A fluid mixing system includes a flexible bag having a first end, an opposing second end, and an interior surface bounding a compartment. A first rotational assembly includes a first casing mounted to the first end of the flexible bag and a first hub rotatably mounted to the first casing. A second rotational assembly includes a second casing mounted to the second end of the flexible bag and a second hub rotatably mounted to the second casing. An elongated member has a first end coupled with the first hub and an opposing second end coupled with the second hub, the connector being flexible and having a uniform flexibility along its entire length. A first impeller is mounted to the connector.