You are quite right about the differences of detent and holding torques. See, it appears to be hard to admit, but its not that hard, and the fact itself has a great deal of benefits, in other words, its well worth saying. Its a feat of doing stuff that is worth doing, saying that or doing this is equal to learning. And saying "you are right" is as consequence, a feat of ppls that were able to learn from others. Without this, i would be abnoxious, pretending to be always right, trying to play with words to back up weird stuff, and as consequence not being able to improve. Getting out of a state of mind like that is worth anything, any effort. Ofc, this is my opinion.
We have 2 waveforms to study, voltage and current. The driver puts the voltage across the inductor, on and off, so the voltage waveform is a simple square wave. The current in inductor by its element law, is defined to be the integral of the voltage by time, so when the voltage starts to be on, then the current starts from zero, and has a rising edge. This rising edge initially grows fast, then tends to grow very slowly. This is because the integral definition makes the grows to be the new addition versus the old one, so after some time it grows very slow because each new portion of addition is relatively smaller in comparison to the bigger "past" integral. In the end this current would tangentially reach the point of ohms law for the voltage and coil resistance, but much before that, the driver will interrupt the voltage. After voltage interrupts the inductor current has a falling edge, that has a different shape but it goes to zero as the voltage stays off. So this is what makes the current sort of speaking.
We can not use a battery and resistor to "get same effect". If we ignore the resistor divider action and that resistor losses, then we are left with a current source which we cant use for inductor, because we would need a voltage source. So what we could actually use is a battery with just a switch instead of resistor. But well it turns out this is what we are actually using, a voltage source that is driver input voltage (e.g. battery), and driver mosfet (which is a switch).
Textually, talking of sinusoid currents here is interesting choice of words. We do not take a current sinusoid and put it in the coil - its not how it is, and anyway pure sinusoids are not that easy to come by with h-bridge. There are two perspectives here, one large scale, one small scale. Its ok for large scale to say that under the circumstances like microstepping the current levels will average and one would appear to be like a sinusoid, even if motor positions are discrete levels (e.g. positions are not continuous). This is because to microstep, the driver needs to change the discrete levels from one step to the next, and incidentally this is what a sinusoid is by definition, a smooth transition from one position to its reverse. So even if our driver levels are discrete (not continuous) we can talk about sinusoid in large scale context. In large scale, it appears to be a sinusoid, or actually a level stepped sinusoid, even if once you zoom in enough, then its something else. But to say in the small scale perspective, that you take a sinusoid and put it in the coil to drive the motor - thats a little different. To see this, you can query for example what changes to that sinusoid when the motor is in full step mode.
First, the current is not generated by the driver at all. The driver is not a current source. The driver just plays with the voltage by its mosfets. The current is "generated" or better said, it grows and decays inside the inductor itself. And that current is anything but "constant". Its switched mode, e.g. pulsating or else, otherwise not constant.Quote
uncle_bob
When the motor is still there is a constant DC current through the motor. How that current is generated by the driver does not matter. You could use a battery and a resistor to get the same effect.
We have 2 waveforms to study, voltage and current. The driver puts the voltage across the inductor, on and off, so the voltage waveform is a simple square wave. The current in inductor by its element law, is defined to be the integral of the voltage by time, so when the voltage starts to be on, then the current starts from zero, and has a rising edge. This rising edge initially grows fast, then tends to grow very slowly. This is because the integral definition makes the grows to be the new addition versus the old one, so after some time it grows very slow because each new portion of addition is relatively smaller in comparison to the bigger "past" integral. In the end this current would tangentially reach the point of ohms law for the voltage and coil resistance, but much before that, the driver will interrupt the voltage. After voltage interrupts the inductor current has a falling edge, that has a different shape but it goes to zero as the voltage stays off. So this is what makes the current sort of speaking.
We can not use a battery and resistor to "get same effect". If we ignore the resistor divider action and that resistor losses, then we are left with a current source which we cant use for inductor, because we would need a voltage source. So what we could actually use is a battery with just a switch instead of resistor. But well it turns out this is what we are actually using, a voltage source that is driver input voltage (e.g. battery), and driver mosfet (which is a switch).
A switch is simply only one part: a switch is a mosfet or bjt or igbt, etc. Even a simple diode is a switch. Switches dont have more parts, what they do have are quadrants, and quadrants just show on which direction they conduct or block voltage or current. The quadrants help the designer to establish how a switch is implemented, e.g. why we would choose a diode specifically for that spot - see "switch realization". Other parts associated with switches may be things like snubbers, but those are not technically part of the switch itself, just support components or stuff to deal with imperfections of the switch or the load.Quote
uncle_bob
They only count if you believe the driver running as an ideal switcher. Due to the Q of the motor coil they are far from an ideal switcher. Since there is no "C" in the system they have some other issues as well. A normal switch configuration has more parts than one of these drivers does.
So again, its not a current sinusoid that is generated eslewhere than forced into the coil. Current just grows in the coil as result of playing with voltage, and that is the elemental law of the inducutor. Voltage across inductor builds the flux, to which the current is proportional. Now if you understand that, you will see previous statements differently and, even if most ppls dont see it, some other parts.Quote
uncle_bob
You have an R-L circuit. You generate a sine wave current to drive it. All of the switching stuff is just an odd way to generate a sine wave current. You would get exactly the same motor performance if you drove it with a stereo amplifier, a couple of resistors, and signals out of your PC. The switching stuff just confuses things because it applies only to the "amplifier" that's driving the coils.
Textually, talking of sinusoid currents here is interesting choice of words. We do not take a current sinusoid and put it in the coil - its not how it is, and anyway pure sinusoids are not that easy to come by with h-bridge. There are two perspectives here, one large scale, one small scale. Its ok for large scale to say that under the circumstances like microstepping the current levels will average and one would appear to be like a sinusoid, even if motor positions are discrete levels (e.g. positions are not continuous). This is because to microstep, the driver needs to change the discrete levels from one step to the next, and incidentally this is what a sinusoid is by definition, a smooth transition from one position to its reverse. So even if our driver levels are discrete (not continuous) we can talk about sinusoid in large scale context. In large scale, it appears to be a sinusoid, or actually a level stepped sinusoid, even if once you zoom in enough, then its something else. But to say in the small scale perspective, that you take a sinusoid and put it in the coil to drive the motor - thats a little different. To see this, you can query for example what changes to that sinusoid when the motor is in full step mode.