The preparation of flax retted straw is recognized as a critical stage in the flax production cycle. The performance of mechanized equipment used in this process significantly impacts the quality indicators of the resulting retted straw. (Research purpose) To analyze the dynamics of the ribbon pickup mechanism and examine the interaction between the pickup drum fingers and flax stems, taking into account the drum's design parameters and challenging harvesting conditions. (Materials and methods) Theoretical analysis of the pickup drum dynamics and the interaction between its fingers and the flax stems was conducted using Lagrange’s equations of the second kind. (Results and discussion) The study established the regularities governing the interaction between the drum fingers and a group of flax stems. A time-dependent function was derived to describe the polar radius of coupled stems, along with the conditions required for their stable transport without slipping off the fingers. It was determined that effective transport occur when the relative velocity is zero or negative and directed from the fingertip toward the center of rotation. Graphs were constructed to illustrate the effect of key parameters, such as the drum's angular velocity, deviation angle, drum radius, and the coefficient of sliding friction, on the polar radius of the stem group. (Conclusions) The analysis revealed that the polar radius is most sensitive to variations in the angular velocity of the pickup drum. The findings of this study were incorporated into the design of a pickup drum for an innovative pickup-and-turning device.