BIGTREETECH BTT002 V1.0 - STM32F407 board for Prusa i3 MK3S and Einsy Rambo alternative

The BIGTREETECH BTT002 V1.0 is a 32-bit controller board developed as a configurable alternative to the Einsy Rambo used by the Original Prusa i3 MK3S. It features a 168 MHz STM32F407VGT6 microcontroller, runs from 12 or 24 V and uses replaceable StepStick drivers instead of soldered motor drivers.

Its size and mounting centres make an MK3S conversion easier, but this is not a plug-and-play replacement: connectors and pinout must be checked, suitable drivers must be installed and Marlin must be built for the actual mechanics, sensors and wiring. It does not directly run the original Prusa firmware or automatically reproduce its specific features.

Main features

• STM32F407VGT6 microcontroller: 168 MHz, 32-bit ARM Cortex-M4 architecture.
• 12 or 24 V DC input and 3.3 V logic.
• Four replaceable driver sockets: X, Y, Z and E.
• Five motor connectors: X, Y, ZA, ZB and E; both Z outputs share one driver.
• Documented support for TMC2208/TMC2209 through UART and TMC2130/TMC5160/TMC5161 through SPI, plus compatible STEP/DIR drivers with the appropriate jumpers.
• One heated-bed output and one hotend-heater output.
• Three external temperature inputs and an on-board NTC 100K sensor for board monitoring.
• Two controlled fan outputs, tachometer inputs and auxiliary fan connections.
• X-MIN, Y-MIN and Z/Probe inputs, filament sensing and power-loss detection.
• USB-B, EXP1/EXP2, serial TFT, EXP3 expansion, WiFi/ESP3D and SWD.
• Replaceable automotive fuses for circuit protection and servicing.

Technical specifications

Board connections and layout

The board separates the main POWER IN terminals from the heated-bed BED IN/BED OUT circuit. It also provides HE0, temperature inputs, fan outputs, RGB, sensors, display headers and expansion ports. Every connection must be checked against the silkscreen before installation: a connector matching an Einsy Rambo plug mechanically does not prove an identical electrical pinout.

Prusa i3 MK3S and Einsy Rambo compatibility

BIGTREETECH designed the BTT002 V1.0 around the size, mounting points and application of an Einsy Rambo replacement for the Original Prusa i3 MK3S. This should be understood as a conversion platform, not a transparent replacement.

• Mounting: 95 × 61 mm mounting centres simplify installation, but plug-in drivers increase total height and the original enclosure may not close. An adapted enclosure or bracket may be required.
• Wiring: polarity, pinout and connector type must be checked. Never connect a harness merely because its plug fits.
• Drivers: an MK3S without mechanical endstops needs drivers and firmware capable of sensorless homing. The manufacturer recommends TMC2130 or TMC2209 for this application.
• Firmware: Marlin must be built for the board and adapted to the printer. Original Prusa firmware cannot simply be installed, and its special features are not reproduced automatically.
• Display: the display must be electrically compatible with EXP1/EXP2 and enabled in firmware; it may also provide the SD slot used for firmware updates.

The BIGTREETECH TMC2209 V1.3 is a related replaceable-driver option, subject to correct orientation, jumpers, cooling, current and UART setup. The BIGTREETECH TFT35 V3 and BIGTREETECH MINI12864 V2.0 are related display options, but final compatibility depends on the selected revision, wiring and firmware.

Replaceable drivers: UART, SPI and STEP/DIR

The four sockets allow the driver to be selected for the application and replaced after an upgrade or failure. The board documents TMC2208 and TMC2209 through UART and TMC2130, TMC5160 and TMC5161 through SPI. Compatible STEP/DIR modules can also be used with their microstep jumpers configured appropriately.

Do not mix communication modes and jumper layouts. Before power-up, check driver orientation, pinout compatibility, selected mode and permitted voltage. Start with conservative current based on the motor, load and cooling; a driver's chip rating is not automatically a safe continuous rating for every module or enclosure.

EXP1 and EXP2 pinout

These tables show the assignment used by the current Marlin definition for BTT002 V1.0. Also check the connector's physical orientation and pin-1 marker before fitting a ribbon cable.

