Use a RevoluteJoint. And make your paddle rotate around another object. Like so:
Body motorPaddle = CreateMotorPaddle();
Body motorPaddleAxle = BodyFactory.CreateCircle(World, 0.1f, 1f);
var j = JointFactory.CreateRevoluteJoint
(
World,
motorPaddle,
motorPaddleAxle,
new Vector2(0.0f, 0.0f),
new Vector2(-14.0f, 10.0f)
);
// set speed and torque
j.MotorSpeed = MathHelper.Pi;
j.MotorImpulse = 100;
j.MotorEnabled = true;
j.MaxMotorTorque = 100;
More details here