Re: Encoders (What's up with those?)
 

This is actually just a habit now. When I made my first feedback control loop for a flywheel last year, I had some trouble getting it to work using the counter. On a whim, I tried inputting them as encoders and it worked great. I've since figured out how to do it with the counter VI (some simple problem with the math I had), but never switched back.

This was the recommendation of a mentor. His explanation was that it allowed for a 'finer' count. I have tried it with just one piece of tape and didn't notice any significant different (just different scaling).

I should have said, the PID controller keeps the flywheel within a .2% error based on the readings from the photoelectric sensors. If those readings themselves are incorrect, then I'd have to rescind that statement.

See post by team member above. Directly connect w/ 4:1 gearboxes.

See above - talons.

Do you mean in RPM? I'd have to check my documentation at the shop, I can't remember off the top of my memory.

The LabVIEW PID has worked fine for us in the past, but it's always more fun to write the code yourself, to a reasonable extent. Better learning opportunity for rookie programmers. I don't have much experience with the half-back or bang-bang controllers, so I can't comment on those. Would be interesting to try them though and see how they compare. Sorry I don't have a good response for this one!

Re: Encoders (What's up with those?)
 

Thanks for the detailed answers.

I don't have access to the LabVIEW help files here, so one more question:

Can you tell me what the "12" input is for in the "Configure Timer" vi, and why did you chose that particular number.

Re: Encoders (What's up with those?)
 

Number of samples to average. I think it was a bit of trial and error until we got a smooth reading from the photoelectrics.

Re: Encoders (What's up with those?)
 

Can you tell me, the way you have the encoder configured, is it sampling both rising and falling edges?

Re: Encoders (What's up with those?)
 

I believe it's configured to only count on the rising edge. I can check this tomorrow if you'd like.

Re: Encoders (What's up with those?)
 

Yes, please do. I'm going somewhere with this...

Re: Encoders (What's up with those?)
 

Now that you're making me rethink this, it may not make a lot of sense to be averaging every 12 samples. It looks like the default is actually 1. I'm not sure if this is an error or not... I will definitely investigate this tomorrow.

It works wonderfully right now, but this could be the path to making it better.

Re: Encoders (What's up with those?)
 

You probably don't want the default of 1 with six pieces of tape, especially if it's sampling both rising and falling edges.

Try this: one piece of tape with the default sample size of 1 and setup to sample rising edges only. That way, it's always sampling the same edge of the same piece of tape, so the spacing is perfect... and with your 20ms update rate, you'll be getting a fresh reading every execution or your controller loop at wheel speeds of 3000 RPM or higher.

Re: Encoders (What's up with those?)
 

I will give this a go tonight and let you know the results. Thanks for the recommendations.

Re: Encoders (What's up with those?)
 

Sorry, didn't have any opportunity to do the tests this evening. I will send you a private message with the results when I do have a moment with the robot so as to not clutter up this thread any more.

Re: Encoders (What's up with those?)
 

The Banner photoeyes they used are retroreflective units - they have an emitter and detector in the same housing.