This thesis is the result of the investigation and solution of a mechanicalproblem regarding flywheel malfunctions. A flywheel is, in short, a devicethat relies on a rotating object’s moment of inertia to store energy overshort time spans. This project is part of the development of a fourthflywheel prototype at the division for electricity at Uppsala university,which uses magnetic levitation to keep a hollow cylinder rotating at veryhigh speeds inside a vacuum chamber. Should the magnets fail however, orsome other error occur that leads to an uncontrolled state of rotation, thecylinder needs to be stabilized mechanically by a device usually referredto as ‘back-up bearing’. This contraption might, like an airbag of a car,never be used but needs to be included if an emergency occurs to protectother parts of the flywheel which would otherwise be destroyed by theunrestrained rotor. A theoretical pre-study was conducted to determine what challenges andrespective solutions the design of such a device would encounter, forexample the amount of energy in the rotor and possible ways to dissipate itin the event of a malfunction. The benefits and downsides of materials andmachine elements such as bearings were investigated in order to design aset of backup bearings. The modelling was done using SolidWorks, which wasalso used to conduct thermal and mechanical simulations on differentconcepts. MatLab was used for calculations, using formulae from themanufacturers and from different websites. The project concluded that the sheer energy of the flywheel at top speedpresents considerable thermodynamic difficulties. A solution capable ofhandling this was however achieved, albeit barely. Unfortunately onlysimulations and calculations confirm this result as no practicalexperiments could be conducted, therefore caution is advised in futureexperiments where the flywheel speed approaches maximum levels.