12. Firmware

Follow this step-by-step guide to flash RepRapFirmware binary, apply pre-defined parameters by SecKit and wirelessly control your SK-Tank with a desktop/mobile browser.

Highly recommend to control your SK-Tank by the wireless approach than a display panel. The web control interface Duet Web Control (DWC) as shown in the picture allows you to modify firmware parameters in seconds and fully control your printer.

If you are interested in all the details or trying to upgrade to the latest firmware version, start from this page by TeamGloomy.

General Idea

  1. Flash RepRapFirmware to control board

  2. Flash WIFI firmware to the onboard WIFI module

  3. Get an IP from your WIFI access point

  4. Control SK-Tank with Duet Web Control (DWC) web interface.

PSU 24V and USB power

Mellow Fly CDY v2 board can be powered by 2 sources: 24V by the PSU, and USB.

Initially when you're flashing the firmware and verifying the functionalities you want the board to be powered by USB exclusively, for a more conservative and safer reason. With a USB type-C cable only the main processor, WIFI and peripherals (endstops, thermistors, fans, etc) are powered, but not for the energy-consuming driver modules and heaters.

The driver modules are powered by 24V so it's normal that the diagnose command M122 shows "no driver detected" when 24V is OFF.

If you want a USB cable is inserted when the PSU is ON, the correct power up sequence is:

  1. Pull the USB cable out, and turn the PSU OFF

  2. Turn ON the PSU 24V first

  3. Insert the USB cable later

Flash RepRapFirmware

  • Mellow Fly CDY v2 control board

  • A micro SD card formatted as FAT32, with max capacity 32GB. 64GB and larger are not supported.

  • The all-in-one zip file (RepRapFirmware, WIFI module firmware, DuetWebControl server, SK-Tank parameters) from SK-Tank GitHub repository


Extract the zip file and copy all contents under "SK-Tank RRF on Fly CDY v2" directory to the root of a micro SD card.

Make a copy of firmware-stm32f4-esp8266wifi-x.x.x.bin and rename it to firmware.bin.

Insert the SD card to control board, power it up by a USB type-C cable. Leave the PSU OFF at this stage.

The control board will rename firmware.bin to FLY.CUR if firmware is successfully flashed.


Check the SD card in your desktop. If the firmware is flashed successfully, the firmware.bin will be renamed as FLY.CUR.

Flash WIFI firmware

  • Download SerialTools (Windows / MacOS) or putty which are tools allowing you to send G-codes to control board from your desktop.


Connect your desktop and control board with a USB type-C cable.

Open the serial port in the software tool with the options shown as in the picture.

Input G-codes below and it should output similar info as shown:

(Get Firmware Version and Capabilities)

M997 S1
(Flash the WIFI firmware to the onboard WIFI module)

Check the RTS and DTR checkboxes in SerialTools or putty if no message returned.

Get an IP from your WIFI access point

  • The SSID and password to your WIFI access point.

  • Assuming DHCP is enabled (which gives you a random IP) in your WIFI access point.


M552 S-1
(Disable WIFI module)

M552 s0
(Enable WIFI module)

M587 Ixx.xx.xx.xx S"your SSID" P"your password"
(Request an specific IP, save IP and SSID info into control board. Copy & paste, backspace, delete key might input invisible characters and result in a failure connection. Manually key in each case sensitive character.)

(List and check saved SSID info)

M552 S1
(Connect to and get an IP. Wait a few seconds and the blue LED should start blinks and then ON.)

M588 S"your SSID"
(Optional. Remove SSID entry if you fail to get an IP)

Some programs will always convert lowercase to uppercase thus fails your password. Please add a leading single quotation mark before each character that has to be lowercase. Check the this explanation.

If the 'I' parameter in M587 is not used, a dynamic IP dispatched by the DHCP server in your WIFI access point will be used and result in different IP in each time you turn on the printer. You can bind a static IP to the M.A.C. address (Media Access Control address, in xx:xx:xx:xx:xx:xx format) of the printer in your access point configuration web page too.


Actions to WIFI module might take 3~20 to respond. If the console doesn't respond "ok" or any other info, retry the G-code, or start from disabling WIFI module, or even reset the board.

Check TMC Driver Status


The power up sequence matters.

  1. Pull the USB cable out and turn OFF the PSU.

  2. Turn ON the PSU first.

  3. Insert the USB cable later.

  4. Open the serial port again and input G-code M122 (diagnose command) and a similar result should be shown as in the picture.

Open Duet Web Control interface

Input the responded IP previously you got in the WIFI setup step in your browser and start using SK-Tank.

(The IP shown in the picture is just an example.)