What Makes eVTOL Motors Different Than EV Motors?

Electric vehicles, whether they're cars on the road or electric vertical take-off and landing (eVTOL) aircraft, share a common foundation in their electric motors. However, when it comes to designing and building these motors for eVTOL applications, the priorities and challenges diverge significantly from those of traditional electric vehicles. Jon Wagner, who spent five years as the senior director of battery engineering for Tesla before joining California-based eVTOL developer Joby Aviation in 2017, sheds light on the nuances of eVTOL motor design.

As the lead of power train and electronics at Joby Aviation, Wagner spoke with IEEE Spectrum about the key differences in engineering between cars and aircraft. According to Wagner, the primary distinction lies in the trade-offs between cost and mass. In ground transportation, cost tends to be the dominant factor, whereas in aviation, the balance between cost and mass is more delicate.

The safety considerations for eVTOL aircraft also introduce unique design requirements. Since the failure modes for electric motors in both ground transportation and aviation are similar, eVTOL designers must prioritize mitigation strategies to ensure continued safe flight and landing. This often involves incorporating redundancy into the design, as there is no option to pull over in the event of a failure.

In contrast, ground vehicles can often safely pull over to the side of the road in case of a malfunction. Wagner notes that redundancy is not typically designed into electric vehicle drive systems for the purpose of redundancy alone. However, some cars with all-wheel drive configurations do offer a secondary benefit of redundancy.

Joby Aviation's approach to eVTOL manufacturing also differs from traditional EV manufacturing. By designing highly integrated solutions, the company can avoid the inefficiencies that arise from outsourcing components to suppliers. Wagner expresses excitement about certain materials, such as Permendur, a cobalt-iron alloy that offers improved performance but comes at a significantly higher cost.

This material may not be practical for ground transportation due to its cost, but it presents an interesting opportunity for aviation applications. As for the future of electric aircraft, Wagner remains optimistic, citing the need for patience in power-train development. With Joby Aviation and others undertaking this endeavor, he is confident that the aviation industry will make significant strides in electric propulsion.