GRBL - how many stepper motors?

I'm only asking this because I know there are a few people here who are familiar with GRBL.

My impression is that Grbl can only handle X Y and Z motors and cannot operate a separate 4th axis. The PCB that came with my CNC mill only has space for 3 stepper drivers and I think the same is true of the CNC shield. I have a Ramps shield for a Mega which does have space for 4 drivers.

Having found some simple software called DeskProto that can generate GCode for a 4-axis system I'm toying with adding a 4th axis to the CNC 3018 mill that I have for a year and have hardly ever used.

Assuming Grbl cannot control a 4th axis I believe, from some YouTube videos that Marlin can - as it is designed to operate X, Y Z and an extruder. However it seems that GCode for Grbl does not work properly with Marlin and therefore it would be nice to discover that Grbl can, in fact, control a 4th independent motor.

...R

PS ... while the multi-axis version of DeskProto costs money you can use it for free as long as you like if you don't object to it engraving a watermark on your project.

GRBL for Stm32 can handle 6 steppers regularly, 8 stepers if you sacrifice ISP. GRBL-mega can do 6 axis, too (ar least the copy I have here). but if you want to go beyond playing, use linuxcnc.

Most of the Arduino UNO based approaches can use a 4th axis but that is often just a mirror of another axis.
Mostly used for rotary type work.

Avoid grbl on a MEGA as the development has almost stopped in favour of the STM boards.
My ramps board has space for 6 drivers but 4 were enough for a 3d printer with a shared Z axis.

ballscrewbob:
My ramps board has space for 6 drivers but 4 were enough for a 3d printer with a shared Z axis.

I don't want a duplicate 4th motor, I want it completely independent of the other 3.

So I guess GRBL (on an Uno or Mega) is ruled out.

Thanks.

...R

Get a Stm32 BluePill, I can send you the code if you don't find it online.

zwieblum:
Get a Stm32 BluePill, I can send you the code if you don't find it online.

Not at this stage.

I want to build this as cheaply as possible with stuff I already have. This is something I might build and only use once or twice.

If I get really enthusiastic and if I find the Mega does not perform well enough then I might consider an STM32.

...R