T200 Thruster No Beeps but 1500 us PWM present

Blue Robotics Products
1

Hi,

We have an custom, eight thruster vehicle fitted with eight T200 thrusters. We are using BasicESCs to run the thrusters - 7 of 8 thrusters function when power is applied, but the 8th does not.

It is probably worth mentioning that our ESCs are located in small, oil filled pressure housing in close proximity to the thrusters (not in the 4" housing, as is common), so our ESC/Thruster assembly is sort of all one assembly. The PWM path form the Navigator servo pins to the ESCs is long (perhaps 2 m), that being said, most of the thrusters are working.

We have taken the ESC and thruster assembly that is not working and swapped it to another PWM servo channel on the Navigator, and it then the motor turns as expected. We therefore suspect that the ESC and Thruster are OK and not the issue. We have also determined the following:

  1. We have put our oscilloscope onto the signal and ground pins for the PWM servo channel that is ‘suspect’ (i.e. does not allow the thruster to turn), and we see a 1500 us signal as expected. Furthermore, we can see the PWM signal narrow and widen on the scope when we test the motors in QGC by dragging the motor slider up/down.

  2. The amplitude of the PWM signal is at the expected 3.3V.

  3. We confirmed that there 17.5V DC going into the ESC, so should be getting enough power.

  4. We have kind of checked the DC resistance in the non-working path, in case perhaps the ESC cannot pull enough current, but not sure what exactly to look for in this case - i.e. what measure of resistance in the DC power to the ESC would be cause for concern.

Having said all that, when we are connected to the PWM channel that is suspect, we never hear the expected 3 beeps from the thruster upon power up, even though we are seeing a clean, clear 1500 us PWM signal when we test on our oscilliscope – not sure if this is a clue that is helpful for diagnostics?

Any thoughts on this woudl be great, we are sort of scratching our heads on what to try next,

Thanks,

Ben

2

The initial 3 rising beeps indicate the phases of the motor being connected correctly to the ESC, and should sound regardless of the input signal to the ESC. The final 2 beeps are the control signal ones, where the first long low tone indicates a PWM signal in the expected range, and then the final long high tone indicating that a valid “stop”/neutral signal is detected and that the ESC is now armed and ready for motor control.

If you’re not hearing any beeps then either your thruster isn’t connected properly to the ESC, or there is something wrong with the ESC or the thruster.

Have you tried measuring at the ESC end, to see whether it’s getting the signal that’s being sent? It could be necessary to trim the signal, although given it’s working fine for the other motors that seems unlikely.