The motor turns too much
Reverse‑engineering a Hyundai Kona electric drivetrain reveals how tightly modern EV components are coupled and how control software can cause an unloaded motor to spin to very high RPM under minimal torque. Commenters use this case to explore broader issues: the extreme electronic and software complexity of current cars, safety behaviors when sensors fail, and how design choices affect repairability and DIY conversions. The thread also branches into why Chinese makers like BYD can undercut Western EV prices, weighing factors such as supply‑chain integration, labor costs, government policy, and the slow transition of legacy automakers from ICE‑centric platforms.
Integrated EV Drivetrains and Chinese Cost Advantage
- BYD’s “e-axle” (motor, inverter, diff, charger in one CAN-controlled module) seen as a major reason they can reuse hardware across models and undercut Western OEMs.
- Debate over why Chinese EVs are cheaper:
- One side: low Chinese wages, lax regulations, subsidies, tightly protected domestic market, and long-running state backing of EVs and batteries.
- Other side: labor is a small share (often cited 5–15%) of car cost; key edge is early national push into EVs and LFP batteries, vertical integration, and faster innovation.
- Disagreement on how much current per-car subsidies in China vs. US still matter; some argue US tax credits are now larger, others say true support levels are opaque.
Complexity of Modern EVs
- Hyundai Kona example: many CAN buses, ~100+ ECUs, 10+ kg of low-voltage wiring; some find this “sad” given EVs could be simpler.
- Counterpoint: similar complexity exists in ICE vehicles due to safety, infotainment, and comfort systems; not just the powertrain.
- Some argue Tesla and Chinese newcomers started with cleaner-sheet EV designs but are now accumulating legacy complexity too.
Control Logic, Safety, and “Runaway” Behavior
- Bench tests show Kona motor will spin to high RPM under tiny constant torque with no load or brake, including in “Neutral”.
- Engineers in thread note:
- Torque is very low (~5 Nm), easy to stop with brakes in a real car.
- Under no-load, vector-controlled motors naturally ramp RPM if any nonzero torque is applied.
- ABS sensors and safety standards (e.g., ISO 26262) are meant to make dangerous wheel-speed-sensor failures vanishingly rare.
- Some remain uneasy that ECUs don’t explicitly detect “no vehicle inertia” cases; others say extra checks add complexity and new failure modes.
Human Factors and Unintended Acceleration
- Long subthread on past ICE unintended-acceleration incidents:
- Many cases attributed to driver error and panic, especially with automatics and older drivers.
- Suggestions: shift to neutral, stand hard on brakes, or kill ignition—but several argue most drivers won’t think of this under stress.
- Concern that increasing “drive-by-wire” (throttle, shift, sometimes brake/steer assist) moves more risk into software and human-interface design.
EV Conversions and Modularity
- Converting ICE cars to EVs seen as technically difficult and often uneconomic:
- Battery packaging, weight and suspension changes, torque vs. transmissions, accessory drives, heating, and regulatory approval are major hurdles.
- Some niche success exists (classic cars, Tesla-salvage builds, open-source inverter projects), but it’s labor- and skill-intensive.
- Several note that modern EVs are more like tightly coupled “eggs” than modular “onions,” making partial reuse of OEM drivetrains harder than expected.