From the user side, you provide 5v step/dir signals and need to pay attention to which active edge the driver uses, and know the microstep multiplier inside the drive.
Inside, it's a constant-current PWM. If it's microstepping, it advances through a sinusoidal approximation of current targets whose PEAK value is equal to the motor current rating. Steppers run on a constant current regardless of load. However a stopped or unloaded stepper has minimal back EMF and draws little power (voltage * current). Under heavy load, back EMF and the power increases, this is observable as greater power draw from the supply. Motor heat increases only a small amount with load. Stepper drivers vary a LOT in effectiveness. Short answer is AM882/DM542 DSP drives are "the best". MX4660 is also a DSP but lacks the fine-tuning control interfaces of the other 2x. Geckdrive G540 was one of the first quality drives, still good, but not as great as the other ones here. Danny On 9/3/2016 12:58 PM, Chris Albertson wrote: > I want to understand stepper motor controllers. Yes I know I can just > read the specs and buy one but I want to understand what's inside. > Preferably someone has a link > > My use of stepper motors has been, I guess primitive. I can write software > to toggle bits on an output port and then I connect these logic level bits > to MOSFETs that switch a power supply to the coils in the motor. I can do > full and half steps this way. > > But now I see something like the Geko driver that takes 40 volts input. I > know that if it simply switched that 40V into the coils it would burn out > the motor in short order. As the motor is typical rated for 7 volts DC or > close to that. OK I can understand that if it is switching an inductive > load the voltage raise is slower and maybe not get past 7V before the coil > is switched off. But what if the motor is running slow? So my final > guess is that these kinds of drivers are supplying a constant current and > applying whatever volts is required up to the supply voltage. > > Is it as simple as that? A constant current power supply and some MOSFET > H-bridge switches? > > > > ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
