Can i connect 1 28BYJ-48 stepper motor and 3 Nema 17 motors to CNC shield?
There are instructions on the net on how to make a 28BYJ motor work with an A4988 or DRV8825 driver. If you do that then you can set the shield up to use the forth motor independently by setting the jumpers properly. Search for "how to make a 28BYJ motor work with an A4988"
I'm a beginner, does it matter how much the power supply is? (in my case it is 12V 6A)
The power supply to the A4988 drivers must me at least 8V so 12V is good. You could go even higher for better speed and torque up to the driver maximum voltage (35V).
The 5V rating of the 28BYJ stepper is irrelevant. The A4988 driver (and other drivers like it) will limit the stepper coil current as long as the voltage is below the maximum allowed by the driver. The coil current must be set before using the motor or the motor and/or driver can be damaged.
Read some of the pages, that you will get with that search, for more information. If there is something that you do not understand, ask here.
Thank you very much for the information.
How is the motor coil current adjusted?
The coil current should be found in the motor data sheet. Set the current to less than or equal to the spec current. To set the current limit you will need to know the value of the sense resistor on the A4988 driver board. Then enter the value of the resistor and the required coil current into the formula Vref = Imot x 8 x Rsen where Imot = the coil current and Rsen = the value of the sense resistor. The Pololu A4988 page covers how to set the Vref but you must use the sense resistor value on YOUR board.
The yellow box shows the location of the sense resistors. Most of the Chinese clone A4988 drivers that I have seen have 0.1Ω (R100) sense resistors. Again, make sure that you know what the sense resistor values on your modules are before using the formula to calculate Vref.
Setting the coil current to less that the max is OK as long as the motor performs properly and does not miss steps. The motor and driver will run cooler and last longer.
is it possible that it is on the board R10? sorry for the large number of questions
And one more question, is it possible to connect 2 servo motors to the CNC shield?
Do you mean the resistor marking? If yes, I would expect that that means 0.1Ω. Like I said, 0.1Ω is the common value for current sense resistors on Chinese manufactured A4988 boards.
Sure. Here is how to connect one. Duplicate this with a different pin for two servos.
The servo can connect to any free pin, digital or analog. As shown the servo connects to A0.
You will probably need a separate power supply for the servo since most servos will not run from 12V (or higher) and the Uno 5V supply cannot supply the current required by a servo.
Here is how the CNC shield pins are mapped to the Uno pins.
Where should I adjust the motor coil current? Could you explain the procedure?
An external supply is a supply that is separate and independent from the stepper driver or the Uno power supply. The 12V (minimum of 8V) for the stepper drivers is too much for servos. They are usually specified at like 4.8V to 7.2V. Higher voltages will kill the servo. The 5V supply from the Uno, whether derived from USB or the on board 5V regulator (Uno powered via Vin or the power jack) does not have the current capability to drive one servo, let alone two. A good external supply for the servos would be a 4 AA cell battery pack. Make sure (as the image shows) to connect the battery ground to the Uno ground as well as the servo ground.
Where should I adjust the motor coil current? Could you explain the procedure?
The Pololu A4988 page that I linked in post #6 has written instructions and a video showing how to adjust the voil current limit. You do so by adjusting the tiny potentiometer on the A4988 module PCB.
Why do I need to write a tutorial for something that is explained on that Pololu page as well as several places on the internet that can be found with a search?
What dont you understand about the procedure?
I am confident that those are 0.1 Ohm sense resistors.
probably some mistake in the manufacture of the resistor
I did a bit of checking and there are 3 digit SMD resistors and there are 4 digit SMD resistors.
R10 (3 digit) and R100 (4 digit) are both 0.1Ω.
ok, so i count with 0.1 ohm, thanks!
What is the I in amps that I need to calculate the Vref for the 28BYJ48 stepper motor? I can't find it anywhere
My reading of the information on the net says to start at 0.10V for Vref when using the A4988 driver with a 28BYJ stepper. Then if the motor does not get too hot and you want more speed and/or torque increase from there.
Steppers can run hot enough to be uncomfortable to hold your fingers on and still be OK.