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Old Fri 05 October 2007, 22:25
Aubrey
Just call me: Aubrey
 
Jhb
South Africa
Hi All
Just to let you all know that I have not fallen off the face of the earth.
Quote:
Originally Posted by Bill McGuire View Post
Aubrey...
Good luck putting your board together...
Hope your Dr's visit went well...
Thanks Bill. Dr visit went ok. Almost got full mobility back, strength is still not so good but the pain is gone.

I have to get a couple of boards etched this week so I'll sneak in the logic board as well. The power board will be done on Veroboard for the meantime.

Busy battling with PICBasic Pro, cant get it working properly. If its not up and running properly by Monday, I'll be taking a crash course in mnemonics programming.
May be for the good. Fortunately, I pick up programming languages very quickly. EXCEPT C for some reason or other but I do PHP which is evidently much the same.
Maybe I suffer from "C" dyslexia or something. (No insult intended at all, some of those people who suffer from dyslexia really have it tough. But they survive and have my respect.)

About the opto-isolator thing, initially going with the unit proposed. There WILL be an upper speed limit but this is the first step of a development and there are probably going to be a number of other "problems" to overcome before it becomes a real issue to going forward.

Did some reading on reference material that I downloaded but had not yet got to. Evidently, if you full step using 2 coils (one North, one South) the resonance frequency is different to the one using only 1 coil (North only).

Basically what the author suggested is stepping using the method with the highest resonance frequency untill you are past the resonant frequency of the lower one and then switch to the method with the lower frequency. That way you never actually achive resonance.

For example, method 1 resonates at 2000 steps/sec, method 2 at 2500 steps/sec. So you use method 2 below 2250 steps/sec and method 1 above 2250 steps/sec. There is also a warning that every design of motor (and individual motors within the same model series) have different resonance frequencys. Maybe it would be a good idea to make the threshold frequency adjustable using a trimpot on the board. That way it is adjustable without playing around in the PIC's program.

He also warns that microstepping is not an exact science in that a 1/8th step's position probably wont be exactly in the center of the leading and trailing 1/4 step. Also, 2 identical motors can behave in different ways and/or positions using identical input signals. However the same is also true when full stepping he says. The difference is that a 0.1 degree error in positioning is far less of an issue when stepping 1.8 degrees (5.5%) than it is when stepping 0.225 degrees (44.4%)

Isnt it wonderfull having so many variables! Yea - Right!

But then again, the hobby machinist is not dealing in microns. My personal opinion is that a theoretical accuracy of 1/100th of a millimeter is way more than sufficient. Anyone who boasts of better than that (especially on wood or plastic) is probably kidding themselves. I'd like to know how to measure a micron on wood! My micrometers cant get that accuracy reliably on metal and metal is far more dimentionally stable than wood. Are we trying to machine parts for the shuttle or what?

All the best
Aubrey
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