by the armature coils 202 the maximum ambient temperature and an understanding of the temperature limitations of the coils and magnets the heat transfer coefficient that is sufficient to limit the temperatures of sensitive motor components can be calculated because the heat transfer coefficient is a function of the properties of the fluid the flow velocity and the flow geometry it is possible to iterate a motor design in order to optimize the design for performance and cost for instance reducing the gap between the coils increases the impedance of the motor to air flow to compensate for the increased impedance the fan performance is increased to produce sufficient velocity to achieve the desired heat transfer coefficient a larger gap between the coils will lower the air flow impedance but generally necessitates higher air flow rates to obtain the desired heat transfer coefficient thus in general an iterative process using motor impedance i e geometry and or gap size fan performance and cost as variables is employed to optimize the design of the motor as an example a motor designed based on such an iterative process produces 7 5 kn of force output and dissipates about 1 8 kw of heat through its four armature coils or 450 watts per coil the gaps above and between the coils are 10 mm the motor has external dimensions of 44 5 cm u00d7 27 2 cm u00d7 43 7 cm and weighs approximately 95 kg the arrangement of gaps 222 228 is also subject to maintaining suitable magnetic performance of the motor components in a conventional motor with no gaps between the armature coils the magnet transition line i e the n to s magnetic orientation change is.