Build Me A Body

by Karl Lunt


Time to build another 'bot. And one of the first questions to address is: How will I build the frame?

Some of my past choices for frame materials qualify as "Nice try." I have used, and abandoned, plywood, aircraft-grade steel parts, and thick acrylic sheet. The reason was the same in all cases; I couldn't do fine machining on the frame material.

Note that I don't have what you call precision tools with which to work. I've got your basic Black and Decker 1/4" electric hand drill and your B&D electric hand jig-saw. I also have a cardboard box that makes a fine drill stand.

And I have an immovable tool chest crammed with hand tools, most of which I can use, but often not in the usual way, if you get my drift.

I do have an Ernst-special drill press set up in the garage. But to use it, I have to first open the garage, then back out the truck. In the winter, this causes the temperature to immediately plunge from a normal of 32 degrees to 28 degrees, a level I find too uncomfortable for delicate work.

But the drill press is perfectly useable in other seasons, and explains the striking differences between my summer and winter robots. The winter robots have holes in them that are misplaced and misaligned, since they were drilled by hand. The summer robots have holes that are perfectly aligned...

But I have discovered that the right material can significantly hide the flaws of my construction abilities. I currently use one of four types of materials.

Sintra plastic is, admittedly, not easy to get. I once almost emptied the scrap bins of Laird Plastics, in downtown Seattle, of all the 1/4th inch Sintra that they had. The price was only $1 a pound, or suchlike, and I bought enough to build several years of robots.

Also at Laird, I found some industrial-design grade foamcore. This is sturdy, light, and pretty cheap. I nearly filled the truck for about $10. It is an ideal material for building photovores or low-weight line followers.

This foamcore has a very tough outer skin, much stronger than the type of foamcore you find in art shops. You really need a saw to cut it properly, so you can imagine what it looks like when I finish hacking on it with my tree-trimming knife.

When I don't feel like driving to downtown Seattle for robot material, I always turn to Fred Meyer's. Every Freddy's has a great robot frame section, laughably labeled Garden Shop.

I built CBE-1, my line-following robot, from a plastic drip pan for a flower pot. The round pan measures 1 foot across, and has a lip about two inches high on its circumference. Easy to drill, flexible yet rugged, and with a low-tech, dirt-brown color scheme.

I have also used smaller flower pot drip pans as wheels. You can get these pans down to four inches in diameter, and their smooth surface makes them easy to drill and mount onto motor shafts.

And the price for these plastic parts, especially during the off-season, is quite low, especially when you factor in time and frustration. I can buy a really nice robot frame from Freddy's for about $6. Trying to build a frame from scratch, starting with a sheet of Sintra, would probably run $20 just for the beer.

But I have the most fun building frames from blank copper-clad and brass rod and tubing. You can get the copper-clad from Vetco or any of the large mail-order houses. Be sure to use double-sided board; the fiberglass stuff is very sturdy and works well.

Hobby stores and hardware stores carry the brass rod and tubing, usually in 2- or 3-foot lengths. I usually load up on 1/16th- and 3/32nd-inch brass rod, with an occasional length of 1/8th-inch if I decide to build a really substantial frame.

Most of the tubing I use is 5/16th-inch OD or less. This comes in handy if I need to build hinges or pivots, or other moving or sliding elements. Be sure to get one of those clamp-and-twist tubing cutters also. This does a super job of cutting the brass tubing, far better than using a hacksaw. (Go ahead, guess how I know.)

Be on the lookout for brass spacers and nuts, in the #4 and #6 sizes. You can solder these babies directly onto the brass members of your robot frame, then bolt circuit boards or other doobers directly to them. Vetco and Radar Electric usually have a supply of brass hardware.

And many large hardware stores, such as McClendon's in Marysville, have lots of brass hardware intended for other uses that make great solder-on robot parts. Browse through the screen-door, drawer, and plumbing sections for useful stuff.

Note that you will need a 100- to 140-watt Weller solder gun for this type of soldering. If you try using a little 20-watt solder iron, you will likely end up sticking your iron to the brass frame, and, boy, will you feel foolish! I know I did.

Also get a small tin of acid-free soldering flux paste. You need to smear a little of this on the brass part just before you try soldering to it. As the flux heats, it also cleans the brass so you get a strong mechanical connection.

I use a product called Rubyfluid, available at most hardware stores. The tin measures two inches across, cost about $2, and holds enough flux to build, oh, maybe forty godzillion robots.

This is greasy, smelly, purplish, yucky stuff, guaranteed to spread all over your worktable and nearby surfaces. You bachelors won't have any problems with it.

I usually start building a frame by using straight-cut tin snips to cut out a square-shaped piece of copper-clad. Trim off the more lethal-looking jagged edges before you take this out into public.

Alternatively, you can use a jig-saw with a fine-tooth blade to cut the copper-clad. Note that this creates a loud screaming noise if you try it in a quilting craft room and don't warn your wife in advance.

Swab a little flux paste onto the chosen area of the copper clad, then use the Weller to flow some solder onto the area. Cut the brass rod to length, coat the chosen area with flux, and flow some solder onto it as well.

Next, grab the brass rod with some pliers or Visegrips, place the two soldered areas in contact, and heat the junction with the Weller. After the solder on both pieces has melted and flowed smoothly together, pull the Weller away and release the trigger, then continue holding the brass pieces perfectly still until the solder has solidified. This last step can take five seconds or more.

Use this same technique to add other pieces of brass rod, copper-clad, tubing, or brass hardware to your creation. You will be amazed as the shape evolves before your eyes. Kinda like those crayon drawings your two-year-old made, but in 3D. Try sticking one of these babies on the refrigerator door!

These free-form robot frames can be remarkably sturdy. They will easily hold a set of C-cells, and make great frames for servo-based robots such as Huey or Zippy. You can increase their strength, if necessary, by adding strategically placed sections of brass tubing or copper-clad.

They are also very light, since the frame consists mostly of air and it only has metal where you want it to have metal.

So give these brass 'bot frames a try. I think you'll have fun putting one together, and it certainly won't look much like anyone else's robot. I guarantee that!


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