I have an unknown DC motor with specifications I was testing. I used a Prony Brake setup and scale to evaluate torque, a tachometer for RPM, and multimeters for voltage and current.
I get a linear graph relating torque and RPM. However, when I physically stalled the motor and checked the stall torque, it was much lower than what the linear graph expected! Almost 1/2 the expected value!
Is there a physical reason to explain this? This outlier is pretty consistent through 4 trials. Is it possible it's due to the Prony Brake? Or perhaps something within the motor? Back EMF or something due to friction? I'm at a loss as to why such a data occurred, and not only once but multiple times!