Single Joystick Tank Drive

[Ether]

Originally Posted by Shantali

But if trying to pull the joystick back-left, the left motor is working 100% backwards, which essentially moves the robot's back to the right. If pulling back-right, the right motor is working 100% backwards, which moves the robot back to the left. Intuitively when trying to do that, you'd expect it to work like a car would, turning left would make the back go left..

I would like to change that so drivers could have it more intuitively.

That's what this is supposed to do. Try it.

[Shantali]

I was trying to work around that using

double m_y = m_driveStick.getY();
double m_x = m_driveStick.getX();
if (m_y >= 0) //the Y axis is inverted, so going forward is negative number
    m_x = 0-m_x; //inverting X value
m_robotDrive.arcadeDrive(m_y, m_x);

The problem I faced with that was that the joystick wasn't giving me a perfect 0.. I added a simple println statement to get the y values, and it ranged anywhere from -0.3 to 0.3...

Ether, it looks like your solution

if(Yj<=0){L=-Yj+Xj; R=-Yj-Xj;}

would have the same problem.

I tried something like if m_y >= -0.3, but it results in motors rapidly switching directions if starting slowly..

Another possible solution would be treating anything within .2 or so from the axis as 0.. but it doesn't seem like the best way of doing it either.

Thanks in advance,
j.

[Ether]

Originally Posted by Shantali

The problem I faced with that was that the joystick wasn't giving me a perfect 0.. I added a simple println statement to get the y values, and it ranged anywhere from -0.3 to 0.3...

Are you saying you got readings in the range -0.3 to 0.3 for Y when the joystick was in the null position?

[Shantali]

Yup

[Ether]

Try a different joystick.

[rsisk]

I believe you can also go into the windows control panel, find the Game Controllers adapter and use it to center the joystick (ie, the joystick reads 0,0 when centered).

[Shantali]

It does say 0.0 at the beginning, but after driving it for a bit then letting go, it doesn't always center perfectly.

Both of our joysticks do that :\

[Ether]

Originally Posted by Shantali

It does say 0.0 at the beginning, but after driving it for a bit then letting go, it doesn't always center perfectly.

Both of our joysticks do that :\

Clean the Mountain Dew out of them.

[Shantali]

They're clean outta the box ones... :'(

[Ether]

Originally Posted by Shantali

They're clean outta the box ones... :'(

Maybe there's an error in your software?

Try loading the default code that came with the LabVIEW installation and run it and see if it does the same thing.

[Shantali]

After updating and running stuff again, joysticks center within 0.05 from center. Still not a perfect 0.

However, after playing around with various types of if statements, I'm starting to get the impression that the default way is the only way of making it operate smoothly.

If you look at the http://web.goodrobot.com/blog/wp-con.../tankdrive.png diagram clockwise, by default we get the "motor forward x3, motor off, motor backward x3, motor off" pattern.. That way there is never a situation where the motor has to abruptly switch directions.

If swapping the reverse directions, we get "motor forward x3, motor backward x3, motor off, motor backward, motor off". That way at some point there's an abrupt change in motors from going backwards to forward. That is the issue I've been having and at this point I see no way of avoiding it.

If I'm wrong, please correct me.

[Ether]

Originally Posted by Shantali

After updating and running stuff again, joysticks center within 0.05 from center. Still not a perfect 0.

However, after playing around with various types of if statements, I'm starting to get the impression that the default way is the only way of making it operate smoothly.

If you look at the http://web.goodrobot.com/blog/wp-con.../tankdrive.png diagram clockwise, by default we get the "motor forward x3, motor off, motor backward x3, motor off" pattern.. That way there is never a situation where the motor has to abruptly switch directions.

If swapping the reverse directions, we get "motor forward x3, motor backward x3, motor off, motor backward, motor off". That way at some point there's an abrupt change in motors from going backwards to forward. That is the issue I've been having and at this point I see no way of avoiding it.

If I'm wrong, please correct me.

I think you are correct.

I believe the pseudo-code below implements the behavior shown in the diagram you referenced:

float Xj, Yj, L, R;

float max, sum, dif;

max = abs(Xj); if (abs(Yj)>max) max = abs(Yj);

sum = Xj+Yj; dif = Xj-Yj;

if(Yj<=0)
 {
 if(Xj>=0)
  {
  // first quadrant
  L =  max;
  R = -sum;
  }
 else
  {
  // second quadrant
  L =  dif;
  R =  max;
  }
 }
else
 {
 if(Xj>=0)
  {
  // fourth quadrant
  L =  dif;
  R = -max;
  }
 else
  {
  // third quadrant
  L = -max;
  R = -sum;
  }
 }

If you want to reverse the direction of rotation when backing up, I believe the following modified code would do that (note the addition of some deadband to address your concern about abrupt motor direction changes*):

float Xj, Yj, L, R;

float max, sum, dif, deadband;

if (Yj>-deadband)&&(Yj<deadband) Yj=0;

max = abs(Xj); if (abs(Yj)>max) max = abs(Yj);

sum = Xj+Yj; dif = Xj-Yj;

if(Yj<=0)
 {
 if(Xj>=0)
  {
  // first quadrant
  L =  max;
  R = -sum;
  }
 else
  {
  // second quadrant
  L =  dif;
  R =  max;
  }
 }
else
 {
 if(Xj>=0)
  {
  // fourth quadrant
  L = -max;
  R =  dif;
  }
 else
  {
  // third quadrant
  L =  -sum;
  R =  -max;
  }
 }

*if using Jaguars, you may want to experiment with putting the jumper in the "coast" setting to avoid abrupt motor braking when transitioning into/out_of the deadband zone