for two years, and I guess old habits are hard to change.

You SHOULD do this:

Code:

magnitude = leftStick.getMagnitude();

direction = leftStick.getDirectionDegrees();

rotation = rightStick.getX();

driveRobot.mecanumDrive_Polar(magnitude, direction, rotation);

^ This is what we call the FPS drive system (aka. xbox controller style). Left joystick controls w,a,s,d (forward, back, left, right) and diagonal movements. Right joystick controls rotation.

General25

03-02-2011 16:01

Re: Programming Mecanum?

I have the same question, execpt for Labview. i can't figure how to put the motors in the Begin.vi and how to incoorpoate it into Telop. This is my first time changing our robot to mecanum

Robby Unruh

03-02-2011 20:53

Re: Programming Mecanum?

Our team is simply using arcade drive, since we've been having trouble with both the Polar and Cartesian driving. We have a toggle button that inverts the motors to strafe.

@General25:
You'd probably get better answers in the Labview section, since this is Java.

General25

04-02-2011 18:11

Re: Programming Mecanum?

@General25:
You'd probably get better answers in the Labview section, since this is Java.[/quote]

sorry, just searched for mecanum and programing

Robby Unruh

07-02-2011 07:04

Re: Programming Mecanum?

I've had a little problem programming the mecanum wheels myself. In my post before I said I had inverted the motors to strafe. Well, turns out that makes a nasty ugly strafe. Anyone have tips regarding how to actually program a strafe with arcade drive?

Thanks.

here's our current code:

Code:

if(joystickL.getTrigger() && state == 0) {

    robotDrive.setInvertedMotor(frontLEFT, true);

    robotDrive.setInvertedMotor(rearRIGHT, true);

    // robotDrive.setInvertedMotor(frontRIGHT, false);

    // robotDrive.setInvertedMotor(rearLEFT, false);

    this.state = 1;

} else if(joystickL.getTrigger() && state == 1) {

    robotDrive.setInvertedMotor(frontLEFT, false);

    robotDrive.setInvertedMotor(rearRIGHT, false);

    // robotDrive.setInvertedMotor(frontRIGHT, false);

    // robotDrive.setInvertedMotor(rearLEFT, false);

    this.state = 0;

}

Ether

07-02-2011 09:18

Re: Programming Mecanum?

Quote:

Originally Posted by Robby Unruh (Post 1017439)

Yes. There's an explanation here.

Robby Unruh

07-02-2011 10:40

Re: Programming Mecanum?

Quote:

Originally Posted by Ether (Post 1017483)

Yes. There's an explanation here.

Thanks for the link. I'm still a little confused here, though.
Could you please explain how I'm supposed to use forward/backward/clockwise in the drive train programming?

Ether

07-02-2011 11:32

Re: Programming Mecanum?

Quote:

Originally Posted by Robby Unruh (Post 1017530)

Thanks for the link. I'm still a little confused here, though.
Could you please explain how I'm supposed to use forward/backward/clockwise in the drive train programming?

That is explained on the second page:

Code:

front_left = forward + clockwise + right;

front_right = forward - clockwise - right;

rear_left = forward + clockwise - right;

rear_right = forward - clockwise + right;

// Finally, normalize the wheel speed commands

// so that no wheel speed command exceeds magnitude of 1:

max = abs(front_left);

if (abs(front_right)>max) max = abs(front_right);

if (abs(rear_left)>max) max = abs(rear_left);

if (abs(rear_right)>max) max = abs(rear_right);

if (max>1)

{front_left/=max; front_right/=max; rear_left/=max; rear_right/=max;}



// You're done. Send these four wheel commands to their respective wheels

front_left, front_right, rear_left, rear_right are the commands to send to each mecanum wheel.

If that's not what you were asking, please clarify your question and I'll try again.

Robby Unruh

08-02-2011 08:10

Re: Programming Mecanum?

Quote:

Originally Posted by Ether (Post 1017558)

That is explained on the second page:

Code:

front_left = forward + clockwise + right;

front_right = forward - clockwise - right;

rear_left = forward + clockwise - right;

rear_right = forward - clockwise + right;

// Finally, normalize the wheel speed commands

// so that no wheel speed command exceeds magnitude of 1:

max = abs(front_left);

if (abs(front_right)>max) max = abs(front_right);

if (abs(rear_left)>max) max = abs(rear_left);

if (abs(rear_right)>max) max = abs(rear_right);

if (max>1)

{front_left/=max; front_right/=max; rear_left/=max; rear_right/=max;}



// You're done. Send these four wheel commands to their respective wheels

front_left, front_right, rear_left, rear_right are the commands to send to each mecanum wheel.

If that's not what you were asking, please clarify your question and I'll try again.

Okay, thanks again. So I just send those wheels in the drive train like so:

Code:

RobotDrive driveTrain = new RobotDrive(front_left, rear_left, front_right, rear_right);

Then invert the motors like I've been doing, or...?

Ether

08-02-2011 08:24

Re: Programming Mecanum?

Quote:

Originally Posted by Robby Unruh (Post 1018292)

Then invert the motors like I've been doing, or...?

Without knowing how you have your motors wired I cannot tell you whether or not you need to invert them.

I can tell you this: If your motors are wired so that when you give them a +1 command they go in the "forward" direction, then no inverting is required.

I recommend that you put the robot up on blocks and push the joystick(s) straight forward. If all four wheels spin in the "forward" direction, you're good to go. If not, then invert any motor that is spinning backwards.

omalleyj

08-02-2011 10:32

Re: Programming Mecanum?

Quote:

Originally Posted by Robby Unruh (Post 1018292)

Okay, thanks again. So I just send those wheels in the drive train like so:

Code:

RobotDrive driveTrain = new RobotDrive(front_left, rear_left, front_right, rear_right);

Then invert the motors like I've been doing, or...?

No, RobotDrive takes SpeedControllers in its constructor, not actual values. The example was giving you numbers to pass directly to your Jaguars. The sum total of the algorithm and motor control make your own robot drive method, you don't need the wpilibj version.

iNiLz

10-02-2011 01:56

Re: Programming Mecanum?

Sorry for the late reply.
So far this is what I currently have done and understand well.

Code:

import edu.wpi.first.wpilibj.SimpleRobot;

import edu.wpi.first.wpilibj.Compressor;

import edu.wpi.first.wpilibj.GenericHID;

import edu.wpi.first.wpilibj.Gyro;

import edu.wpi.first.wpilibj.Victor;

import edu.wpi.first.wpilibj.Timer;

import edu.wpi.first.wpilibj.Jaguar;

import edu.wpi.first.wpilibj.RobotDrive;

import edu.wpi.first.wpilibj.Joystick;



//Program

public class RobotTemplate extends SimpleRobot {

    //Drive Program

    RobotDrive drive = new RobotDrive(1, 3, 2, 4);



    //Joystick

    private Joystick leftStick = new Joystick(1);

    //private Joystick rightStick = new Joystick(2);



    //Autonomous Program

    public void autonomous() {

        

    }



    //Teleop

    public void operatorControl() {

    getWatchdog().setEnabled(true);



        //WatchDog Enabled //Infinite Loop

        while (isEnabled() && isOperatorControl()) {

            getWatchdog().feed();

            drive.mecanumDrive_Polar(leftStick.getDirectionDegrees(), leftStick.getMagnitude(), leftStick.getTwist());

            Timer.delay(0.005);

    }



   }

}

I haven't tested it yet but will tomorrow.
Once I figure out how Cartisian works, I'll update the code.
Now to figure out the gyro and encoder.

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