New Programmer
 

Hi,I'm a new programmer and I was following a tutorial and it kept using a certain vi,but i couldn't recognize it or find it in the tool pallet.Can someone tell me what it is and where to find it

Re: New Programmer
 

Feedback node. Located in the Programming -> Structures pallet.

Re: New Programmer
 

That is called a feed back node. It stores the last value fed in so that you can compare a variable or value to itself. It is found in the Structures pallet towards the bottom right.

Re: New Programmer
 

Thank You

Re: New Programmer
 

Oh one more.Sorry for the nuisance

Re: New Programmer
 

No need, that's why we're all here; to help.

That is a Boolean> True/False. Depending on which letter, T or F, has green behind it tells you which is running. (i.e. Green-background T means it's running True).

Re: New Programmer
 

The feedback node is found in the Structures palette. It points from right to left by default. The diamond underneath it is how older versions of LabVIEW marked the initializer terminal; this year it looks like an asterisk which becomes a cursive i when wired.

The green T/F is a Boolean constant from an older version of LabVIEW. It would alternately highlight the T and the F when clicked on. LabVIEW 2012 instead displays it as a single square with either a T or an F in it. You'll find the T and F constants in the Boolean function palette.

Re: New Programmer
 

Now I'm trying to insert a process much like this which will set a servo to 90 activate a relay forward and then set both of them back to their natural position
but it seems to be running too fast and starving the drive system any pointers

Re: New Programmer
 

Unless we see what you're actually doing, we won't be able to give much in the way of help. Show us your code, not the example you're emulating.

Re: New Programmer
 

oh sorry yes here

Re: New Programmer
 

If you place the code into teleop, it will prevent teleop from running frequently enough. Try moving it to Periodic tasks.

Greg McKaskle

Re: New Programmer
 

I can't be the only LabVIEW developer that despises the use of the feedback node, can I? IMO, while feedback nodes *can* make a diagram cleaner, they actually make it *harder* to understand, as compared to using the equivalent shift register.

Re: New Programmer
 

I attempted this and it still says it is starving the drive loop

Re: New Programmer
 

You can attach your vi's directly to a post.
Show us your Teleop.vi & Periodic.vi, and any other vi you might have added code to.

The code you posted looks fine as long as it's in Periodic Tasks.vi (it would not work in Teleop).

Re: New Programmer
 

I also learned LV long before there were shift registers and in many ways prefer them, but I now use both, typically for different things. I really like the compare to last with a shift register, but otherwise typically use shift registers.

Greg McKaskle

Re: New Programmer
 

I almost never use feedback nodes, but I find myself using feed forward nodes quite frequently. They make more sense to me because the flow of the code keeps moving forward. If I'm in a loop, though, I'll always use shift registers.

Re: New Programmer
 

Here are my tele op and periodic vis neither has much extra really

Re: New Programmer
 

I looked at the code and I don't see anything wrong with it.

Basically, the starvation occurs if you don't call the Arcade Drive VI every 100ms. Having the VIs open (front panel or block diagram) can cause this. Try closing a few windows and see if that helps.

Seeing the starvation message is completely normal on non-built code (not saying it's good though). If you see it all the time after you build and deploy your code, then you have an issue.

Even with the message, can you drive the robot around? Do you notice it?

Re: New Programmer
 

@Greg McKaskle: I really like several of the changes that have come about since the birth of the idea exchange a couple years ago. Things like shrinking the boolean constant, changes to local variable graphics, integrated labels for structures, better alignment of vi.lib vi's I/O and so on.

For my non-FRC applications, I REALLY like the JKI string-based state machine template.

Re: New Programmer
 

Is "feedforward node" generally accepted terminology for a feedback node that simply has the arrow direction changed to make the wiring cleaner? If so, it seems unfortunate. The function of the node remains the same regardless of arrow direction.

Re: New Programmer
 

As far as I know, they're only called feedback nodes. Changing the direction doesn't change their functionality. It just makes the code 'flow' more smoothly sometimes.

Re: New Programmer
 

I guess it's not technically called a feed forward node, but that's what I have come to call them for reasons that are unclear to me. I think one of our mentors called it that, and it stuck.

But it does go forward...so I think I'm gonna stick to the "feed forward" name. :P

Re: New Programmer
 

Rather than feed forward, how about previous value or delay by one or some name that explains its purpose rather than its appearance.

Greg McKaskle

Re: New Programmer
 

When I'm teaching it I use Greg's suggestion and just call it the "previous value"

Re: New Programmer
 

How about calling it a Z^-1 node?

Just kidding. That doesn't help new learners.

I like Mark & Greg's "previous value" moniker. Students seem to understand that phrase immediately, and it's accurate.

@bvisness: the reason I said "feedforward node" is unfortunate is because feedforward has a completely different meaning in control theory.

Re: New Programmer
 

"Previous Value" is nice, so I think I'll try to call it that from now on. (And I was unaware that "feed forward" has another meaning in control theory...sorry about the confusion.)