My latest 3D printer design uses a belt lifted Z axis that has proven to be a very good performer. The 300x300x8mm MIC6 bed and its support (3.5 kg) are lifted on two linear guides using two steel core belts. The belts are driven by a NEMA-23 motor mounted on an OnDrives Rino 30:1 worm gear reducer that prevents the bed from dropping when power is shut off. Maximum speed is 20 mm/sec (the motor is spinning at 333 rpm!), even with a 4 kg print load. The motor is rated for 1.8A, but I operate it at 1A and it never gets more than 5C above ambient temperature. It is driven directly by the driver chip on a SmoothieBoard controller. I have measured belt stretch and determined that it is negligible.