Programming Mecanum?

[Ether]

Originally Posted by Robby Unruh

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?

Yes. There's an explanation here.

[Robby Unruh]

Originally Posted by Ether

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]

Originally Posted by Robby Unruh

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:

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]

Originally Posted by Ether

That is explained on the second page:

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:

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

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

[Ether]

Originally Posted by Robby Unruh

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]

Originally Posted by Robby Unruh

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

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]

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

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.

[Robby Unruh]

Cartesian/Polar will only work if your wheels are similar to

\/
/\

or

/\
\/

I'm not sure in which order though. Our team made the mistake of putting our mecanum wheels straight on all four sides so that's something we had to program around.

@Esther:
I managed to get the drive train programmed with your help. Thanks so much!
*edit* my bad, I mean Ether.

[Ether]

Originally Posted by Robby Unruh

Our team made the mistake of putting our mecanum wheels straight on all four sides so that's something we had to program around.

The wheels are supposed to be "straight", i.e. the plane of all 4 wheels should be parallel to each other.

The rollers on each wheel are at a 45 degree angle to the plane of the wheel, and should form a visual pattern that looks like this when viewed from the top:

\...../
 .....
 .....
 .....
/.....\

... or this when viewed from the bottom:

/.....\
 .....
 .....
 .....
\...../

[Robby Unruh]

Oh, alright. I guess I must've misunderstood some posts around here. Thanks for clearing that up.