Calibrating Wantai Nema 17 2.5A motors

Hello all, new member here and new to 3D printers in general.

I have a P3 steel clone given to me by a friend. I'm not sure which one it is, seems he had bought it from HTA3D in Spain.
The printer uses a RAMPS 1.4 SB Premium from staticboards and DRV8825 stepper drives with Wantai Nema 17 motors.
The Wantai stepper motors are rated at 2.5A and 1.25 Ohm/phase resistance.

I've spent more than a month fiddling with the printer, understanding the connections and Marlin, flashed it with the latest stable version,
and made some improvements, such as getting a Chinese clone of an E3D V6 hotend, adjusting the extruder from direct to bowden, etc.

The printer was badly configured, X axis was reversed (0,0,0) was at the bottom right side, and its accuracy wasn't very good (it would easily miss 1mm or more when printing).

I went through the process of calculating steps per unit for X and Y axis, and now I'm trying to figure out how to do the same for the extruder.
My first problem is that Marlin seems to default to 1/16 microsteps, but the DRV8825 does 1/32 microsteps.
So first question, what is the formula to adjust accordingly the steps per unit for the extruder?

The extruder has no gears, just an extruder hobbed drive pulley which I haven't measured, but is most likely 5mm diameter.

Furthermore, I have seen videos and posts of people adjusting their POTS on their drives.
I measured the current and voltage of each drive under idle and load, and found it to be:

X axis: 0.7 volt ~ 0.04A @ 5V or 0.03A @ 12V
Y axis: 0.5 volt ~ 0.06A @ 5V or 0.05A @ 12V
Z axis: 1.0 volt ~ 0.14A @ 5V or 0.13A @ 12V

I took readings twice, once by grounding to the 5V pin on RAMPS, and once by grounding on the 12V pin on RAMPS.
Motors where moving when I took the readings (e.g., not idle but under load).

I haven't measured the Extruder yet, because the fan of the hotend isn't working and don't want to risk melting the clamp.
Second question: how do I formulate or calibrate the motors properly?
Empirically by adjusting it as low as possible and then turning it up or is there a specific value(s) I should be aiming for?

Many thanks for anyone who can help!

The printer was probably set up correctly when you got it. The origin can be at either the left front or right rear of the machine. If you changed that your prints will come out mirrored.

DRV8825 drivers have a known problem of skipping usteps at low speeds (like when printing curved surfaces). You can put diodes across the motor leads to correct the problem.

Normally, motors are operated at about 80% of their rated current, but since your motors are rated for 2.5A and you're probably using plug-in motor driver modules, you're going to have to keep the current down to maybe 1.2-1.5A to avoid burning up the driver chips that are poorly heatsinked on the tiny modules.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

@the_digital_dentist

Hi, thanks for the reply.
The printer was printing mirrored in the first place (my friend must have changed it) so I had to put it back to left front (it was right front).
I have seen the skipping issue indeed. I am guessing the solution is what is described in this blogspot: [cabristor.blogspot.com] ?
So I need 4 diodes (1N5404 to 1N5408) per motor according to that blogpost?

Regarding the Amps, from what I understood I can increase them, provided I keep them below 1.5A?
The drivers are heatsinked, never gotten warm to touch (or the motors) and the board I have is rated to 15A, whilst the PSU is 25A.
So is it safe to assume I am running them very low?

Again, many thanks!
A.