Step 1. Print the box.
Step 2. Mount the knurl nuts in place using a solder iron. Make it hot and let it melt into the correct position.
Step 3 (optional). If you want to make the box nice spend some time to sand and plaster it smooth before applying paint.
Step 4. Glue magnets to box and supports. I use CA-glue with accelerator
Step 5. Insert a USB cable through the center hole of the box and solder to the BU0836. I use a rubber grommet to reduce dirt coming into the box.
Step 6. Solder USB cable to BU0836. IMPORTANT: Use a 3.3V LDO voltage regulator to lower the voltage since the Frsky M7 can only handle 3.3V. The BU836A is fine to run on 3.3V.
Step 7. Solder the numpad to the BU836A. Pads 1-4 to columns 1-4 and pads 5-8 to rows 1-4 which equals inputs 1-4, 7-10, 13-16, 19-22.
Step 8. Solder the BU0836 cards.
Step 9. Attach controls; joystick gimbals, numpad and dials to the lid.
Step 10. Attach controls, thumb stick and hat switch to the box.
Step 11. Solder cables to the controls, twist them to reduce interference and make sure they are just a bit longer then you need.
Step 12. Trim cables with some extra cm to spare if the BU0836 is on the center bottom of the box.
Step 13. Solder push controls to the BU0836 cards. Take care to not use any connections already in use by the numpad, I chose 5, 6, 11, 12, 17, 18, 23, 24.
Step 14. Solder analog sticks to analog inputs. Left stick to analog 1-2, right stick to 3-4, thumb stick to 5-6, diala to 7 and 8.
Step 15. Solder hat switch to inputs 33-26 (I do not use the push function).
Step 16. Solder slider switches to inputs 25-28 and 29-32.
Step 17. Position BU0826 card in the bottom center of the box and pull on the USB cable so you have a few cm spare cm inside the box and attach the zip tie between the BU0826 and rubber grommet where it'll work as a strain relief.
Step 18. Hot glue the BU0836 cards (two dabs on either side so it is easy to detach if necessary).
Step 19. Attach the hat switch knob. I used a solder iron to heat up the bottom of the knob and then (while the plastic is soft) pushed it onto the switch for a perfect fit. Once cooled I glued them together.
Step 20. Use M3 screws and attach lid to box.
Step 21. Setup as a standard joystick in the simulator of your choice! :)
PS: You might benefit from calibrating the joystick in windows: https://www.howtogeek.com/241421/how-to-calibrate-your-gaming-controller-in-windows-10/