Robotic actuators depend on smooth control of torque and motion. Stepper motors have good torque at low speeds and are very inexpensive, but are usually not an acceptable solution for robotics since they don’t have smooth, controllable torque. Inspired by the mechaduino project, Deft developed a stepper motor controller that essentially converts a low cost stepper into a high-performance robotic actuator. Achieving this brings together several recent innovations in sensor technologies: magnetic encoders with 14 bit resolution, dual DC motor drivers each rated for 2A, 12 bit resolution, and a 64 MHz microcontroller that can run a control loop for the motor while reporting and accepting input commands as an SPI device using DMA. These actuators are used in several robotics projects at Deft including the cost-effective Dexapod robots. For these prototype machines (video below), the gripper uses an independent stepper-servo while the arm actuator controller board is centralized and only the encoders are attached on each motor. To learn more about smooth torque control from stepper motors, check out our white-paper “On Stepper Motors“.
