The editorial frames Renault's move as significant not for novelty but for timing: China's April 2025 export controls on heavy rare earths like dysprosium and terbium turned a fifteen-year-old theoretical concern into an operational crisis. A mainstream European automaker architecting its next-gen Ampere platform around zero permanent magnets signals that supply-chain de-risking is now a platform-level engineering mandate, not a research curiosity.
Renault's own explainer is candid that the wound-rotor synchronous motor is textbook 1890s electrical engineering, with peak efficiency roughly 1-2 percentage points below a comparable PMSM, more copper mass, and a more complex rotor. The company positions the design as a conscious trade: accept modest efficiency and mechanical complexity in exchange for eliminating neodymium, dysprosium, and terbium dependence entirely.
By submitting the Renault technical explainer to Hacker News where it reached 595 points, the submitter elevated a piece that explicitly frames EESM as a known, mature topology (Tesla Model S 2012, BMW iX3 2020) rather than an invention. The framing implicitly endorses the view that the news is about industrial deployment at scale, not technical novelty.
Renault Group published a technical explainer this week — picked up by Hacker News at 595 points — detailing the wound-rotor synchronous motor (often called EESM, externally excited synchronous motor) it has been shipping in the Megane E-Tech and Scenic E-Tech, and which will anchor the next generation of its Ampere EV platform. The claim is simple and the engineering is not: a traction motor with zero permanent magnets, and therefore zero neodymium, dysprosium, terbium, or any of the heavy rare-earth elements that China controls roughly 90% of refined production for.
The mechanism is textbook 1890s electrical engineering dressed up for 2026. Instead of embedding sintered neodymium magnets in the rotor to create a fixed magnetic field, Renault winds the rotor with copper, runs DC current through it via brushes or — in the newer design — a brushless rotary transformer, and generates the field electrically. The stator does what stators do. The trade-offs are well known: slightly lower peak efficiency (Renault cites a delta of ~1–2 percentage points versus a comparable PMSM at peak), more copper mass, a more complex rotor assembly, and the engineering headache of getting current into a spinning part without brushes wearing out.
The story isn't that Renault invented this — Tesla used a similar topology in the original Model S in 2012, and BMW's iX3 motor has been rare-earth-free since 2020 — it's that a mainstream European automaker is now treating rare-earth exposure as a P0 supply-chain risk and architecting around it at platform scale.
The rare-earth question has been theoretical for fifteen years and operational for about eighteen months. China's October 2024 export controls on gallium, germanium, and graphite were a warning shot; the April 2025 controls on seven heavy rare earths — including dysprosium and terbium, the elements that keep neodymium magnets working above 100°C — were the real escalation. Every automotive supply chain VP has had the same conversation since: what's our exposure, and how fast can we cut it?
The answers split along predictable lines. Tesla announced in March 2023 it would design its next-gen platform without rare earths and has been quiet about progress since. BMW shipped first. Renault is now the loudest, partly because Ampere is a standalone EV spin-off with no legacy ICE supply chain to defend and partly because France's strategic-autonomy doctrine makes rare-earth independence politically valuable independent of the unit economics.
The interesting engineering question isn't "can you build a motor without magnets" — obviously you can, induction motors have existed since Tesla (the inventor, not the company) — it's "can you match a PMSM's torque density, efficiency curve, and thermal envelope in the same package volume." Renault's answer is: mostly. The peak efficiency gap is real but the *average* efficiency over a realistic drive cycle is within rounding error, because PMSMs leak magnetic field losses at low load and EESMs don't (you just turn the rotor current down). For a daily commuter that spends 80% of its time at 30% load, the EESM may actually win on range. For a 0–60 dragster, the PMSM still wins.
The community reaction on HN is worth reading because it splits cleanly between two camps. The first camp — mostly EE practitioners — points out that this is a solved problem and the only reason PMSMs dominated was a roughly $30/kg neodymium price that made the BOM math irresistible. The second camp — mostly supply-chain people — points out that the BOM math is now contingent on a single country's export-control policy, which makes the "slightly worse efficiency" trade look like cheap insurance. Both are right. The question is whether the insurance premium is worth paying when your competitor doesn't.
If you don't build motors, this still matters, because the rare-earth supply story is the canary for every China-dependent hardware bill of materials you ship. Permanent magnets show up in places software people forget about: hard drive actuators, the voice coils in headphones and AirPods, every brushless drone motor, the haptics in your phone, the servos in industrial robots, the generators in wind turbines, the compressors in heat pumps. If your hardware roadmap assumes neodymium magnets stay below $80/kg and unrestricted, you are running an uncovered short on Chinese trade policy.
The pattern Renault is modeling is the one to copy: identify the part of your BOM with the highest geopolitical concentration risk, accept a small performance penalty to eliminate it, and use the resulting marketing story ("sovereign supply chain," "no rare earths," "made in Europe/America/wherever") to justify the price you'd have charged anyway. This is not unique to motors. The same playbook applies to lithium iron phosphate (LFP) versus NMC batteries, to silicon carbide versus gallium nitride power electronics, to whatever ARM-vs-RISC-V conversation your hardware team is having.
For software-adjacent practitioners, the second-order effects are where the alpha lives. Wound-rotor motors need more sophisticated control software because you're now managing two coupled magnetic fields instead of one fixed one — the field-oriented control loop has an extra degree of freedom. Expect a wave of hiring for motor-control engineers who can write efficient observer code for field current estimation, and expect the embedded ML crowd to discover that learned rotor-position estimators are suddenly interesting again.
The near-term bet is unsexy and almost certainly correct: EV motor architectures will bifurcate by 2027, with PMSMs surviving in performance and premium segments where the efficiency delta matters and wound-rotor machines taking over the volume segment where the supply-chain delta matters more. The interesting question is what happens in the categories Renault hasn't entered yet — robotics, drones, consumer electronics, white goods — where the magnet content per unit is tiny but the cumulative exposure across a product line is enormous. If you're a hardware founder shipping anything with a brushless motor in 2026, the smart move is to have a magnet-free SKU on the roadmap before your VP of procurement is forced to put one there.
A historical pioneer in the complex technology of electric motors without magnetsThose who know the history of electric machines will find the title and verbiage very amusing. Motors with no permanent magnets were the first practical ones, and at this point wound-rotor motors are over a century old.
BMW also makes rare-earths-free motors for their EVs and - at this very moment - theirs are far more advanced. They offer almost twice the power (up to 300kW vs 160kW) and are on a 800v architecture.
Clearly making a motor with induced magnetic fields both for the stator and rotor isn't the innovation here, since a large fraction of industrial motors do not have permanent magnets.I would assume the innovation here would need to be making it small and efficient for any meaningful torque outp
It's interesting that this is a brushed design. In the RC car community, brushless motors are generally regarded as superior, but those of course have the rare earth magnet problem.Technically the brushes can wear out, although there are claims they are good for 150,000-250,000 miles it seems.
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Unfortunately, their Web page does not say a single word about the important problems of their motors.The electrically excited synchronous motors have been known forever, but they had not been used in EVs because of 2 disadvantages.The first is that traditional EESMs require brushes, i.e. sliding el