In an image output calibrating system for cameras, a camera is supported so as to be directed at a plurality of different angles, and a light source is placed in front of the camera. An HVCA can include a DCDC converter configured to boost a lower input voltage from the LV battery to a higher output voltage provided to the HV battery. The existence of a seized or still standing roller is established when the load deviates from a predetermined value by virtue of a force induced on the roller by seizure or stoppage of the roller at the contact with the transported material. The winch framework may be released from the rear portion of the tractor and coupled to a storage frame mounted elsewhere on the tractor when the winch is not in use.