Experimental parameter estimation of a Fractional Horsepower DC motor with unknown loads and its velocity control

Fractional Horsepower DC motors find broad applications in the automotive industry, household appliances and other consumer electronic products. Precise velocity control is often required in applications such as computer disk drives. However, one of the challenges encountered is, often times, it is hard to exactly determine the loading condition of the motor. The inaccurate model from this uncertain loading condition may result in erratic velocity control. This paper presents an experimental approach to characterize a DC servo motor loaded with an unknown torque: a steady-state approach is proposed to estimate the parameters of the entire loaded system. Based on the transfer function, a PID controller is designed to validate the resulted model. In the demonstration, a DC servo motor included in a Feedback® 33-100 mechanical unit was utilized. The PID controller was implemented on a BasicStamp® microcontroller with an external analog-to-digital converter (ADC) and an external digital-to-analog converter (DAC).