Animal locomotion results from a combination of power modulation and cyclic appendage trajectories, but combining these two properties in small-sized robots is difficult. Here, we introduce and characterize a new elastic actuation system based on an inverted cam that is capable of generating cyclic locomotion with controlled elastic energy charge and release for small-sized robots. We designed a leg linkage and attached to the inverted cam to develop a single legged hopping platform with one actuated degree of freedom. The hopping platform was able to continuously hop forward at 1.82 Hz. The average horizontal hopping distance was 18.7 cm, and the average forward speed was 0.34 m/s. This speed was corresponding to a Froude number of 0.14. The energy consumed for one hop was 2.09 J, and the corresponding energetic cost of transport was 6.43. The combination of inverted cam and cyclic trajectory generation has the potential to be used in other robotic applications, such as flapping wings in the air and tail fin waving in water.