Gyroscopes are challenging underactuated systems which are commonly used as actuators in many kinds of plants, including underwater vehicles (Xu et al., 2018), satellites (Keshtkar et al., 2018) and ungrounded haptic devices (Walker et al., 2017), among others. Several works have been devoted to gyroscope control design, see Abbas et al. (2014); Reyes-Rodr´ıguez et al. (2017); Keshtkar et al. (2018). Those systems are subjected to unknown disturbances in the form of external torques. In this context, sliding mode control is a widely used strategy to cope with matched disturbances (Utkin, 1992). Sliding mode methods, however, are fragile when dealing with unmatched perturbations typically involved in underactuated systems. Many strategies have been developed to design robust control of underactuated systems towards the compensation (Aguilar-Iban˜ez et al., 2017) or attenuation of the disturbance effects (Castanos and Fridman, 2011