Bot Body Basics

Building Robot Bodies -- the Basics ¶ 

The original content for this page was an except from Chapter 5 of Gordon McComb's Robot Builder's Bonanza, 4th Edition. The copy has been changed since then.

So we know robots are a clever combination of mechanics and electronics. The mechanical part constitutes the "body" of the robot-call it a frame, a base, a platform, it's all the same.

Constructing a robot body comprises three straightforward tasks:

• Choose the material (you can mix and match).
• As needed, cut it to shape, and drill holes for mounting parts.
• Put it all together.

In this article, you'll be introduced to the principal materials used in constructing amateur robots. Also see the piece on the basic tools you need to form the material into the size and shape you want.

RoboTip:

Expensive, fancy tools are not required to complete most hobby robot projects. All you need are basic shop tools-you probably already have them in your garage, or you can borrow them from a friend or relative.

Picking the Right Construction Material

Your robots can be constructed out of wood, plastic, metal, even heavy-duty cardboard, or foam. But which to choose?

That all depends on the design of the robot: how big and heavy it is and what you intend to use it for. It can be as simple as a piece of wood. Or it can be a fancy amalgam of high-tech plastic covering a body of extruded aluminum and steel support brackets.

Your budget and construction skills, plus the availability of heavier-duty tools, will also influence your choice of materials. It takes a lot less sweat to use a 1/4" sheet of plywood or 1/8" plastic than it does to cut or drill aluminum and steel. And it's easier still to make a robot using foamboard you purchase at the craft store.

• Wood. Wood is easy to work with, can be sanded and sawed to any shape, doesn't conduct electricity (avoids short circuits) unless wet, and is available everywhere.

• Plastic. Pound for pound, plastic has more strength than many metals, yet is easier to work with. You can cut it, shape it, drill it, even glue it. Some unique plastics might be harder to get unless you live near a well-stocked plastics specialty store; mail order is a great alternative.

• Metal. And by metal we're talking mostly aluminum here, though copper and brass sheets and tubes are commonly available in hobby stores. All three are great for building robots.

• Lightweight composite materials. Art supply stores stock what's known as "foamboard," also called Foam Core, a popular brand. Foamboard is a sandwich of paper or plastic glued to both sides of a layer of densely compressed foam. Heavy-duty cardboard and lightweight plastic board used to make signs are also contenders.

Let's take a closer look at these. Even more details on these construction materials are found in later chapters.

Wood ¶ 

If Noah can build an ark out of wood, it's probably good enough for robots. Wood is reasonably inexpensive and can be worked using ordinary tools.

Avoid soft "plank" woods, like pine and fir; and instead select a hardwood plywood designed for model building. Though more expensive-about $7 to $10 for a 12" x 12" square-this material is superior for robot building. These plywoods are less likely to warp, crack, or fleck. They're available at hobby and craft stores.

Plastic ¶ 

There are literally thousands of plastics, but don't let that alarm you. For robotics, there are just a small handful of plastic materials that are both affordable and readily available. These same plastics also tend to be the ones most easily worked using standard shop tools.

• Acrylic is used primarily for decorative or functional applications, such as picture frames or salad bowls. It's usually clear but also comes in solid and translucent colors. You have to be careful of cracking caused by too much weight.

• Polycarbonate is similar in looks to acrylic but is considerably stronger. This plastic is a common substitute for window glass; because of its increased density, it's much harder to work with and is more expensive.

• A special type of PVC that comes in sheets, called expanded PVC, is ideal for making small and medium-size robots. An example robot made with PVC is shown in Figure 5-1. It's easier to work with than either acrylic or polycarbonate plastic.

• Specialty plastics. And last, there are a couple of plastics that are a bit harder to find (you get them at specialty plastics outlets; check your local Yellow Pages), but they offer certain advantages. These include ABS, acetal resin, and nylon.

Metal ¶ 

The archetypal material for robots is metal. It's among the most expensive materials for robots-in terms of both cost and weight-and is harder to work unless you have the proper tools and skills. That said, metal is a must if your robot will be bashing other robots to death in combat or if it's made for rugged outdoor use.

For robots, aluminum and steel are the most common metals. Aluminum is a softer metal, so it's easier to work with. But steel is several times stronger, and it's easier to weld if you're planning on building a large robot.

