Hello, I am planning to build one MP CNC, and stepper motor/driver is my first concern.
I read carefully all thread, but I don’t find anything about the link between stepper motor, driver and power supply, but if you understand that it is easy to choose what you want to do.
The driver provides electrical power to the coils of stepper motor in right order and allows limiting the maximum current. The wiring (wires and connectors) and the motor have impendency that limit the rising time of current. The rising curve is linked to the tension of power supply.
Due to that if you power only one stepper with a driver, the rising time of current is nearly linked to the difference of voltage between the power supply and stepper motor voltage per phase.
If the motor run slowly, the rising time can be forgotten, but when you increase the speed this is not the case and this rising time result is to lower the average current of each pulse and decrease the torque of motor stepper.
If you add another stepper motor in serial (without any other change) the difference of voltage between the power supply and the 2 stepper motors voltage per phase decease also (can be negative according the type of stepper motor) and due to that the rising time is bigger and the average current lower and torque lower.
If you put in parallel, the first impact is to nearly double the current, but there are other things to take into account: wiring, and motors. Even you take care to have the same wiring for the 2 motors (length/ section / connectors…) each motor are slightly different , and the current in each of 2 stepper motor are also slightly different, and this is difficult to manage.
Due to that “industrial” solution is to use one stepper for one stepper motor and to measure the real current in both motor (with scope) and adjust the 2 stepper motor at the same current.
– You can put stepper motors in parallel if they are from the same batch and the sum of currents is under the maximum current of the driver, you must take care also of the length of the wire to each motor and keep them equal.
– You can put stepper motors in series, if the double of tension per phase of each motor is under of tension of power supply minus 5V. For 12V power supply tension per phase of stepper motor must stay below 3,5V.
– After according your skill you can put one driver per stepper motor, and modify the software or the hardware of the RAMPS. And if you want to add an extruder ( or more) you can make or buy an driver expander like this one: http://reprap.org/wiki/Stepper_Expander
See stepper motors data sheet: http://www.osmtec.com/downloads/stepper_motor/stepper_motor.pdf
Excuse my bad English, I am French.