Providing oral capsule robots with additional degrees of freedom (DOF), such as robotic arms, is crucial for enhancing their functionality within the body. However, a key challenge arises when using rotating magnetic fields to drive the motor within the robot, as the resulting torque causes the entire capsule to rotate. In this work, we propose a novel approach to actuate a 2 DOF parallel link robot arm integrated into a capsule robot, using external magnetic fields. Our method employs two identical magnetic motors we proposed in a previous study, each driven by an oscillating magnetic field, which alternates direction along a specific axis. By independently controlling the rotation of each motor through the same magnetic field, ensemble control is achieved. The symmetrically arranged motors exhibit different angular velocities, enabling dexterous movement of the robot arm. We further theoretically show that this approach significantly reduces the torque exerted on the robot compared to traditional approaches using rotating magnetic fields. Finally, we demonstrate the performance of the robot by moving its arms and the attached end-effector along a pre-defined trajectory.

This paper addresses the challenge of actuating millimetre-sized motors, which are wirelessly driven by external magnetic fields. Traditional approaches, relying on rotating magnetic fields, often inadvertently cause the entire robot – especially if it is small and lightweight – to rotate, instead of a specified shaft in the motor. To overcome this issue, our study introduces a novel mechanism that leverages symmetrically configured magnetic motors to cancel out the torques, thus preventing unwanted rotation of the robot. This is achieved by utilizing a magnetic field along a single axis to induce rotational movement. The design features two millimetre-sized rotating magnets that interact to achieve a 90◦rotation, complemented by an external magnetic field that accomplishes the remaining 270◦, thus completing a full rotation. Furthermore, we demonstrate that applying a perpendicularly oriented magnetic field can inversely affect the motor’s rotation direction. A proof-of-concept experiment employing this mechanism successfully actuated a gripper in a water tank while it is free-floating, showcasing its potential for enhancing robotic applications at the sub-centimeter scale, where the small net torque of a miniature motor is essential.