Methods, apparatuses and systems directed to calculation of a reel motor torque constant ("K.sub.T"). In one implementation, calibration logic energizes supply and take-up reel motors to wind tape from a supply reel to a take-up reel. The calibration logic, during winding, selectively disengages the supply reel motor and measures one or more attributes of the supply reel motor, such as the resulting voltage observed at the winding terminals of the supply reel motor and the angular velocity of the supply reel motor during the period of disengagement. The calibration logic then calculates K.sub.T based on the observed attributes.