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Segway RMP 50 Tracked Robotic Platform

Edrees Siddiqui | John Banh | Ryan Lin | Mahin Khan | Michael Fagley

MAE 156B | WINTER 12 | TEAM 15

Sponsor: SPAWAR - Aaron Burmeister

BACKGROUND:

        Military robots are becoming increasingly popular because one of the main advantages of having remote controlled robots is that they can be used in places that pose threats to human/soldier's lives.  Being able to use robotics to obtain valuable information without actually being present in a danger zone can save soldier's lives and aid operations. Overseas, robots can save soldiers lives in cases where land mines are hidden beneath the surface of the earth.  The robots can be used to disarm the land mines or detect where they are using remote controlled commands.  In the case that these robots get destroyed unintentionally, it would be quite inefficient if the robots costa fortune to manufacture. This poses the question of how it is possible to make relatively cheap tracked robotic vehicle with a simple controls framework.  The Segway RMP 50 costs $7,210 USD and can easily be given commands from a CAN serial bus interface.  Ideally, this type of robot could be used as a vehicle for a variety of different possible applications.

OBJECTIVE:

        The main objective of this project was to design and implement a track system for the Segway RMP 50.  The sponsor of this project, SPAWAR, wanted us to design a track system that could easily be attached onto a stock RMP 50.  With this in mind, we were instructed to research different methods of successfully transforming the two wheeled robot into a tracked vehicle.  The final design was required to be able to traverse over rugged terrain and be able to climb a 45 degree slope.  Additionally, it would be required to carry 100 lbs of payload.  We were advised to look into snowmobile tracks considering the fact that one sample bot at SPAWAR had already been successfully built with snowmobile tracks.  With these requirements in hand, we decided to go ahead and use one snowmobile track and cut it in half.  This would allow us to be economical with our resources since one snowmobile track was wide enough for two individual tracks according to the dimensions of our segway.EXECUTIVE SUMMARY:

The Space and Naval Warfare Systems (Spawar) uses autonomous robots for a wide variety of military applications.  In certain cases, these robots can be used to surveillance potentially dangerous areas of enemy territory and in other cases they can be equipped with weapons to substitute live soldiers.  With emerging technologies, the costs of these robots increase.  Military entities dealing with budget cuts are constantly searching for less expensive solutions and rely on engineering design to alleviate the high costs.  Spawar is interested in using an open sourced, Segway RMP 50 robot platform for such purposes.  The project objective was to remove the road wheels currently attached to the RMP 50, and design a mechanical track assembly which could be installed with minimal work.  This track assembly would provide reliable motion, be robust, and able to operate in rugged terrain environments such as mud, sand, and snow.  Another primary objective was to have the completed assembly carry a 100 lb. payload at an upward 45° angle.  Design of the system required creative ingenuity due to having a $6000 dollar budget, and  tight schedule constraints, essentially three months to design, construct, and providing intermitted presentations throughout the project.  Initial calculations were conducted to verify if the RMP 50 could provide enough torque to drive the system through the 45° incline.  A gear ratio of 1:1 was sufficient to handle the task.  The next objective was to integrate into the design the lightest material which still could provide a safety factor of 2 to handle the various applied loads to the system.  Aluminum 6061 was chosen for the supportive frame due to ease of machining of the material, and its light weight compared to other alloys such as steel.  Tensioning of the tracked system was necessary to avoid derailment of the track from the drive sprockets, and the roller chain from the drive chain sprocket.  After many iterations, a track tensioner was designed to apply tension using a bars attached to gas compression springs, and an idler wheel.  After the desired tension is applied, a locking mechanism fixes the tensioner.  A linear COTS(commercial off the shelf) tensioner was purchased to tension the roller chain of the drive system.  Unique designs were used to incorporate unusual fixed parameters such hexagonal bore track sprockets, and non standard hub adapters specific to the RMP 50.  This required incorporation of special machining and welding to accommodate these issues.  Testing of the completed assembly required special programming  which used the Ubunto computer language.