Motors taking uneven time to arm in differential thrust autonomous boat

Hello everyone,

I’m currently trying to build an autonomous swarm of boats, starting by one autonomous boat. After a slow start with PX4, I moved on to ArduRover 4.1.5 with Mission Planner 1.3.77.

I’m using hardware components from the QAV250 kit (DIY Complet Kit Holybro QAV250 avec Piwhawk 4 Mini):

I want the boat to use differential thrust to drive, and it is powered with 3S LiPos

I’ve done:

  • Frame setting to boat (FRAME_TYPE : 0 and FRAME_CLASS : 2)
  • Accel Calibration
  • Compass Calibration
  • Radio Calibration (I’m using Taranis QX7 with R-XSR receiver from FrSky)
  • I’ve plugged motors on pins 1 and 2 and set SERVO1_FUNCTION : 73 and SERVO2_FUNCTION : 74

When I start the boat, it takes time to make the noise that indicates the motor is armed (sometimes more than 2 minutes). The left motor arms fine after a few seconds, but the right one takes a lot of time emitting random beeps (not regular, but tends to be faster and faster), and then eventually makes a melody and arms itself. I’ve tried it on 2 different boats, with different ESCs, FC, PDB, the result is the same.

I can’t calibrate my ESCs on Mission Planner as I’m not using ArduCopter 3.3+ (but ArduRover 4.1.5), and I’ve tried calibrating them on QGroundControl with PX4 then switching to ArduRover, but it doesn’t change anything. I’ve also tried manual calibration (with the description explained on the ArduPilot documentation) but it doesn’t make any noise and simply doesn’t seem to work.

If anyone knows what the problem is and how to solve this issue, it would be a pleasure to talk about it. And of course, if you need more information, feel free to ask.
Thanks in advance,


For information,

I’ve swapped ESCs for another model, which I could calibrate with the procedure explained on the ArduPilot documentation, and it seems to work great, motors are arming together after like 3 seconds.



Great that you figured it out. The underlying problem was probably that the original ESCs only spun forward and expected the PWM input range to be 1000 pwm to not spin and 2000 pwm to spin at full speed. ESCs for boats need to spin in both directions so the autopilot will send 1500 pwm for the motors to not spin, 1000 pwm to spin backwards at full speed and 2000 to spin forward at full speed.

Although I have reversible ESCs, I can’t manage to have access to them via any online configurator, so I can’t set them to both directions. I get this message, and I can’t solve it with info found on the internet:

“Port already in use by another application - try re-connecting”

Currently I’m fine with the steering, because one motor stops and the other spins forward and it works pretty well, but if you have any idea of why I get this message when trying to connect, it would be a relief.

Thanks in advance,

Hi @Lathres,

I guess the ESCs are connected directly to the PC using a USB cable? … and I guess on the ESC configuration software (are you using BLHeli maybe?) it allows you to select a COM port? If “yes” then I think the wrong COM port may have been selected. This is all just a guess, the issue is certainly on the PC and not the autopilot I think.

Hello @rmackay9 ,

My ESCs are soldered to a PDB linked to the PixHawk 4 mini, which I connect by USB to my computer. I’ve tried all the ports of my computer but they fail to connect, whether with the message I mentioned before, or with this one:

“Connection failed, ensure that you have selected the correct port or restart your device.”. I’ve tried all COM ports the window propose me, restarted the flight controller multiple times but it doesn’t change anything.

When I go into the device manager to see what are those COM ports, I have “Ardupilot MAVLink” and “Ardupilot SLCAN” respectively on COM8 and COM9. I don’t know if I’m missing something, if I should wire them directly to the computer? (And if yes, how?)

Thanks for your precious time and answers,

Hi @Lathres,

It’s not clear what application you’re trying to connect with when the, “Connection failed, ensure that you have selected the correct port or restart your device” message appears…

If you’re using BLHeli then this page re passthrough support could be useful.

I used BlHeli Configurator when I got this message: “Connection failed, ensure that you have selected the correct port or restart your device”

I used ESC Configurator when I got this message: “Port already in use by another application - try re-connecting”

Obviously with the “Port already in use by another application - try re-connecting”, I’ve restarted my computer to make sure that no other application was running.

I’ll check the link you’ve sent, thanks for your help!