Electric vehicles , whether they’re cars on the road or electric vertical take-off and landing ( eVTOL ) aircraft, are built around similar electric motors . But there are vital differences including component costs, mass, and redundancy. Jon Wagner spent five years as the senior director of battery engineering for Tesla before joining California-based eVTOL developer Joby Aviation in 2017. He spoke with IEEE Spectrum about how engineering differs between cars and aircraft. ​Jon Wagner  Jon Wagner leads power train and electronics at Joby Aviation . How do eVTOL motors differ from car motors? Jon Wagner: In general, ground transportation has a different focus on cost versus mass. You know, would you be willing to spend more on the parts in order to save a certain amount of mass? The trade-offs end on the ground vehicle and at a certain point the cost is dominant, whereas with aviation, the trade-offs between cost and mass go a lot deeper.…