Regarding the answer from dc42: What is the filesize of your firmware file?
As I said I need the log from your kernel as you connect the device because it gives information about if the device is detected and in which state (firmware properly flashed or no firmware found?). But the name of the logfile depends on your distribution. It could be /var/log/messages or /var/log/kernel.log or /var/log/user.log and so on.
Often the last lines of "dmesg" are enough beginning with "detecting new USB hardware" something like this, I do not know the exact text without probing and testing it.
Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.
