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paper: LabVIEW Mecanum Programming
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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:
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;Example LabVIEW code for the second line in the code block above can be found here. |
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.
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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
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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.
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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?
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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.
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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 |
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? |
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 |
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". |
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 |
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.
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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 |
Re: paper: LabVIEW Mecanum Programming
Quote:
(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.) |
Re: paper: LabVIEW Mecanum Programming
Thanks for all your help. I've got a few more questions here, and then I think I'll have it.
Do I need to create a global variable called "header"? If so, what properties does it need to have? And... what is connected to the PID on page 15? Thanks again, David |
Re: paper: LabVIEW Mecanum Programming
Hello David. You do need to add a global variable called "header" (numeric), which is used to store the gyro angle each time rotate_mode changes to "straight".
For tuning the PID function, first right click on the "PID gains" terminal and add a control or a constant, and follow the instructions on page 16. There are plenty of good resources around the web for PID tuning specifics: http://zone.ni.com/devzone/cda/tut/p/id/3782. If you have more implementation-specific questions, feel free to PM me. |
Re: paper: LabVIEW Mecanum Programming
Ok My names Ernesto
I am still stuck on the global header and would like to ask if you could explain more on how to make it. |
Re: paper: LabVIEW Mecanum Programming
I am also trying to figure out the global variable header. I wasnt sure where to create it or how. So i created a numeric and then create a local variable from the numeric and called it header and used that within my teleop code. Will this work or do i need to create a global somehow?
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Re: paper: LabVIEW Mecanum Programming
The Robot Global Data.vi is where you create global variables (if you need them). It's only a front panel, with no block diagram. Place (or paste) a control of the appropriate type on the front panel, then right-click it and make its label visible if it isn't already. Change the label to whatever name you want the global variable to be.
To use a global variable, you can either copy one from elsewhere, or use the "Select a VI" item in the function palette to pick the Robot Global Data. You'll end up with something on your block diagram with a popup menu that lets you choose among all the globals. You can use the right-click menu to make it a "read" or a "write". |
Re: paper: LabVIEW Mecanum Programming
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Re: paper: LabVIEW Mecanum Programming
Quote:
There are only two Case structures, right? The inner Case structure (inside the outer Straight case) should contain the True case you showed, along with an empty False case. The outer Case structure should contain a case for every possible value of the Rotation_mode enumeration. You're only showing us the Straight and L1 cases. Are any of the others missing? |
Re: paper: LabVIEW Mecanum Programming
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Re: paper: LabVIEW Mecanum Programming
Is there a blank in the enumeration list?
Sorry, I can't see your posted images. They get blocked where I am. |
Re: paper: LabVIEW Mecanum Programming
Thanks, that was it. A blank space in the enumerated list.
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Re: paper: LabVIEW Mecanum Programming
Quote:
Double-check the list of possible values of Rotation_mode. Make sure there are only the five you expect. You might accidentally have inserted an unnamed value at the end. |
Re: paper: LabVIEW Mecanum Programming
Thanks, that was it. Program runs.
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Re: paper: LabVIEW Mecanum Programming
Quote:
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Re: paper: LabVIEW Mecanum Programming
There is no Block Diagram for Global Data, so ignore that.
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Re: paper: LabVIEW Mecanum Programming
We purchased a Mecanum kit as an off-season project and played with the code last night. I believe there are some errors in the code, that I thought I would post here in case others also did not get the results expected.
First, let me thank you for taking the time to develop this, it was a huge asset with trying to get students to get the code working. Now to the issues. On page 14, I believe the feedback node needs to be outside of the case structure for "Straight"... What we saw is that the only way you can get into the "Straight" structure is for the rotate_mode to be equal to "Straight" and therefore the feedback node can only be equal to "Straight" and since they never not equal each other, you never update the "Header" value. When you add the PID on page 15, the PID now will unwind whatever rotation you do, because the Header is not updated, and stuck at the default, which we set to 0. So spin the bot 3 times CCW, and the let go of the sticks, the PID runs the 3 times CW and stops. The simple fix for this is to move the feedback node out, and the header updates correctly. On slide 17, when you add the case structure to make sure the rotate momentum is less than 10, this also breaks Header updating. As written the Header can only update the first loop after you took your finger off the sticks, so if you are spinning faster than the 10, the Header will not update, and if spinning slower than 10, you really didn't need this case anyways.... I have not fixed this one yet. It seems we almost need another enumeration state.. Say the joysticks put you in a "WaitingForStraight" and the case structure for WaitingForStriaght would check that rate less than 10 while sending 0 to the rotation, once the rate is less than ten we would write Straight to the "Rotate_Mode" I'll post back in a couple weeks on this fix, and debugging of page 21. |
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