ZTW Spider 40A OPTO Small ESC with stock SimonK firmware can be easily flashed with BLHeli using Cleanflight interface. I just did it, the whole process took few minutes. To be true, it took me more time to find out which firmware should those ESC be flashed with, than to flash them. For unknown reason this information is well hidden in the internet! So, here is short guide:

  1. We will be using Cleanflight BLHeli passthrough interface. It is build in in laster Cleanflight / Betaflight / INAV firmwares
  2. Use latest BLHeliSuite. I used 16.3.14.7.0.0
  3. Connect ESC to flight controller
  4. Connect flight controller to USB port
  5. Run BLHeliSuite software
  6. From Interface menu select ATMEL BLHeli / SK Bootloader (Cleanflight)
  7. Select COM port and click Connect
  8. Connect ESC to battery
  9. Click Check to detect connected ESCs
  10. BLHeliSuite will detect unknown firmware with SimonK bootloader
  11. Select ESC (1, 2, 3 or 4) and click Flash BLHeli
  12. Here comes funny part. There is no ZTW Spider 40A OPTO Small formware! Documentation states that ZTW Spider 40A should be flashed with BlueSeries 30A firmware. But images in docs and mine ZTW Spiders differs a little. But, looks like it is not a problem. Select BlueSeries 30A MULTI firmware and flash
  13. BLHeli 14.x enables Damped Light by default. That might not be a best idea for big (> 8") propellers so you might want to disable it

blheli on ZTW Spider 40A Opto

ZTW Spider 40A OPTO Small ESC running BLHeli

Bottom line: ZTW Spider 40A OPTO Small ESC should be flashed with BlueSeries 30A BLHeli firmware!