An unloader for unloading material from a container. In some embodiments, the unloader can include an unloader arm movable within the container, a first chain coupled to the unloader arm and movable to unload material from the container, and a second chain coupled to the unloader arm and positioned to engage material within the container upon movement of the unloader arm. The unloader can have a sensor adapted to transmit signals indicative of a force applied to the unloader arm, the first chain, and/or the second chain. A controller can receive the signal from the sensor, and can alter an operation of the unloader arm, the first chain, and/or the second chain based upon the signal received from the sensor.