Randy- Thanks for the information. A few more details for you to mull about: The pixhawk 2.1 and LIDAR are powered by a mauch power cube 4 (v3). The pixhawk has independent 5v sources for primary and secondary power, while the LW20 and rfd900 radio share a 5V power supply.
When I connect the batteries, the powercube has a 2 second delay, at which point it powers the pixhawk, rfd900 radio, and lw20 lidar simultaneously. If I power the UAV by connecting the battery, I get no signals from the lidar (although the rfd900 works perfectly). If I power the pixhawk first via USB, then connect the batteries to power the pixhawk, rfd900, and LW20, the lidar connects and works well (proper distance readings in the ‘sonarrange’ status tab).
My current workaround is a small delay circuit inline with the LW20, which waits for 2 seconds after the BEC turns on before powering the LW20. So far this fix seems to work, although it does require an extra small PCB. If this could be fixed in software that would be great, as I could ditch the extra hardware workaround.
There is also an operational workaround in that I can power the pixhawk via USB (laptop or similar) and then power the rest of the peripherals with the battery once the pixhawk is initialized. This seems to work well, but it is a pain in the field, and not always practical. BTW this behavior was observed on 3.6.6 NutX and 3.6.7-rc1 ChibiOs. 3.6.6 ChibiOs did not seem to cooperate for me with this setup.