YOU CAN BUILD THE 15,000-DOLLAR MOTOR TEST RIG FOR 370 DOLLARS

If you are building or reverse-engineering electric drive systems — e-bike motors, robot actuators — and you need to know what they actually do under load, this is a low-cost dynamometer design with published validation. The commercial benchmark the authors cite, a Magtrol DSP6001, costs over 15,000 dollars. The clever part is that it does not reinvent the measurement stack: the Votol EM-50 ESC already reports voltage, current, RPM and temperature over serial telemetry, so the ESP32 only has to decode that stream and read an HX711 load cell for torque. The paper describes splitting this across the ESP32's two cores; the firmware in the repository is a simpler single loop, so check which version you are running. The mechanical load is a bicycle disc brake on a floating caliper. They validated the rig against a motor model and report an error of 14.8 RPM on step response, plus torque error below 5% after weight calibration. The build will take a weekend-plus because you are welding a steel frame that holds a spinning motor and brake caliper under tension, and you may need to adapt the mechanical design to whatever brake and load cell you can source locally. The single thing most likely to go wrong is assuming the telemetry protocol is standard across ESCs — it is not, and if you use a different controller you will need to decode its specific serial format. The CERN-OHL-S licence means any product you distribute based on this must also be open hardware, so this is not a prototype for a closed commercial tool. For research, education, or one-off motor testing, it is a genuine 370 to 488 dollars alternative to a five-figure instrument.