hey guys, I'm relatively new to labview, and am currently trying to make a multi stage snake like robot. I'm interfacing with USB controllers from pololu and want to manualy control the first stage and have the remaining stages follow, I've got the first stage working with commands from the front panel. I use a producer consumer template and have button pushes activate an event and then queue a case in a second "hardware loop". my current problem is now I want to start working on controlling the secondary stages passively, so I want to move the front stage angled up and then start to drive foward and the second stage begins to follow into the same position. I want to regularly interrupt and check the positions on the servos to compare and act accordingly. my first thought is to interrupt on timeout in the event structure and test if the servos are at the same postion. the problem is my visa reference is in the other loop. what would be the best way to go about this? should I just queue into my hardware loop on a time out and test the servo positions. or is there a way to share my visa resource in the producer loop? I originally wanted to store the reference in the producer loop and pass it everytime I went to the consumer loop but I couldnt figure out a good way to return the updated reference and I kept getting errors. are timed loops an option here? any advice would be helpful. even if you have a better structure to redo the whole project. I'd love to hear it for next time if nothing else. also if theres a better sub forum ill gladly move the post. thanks guys

1. I'd aim to pass info/data back to the UI Reactor loop. Let the UI Creator loop just catch GUI events and dispatch work to the Reactor loop. You can build in more brains to the Reactor loop and let it also receive info/work from the Hardware loop(s). 2. One simple concept for a regular request for servo position would be an additional loop. It's only job is have a wait timer and then queue up a request to the Hardware loop to ask it to send the servo position. It will send it to the Reactor loop, as always, and the Reactor loop will have been built to react appropriately when it gets servo position info. 3. I would not talk to the servos from any other place than the Hardware loop. It's all kinds of messy if you can send serial commands from different loops at the same time, then receive the wrong reply or none at all. Sorry, don't have any more time to get into finer details, but hope this helps a bit as you think about building up the app. -Kevin P 4. P.S. I meant to also mention: it looks like both your Reactor and Hardware loop are consumers of the same Queue. Even though I see how you're previewing first and then only dequeuing if relevant, it's still not a recommended approach. Consider: if one loop gets stuck while one of its msgs is in front of the queue, it will make the other loop get stuck too.

LabVIEW

interrupting a prodcer consumer structure to test servo position regularly

Solved!

Since you've already tackled the idea of fairly generic messaging using a String + Variant data structure, I'd suggest you start looking into and studying the Queued Message Handler template. From the File menu, select "Create Project...", then pick the Queued Message Handler template.

The essential idea Is that every loop is the only consumer of its own message queue, but every loop can also act as a producer to send messages to other queues (and therefore to other loops). I've adopted the habit of usually restricting myself to one central "Main Brain" loop that coordinates all the other subservient loops. Each of the subservient loops talks back and forth only to the Main Brain. I find that this helps a lot with developing and debugging the individual subservient loops.

-Kevin P

ALERT! LabVIEW's subscription-only policy came to an end (finally!). Unfortunately, pricing favors the captured and committed over new adopters -- so tread carefully.