Lower limb robotic prostheses are recent developments that attempt to overcome limitations of passive prosthesis technology, which lacks the capability to introduce or dissipate energy during Activities of Daily Living (ADL). The small number of available robotic devices in the global market underscores the importance of new developments and experiments, considering different ADL, such as walking outdoors, ascending and descending stairs, and ramps. In this direction, this study presents the hardware development of a robotic leg prosthesis containing actuators in the knee and ankle joints, which are controlled by a custom embedded hardware that is battery-powered and capable of wireless communication, thus enabling untethered operation. Results show the performance of the prototype across different ambulation modes, including walking outdoors (outside the laboratory environment), stair ambulation, and the transition between activities, with great correlation with biomechanical data.