T100 response difference

My two T100’s respond differently to incoming pulses. With voltages to both the same, and both immersed in water, one motor starts turning at 1527 and the other starts “clicking” and vibrating back and forth at 1527, and doesn’t commences rotation until 1533. Both motors turn freely by hand. I am concerned mostly with the motor which doesn’t want to start freely. Again, there is no binding. each motor is fed by its’ own BR ESC.

I made a video of what’s going on. Both thrusters are receiving the exact same ramp up of PWM from 1520 to 1540 usec, with 1 second between each 1 usec width increase. The fist clip is two ramp up cycles on the well behaved motor. You can see the smooth starting at 1527. The second clip is the problem child. The jumping starts at 1527, and smooth rotation didn’t happen in this case until 1537. Clearly something not so good going on here.



You are only talking about a difference of 6 microseconds between the two PWM value starting points.

What is the neutral PWM value (S/B 1500 us) being sent to the BlueESC when powered is applied to the Thruster?



Both thrusters are receiving the exact same pulse train ramp up. At power up both get 1500 with a 3 second delay. I am not so concerned about the 6 usec difference as I am about the jumping back and forth behavior of the second thruster. Sometimes there is as much as 10 usecs difference before the second thruster starts rotating. That is a significant difference when you are doing heading hold control with PID.


It’s normal to have some small difference in internal friction, motor windings, etc that can cause small variations in the starting point between thrusters. This is normal.

The thrusters (like any motor) are nonlinear around the center deadband so it will be difficult to hold heading perfectly when both thrusters are centered around zero, especially with a small vehicle with low moment of inertia. We’ve been able to achieve about +/-2 degrees with out vehicles, but they pulse on and off a bit.




Are you saying that the jumping around before rotation on that one motor is okay and to be expected with some motors due to manufacturing tolerance? The other thing I notice is that the smooth starting motor coasts to a stop when I quickly re-center the joystick. The late starting, “jumpy” motor stops abruptly.


That is correct. Sounds like the “jumpy” motor might have a bit more internal friction then. It you think it’s really excessive then we can take a look at it, but I think the 10 µs difference is fairly normal.


Okay, thanks for responding to my questions.