GRBL, grblHAL and the controller box

The free firmware inside many hobby CNC machines, where it came from, and what the makers in the record use.

Between your computer and the motors sits a small box of electronics: the controller. Its job is to read G-code one move at a time and turn each move into precisely timed pulses for the motor drivers. On a lot of hobby machines, the software running inside that box is GRBL or grblHAL.

GRBL

GRBL is free, open-source firmware. Its project page describes it as "a no-compromise, high performance, low cost alternative to parallel-port-based motion control for CNC milling" and says the main version "runs on an Arduino with a 328p processor". It "accepts standards-compliant g-code", supports arcs and circles, and plans its speeds ahead: it will "look up to 16 motions into the future" so it can accelerate smoothly into corners. It's released under the GPLv3 licence.

grblHAL

grblHAL is a descendant of GRBL for more powerful chips. Its README says it is "based on the Arduino version of grbl" and "mainly aimed at ARM processors (or other 32-bit MCUs)", with drivers for "more than 15 different processors". It also has an open plugin system for adding features. When I read the repository on 1 November 2026 it listed a latest build dated 20261015.

What the machines in the record use

Machine	Controller and motors, as published
SainSmart 3018-PROVer V2	32-bit board, GRBL (version not published). Power supply 24V/4A.
SainSmart 3020-PRO MAX V2	Grbl V1.1 with 32-bit TB67S109 drivers; upgraded offline controller
SainSmart 4040-PRO	Offline controller CTL4040; GRBL on a 32-bit MCU, TB67S109 drivers. NEMA 17 steppers.
FoxAlien Masuter Pro	Control box with e-stop and home buttons; firmware not published. 12V/5A supply. Steppers 1.3 A, 0.25 Nm.
FoxAlien Masuter Pro Max 2x2	Control box included; firmware not published. NEMA 17 steppers.
SainSmart 4040-PRO MAX	GRBL on a 32-bit MCU, TB67S109 drivers. Offline controller CTL4040 sold separately.
Onefinity Apprentice	Redline CNC controller. Open-loop 1.2 Nm NEMA 23 motors. Computer required.
FoxAlien Masuter 3S	Controller box with shortcut buttons; supports an offline controller. Four NEMA 23 closed-loop steppers, 2.2 Nm.
Sienci Labs LongMill MK3 30x30	SLB-LITE controller, grblHAL. Closed-loop NEMA 23, 1.2 Nm.
Onefinity Gen 2 Elite Woodworker	Redline CNC controller. Closed-loop 2 Nm X/Y, 1.2 Nm Z. Computer optional (15" screen option); WiFi, Ethernet.
Carbide 3D Nomad 3	Not published. Carbide Motion control software.
Sienci Labs AltMill MK2 4x4	SLB-EXT controller with e-stop. Closed-loop steppers; "over 600IPM".
Carbide 3D Shapeoko 5.1 Pro 4x2	Not named. Optically isolated electronics, internal supply, 110/220V.
Sienci Labs AltMill MK2 2x4	SLB-EXT controller with e-stop. Closed-loop steppers on all three axes; about 600 in/min.

Not every maker uses GRBL. Onefinity uses its own Redline controller; Carbide 3D doesn't name its controller but ships Carbide Motion as the software to run it. The practical difference for a beginner is which sender programs will talk to the machine. GRBL-based machines generally work with the free GRBL senders; a machine with its own controller usually comes with its own software.

32-bit

You'll see "32-bit" on several spec sheets. SainSmart describes the 4040-PRO as running GRBL "on a 32-bit MCU", and the 3018-PROVer V2 as having a "32-bit control board". The original GRBL ran on an 8-bit Arduino chip; the 32-bit boards run later firmware on newer chips. The spec sheets don't say what that changes for the user, so I won't guess.

Sources

Read on 1 November 2026. Quotes are copied from these pages.