FLY-SHT36 Pro Bootloader (Katapult) Recovery

For unbricking recovery only

The FLY-SHT36 Pro comes with Katapult pre-flashed from the factory. Do not re-flash the firmware on this page during normal use or when updating Klipper firmware; this page is only for unbricking recovery after the Bootloader is damaged.

Firmware Description

Name Explanation

Katapult was formerly known as CanBoot, and both names may appear simultaneously in older tutorials or firmware names.

Katapult is a bootloader used to boot and update Klipper:

• Katapult itself cannot be used as a Klipper MCU; after flashing, you still need to write Klipper firmware that matches the hardware and communication method.
• Supported tool boards can enter Katapult by quickly double-pressing the RESET button; after entering, there is usually a status light blinking.
• CAN, RS232, and USB use independent Katapult firmware; you cannot simply modify file names or mix them directly.
• For CAN firmware, you must also select the correct bus speed, with common speeds being 500K and 1M.

• The FLY-SHT36 Pro uses CAN communication.
• This page provides Katapult firmware for both 500K and 1M CAN bus speeds.

CAN Speed Must Match

Select only one firmware that matches your actual CAN network speed. The host, mainboard, and all CAN devices on the same bus must use the same speed.

Entering Bootloader Mode

Power Off

Before starting, completely shut down the printer and disconnect the power supply. Do not plug or unplug cables, rearrange wiring, or touch terminals while the system is powered on.

The BOOT pads are marked in the image:

1. Ensure the toolhead board is completely powered off.
2. Use a jumper cap to short the BOOT pads.
3. Connect the toolhead board to your computer or host using a Type-C cable that supports data transmission.
4. After the device is recognized, remove the BOOT jumper cap.

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Flashing Firmware

• Windows
• Linux / FLYOS

1. Confirm that the device has entered UF2 flashing mode, and a removable disk named RPI-RP2 appears on the computer.

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2. Release the BOOT button or remove the BOOT jumper.

Windows file extension display

Windows may hide file extensions. Please check "File name extensions" in File Explorer, and confirm that you are using .uf2 firmware; do not modify the firmware extension.

3. Download the Flash erase firmware:

• nuke_universal.uf2

Windows 默认可能隐藏文件扩展名。下载后请确认文件扩展名未被修改，不要保存成 .txt 或其他扩展名。

The directory of the erase firmware in the repository is:

FLY-Firmware/RP2040

4. Copy nuke_universal.uf2 to the RPI-RP2 disk to erase the old firmware already present on the device.

5. After the copy is complete, the RPI-RP2 disk will automatically disappear; after the device erases the Flash, it will appear again as an RPI-RP2 USB drive, and at this point the Flash is already empty.

6. Download the FLY-SHT36 Pro Katapult firmware:

• FLY_SHT36PRO_CANBOOT_500K.uf2
• FLY_SHT36PRO_CANBOOT_1M.uf2

Windows 默认可能隐藏文件扩展名。下载后请确认文件扩展名未被修改，不要保存成 .txt 或其他扩展名。

The directory of the firmware in the repository is:

FLY-Firmware/ToolBoard/SHT36

7. Copy the Katapult .uf2 firmware to the newly appeared RPI-RP2 disk.

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8. After the firmware is written, the RPI-RP2 disk will automatically disappear, indicating that Katapult has been flashed successfully.

1. Compile the RP2040 flashing tool. Skip this step if it has already been executed.

cd ~/klipper/lib/rp2040_flash/
make

2. Confirm that the device has entered UF2 flashing mode.

lsusb

If 2e8a:0003 appears in the output, it indicates that the device has entered RP2040 flashing mode. The device name displayed may differ across systems; the USB ID should be used as the reference.

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Device not recognized

Do not continue flashing if 2e8a:0003 does not appear. Please disconnect the device power again and repeat the steps in "Entering flashing mode" on this page.

3. Pull or update the precompiled firmware repository.

• Linux
• FLYOS

First-time download:

cd ~
git clone https://cnb.cool/3dmellow/FLY-Firmware.git

Update the repository if it has already been downloaded:

git -C ~/FLY-Firmware pull --ff-only

First-time download:

git clone https://cnb.cool/3dmellow/FLY-Firmware.git /data/FLY-Firmware
ln -s /data/FLY-Firmware /root/FLY-Firmware

Update the repository if it has already been downloaded:

git -C /data/FLY-Firmware pull --ff-only

4. Flash the erase Flash firmware to clear the old firmware already present on the device:

sudo ~/klipper/lib/rp2040_flash/rp2040_flash ~/FLY-Firmware/RP2040/nuke_universal.uf2

After the command finishes, the device will automatically restart and return to BOOTSEL / UF2 mode. lsusb will show 2e8a:0003 again, and at this point the Flash is already empty.

5. Depending on the CAN rate, execute only one of the flashing commands:

CAN 500K:

sudo ~/klipper/lib/rp2040_flash/rp2040_flash ~/FLY-Firmware/ToolBoard/SHT36/FLY_SHT36PRO_CANBOOT_500K.uf2

CAN 1M:

sudo ~/klipper/lib/rp2040_flash/rp2040_flash ~/FLY-Firmware/ToolBoard/SHT36/FLY_SHT36PRO_CANBOOT_1M.uf2

6. After the successful flashing message appears, proceed with the power-off operation.

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Completing the Flash

Power Off

After flashing is complete, disconnect the toolhead board's USB and external power first, then restore normal wiring. Do not plug or unplug toolhead board cables while the system is powered on.

After re-powering, the status LED will blink when Katapult starts normally:

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