paper: LabVIEW Mecanum Programming

[Jogo]

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

LabVIEW Mecanum Programming by Jogo

[Ether]

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:

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:

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.

[Jogo]

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.

[maria_edu]

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

[Alan Anderson]

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.

[maria_edu]

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?

[Alan Anderson]

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.

[2829ron]

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

[Alan Anderson]

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?

[2829ron]

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

[Alan Anderson]

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".