There are two general approaches to metal construction in robots, shown in Figure 5-2:

• A flat frame provides the base of the robot and lends it support. A box-shaped frame is just what its name implies: a 3D box with six faces. It's well suited for larger robots or those that require extra support for heavy components.

• A shaped base is a piece of metal cut in the shape of the robot. The metal must be rigid enough to support the weight of the motors, batteries, and other parts without undue bending or flexing. Some very capable robots are basically a piece of sheet metal on wheels, with a laptop PC resting on top.

Robots made of wood, plastic, or other materials may nevertheless use metal (typically aluminum) in their construction. Common metal parts include brackets, to hold pieces together, and nuts, screws, and other fasteners.

Lightweight Composites ¶ 

Not every robot needs to withstand a winter sandstorm on Mars. A technique known as rapid prototyping uses lightweight materials that are cut with basic hand tools, like knives and hobby saws, and awls or even nails for punching out holes. With rapid prototyping you can make a robot in less time, for less money. It's a good way to test out a design before you build it using stronger materials.

Rapid prototyping is such an important concept in amateur robot building that the subject gets its own chapter:

• Heavy-duty cardboard is surprisingly strong, yet easy to cut and drill. This stuff is heavier (and thicker) than your average cardboard box, but the concept is the same. It's made by sandwiching paper over a corrugated middle. Heavy automotive parts are often shipped in heavy-duty cardboard boxes, and you can buy the cardboard new.

• Laminated composite materials include foamboard, which is a piece of plastic foam inside two sheets of heavy paper. Other kinds of laminated composite sheets may use a combination of wood, paper, plastic, even thin metal.

• Corrugated plastic is a favorite among sign makers. They use sheets of it to make lightweight (and very affordable) indoor and outdoor signs. These look like cardboard, as in Figure 5-3, but they're entirely made of plastic.

In Review: Selecting the Right Material

Let's review the four main construction materials for building robots and compare their good and bad sides.

Material

Wood

PRO: Universally available; reasonably low cost; easy to work with using ordinary shop tools; hardwood plywoods (recommended wood for most robot bases) very sturdy and strong

CON: Not as strong as plastic or metal; can warp with moisture (should be painted or sealed); cracks and splinters under stress

Plastic

PRO: Strong and durable; comes in many forms, including sheets and extruded shapes; several common types of sheet plastic (acrylic, polycarbonate) readily available at hardware and home improvement stores; other types can be purchased via mail order

CON: Melts or sags at higher temperatures; some types of plastic (e.g., acrylic) can crack or splinter with impact; PVC and many other plastics are not dimensionally stable under stress so they can bend out of shape; exotic types hard to find; better plastics are expensive; some specialty tools required for professional-looking cuts and holes

Metal

PRO: Very strong; aluminum available in a variety of convenient shapes (sheet, extruded shapes); dimensionally stable even at higher loads and heats

CON: Heaviest of all materials; requires power tools and sharp saws/bits for proper construction; harder to work with (requires more skill); can be expensive

Composites

PRO: Lightweight and very easy to cut and drill using ordinary tools; allow rapid prototyping to test new designs and ideas; very inexpensive; come in many thicknesses

CON: Not as strong as other materials; composites made with paper or wood can be damaged by moisture; some kinds may not be as easy to find except at specialty stores or online

Remember! There is no single "ideal" material for constructing robots. Each project requires a review of:

The robot itself, especially its physical attributes-large, small, heavy, light.

The tasks the robot is expected to do. Robots that do not perform heavy work, such as lifting objects or smashing into other robots, do not require heavy-duty materials.

Your budget. Everyone has a limit on what he or she can spend on robot materials. Tight budgets call for the least expensive materials.

Your construction skills. Robots made from wood, plastic, and composites are easier to build than metal ones.

Your tools. Building robots with metal or thick plastics require heavier-duty tools than when building wood or thick plastic bots.

Robots from "Found" Parts

Before leaving the subject of robot materials, I want to touch on a special construction style known as found parts. Here's a quick overview.

With found parts you adapt some ready-made manufactured product that you find (in a store, in your house, on the side of the road) to serve as the base of your robot. Inexpensive housewares, hardware items, and toys can be used in various creative ways to make robot building faster and more economical. Examples of found parts include old CDs and DVDs and plastic container boxes.

For more on the tools you'll need for bot body building, check out this brief rundown.