@Jimk_Aero Please ignore the previous question. I just needed to reboot the Flight Core and all is OK.

At the point in the ESC calibration python program where I attach the USB cable and reconnect power to our flight core, I receive the following message:
Using portname /dev/serial/by-id/usb-ModalAI_PX4_FMU_ModalAI_FCv1_0-if00
connecting...
Error: Unable to open port

I'm using Castle Multi-Roto 35 ESC's and I cannot get all the motors to spin.

This is my last try. I've about given up on the flight core.

After spending several days trying to get my motors to spin, calibrating ESC's, reading a bunch of different posts, etc. I have concluded that you do not either power the "middle" pin across the pwm array nor do you tie the positive pins together so they may be powered by an external source like a BEC. We have 4 Castle ESC's (with one BEC) hooked to 4 motors which all work fine when attached to a pixracer. Only the motor attached to the ESC with a BEC will turn when this array is attached to the flight core. I can surely understand why you don't power the middle pin with the flight core power as hooking a couple of servos to that array would surely burn out any voltage source you could provide, but I don't understand why you don't hook all the middle pins together so that they may be powered by one ESC/BEC as every other flight controller I have used does. Further, I don't understand why that pin even needs power for the ESC's. Basically you are providing a PWM signal versus a common ground for all controlled ports. As long as that signal is above about 1.5 volts, most ESC's should interpret that as a one, and below .5 volts is a zero. I can only assume that ESC's want to know whether the signal range is 3.3 or 5 volts. Either way, unless I jumper the middle pins together, I will have to provide 4 ESC/BEC's to get my motors to run. I obviously am not the first one to notice this problem. Why don't you tie those pins together?

Hello again. In my previous post I spoke about not being able to calibrate ESC's in order to run all 4 motors on my quad. At that time, 3 motors ran and 1 motor did not. I finally concluded that I had either a motor or ESC problem, so ended up getting 4 new motors and 4 Castle ESC's. Now only 1 motor will run. That one motor has an ESC with a BEC to power the PWM rail as is the norm in most quad builds. Am I correct in assuming that the PWM +'s and grounds are all connected together so that one BEC should power all the ESC's? With that one ESC hooked up I do not see power on the other pins, which is confusing. Can you help?

Thanks for your suggestions. I ran the pwm test command in the MavLink console and confirmed all motors except the suspect one so looks like I'm going to replace an ESC. I do appreciate your guidance.

Setting up a flight core on a 550 quad that was previously successfully flown with a pixhawk cube. Everything is working fairly well, except one of my four motors won't spin. I have used the Python tool several times in an effort to recalibrate that last ESC which I know worked previously, but now it won't. Can you offer any ideas on how to proceed? Thanks, Jim.

@Jimk_Aero Please ignore the previous question. I just needed to reboot the Flight Core and all is OK.

After setting up a flight core as recommended and upgrading firmware to modalai_fc-v1_default.px4 we connected a Spektrum SPM9745 to port 12 using the supplied MCBL-00005 cable. Using QGround Control we then opened the radio tab, clicked on Spektrum Bind, and selected DSMX-8. We then powered on our DX8e with the bind button pressed. The blinking orange LED changed to constant and the DX8e showed DSMX bound. All this looks OK, but when we press the calibrate button and OK we receive the message "Detected 0 radio channels. To operate PX4, yu need at least 5 channels." We've repeated this process many times with similar results. Can you suggest what is not correct?