Chief Delphi - Acceleration Curve java help

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choas500

17-02-2015 13:43

Acceleration Curve java help

Hey does anyone know how to program an acceleration curve for cim motors??

GeeTwo

17-02-2015 14:12

Re: Acceleration Curve java help

What are you trying to accomplish?
If you really want to control/limit acceleration, you can set up a PIDController using the motor speed(s) as the system input and the acceleration (from the RoboRIO's built-in accelerometer, for example) as the system output.

Ether

17-02-2015 15:32

Re: Acceleration Curve java help

Quote:

Originally Posted by choas500 (Post 1445760)

Hey does anyone know how to program an acceleration curve for cim motors??

As GeeTwo asked, what is the problem you are trying to solve?

If you are simply wanting to prevent driver "jackrabbit" starts and stops so the totes won't fall off the stack you are carrying, a simple solution would be to add a slew rate limiter to your joystick commands.

JacobD

17-02-2015 17:34

Re: Acceleration Curve java help

I'm assuming you want something like this.

Code:

double magnitude = Math.pow(2,(driveStick.getMagnitude())-1; 

chassis.mecanumDrive_Polar(magnitude, driveStick.getDirectionDegrees(), driveStick.getRotationDirection());

this should make a pretty decent magnitude:acceleration ratio.

It is an exponential function that increases the speed of the robot when reaching the upper bounds.

You can just edit this so that it works with your drive and controls. Or, if you post the code I will do it for you.

Ether

17-02-2015 17:45

Re: Acceleration Curve java help

Quote:

Originally Posted by JacobD (Post 1445958)

I'm assuming you want something like this.

Code:

double magnitude = Math.pow(1.3,driveStick.getMagnitude()); 

chassis.mecanumDrive_Polar(magnitude, driveStick.getDirectionDegrees(), rotationDirection);

this should make a pretty decent magnitude:acceleration ratio.

You can just edit this so that it works with your drive and controls. Or, if you post the code I will do it for you.

Since the OP has not responded to requests to clarify the nature of the problem he is interested in solving, you might want to qualify your suggestion with an explanation of what problem it is intended to solve... lest he take your suggestion and apply it to a problem different from what you inferred.

You might also caution that your suggestion maps the domain -1..+1 to the range 0.769..1.3

JacobD

17-02-2015 18:54

Re: Acceleration Curve java help

Quote:

Originally Posted by Ether (Post 1445960)

You might also caution that your suggestion maps the domain -1..+1 to the range 0.769..1.3

Yeah, I wasn't thinking. I fixed that. Also, the domain is [0,1] because you cannot have a negative magnitude. But, that assumes that he is using mecanum drive. If not, another solution will be needed.

Code:

Joystick stick1, stick2;

double stick1val,stick2val;



stick1val = Math.pow(stick1.getX(),3);

stick2val = Math.pow(stick2.getY(),3);



chassis.tankDrive(stick1val, stick2val);

That would let you take input with a domain of [-1,1] and use it with tank drive.

choas500

17-02-2015 19:19

Re: Acceleration Curve java help

We are trying to fix the automatic jump the robot gets as soon as you move the joysticks.

JacobD

17-02-2015 19:35

Re: Acceleration Curve java help

Can you show us your code right now? Otherwise, tell me the type of drive you are using.

Tank Drive:

Code:

Joystick stick1, stick2;

double stick1val,stick2val;



stick1val = Math.pow(stick1.getX(),3);

stick2val = Math.pow(stick2.getY(),3);



chassis.tankDrive(stick1val, stick2val);

Mecanum Drive:

Code:

double magnitude = Math.pow(driveStick.getMagnitude(),3); 

chassis.mecanumDrive_Polar(magnitude, driveStick.getDirectionDegrees(), driveStick.getRotationDirection());

GeeTwo

17-02-2015 20:08

Re: Acceleration Curve java help

Quote:

Originally Posted by choas500 (Post 1446010)

We are trying to fix the automatic jump the robot gets as soon as you move the joysticks.

Then the slew limiter Ether suggested is probably your best solution:

Quote:

Originally Posted by Ether (Post 1445847)

If you are simply wanting to prevent driver "jackrabbit" starts and stops so the totes won't fall off the stack you are carrying, a simple solution would be to add a slew rate limiter to your joystick commands.

choas500

17-02-2015 22:04

Re: Acceleration Curve java help

This is our regular code

package org.usfirst.frc.team4640.robot;

import edu.wpi.first.wpilibj.CameraServer;
import edu.wpi.first.wpilibj.SampleRobot;
import edu.wpi.first.wpilibj.RobotDrive;
import edu.wpi.first.wpilibj.Joystick;
import edu.wpi.first.wpilibj.Timer;

public class Robot extends SampleRobot {
RobotDrive myRobot; // class that handles basic drive operations
Joystick leftStick; // set to ID 1 in DriverStation
Joystick rightStick; // set to ID 2 in DriverStation
CameraServer server;

public Robot() {
myRobot = new RobotDrive(0, 1);
myRobot.setExpiration(0.1);
leftStick = new Joystick(0);
rightStick = new Joystick(1);
server = CameraServer.getInstance();
server.setQuality(50);
//the camera name (ex "cam0") can be found through the roborio web interface
server.startAutomaticCapture("cam0");

