A multi-axis electric stepper motor has been developed at RaM, which uses three rotors driven by a singular, homogeneous stator using the superposition of waveforms. Such a motor has certain advantages, such as smaller volume and fewer cables (at the cost of somewhat lower torque and/or efficiency) compared to separate single-axis stepper motors with comparable rotor sizes.
The output shafts are all aligned concentrically. This may be a limitation in many applications, but it also offers unique opportunities in specific cases. One interesting potential application is the VIA (variable impedance actuator) which is especially useful in robots interacting with the environment by dynamically changing the output shaft between stiff and soft spring behaviour. VIAs are often complex and bulky, so a cleverly designed multi-motor-driven VIA could be a step forward in this research field.