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#1
02-19-2011, 11:53 PM
 Jogo Registered User FRC #0353 (Pobots) Team Role: Programmer Join Date: May 2009 Rookie Year: 2007 Location: NY Posts: 83
paper: LabVIEW Mecanum Programming

Thread created automatically to discuss a document in CD-Media.

LabVIEW Mecanum Programming by Jogo
#2
02-20-2011, 01:22 AM
 Ether systems engineer (retired) no team Join Date: Nov 2009 Rookie Year: 1969 Location: US Posts: 9,126
Re: paper: LabVIEW Mecanum Programming

Nice presentation. This should prove helpful to teams just getting started with LabVIEW and mecanum.

There's a small error on Page 19 which may lead some astray:

Quote:
 Wouldn't it be convienient to--on the push of a button--rotate to the direction you're traveling? ▪To calculate this angle, do Math.atan2(Joystick X, -Joystick Y) ▪Implement a PID loop--the setpoint is the joystick angle, and the process variable is the gyro angle
The above won't work very well. The joystick angle will be -180..+180, and the gyro angle will be 0..360+

You can't just pass the joystick angle and gyro angle to the PID as-is. The PID will not like that at all.

For example, if the joystick angle is -1 degree and the gyro is reading +359 degrees, the PID will calculate (and act upon) an error of -1-359 = -360 degrees... even though the vehicle is already pointing in the desired direction.

To use the LabVIEW PID in this situation, you need to do something like this:

Code:
```angle_error = joystick_angle - gyro_angle;
angle_error -= 360*floor(0.5+angle_error/360);
setpoint = gyro_angle + angle_error;
process_variable = gyro_angle;```

Example LabVIEW code for the second line in the code block above can be found here.

Last edited by Ether : 02-20-2011 at 02:05 AM.
#3
02-20-2011, 08:26 AM
 Jogo Registered User FRC #0353 (Pobots) Team Role: Programmer Join Date: May 2009 Rookie Year: 2007 Location: NY Posts: 83
Re: paper: LabVIEW Mecanum Programming

Thank you Ether. I added in a solution that I used but neglected to include in the first version. Now that I look at your solution closer, however, yours seems a great deal more elegant.
#4
02-02-2012, 08:04 PM
 maria_edu Registered User FRC #1811 Join Date: Jan 2012 Location: Newark, NJ Posts: 13
Re: paper: LabVIEW Mecanum Programming

I have a question on slide 9; what is the blue thing within the case structure? Sorry 1st time programming mechanum drive. Very helpful presentation
#5
02-02-2012, 09:16 PM
 Alan Anderson Software Architect FRC #0045 (TechnoKats) Team Role: Mentor Join Date: Feb 2004 Rookie Year: 2004 Location: Kokomo, Indiana Posts: 9,163
Re: paper: LabVIEW Mecanum Programming

I don't know what it is you're referring to. Can you describe the "blue thing" a little better? Blue typically means an integer value.
#6
02-02-2012, 09:22 PM
 maria_edu Registered User FRC #1811 Join Date: Jan 2012 Location: Newark, NJ Posts: 13
Re: paper: LabVIEW Mecanum Programming

Sorry about that; I mean in the true/false case structure, there is the"blue thing" that says"L1 rotate_mode." My question is where is that located in labview?
#7
02-02-2012, 09:30 PM
 Alan Anderson Software Architect FRC #0045 (TechnoKats) Team Role: Mentor Join Date: Feb 2004 Rookie Year: 2004 Location: Kokomo, Indiana Posts: 9,163
Re: paper: LabVIEW Mecanum Programming

rotate_mode is a global variable that was defined on the immediately preceding slides. L1 is an enumerated constant that was obviously created by right-clicking the input terminal of the variable and choosing Create Constant.
#8
02-06-2012, 08:26 PM
 2829ron Registered User FRC #2829 Join Date: Jan 2009 Location: USA Posts: 92
Re: paper: LabVIEW Mecanum Programming

Hello,

I did all the steps in page 8, but can not get my robot global data to read the "rotate mode" enum. Any help would be appreciated.

Thanx,

David
#9
02-06-2012, 10:36 PM
 Alan Anderson Software Architect FRC #0045 (TechnoKats) Team Role: Mentor Join Date: Feb 2004 Rookie Year: 2004 Location: Kokomo, Indiana Posts: 9,163
Re: paper: LabVIEW Mecanum Programming

I'm not sure what you mean. The robot global data doesn't "read" or "write" the values. It just provides a place that contains them.

Are you trying to say you can't get the global variable to appear on the Teleop block diagram?
#10
02-07-2012, 09:26 AM
 2829ron Registered User FRC #2829 Join Date: Jan 2009 Location: USA Posts: 92
Re: paper: LabVIEW Mecanum Programming

Yes sir. That is what I meant. I defined it's values in the Robot Global Value.vi but they won't show in teleoperated.

Thanks,

David
#11
02-07-2012, 10:56 AM
 Alan Anderson Software Architect FRC #0045 (TechnoKats) Team Role: Mentor Join Date: Feb 2004 Rookie Year: 2004 Location: Kokomo, Indiana Posts: 9,163
Re: paper: LabVIEW Mecanum Programming

It's not exactly obvious how to place a reference to an existing global variable. Here's how to do it:

Right-click on an empty spot in the block diagram to call up the function palette. Choose "Select a vi..." and navigate to the folder containing your robot project. Open "Robot Global Data.vi" and you'll have a global variable attached to your cursor (it will likely be named "Enable Vision" -- don't worry about it). Click to place that variable on the block diagram. Now you can click on the middle of the variable to bring up a list of all the globals that are part of the Robot Global Data vi. Choose the one you want.

The default is to make a "write" reference. To change it to "read", right-click on the variable and choose "Change To Read".
#12
02-07-2012, 11:00 PM
 2829ron Registered User FRC #2829 Join Date: Jan 2009 Location: USA Posts: 92
Re: paper: LabVIEW Mecanum Programming

Okay. I got the global variable to show up, and I can connect the constant to it. But when I change the global variable to read, I can't connect my constants anymore. Did I totally mess up somewhere? This is my third year programming, but I've never messed with the global robot data vi.

Thanks,

David
#13
02-07-2012, 11:43 PM
 Alan Anderson Software Architect FRC #0045 (TechnoKats) Team Role: Mentor Join Date: Feb 2004 Rookie Year: 2004 Location: Kokomo, Indiana Posts: 9,163
Re: paper: LabVIEW Mecanum Programming

If you want to put a constant in the global variable, you need to write to it. You would read it if you want to do something with the value it contains.
#14
02-08-2012, 08:49 PM
 2829ron Registered User FRC #2829 Join Date: Jan 2009 Location: USA Posts: 92
Re: paper: LabVIEW Mecanum Programming

Okay. On to page 14 I'm getting tired of asking questions. But thanks to everyone for your help. The rotate mode runs into the case structure and then connects to the symbol I can't seem to find. It's blue with an arrow and a box with a circle under it.

Also, do need to create a global variable called "header"? If so, what properties does it need to have?

And... what is connect to the PID on page 15?

Thanks again,

David

Last edited by 2829ron : 02-08-2012 at 08:57 PM.
#15
02-08-2012, 10:53 PM
 Alan Anderson Software Architect FRC #0045 (TechnoKats) Team Role: Mentor Join Date: Feb 2004 Rookie Year: 2004 Location: Kokomo, Indiana Posts: 9,163
Re: paper: LabVIEW Mecanum Programming

Quote:
 Originally Posted by 2829ron The rotate mode runs into the case structure and then connects to the symbol I can't seem to find. It's blue with an arrow and a box with a circle under it.
It's called a Feedback Node. You will find it in the Programming>Structures function subpalette. Its output is the value that was connected to its input the previous time through the loop. It changes color based on what type of data it's connected to; in this case it's blue because the data is an (enumerated) integer type.

(The Feedback Node look has changed slightly between LabVIEW 8.6 and LabVIEW 2011. The "box with circle" is now a wider box with an asterisk.)

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