<div class="htmlview paragraph">This paper describes a computer program for optimising the bending and contact strength of the spur gears in a planetary hub reduction set. Classical optimisation techniques are not employed because of the complexity of the problem and the number and variety of constraints encountered. Instead, the approach described covers the complete design space and successively filters out solutions that do not meet the required constraints. Thus the very large design space is reduced to a relatively few possible solutions whose properties can then be examined by the designer, leaving the final trade-offs to his discretion.</div>