Towards a dynamic actuator model for a hexapod robot

We describe a model predicting the output torque of the battery-amplifier-actuator-gear combination used on the hexapod robot RHex, based on requested PWM (pulse width modulation) duty cycle to the amplifier, battery voltage, and motor speed. The model is broken into independent components, each experimentally validated: power source (battery), motor amplifier, motor and (planetary) gear. The resulting aggregate model shows <6% full scale RMS error in predicting output torque in the first quadrant of operation (positive torques). Understanding the key ingredients and the attainable accuracies of torque production models in our commonly used battery-amplifier-actuator-gear combinations is critical for mobile robots, in order to minimize sensing, and thus space, size, weight, power consumption, failure rate, and cost of mobile robots.