}

/**
* Runs the motors with tank steering.
*/
public void operatorControl() {
myRobot.setSafetyEnabled(true);
while (isOperatorControl() && isEnabled()) {
myRobot.tankDrive(leftStick, rightStick);
Timer.delay(0.005); // wait for a motor update time

}

}
}

JacobD

17-02-2015 22:27

Re: Acceleration Curve java help

Code:



package org.usfirst.frc.team4640.robot;





import edu.wpi.first.wpilibj.CameraServer;

import edu.wpi.first.wpilibj.SampleRobot;

import edu.wpi.first.wpilibj.RobotDrive;

import edu.wpi.first.wpilibj.Joystick;

import edu.wpi.first.wpilibj.Timer;







public class Robot extends SampleRobot {

    RobotDrive myRobot;  // class that handles basic drive operations

    Joystick leftStick = new Joystick(0);  // set to ID 0 in DriverStation

    Joystick rightStick = new Joystick(1); // set to ID 1 in DriverStation

    CameraServer server;

    double leftStickVal,rightStickVal;

    

    public Robot() {

        myRobot = new RobotDrive(0, 1);

        myRobot.setExpiration(0.1);

        leftStick = new Joystick(0);

        rightStick = new Joystick(1);

        server = CameraServer.getInstance();

        server.setQuality(50);

        //the camera name (ex "cam0") can be found through the roborio web interface

        server.startAutomaticCapture("cam0");

            

    }



    

    /**

     * Runs the motors with tank steering.

     */

    public void operatorControl() {

        myRobot.setSafetyEnabled(true);

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



                leftStickVal = Math.pow(leftStick.getY(),3);

                rightStickVal= Math.pow(rightStick.getY(),3);

 

                myRobot.tankDrive(leftStickVal, rightStickVal);

            Timer.delay(0.005);                // wait for a motor update time

           

           

            }

        

        }

    }

Use this code exactly and your problem should be solved.

GeeTwo

18-02-2015 01:41

Re: Acceleration Curve java help

For those trying to learn from this thread, the non-whitespace differences between the intitial (21:04) and updated (21:27) code are:

Code:

# diff -w initial.txt updated.txt

14,15c14,15

< Joystick leftStick; // set to ID 1 in DriverStation

< Joystick rightStick; // set to ID 2 in DriverStation

---

>     Joystick leftStick = new Joystick(0);  // set to ID 0 in DriverStation

>     Joystick rightStick = new Joystick(1); // set to ID 1 in DriverStation

16a17

>     double leftStickVal,rightStickVal;

37c38,42

< myRobot.tankDrive(leftStick, rightStick);

---

>

>                 leftStickVal = Math.pow(leftStick.getY(),3);

>                 rightStickVal= Math.pow(rightStick.getY(),3);

>

>               myRobot.tankDrive(leftStickVal, rightStickVal);

Poseidon5817

18-02-2015 23:27

Re: Acceleration Curve java help

How about using Talon.setVoltageRampRate()? The only downside is it would also slow down deceleration, and I think it only works on CANTalons.

vps	18-02-2015 23:48

Re: Acceleration Curve java help

I wanted Can Motor controllers but we ended up using regular one. I was going to use the setVoltageRampRate function, because we are top heavy, but I had to create something else. The acceleration curve by Math.pow(val, x) wasn't good enough for us, where x is an int. Why? because if the joystick slips, we don't want the robot to rapidly accelerate. So, what I do is that I read the "ReachVal" from the joystick, then, read the "CurrentVal" from what I set to the CIMs (CurrentVal is initialized to 0). Then, I take the difference, divide that by 7500 (trial and error lead me to this constant), add that to "CurrentVal", in my drive thread. This results in a smooth drive and we don't topple over even though we are quite top heavy.

Hope that helps!

Ether

19-02-2015 00:51

Re: Acceleration Curve java help

Quote:

Originally Posted by Poseidon1671 (Post 1446830)

How about using Talon.setVoltageRampRate()? The only downside is it would also slow down deceleration, and I think it only works on CANTalons.

Quote:

Originally Posted by vps (Post 1446844)

I wanted Can Motor controllers but we ended up using regular one. I was going to use the setVoltageRampRate function,

Quote:

Originally Posted by Ether (Post 1445847)

^^Here's the code for the above:

Code:



change = joystickAxis - limitedJoystickAxis;

if (change>limit) change = limit;

else if (change<-limit) change = -limit;

limitedJoystickAxis += change;

Quote:

Originally Posted by vps (Post 1446844)

The acceleration curve by Math.pow(val, x) wasn't good enough for us, where x is an int. Why? because if the joystick slips, we don't want the robot to rapidly accelerate.

Exactly.

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