Quote:
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Originally Posted by gc02
I disagree completly.
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That's ok
Quote:
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Originally Posted by gc02
Take a look at the picture under the "Choosing a frequency based on motor characteristics" section of this website: http://homepages.which.net/~paul.hil...ntrollers.html
It shows the relationship between the PWM signal and the motor's current. If someone  was to figure out the RMS current of that waveform at different duty cycles, I believe there would be a non-linear relationship between the RMS current and duty cycle. |
Really good website btw.
That is exactly what I began to think (I even drew pictures) but then I thought about what happens to voltage (emf) across an inductor. It gets really hairy because a back emf is produced when the current changes. This is an application of Faraday's Law which more or less says that if a change in current occurs, a change in the magnetic field will also occur that is exactly opposite and equivalent of the equivalent current.
This is given by the equation
emf = -Inductance * change in current / change in time
//Given the schematic (slightly modified so it has no whitespace) (why no whitespace Brandon? It makes it tougher for ASCII art
) Comments on schematic, switch represents half of the H-Bridge (in a way) resistor represents resistance of wire windings commutor etc. and inductor represents motor's inductance.
BATTERY____/ __C__^^^^__A__~~~__B___GROUND
//And the pulse produced by the switch (see schematic) potential difference between A and B
Voltage
12 | __
00 |_| |___ time
-12|
//With an inductor potential difference between A and B
Voltage
12 |
00 |_|\_ ___ time
-12|___|/
But what happens when I take into account the resistor? And try to measure voltage between C and B? Will it simply decrease the voltage by an increment (shift downward?) or will it cause a nonlinear response voltage change? I will try to puzzle that out when I am not so tired.
Also, for anyone who wishes to do circuit analysis, OrCad offers a free student copy of their product PSpice which I have yet to play with, however I am told that it can simulate this sort of thing rather nicely. The url is
http://www.orcad.com/downloads/demo/
Cool, goodnight
-Andy