I have a motor that runs at a fixed speed, controlled by a pwm and I would like to measure the load. My first thought was to use a resistor in series and measure the voltage drop, but I'm worried that the pwm and the inductance of the motor would require a rather complex filter.
What are your thoughts?
Its the opposite, the inductance means the current is smoothed, so the voltage across the resistor
will be approximately steady, assuming a high enough PWM frequency.
A problem is if you are using an H-bridge, the sense resistor cannot be at ground potential for both
Its wise to low-pass filter the thing though, as the motor winding inductance may not be large enough.
A simple RC filter is all you need.