Potato production in the Russian Federation and in many countries of the world is important. In the public sector, potatoes are cultivated on farms, personal and subsidiary plots. In connection with the transition to market relations, the area for planting potatoes has sharply decreased, and as a result, the production of potato harvesting equipment. Therefore, an acute question arose of the further creation and production of the simplest potato harvesting equipment and the improvement of their new working bodies. Pre-harvest removal chopping tops occupies an important place in the technology of potato cultivation. During operation, it was noted that rotary machines have a number of disadvantages caused by the imperfection of the rotor design, its kinematic modes, insufficient balance and reliability. In order to eliminate these shortcomings, a rotary topper with a vertical axis of rotation was designed and manufactured. To justify the design and operational parameters, theoretical studies of the process of interaction of the working element of the chopper with the tops of root crops were carried out, as a result of which the main patterns characterizing the working element were identified. In particular, dependence was obtained that allows to determine the cross-sectional diameter of the working element, which takes into account both the design parameters of the developed grinder and the properties of the tops. After calculating the obtained dependence, it was determined that for the operation of the unit with a minimum energy consumption, the diameter of the working element should be 6 mm. Such a working element cuts the tops in compliance with all agricultural requirements. Field experiments conducted later confirmed the obtained value, which indicates the reliability of the results.