Help Capstan driven z axis

Hello guys I am working on a z axis lift driven by stepper to lift and lower the platform precisely . It will be driven by a capstan drum fixed to stepper shaft and cable routing around pulleys . I have a stepper nema23 with 1n-m holding torque . As per my calculation toque required By motor to lift the stage would be FXR since I am looking to design the stage for max payload of 10 kg I assume the motor torque is sufficient but as we know the efficiency of motor is actually less assuming 80% available torque would that be enough since I am running cables through capstan drum with 2-4 wraps and around pulleys will I be having some mechanical advantage so that my motor is capable with available torque? If yes will that be sufficient enough to hold the stage if there is a power failure without slipping I am routing cables similar to this diagram http://ift.tt/1qd1TaG I also thought of increasing torque with torque amplifier design http://ift.tt/1zVkxVB is this feasible enough . Waiting for valuable suggestions