Disclosed are systems, assemblies, and components that relate to power transfer. In particular, the disclosed systems includes a transmission that offers variable speeds and changes between different gear ratios while maintaining constant engagement. Constant engagement may be maintained by tooth-to-tooth contact to be scalable for a variety of applications. An example system includes a phase shifting mechanism. The phase shifting mechanism may include an eccentric gear that provides an oscillating output. The oscillating output creates an overall gear ratio change that slides between gear ratios, thereby allowing changes to occur in small, and possibly infinitely small increments. According to one example, an eccentric gear has a changing base radius and includes a tooth with a hybrid profile that has a base the width of an initial profile, and a width at a top of the tooth that is that of a final profile.