Cable capstan drives are rotary transmission elements widely used in robot applications because of their low inertia, low backlash, high stiffness and simplicity. The cable in capstan drives is typically wrapped around the input and output drums in a figure-eight pattern and is the principle component for power transmission. In this paper an analytical method is developed for predicting the transmission error of capstan drives due to cable slippage on the drum so that designers can include this in the control phase of devices. The theoretical analysis was verified by experiments. (C) 2010 Elsevier Ltd. All rights reserved.