Building the My First Robot Chassis
The Basics: Cutting things to Size
You don't need special tools or techniques to cut wood or plastic for a robot platform like the RBB-Bot. Basic shop cutting tools suffice: a handsaw, a backsaw, a coping saw.
- When cutting plywood or soft plastics (like expanded PVC), use a wood handsaw or backsaw with medium teeth, or a motorized table saw. You'll get the straightest cuts with the table saw.
- When cutting hard plastics (like acrylic), use a saw with fine teeth, or a motorized scroll saw. You can use a table saw if you outfit it with a blade suitable for cutting plastic.
Make sure the blade is made for cutting the material. Wood blades have coarser teeth than blades for plastic. If using a power saw, use a plywood-paneling or crosscut blade. These have more teeth per inch and produce a smoother cut.
The easiest shape of all is square, and that's what you'll begin with, even if you plan on a more elaborate base. After all, what's a circle than a square with lots and lots of corners!
Start with a square or rectangle that's the size of the finished robot base. If you have them, you can use power tools to make short work out of cutting the material.
Problem is, square is not the ideal shape for a robot base, because the corners can snag on things when the bot is driving around your living room.
You can readily turn the square into an octagon, hexagon, or pentagon simply by lopping off the corners.
More elaborate shapes don't take that much longer to produce—just a few minutes per cut, and you'll make a better robot. To create an octagon (8-sided) base, cut the corners off at 45°.
After cutting, use a medium or fine grit sandpaper to smooth the edges.
Cutting and Drilling the Base and Control Panel
The first version of the RBB-Bot is composed of two major pieces: the base of the robot, and a control panel that you hold in your hands -- in later variations of the RBB-Bot, this control panel will become a second expansion deck, mounted directly on the robot.
Both are shown here. I call this Phase 1 of the RBB-Bot. Other phases, described in future articles in this series, use the same basic hardware parts, but in different configurations.
Figures 1 and 2 show the cutting and drilling guides for the base and control panel.
[Figure 1. Cutting and drilling layout for the RBB-Bot base. Use 1/4" thick wood or plastic.]
[Figure 2. Cutting and drilling layout for the RBB-Bot control panel. Use 1/8" wood, plastic, or picture frame mat board.]
Construct the base out of 1/4" thick material, either 1/4" aircraft-grade plywood, or 1/4" (6mm) expanded PVC plastic. You can buy the plywood at most any hobby or well-stocked craft store; get the expanded PVC from a nearby sign-making shop or plastics distributor.
Cut the base from a 6" square piece of material. First cut the base to its 6" square size, then remove the four corners as indicated. Don't worry about getting the cuts absolutely perfect. A fraction of an inch here or there won't matter.
Construct the control panel from 1/8" plywood, acrylic plastic, or picture frame mat board. I used 1/8" acrylic plastic purchased from the nearby home improvement store. For a better look and feel, I used a small belt sander to round off the four corners. If you don't have a belt sander handy, place a sheet of sandpaper on the workbench, and vigorously rub the corners of the plastic against it.
(If you don't feel like constructing the base or control panel, a kit of mechanical parts consisting of precut and predrilled base and control board and all assembly hardware is available from Budget Robotics. See the Sources box.)
Use an electric drill or drill press to make the holes as shown. The sizes of drill bits to use are indicated in the illustrations. The exact location of the holes aren't super-important, except for the four near the center line of the base. These are for mounting the two motors. Measure and drill these very carefully, as misplacement or misalignment of the holes can have a negative effect on the operation of your robot.