Abstract: An energy return device for a midsole of a shoe comprises a resilient foam or matrix structure, such as a domed disk, around a cavity. The resilient structure is arranged to collapse into the cavity under foot strike pressure. The structure may initially resist the pressure primarily by compression forces directed around the cavity. As the cavity collapses these forces may provide decreasing vertical spring rate as the structure bends or as the forces become less vertical, causing the structure to stay more compressed through the midstride and energy return to be delayed until the user has moved further forward in their stance. At full collapse the material of the structure may resist further downward force of the user by direct compression. A lateral expansion limiter may resist lateral expansion to increase vertical force supplied by the compression forces around the cavity and reduce interference with other components. A support structure may help guide the collapse and increase spring force.

Abstract: A hypotrochoid positive-displacement machine includes an inner rotor and an outer rotor with intermeshing projections. During rotation of the rotors, the inward-most tips of the outer rotor trace hypotrochoid paths relative to the inner rotor. A driven rotor, for example the inner rotor, drives a driven rotor, for example the outer rotor, by contact between driving surfaces and driven surfaces of the respective rotors. Improvements are provided, for example in relation to the contact between the rotors. In use of the device contact between the driving surfaces and driven surfaces may move radially outward from a point of initial contact. The driving or driven surfaces or both may be arranged to flex under contact between the rotors. The driving surfaces may be convex. The driven surfaces may be concave.

Abstract: A hypotrochoid positive-displacement machine includes an inner rotor and an outer rotor with intermeshing projections. During rotation of the rotors, the inward-most tips of the outer rotor trace hypotrochoid paths relative to the inner rotor. A driven rotor, for example the inner rotor, drives a driven rotor, for example the outer rotor, by contact between driving surfaces and driven surfaces of the respective rotors. Improvements are provided, for example in relation to the contact between the rotors. In use of the device contact between the driving surfaces and driven surfaces may move radially outward from a point of initial contact. The driving or driven surfaces or both may be arranged to flex under contact between the rotors. The driving surfaces may be convex. The driven surfaces may be concave.