https://github.com/otwieracz/maho-mh300m-feed-controller
A feed rate controller for the Maho MH300M vertical milling machine. The machine was purchased without its original BBC servo drive, fitted instead with a basic open-loop PWM controller that had no tacho feedback, no rapids, and inconsistent speeds under load. After replacing the drive hardware with a Parker 512C closed-loop servo, the front panel feed selector no longer corresponded to actual feed rates.
The controller software maps the MH300M’s original panel selector positions to the correct setpoint voltages for the Parker drive. The feed axes use a 1:10 gear ratio, with working feeds up to 500mm/min (1250rpm, -7.5V tacho) and rapid traverse at 1200mm/min (3000rpm, -18V tacho). The controller computes the appropriate voltage for each selector position so the operator can trust the panel markings.
A custom 10mm potentiometer with 300 degrees of rotation provides fine control over the 0-500mm/min range. The first 30 degrees cover a dead zone below 12.5mm/min for precise low-speed work. The software handles the non-linear mapping between potentiometer angle and motor setpoint, accounting for the tacho feedback characteristics of the Parker drive.