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A few questions reguarding my first NSTC

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Steve Conner

Wed Apr 26 2006, 12:19PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Hi Terry, all,

There's not really much point in phase-locking a DC motor, except that it's a fun project and has a lot of educational value. Jrz is about to learn a lot about control theory pretty quickly. Hopefully he's going to learn it from hazmatt, to save me doing it

Hazmatt_(The Underdog)

Wed Apr 26 2006, 08:44PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

hehehe...oh man. You know..It would be fun, but its hard to remember controls when they have us jumping from topic to topic in college. My major is controls, but I also love instrumentation, which is a great mix, because after all how else can you control something without interfacing? you cant.

Lemme see what I can come up with after the semester ends. Maybe I can bug my controls teacher. He co-wrote a pretty good book on the subject, my major complaint to him was that his book wasn't procedure based! which doesn't help me one bit!

Hopefully I will have enough time after finals/before summer EE411 to work out the system. Getting the inertial response is going to be really critical, so I need to measure that with some real precision. But thankfully, the response is much like that of the Incubator system in the Basic Stamp Program. If you pick up that book/controller kit you will be on your way to having a good system.

Jrz126

Thu Apr 27 2006, 06:06PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

Those basic stamps are pretty expensive...compared to the free samples of PICs that I can get from microchip's website.
Do you really need to take measurments for it? I was planning on just leaving the Kp Ki and Kd as variables and just tune those until I get a nice response.
I'd be working on it right now, but I only have one more pic to use and it doesnt have the bootloader I need to load my programs.

Hazmatt_(The Underdog)

Thu Apr 27 2006, 07:46PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

It's really not about the stamp, its about the compilier and some of the features they wrote into the compilier as reserved words. It also has its Incubator exercise which is pratically the same as a motor. You watch how the resistor heats a film canister and create a heater system with PID control.

What you're getting is a number of things, the controller, a procedure, and an implementation that's almost verbatum with code in the book. To me its worth the cost since I don't have the time to be making mistakes.
Also, the compilier has a function RCtime so connecting a pot and cap to the pin and grabbing the variable is practically coded for you already!

Now you could just use pots and probably get on your feet sooner then I could with all the simulation, but I could probably get more efficiency out of simulation. I'm sure you will get really close though (90 percentile.) and I might get 95%. I'd prefer the practice though, and so I won't have to fiddle with the pots.

A place you might want to start is:
Kp = 1
Kd = 10
Ki = .1 or .01
I think those were my values for my heater system. Good luck with design ;)

Jrz126

Fri Apr 28 2006, 06:15PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

I have the PWM signal working from the microcontroller, but the labs at school only have 1amp max powersupplies, which hampers the acceleration of the motor. So I came up with this little test bench in about an hour or 2.
overall
microcontroller
motor

The motor assembly isnt attached to the powersupply base, it would have been too awkward to carry around school. And the motor isnt finalized either, I just mounted the sensor so I could test it

Now time to go play with it.

Jrz126

Thu May 04 2006, 07:36PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

So close....
I've made quit a bit of progress with the controller.
I mounted an LED to shine on the disk and have it hooked up to a zero crossing detector, so its flashing at 120Hz. This will show if the disk is sync'd or not. The lines on the disk should appear to be stationary (like a timing light for a car).
It's still kinda jittery (as you can kinda see from the movies) I noticed that my PWM signal is more of a full on/full off instead of a PWM, so I've got some adjustments to make with that.
led1
led2
movie 1
movie 2
Sorry about the MOV format, thats what my digi uses.

Jrz126

Sun May 07 2006, 03:32PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

I got the controller all figured out, and the position holds pretty steady. Well atleast until I start to crank up the variac. Once I get to about 10V, the motor goes nuts. The spark gap doesnt even fire.
I saw this problem coming, but atleast I know my speed controller works.

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