Launching a command with a second thumbstick

Technical C/C++
1

We are using an Xbox controller for robot control, and would like to use the right thumbstick to call a command - specifically to be able to use the value from GetRawAxis() to determine the speed at which we activate a Victor. I know how to get a button to launch a command in OI, but don’t know how to make movement of the right thumbstick do the same. Any ideas?

2

Can you have a background command on the relevant subsystem that watches the joystick value and fires off a specific command when the value changes?

But it just sounds like you want a background command that continuously copies the joystick value to the Victor, nothing fancier than that.

3

It seems like you want a command that you schedule in teleopInit() that will just grab the joystick value and drive the motor. It can do that independently from everything else in your teleop code.

4

Do you have an example of setting up a background command? I’ve only done regular commands which require a particular subsystem(s). Is there a particular place the code goes to watch the joystick value? Does it need to be in a loop, or is it constantly being checked?

Thanks in advance for the help

Nick

5

That does sound like what I’m looking for - do I just really put an if statement in the teleopInit() method that grabs the joystick value and launches a command from there? Does teleopInit() run continuously? I was under the impression that teleopInit() only ran once at the beginning of teleop.

Thanks

Nick

6

We ran into the same problem. Our solution that I consider elegant was to make our own AnalogJoystickButton that inherits button.

You can simply create a Button like your would a JoystickButton but also pass in a threshold at which point you consider the joystick “pressed”. This allows the assignment of multiple commands to different thresholds. Typically we use .5 and -.5 to get both directions from the axis.

Once you include the class below you can do the following. I’m assuming you know how to create a JoystickButton in OI. Have the member be an

AnalogJoystickButton* fireDiscButton;

fireDiscButton = new AnalogJoystickButton(shooterStick, XboxController::xbZAxis, -.5);
fireDiscButton->WhileHeld(new FireDiscCommand());

*Note: You need to provide the axis number. We have them defined as enums so we can just use XBoxController::xbZAxis to get at the trigger axis.

In your actual command you can get your joystick from OI and get the actual value of the axis if you need it for speed.

AnalogJoystickButton.h:

#ifndef _ANAOLG_JOYSTICK_BUTTON_H__
#define _ANOLOG_JOYSTICK_BUTTON_H__

#include "WPILib.h"

class AnalogJoystickButton : public Button
{
public:
	AnalogJoystickButton(GenericHID *joystick, int axisNumber, float threshold);
	virtual ~AnalogJoystickButton() {}

	virtual bool Get();
	
private:
	GenericHID *m_joystick;
	int m_axisNumber;
	float m_threshold;
};

#endif

AnalogJoystickButton.cpp:

#include "AnalogJoystickButton.h"

AnalogJoystickButton::AnalogJoystickButton(GenericHID *joystick, int axisNumber, float threshold ) {
        m_threshold = threshold;
        m_joystick = joystick;
        m_axisNumber = axisNumber;
}

bool AnalogJoystickButton::Get()
{
        if(m_threshold < 0)
                return m_joystick->GetRawAxis(m_axisNumber) < m_threshold;
        else if(m_threshold > 0)
                return m_joystick->GetRawAxis(m_axisNumber) > m_threshold;
        return false; 
                
}

Let me know if you have any questions or need help implementing it.

EDIT – Just to make like easier.

XboxController.h:

#ifndef XBOXCONTROLLER_H_
#define XBOXCONTROLLER_H_

#include "WPILib.h"



class XboxController: public Joystick {
public:
        static const UINT32 XboxController::xbLeftXAxis;
        static const UINT32 XboxController::xbLeftYAxis;
        static const UINT32 XboxController::xbZAxis;
        static const UINT32 XboxController::xbRightXAxis;
        static const UINT32 XboxController::xbRightYAxis;
        static const UINT32 XboxController::xbAButton;
        static const UINT32 XboxController::xbBButton;
        static const UINT32 XboxController::xbXButton;
        static const UINT32 XboxController::xbYButton;
        static const UINT32 XboxController::xbStartButton;
        static const UINT32 XboxController::xbSelectButton;
        static const UINT32 XboxController::xbRightBumper;
        static const UINT32 XboxController::xbLeftBumper;
        static const UINT32 XboxController::xbRightStickCLick;
        static const UINT32 XboxController::xbLeftStickClick;
        
        XboxController(UINT32 port);
        virtual ~XboxController();
        
};

#endif /* XBOXCONTROLLER_H_ */

XboxController.cpp

#include "XboxController.h"

const UINT32 XboxController::xbLeftXAxis = 1;
const UINT32 XboxController::xbLeftYAxis = 2;
const UINT32 XboxController::xbZAxis = 3;
const UINT32 XboxController::xbRightXAxis = 4;
const UINT32 XboxController::xbRightYAxis = 5;
const UINT32 XboxController::xbAButton = 1;
const UINT32 XboxController::xbBButton = 2; 
const UINT32 XboxController::xbXButton = 3;
const UINT32 XboxController::xbYButton = 4;
const UINT32 XboxController::xbStartButton = 8;
const UINT32 XboxController::xbSelectButton = 7;
const UINT32 XboxController::xbRightBumper = 6;
const UINT32 XboxController::xbLeftBumper = 5;
const UINT32 XboxController::xbRightStickCLick = 10;
const UINT32 XboxController::xbLeftStickClick = 9;


XboxController::XboxController(UINT32 port) : Joystick(port){}

XboxController::~XboxController() {}
7

kylelanman:

Wow! That is awesome! I’m going to pass this on to my lead programmer and see what he makes of it. I’ll let you know if I have any questions on implementation, but it looks really solid. I appreciate the help!

Nick

8

teleopInit() is only called at the beginning of teleop, but if you schedule a command that doesn’t end from teleopInit(), the scheduler will keep running it throughout teleop.

9

Thank you kylelanman and Roboteers! We’re using a Thrustmaster X this year and decided that the Throttle and it’s slider make for intuitive inputs for an arm we’re using. I was going down a different road, and decided to look for something better. Sure enough, a little search on CD yielded an elegant solution :cool:

Eric