Video: What is a PID Controller?

Very well done! Interesting and comprehensible.

Your plans for the next one include any production suggestions that I'd have.

A couple of content comments:

- in the proportional demonstration, you add the weight and it doesn't recover (to 45). You say " ... it's not at the target angle, cause it has to have some error to develop the drive ...". Well, it does have error - why doesn't it correct? (around 9:00 - 9:40)

- the D & I explanations got around the calculus nicely. What I would have liked to see there was why these aspects are useful. Everyone can see that correcting a proportional error is useful. Why isn't it good enough? Sort of: "Proportional will correct, but when the disturbance is happening rapidly, a stronger correction is better & the derivative does that."

- you probably aren't going to find the time for it, but what about stability? It's so important that wouldn't a few words be justified? Maybe just an aside such as "Another important aspect of D/I is that as the error is reduced, the correcting force is also, reducing overshoot." Or something to that effect which is actually true.

Bob

Oh - I do have a production comment: if the disturbing weight were a magnet, it could be added & removed instantly, with no fiddling required.

If you add too much gain, it turns into an oscillator. (That could be a video title, oscillators everywhere.)

George H.

There's some phase space in P,I controllers, where I turns into the gain and P is the damping... I'd like to understand that better too.

George H.

Yet another another day in computah hell. I run Firefox 46.0.1 on Windoze XP in my palatial office at cable modem speeds and still get Flash as 360p. I would have expected higher resolution and HTML5. However, when I switch to Chrome Version 49.0.2623.112m (last version for XP), your video auto plays in HTML5 at 480p. I can also force it to 720p and 1080p and it plays without buffering.

I also tried both the Firefox and Chrome browsers on Win 7 and Win 10. Here's the table of results for what appeared as the default player and screen resolution:

Firefox Chrome Win XP Flash 360p HTML5 480p Win 7 HTML5 360p HTML5 480p Win 10 HTML5 360p HTML5 480p

So, in Chrome, everything is working normally and correctly, but in Firefox, I have a problem only on my XP machine. Oddly, both Chrome and Firefox on XP show that HTML5 is supported and is the default: I still don't know why my Firefox default to Flash, but I think you can safely ignore this oddity as it seems to be a problem with my XP machine.

Magnets. D'oh. Yes, that's an excellent idea. The tube is aluminum, and the balance weight is lead, but the ultra-classy radiator clamp holding the balance weight is steel.

I'm actually wondering if I should do a video on stability next. Just defining stability by the pole positions is nice, but I think I could spend 15 minutes investigating why an oscillator can be "stable" in one sense and unstable in another, as well as the difference between a soft limit cycle (i.e., a self-starting oscillator) and a hard limit cycle (a clock pendulum's escapement, if you're old enough to remember having to start a clock going).

Having a hard limit cycle in a control system can be a right bitch if you happen to never excite it in the lab and then a customer stumbles onto it in the field. Knowing about their existence makes it harder for them to escape from captivity. Even if they do, knowing about their existence can shorten the duration of the emergency when the screams reach Engineering.

Thank you Tim, really nice to hear the fan working harder/softer - an inspired choice of actuator!

Good clear demonstration, I now can't wait to see a demo of the effects of too much D or too much I and not enough D / I etc and then an introduction on how to tune these or even explain how self-tuning works.

piglet

Yes! I had the same questions.

--Eeyore

I'm not sure if I'll do self-tuning, but yes, the other two need to go into a video -- or two, to fit into YouTube's time limits.

Hi Tim,

Nice video, thanks for posting. I thought the controlled system was the neatest part. My suggestion is that you lead off with showing what the system can do - command a few angles, introduce a few upsets, maybe in rapid succession, and watch the system respond. Then the audience will be receptive to listen to how to achieve those results. I'm not sure how you do that with the time limit. It's a challenge.

you just need to verify your account then that is no time limit

-Lasse

I'm also trying to keep the length down to modern attention spans.

There are various little bits that could be snipped out without losing any content. 15 minutes is plenty really. A fine first video.

NT

You gave me a turn there--I thought for a moment you might be _that_ Eeyore . (There was a Brit who posted here under that nym some years back, who see med to specialize in arguing audio with Phil A. and over-the-top bragging a bout his alleged romantic exploits.)

But you aren't. No worries. ;)

Cheers

Phil Hobbs

One of the things I _didn't_ like about the process was that I started out deciding to film the thing in one go. Then I'd flub badly, go back some random amount, and start over again. The result wasn't always something that could be put back together nicely.

Next time I'm going to do one slide at a time (I'm working off of a power- point-ish presentation), stop the camera, then proceed. I may also see if I can dragoon #1 son, who has time on his hands, to be my cameraman and director (basically to make sure that I really did cover one whole slide, without too much digression).