US Patent 9187301 Self-propel accessory

A self-propel accessory provides an easily attachable optional drive function for a platform device. The platform device is supported by a device frame including a wheel at a rear end and a post at a front end. The self-propel accessory includes an accessory frame attachable to the device frame via a bracket, a driving wheel connected to the accessory frame, a motor operatively coupled with the driving wheel, and a handle connected to the accessory frame. The accessory frame is pivotable between a disengaged position and an engaged position, and a weight of the platform device biases the accessory frame toward the disengaged position.