EXP1

EXP2

Marlin configuration

Current Marlin releases include a dedicated definition for this board. The base selection for the STM32F407VGT6 unit is:

#define MOTHERBOARD BOARD_BTT_BTT002_V1_0

// Example when TMC2209 drivers are fitted to all four channels:
#define X_DRIVER_TYPE  TMC2209
#define Y_DRIVER_TYPE  TMC2209
#define Z_DRIVER_TYPE  TMC2209
#define E0_DRIVER_TYPE TMC2209

Use the BTT_BTT002 PlatformIO environment for the pictured STM32F407VGT6 revision. A separate environment exists for VET6 units, but it does not match this variant and must not be selected merely because its name is similar.

Selecting the board and driver types is only the starting point. Motor direction and steps, current, microsteps, homing, dimensions, Z probe, thermistors, PID, heaters, fans, display, filament sensor and thermal protection must all be adapted. For an MK3S conversion, do not copy an unrelated configuration without checking each section.

Firmware update

The BTT002 has no on-board microSD slot. BIGTREETECH's documented procedure uses the SD slot of a compatible display connected through EXP1/EXP2:

1. Build Marlin with the correct environment and machine configuration.
2. Copy the lowercase, unmodified firmware.bin file to the root of the SD card.
3. Insert the card into the compatible display's SD slot.
4. With power disconnected, recheck EXP1/EXP2 wiring and orientation.
5. Power up or reset the board and allow the update to finish before removing power.

BIGTREETECH advises against routine USB flashing because an incorrect procedure may erase the bootloader and disable later SD updates. SWD or USB recovery should be reserved for experienced users with a verified firmware image.

Using the board with Klipper

The STM32F407 can be used with Klipper, but there is currently no official BTT002 V1.0 generic configuration ready to copy. The board name appearing in auxiliary flashing tools does not provide or validate a complete printer configuration.

Treat Klipper installation as an advanced port: build for the correct MCU and bootloader, validate the flashing method and create printer.cfg manually from the schematic. We do not recommend moving this board to Klipper when a guided installation or machine-specific validated configuration is required.

This product is for you if

• You want to convert a Prusa i3 MK3S or a similar machine to a 32-bit STM32 controller.
• You prefer four replaceable drivers and want a choice of UART, SPI or STEP/DIR.
• Your printer uses one hotend, one extruder and up to two Z motors that may share one driver.
• You can verify wiring, jumpers, cooling, enclosure and firmware before commissioning.
• You intend to use Marlin and can build a machine-specific configuration.

This product is not for you if

• You need a direct Einsy Rambo replacement that works with the original firmware and wiring without adaptation.
• You require two independent Z drivers for separate gantry levelling.
• You need more than one hotend or more than one extruder.
• You want integrated drivers, an on-board microSD slot or an official ready-to-use Klipper configuration.
• You cannot verify the pinout or carry out a controlled first start-up.

Installation and first start-up

1. Work with both the power supply and USB cable disconnected.
2. Confirm a 12 or 24 V DC supply, verify polarity and size wiring, terminals and protection for each load.
3. Fit the board on insulated standoffs and check that the enclosure has enough clearance for drivers and heatsinks.
4. Set the jumpers and fit every driver in the correct orientation before applying power.
5. Check motors, sensors, heaters, fans, endstops, probe, display and power inputs one by one against the silkscreen and schematic.
6. At first power-up, verify communication and cold temperature readings first; an implausible reading usually indicates a sensor or configuration problem.
7. Test endstops and short motor movements with heaters disconnected and conservative current settings.
8. Test the hotend and bed separately, matching each heater to its sensor and confirming thermal protection.
9. Monitor driver, fuse, terminal and cable temperatures during the first prints.

Replace a fuse only with the value specified for the board and circuit. A higher-rated fuse does not safely increase output capacity and may remove essential protection.

Technical documentation

The official BIGTREETECH BTT002 V1.0 repository contains the manuals, schematic, mechanical files and reference firmware. Use a current Marlin release for new builds, while retaining the V1.0 schematic as the reference for the physical hardware.