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The advanced Rover uses a microcontroller, specifically the BASIC Stamp 2, to build a self-contained, autonomous robot. With this version, you program the microcontroller for what you want Rover to do. This smart Rover uses specialized motors that you have to take apart and modify. You can read about how to do that in the section “Modifying the R/C servo motors” later in this chapter.
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Preparing to Build the 'Bot
Before you can drill your first hole or fasten your first nut, you need to lay out the design of your robot, acquire all the materials, and sort out all the parts you’re going to use.
First, get yourself a template
Although you use a circuit schematic for simpler projects, such as those in Chapter 14, you graduate to something called a cutting and drilling template for making a robot. This template serves as the layout for your robot. Draw the layout to scale — that is, the same size and shape that you want the finished pieces to be — on a piece of paper.
Figure 15-1 shows the cutting and drilling template for Rover, a two-deck tabletop robot. The dimensions used in this template are measured in inches.
The template includes the two body pieces, which we call decks, like the decks of a ship. There’s a bottom deck and a top deck. You attach the motors and wheels to the bottom deck. The top deck is left free for future enhancements (such as adding the microcontroller brains, detailed later in this chapter).
A cutting and drilling template for Rover the Robot.
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328 Part V: A Plethora of Projects
The two decks are attached together using risers, which are long pieces of metal that are threaded to attach to machine screws. Read more about risers in the section “Getting to know the pieces,” later in the chapter.
Gathering your materials
You need only rudimentary construction skills to build Rover using a variety of materials for the deck pieces. These are the easiest to work with:
^-inch hardwood plywood: A good choice is 5-ply “aircraft plywood,” available at any hobby store.
K-inch rigid expanded PVC sheet: Commonly referred to as PVCX,
Sintra, or Komatex.
JS-inch acrylic plastic: You can buy this plastic at most plastics specialty stores (you can find these by looking up “Plastics” in the Yellow Pages) and at many home improvement stores.
Our favorite construction material for a robot body is rigid expanded PVC because it’s strong but lightweight, relatively cheap, and easy to cut and drill. You can sand it like wood, and, in fact, residential and commercial builders often use it as a wood substitute. Rigid expanded PVC is great stuff, but hardware and home improvement stores don’t stock it. Look for it at specialty plastics outlets and sign-making shops. We provide some mail-order sources of small pieces in the Appendix.
Our least favorite construction material is acrylic plastic, for a number of reasons:
If you’re not careful, acrylic can shatter when you’re drilling or cutting it. Acrylic dulls tools rather quickly.
Acrylic generates a ton of static electricity, which, as we point out in Chapter 2, can damage sensitive electronics components.
Although acrylic plastic may not be the ideal material, you can use it in a pinch if you have nothing else suitable around.
Getting to know the pieces
You construct Rover’s body with two pieces: a bottom deck and a top deck. The bottom deck measures 6 by 6)2 inches, and you will cut out wells in it for the tires. The top deck measures 6 by 42 inches, and it gives you enough room to mount all kinds of electronics and other goodies on it.
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Getting savvy about machine screw sizes
In the United States and a few other places in the world, folks express machine screw size as two sets of numbers, such as 6-32. Here's what those numbers mean:
The first number: This number represents the diameter of the screw. The smaller this number, the smaller the screw. (Screws that are J'4-inch or larger in diameter drop the number and just use the actual size, such as %- or %-inch.)
The second number: This number represents the threads per inch of the screw.
So, a 6-32 machine screw has a diameter defined as #6 (you don't have to worry about what that translates to, just get the one your project calls for or the one that fits), with 32 threads per inch. Other common screw sizes are 4-40, 8-32, and 10-24. In addition to the screw size, you need to know the length of the screw, such as J2- or %-inch, as well as the type of head on the screw. A screw you often use in building small robots has a round head.
You use a similar numbering scheme with metric screws, but the sizes and threads are expressed in millimeters rather than inches.
The drive motors for Rover, which propel the robot across the floor, are Tamiya worm gear motors (model number 72004). You can buy these parts at Tower Hobbies and many other online resources; check the Appendix for a list of some sources you can try. You buy the motor as a kit; you build it into a compact, self-contained housing. The motor comes with a shaft that you can attach to numerous styles of wheels.