A further method would be to use a variable displacement pump.  Once the pump is configured for reduced displacement, it creates a low volume of oil circulation, producing the hydraulic motor(s) to turn far more slowly and gradually. Merge harvesters utilized variable belt drives as early as the nineteen fifties. https://dominickhteoa.vblogetin.com/38368444/getting-my-gearbox-cvt-to-work