In this study, the performance of a double cylinder flow-induced vibration (FIV) energy converter is experimentally investigated. The central aim is to take advantage of drag force and gap flow to enhance the vibration. The cylinders are free to rotate around a pivot and located in different configurations including both cylinders on the downstream, both on the upstream, a cylinder on each side and one cylinder on the pivot. Each configuration is represented by the gap ratio between the two cylinder (G = gap/cylinder diameter) and center of gravity ratio (CG = gravity center/cylinder diameter). Locating the cylinders in different positions made it possible to activate a wide range of vibration mechanisms including: Vortex excitation (VE), wake-induced vibration (WIV), galloping and gap-switching-induced vibration (GSIV). The most efficient vibration mechanisms are: (1) GSIV for CG = 0 and G = 0.9 (2) VE where CG = 0 and G >= 3.9 (3) drag-assisted vibration where one cylinder is on the pivot point and another one on the upstream side, (4) WIV where one cylinder is on the pivot point and another one on the downstream side, (4) both cylinders on the downstream side with no gap and (5) both cylinders on the upstream side with no gap. (C) 2018 Elsevier Ltd. All rights reserved.