Introduction
Electric motors are the heart of both electric vehicles (EVs) and electric vertical take-off and landing (eVTOL) aircraft. While they share fundamental technology, the engineering priorities diverge significantly due to different operational contexts. This guide, inspired by insights from Jon Wagner—former Tesla battery engineering director turned Joby Aviation power train lead—walks you through the critical design distinctions. By understanding these steps, you’ll grasp why eVTOL motors prioritize mass reduction, redundancy, and integrated design over cost, unlike their EV counterparts.
What You Need
- Basic knowledge of electric motor principles (e.g., torque, efficiency, power density)
- Familiarity with automotive and aerospace engineering constraints
- Understanding of failure modes and safety requirements
- Interest in advanced materials like cobalt-iron alloys
Step-by-Step Guide
Step 1: Evaluate Cost vs. Mass Trade-Offs
In EV design, cost is the dominant factor. Manufacturers optimize for affordable components, even if it means adding weight. For eVTOL, however, every kilogram matters because excess mass reduces payload and flight range. Ask yourself: Would you spend 10× more on a material to save weight? In aviation, the answer is often yes. A prime example is Permendur, a cobalt-iron alloy that costs roughly ten times traditional motor steel. It offers modest performance gains—higher saturation flux density—but that can translate to lighter, more efficient motors. Ground vehicles rarely justify this expense, but eVTOL designers embrace it.
Step 2: Design Redundancy for Safety, Not as a By-Product
When an EV motor fails, the driver can pull over safely. In an eVTOL, there is no shoulder in the sky. You must ensure continued safe flight and landing after a failure. This means redundancy must be intentional, not accidental. Some EVs have all-wheel drive with two motors, which provides a backup—but it wasn’t designed for that purpose. For eVTOL, every critical system (motors, controllers, batteries) needs a duplicate. Map out failure scenarios and ensure that a single point of failure never compromises flight. This drives up complexity and cost, but it’s non-negotiable.
Step 3: Integrate Components to Eliminate Interface Inefficiencies
Automotive manufacturing often breaks a system into pieces sourced from different suppliers. While this works for high-volume, cost-sensitive production, it creates interface boundaries that cause inefficiencies (e.g., extra connectors, weight, and heat losses). For eVTOL, you should design highly integrated solutions—for example, combining motor, inverter, and cooling into a single unit. This reduces overall mass and improves reliability. Avoid the penalty of splitting the problem unless it’s absolutely necessary. Integrate early in the design phase to optimize the whole system.
Step 4: Select Advanced Materials for Performance Gains
Beyond Permendur, explore other lightweight, high-performance materials. For eVTOL motors, the goal is to maximize power-to-weight ratio. Consider using carbon-fiber composites for structural parts, high-temperature superconductors (if feasible), and advanced permanent magnets (e.g., samarium-cobalt instead of neodymium) for better thermal stability. However, weigh the cost vs. benefit carefully: a 5% weight reduction might justify a 50% cost increase for a critical component, but not for a trivial one. Use simulation tools to model material trade-offs early.
Step 5: Optimize Failure Mitigation Strategies
In EVs, the standard mitigation for a motor fault is to stop and get help. For eVTOL, you need strategies that allow safe descent or continued flight. This includes:
- Fault-tolerant control algorithms that detect failuress and reconfigure power distribution among remaining motors.
- Physical separation of redundant systems to avoid common-cause failures (e.g., fire or debris).
- Testing under real-world conditions including single-motor-out scenarios during hover and cruise.
Simulate each failure mode and validate that the aircraft can still land safely. Remember, redundancy is only effective if it’s designed to be independent and robust.
Tips for Success
- Start with a multidisciplinary team: Include aerospace, electrical, and mechanical engineers from day one. The cross-pollination of ideas from EV and aviation fields is invaluable.
- Budget for higher costs: eVTOL motors will always be more expensive per unit than EV motors. Plan your business model accordingly—focus on niche markets (e.g., air taxis, cargo) where time savings justify premium.
- Prioritize testing: Rigorously test every component at extreme temperatures, vibration, and partial failure states. Certification authorities (like FAA/EASA) have strict requirements that go beyond automotive standards.
- Stay updated on materials science: New alloys and composites emerge regularly. Follow research from institutions like NASA or universities working on electric propulsion.
- Learn from automotive then diverge: Use proven EV manufacturing processes as a baseline, but be prepared to deviate for weight and redundancy. For example, use fewer but more complex parts.
Ultimately, the key takeaway is this: designing eVTOL motors forces you to rethink every assumption from the automotive world. Embrace the challenge, and your aircraft will fly efficiently and safely.