In this study it is proposed a photovoltaic powered farming robot system that consists of a delivery vehicle and a working vehicle. The proposed system is designed based on a newly proposed farming method called shaft tillage cultivation. So, we have developed two automatic vehicles, as well as a 2-D localization method for positioning of the working vehicle. In addition, we have developed an attachment for shaft tillage and transplanting which is derived from commercially available transplanting machines. This movable transplanting attachment was mounted over two rails which are disposed transversally on the frame of the working vehicle which in turn permits transplanting multiple rows. The working vehicle is based on a skid steer vehicle with independent left and right motors that allow for motion direction control by turning the left- and right-side wheels at different velocities. However, within the field, even if same turning velocities are applied to both left- and right-side wheels a yaw angle is generated due to the sinkage and rolling resistance. Additionally, controllability of the working vehicle is greatly affected by variable changes of the center of gravity caused by lateral motion of the transplanting attachment. So, this paper focused on the effect of the position of center of gravity on the yaw angle in the working vehicle. The least square method was examined as method to find out the instantaneous center of rotation (ICR) and its effectiveness was confirmed. When the position of center of gravity was on the faster wheels the turning of the skid steer vehicle was more difficult than in other positions. The ICR changed even when the left- and right-side wheels were driven at the same velocities. Therefore, considering the position of center of gravity in the skid-steer vehicle would allow a rational guidance of the vehicle.