MSDN Magazine - June 2008 - (Page 70)

that, in theory, it does not matter whether your robot is virtual or physical—the code used to power the robot and receive data from the sensors will be the same. Some of the code that is used in the simulation project can be reused when working with the actual robot. Now, you may have noticed that I said “in theory.” This is because the simulation cannot completely simulate a real-world environment. The simulation cannot account for noise—the stuff you do not expect, such as obstacles being in the wrong location. What the simulation can do is give you a fairly realistic opporFigure 8 Create BoeBot Entity Type [DataContract] public class BoeBot : DifferentialDriveEntity { Port _notifications = new Port (); // Default constructor, used for creating the entity from XML public BoeBot() { } // Custom constructor for building model from hardcoded values. // Used to create entity programmatically public BoeBot(Vector3 initialPos) { MASS = 0.454f; //in kilograms (around 1 pound) // the default settings approximate the BoeBot chassis CHASSIS_DIMENSIONS = new Vector3(0.09f, //meters wide 0.09f, //meters high 0.13f); //meters long FRONT_WHEEL_MASS = 0.01f; CHASSIS_CLEARANCE = 0.015f; FRONT_WHEEL_RADIUS = 0.025f; CASTER_WHEEL_RADIUS = 0.0125f; FRONT_WHEEL_WIDTH = 0.01f; CASTER_WHEEL_WIDTH = 0.008f; FRONT_AXLE_DEPTH_OFFSET = 0.01f; // distance from center of robot base.State.Name = "BoeBot"; base.State.MassDensity.Mass = MASS; base.State.Pose.Position = initialPos; // chassis position BoxShapeProperties motorBaseDesc = new BoxShapeProperties("BoeBot Body", MASS, new Pose(new Vector3( 0, // Use 0 for X axis offset CHASSIS_CLEARANCE + CHASSIS_DIMENSIONS.Y / 2, 0.03f)), // minor offset in the z/depth axis CHASSIS_DIMENSIONS); motorBaseDesc.Material = new MaterialProperties("high friction", 0.0f, 1.0f, 20.0f); motorBaseDesc.Name = "Chassis"; ChassisShape = new BoxShape(motorBaseDesc); // rear wheel is also called the castor CASTER_WHEEL_POSITION = new Vector3(0, // center of chassis CASTER_WHEEL_RADIUS, // distance from ground CHASSIS_DIMENSIONS.Z / 2); // at the rear of the robot RIGHT_FRONT_WHEEL_POSITION = new Vector3( +CHASSIS_DIMENSIONS.X / 2,// left of center FRONT_WHEEL_RADIUS, // distance from ground of axle FRONT_AXLE_DEPTH_OFFSET); // distance from center, on z-axis LEFT_FRONT_WHEEL_POSITION = new Vector3( -CHASSIS_DIMENSIONS.X / 2,// right of center FRONT_WHEEL_RADIUS, // distance from ground of axle FRONT_AXLE_DEPTH_OFFSET); // distance from center, on z-axis MotorTorqueScaling = 30; // specify a default mesh State.Assets.Mesh = "boe-bot.bos"; tunity to experiment with a new robot design or simulate the interaction of multiple robots. This can be very useful in academic environments where resources are limited and the number of students is high. Each entity can be associated with a mesh, which is what makes the entity appear realistic. For example, in the case of the globe, the mesh is what makes the globe entity appear like the planet Earth. Strictly speaking, it is not necessary to associate an entity with a mesh, but in the case of complex entities, such as robots, a mesh object is preferable. Just about any 3D graphical editing tool can be used to create the mesh. For this article, I was fortunate enough to have a colleague, Steve Grand, create a Boe-Bot mesh for me using a 3D package called SoftImage (see softimage.com for more information about this tool). The files associated with this mesh are included with the downloadable .zip file that accompanies this article. To follow along with the article, download the .zip file, extract the files, and copy the contents of the Boe-Bot folder to the /store/media directory associated with your local MSRS installation. SoftImage is capable of exporting the image to the .obj format. Not all packages are capable of doing this. For example, SolidWorks (see solidworks.com) is a 3D package recommended by MSRS on its Channel9 Wiki (go.microsoft.com/fwlink/?LinkId=114031). Unfortunately, SolidWorks is not capable of exporting to the .obj format, so it recommends a tool named Blender (blender.org) to do the actual conversion. Keep this in mind when selecting a graphics package to create your mesh file. The details involved with creating the Boe-Bot mesh are beyond the scope of this article, but you should know that it was created by joining multiple polygon mesh shapes. For example, the metal chassis began as a cube shape that was modified to represent the size and shape of the Boe-Bot. Additional cylinder shapes were then added to represent the wheels. A hierarchy was established to bind the wheels to the chassis and allow the entire object to function as a single shape. The result (as seen in Figure 9) is an image that represents the physical Boe-Bot. Creating a Mesh Convert the Mesh to Binary Format } MSRS offers a command-line tool that is capable of converting an .obj file to an optimized binary file with a .bos file extension. The benefit of this type of file is that it loads more quickly than the .obj file. The command-line tool, called Obj2bos.exe, can be accessed using the command prompt menu item included with the MSRS installation. When working with a mesh it is important to remember that materials are used to color physical objects and each entity can be associated with one or more materials. Therefore, when you create your .obj file, it will likely include additional material files with a .mtl extensions. It may also include image files used to create textures. These files must be copied to the same location as the .obj file before using the mesh conversion tool. The .obj file and all associated files should be placed in the /store/ Robotics Studio 70 msdn magazine http://softimage.com http://solidworks.com http://go.microsoft.com/fwlink/?LinkId=114031 http://blender.org

Table of Contents Feed for the Digital Edition of MSDN Magazine - June 2008

MSDN Magazine - June 2008 Contents Toolbox CLR Inside Out Cutting Edge Patterns In Practice SAAS Concurrency Robotics Form Filler GUI Library Service Station Foundations Windows With C++ Concurrent Affairs Going Places { End Bracket }

MSDN Magazine - June 2008

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