Autopilot Errors: no motor controller!

[Sparhawk76]

I have a raspberry pi4 running openplotter, connected to one of Sean's IMU sensor modules, which is connected to the motor controller, also purchased from Sean.   I'm guessing I'm missing something simple, but I can't get Pypilot to sense that the motor controller is connected.   There is one red LED on on the motor controller, if that makes a difference. Also the IMU appears to be working, providing relatively accurate heading data, and pitch and roll.

In the web interface for pypilot I see:

pypilot Server: Connected
Servo Flags:
Autopilot Errors: no motor controller!
Web Server Latency: 4 ms

Any ideas what I might be missing?   

Thanks
Sparhawk