Mass-produced electrical machines are subjected to manufacturing uncertainties in terms of geometry. A robust design is inevitable to ensure the consistent performance of the electric motor. Some parts of the rotor geometry are often simplified, like the flux barrier at the end of the magnets. This paper presents a design optimisation regarding the torque ripple and the average torque. The aim is to assess the effects of the flux barrier on the main properties of a permanent magnet synchronous motor. Also, robust design analysis is presented on the flux barrier. The computational burden of the robust design analysis is immense, even if uniform uncertainties are assumed. In this case, different Design of Experiment (DoE) methods reduce the number of simulations. The efficiency of the DoE methods is compared in terms of simulation number and extreme value approximation. We found that the Central Composite method is the most accurate, while the Plackett–Burman is the most efficient in this particular case.