Legends for supplemental material figures Figure S1: Robot and experimental setup: (a) Assembled molecube consists of two halves separated along a plane perpendicular to the long diagonal. (b) The base plates arrangement on the experimental platform. Each base plate has an embossed pattern mechanically compatible with any molecube face, electrical terminals to facilitate power supply to the robot and electromagnets for additional retaining force provision. (c) Dissected view of the mechanical worm gearbox half of the molecube. (d) Molecube servo drive half accommodates the servo, worm gearbox, swivel angle sensor (potentiometer), and voltage regulator for the servo. The electromagnet and the external electrical terminals are embedded in the interfacing plate in the shell of the molecube. (e) Molecube microcontroller half accommodates the microcontroller and voltage regulator. An electromagnet is embedded in the interfacing plates in the shell of the molecube. Figure S2: Two generations of self-reproduction of modular robots. (a) A sequence of frames showing the self-reproduction process of a 4-module robot. The top three rows show a sequence of frames that spans about 2.5 minutes. The entire reproduction process runs continuously without human intervention, except for replenishing building blocks at the two ‘feeding’ locations circled in red. At the end of the process (2:34), the original 4-module robot has created a second, identical, 4-module robot. The lower three rows show a second self-reproduction process where the second robot (just built) produces another replica. (b) A sequence of frames showing the self-reproduction process of a 3-module robot, spanning about 1 minute. More sequences of this type exist in this robotics space for smaller and larger machines.