RAPID: An Inexpensive Open Source Dynamometer for Robotics Applications

This paper describes the development of an automated dynamometer to characterize brushed direct current motors. The unique mechanical design allows the testing of a wide range of motor sizes. The motor under test is subjected to a given pulse width modulated voltage signal and position, current, and voltage measurements are simultaneously recorded from the integrated sensor suite. An electromechanical motor model is developed by combining the voltage and torque balance equations of the system. A least-squares algorithm is used to estimate the parameters that best fit the observed data to the specified gray box model. The system retains a low cost by using off-the-shelf electronics and cheaply fabricated mechanical parts. The inertia and friction of the system are carefully modeled, removing the need for an expensive torque sensor. The mechanical drawings, electrical schematics, and software are open source and freely available for download. Consistent parameter estimates from a set of high-tolerance and well-documented identical motors demonstrate the accuracy and precision of the system.