Problem with Dshot on spare channels

ArduCopter Copter 4.1
1

I have a 5th motor on a quad copter, and I’m having difficulty getting Dshot to function on it. I’m using a PixRacer R15, and have had Dshot working on the primary motor channels for quite a while. I’m running AC 4.1.3, and I’ve set the SERVO_BLH_Mask to 48 to switch outputs for channels 5 and 6 from PWM to Dshot. SERVO_DSHOT_ESC=1 (Kiss ESCs), SERVO_BLH_OTYPE=6 (Dshot600). I am getting telemetry from the ESC in the logged data, but I cannot get the motor to spin. Looking at the output in the command shell for Mission Planner, I see that all 6 channels are set to Dshot600. The channel driving the ESC is configured with a PWM range from slightly below 1000 to slightly above 2000.

If I switch channels 5 and 6 back to PWM instead of Dshot, I can drive the motor just fine, but I cannot get telemetry.

I’m not quite sure what I need to set in the Servo Output tab tab under Setup. I’ve tried RCPassThrough and RCin6. Both work when it’s set to PWM protocol, but neither works if it is configured to Dshot.

Any advice would be most appreciated.

2

I seem to have solved this myself. It turns out that if Dshot is used, the 5th motor won’t run unless the system is armed. If it’s running on PWM, than it runs whether it’s armed or disarmed. I guess this makes sense. If it’s running Dshot than it must be a motor, and it makes sense to protect it with the disarm switch. If it’s running PWM then it could be a servo or some other PWM-driven device, and maybe a user doesn’t want to protect that.