How would I be able to determine the relationship between the PWM and RPM? T100!!
You will need a sensor to measure the RPM, or an ESC capable of telling you the RPM. In our basic ESC (and most hobby-grade ESCs) the pwm signal is commanding torque and the resulting RPM will vary based on conditions.
My ESC is basic ESC. The RPM of T200 has a function relationship with PWM. Does T100 no?
The PWM value sent to the Basic ESC does not set the RPM on the T100, T200, or any brushless motor. The control system is open loop, if you want to set a target RPM you will need an ESC with closed loop control that can run in RPM governor mode.
The RPM of a thruster is a function of both the throttle (PWM) level/duty cycle, and the load. Load will change depending on how quickly the thruster is moving through the water and other environmental conditions.