This paper presents a controller for the vertical height of a hopping robot. The ability to accurately change the hop height every step will contribute toward the traversal of discontinuous terrain with limited safe footholds, with application to bipedal or quadrupedal running. A key feature of the approach presented is the use of information from previous hops/steps to inform the control of the current step. As well as avoiding modelling errors, this allows the robot to make on-line adjustments in response to changes in system parameters or the environment. The algorithm is simple enough to be easily implemented on a low power hardware, not requiring computationally demanding optimisation or numerical simulation. The effectiveness of this approach has been demonstrated for constrained vertical hopping in simulation and on a pneumatically actuated hopper.