Disclosed is an actuator mechanism for a modular robotic system. The actuator mechanism includes a motor, a carrier configured to be secured to the motor, and an actuating member operable by the motor to cause the actuating member to move relative to the carrier. The motor has a drive shaft which defines an output axis, and a body extending away from the shaft, the body defining a maximum width dimension orthogonal to the output axis. The carrier defines a longitudinal axis parallel to the output axis. The output axis is arranged, by the carrier, to be offset from the longitudinal axis by at least half of the maximum width dimension. Also disclosed is a module for a modular robotic system, and a modular robotic system.