Abstract: A rotary engine includes a central rotor having a frustoconical shape with an ellipsoidal groove machined into the outer surface of the rotor. The rotor is rotated by the movement of a series of pistons mounted in cylinders surrounding the rotor. A series of piston rods connected to the pistons have piston followers that engage and follow the elliptical groove on the rotor. The rotor is mounted on a main drive shaft, and a cam assembly is additionally mounted above the rotor on the main drive shaft. Each cam in the cam assembly has a lobe, and is operable to control the intake of fuel and the exhaust of burned gases within the each cylinder according to the rotation of the main drive shaft. In this design, the piston follower encounters less friction and side forces due to the frustoconical shape of the rotor. Additionally, the pistons have a positive movement within each cylinder due to the angular placement of the cylinder in conjunction with the rotor.