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Featured Project
"George" is an autonomous rover-type robot. He has three wheels: two driven and one support caster. The George platform is stable, adaptable, and easy to build. After creating the basic frame described below, you can add a computer, motor driver IC, and sensors as shown in the Projects section.
The George Platform
What you need:
(1) Length of Aluminum angle iron
(1) Support caster (see below for specs)
(2) 12vdc or 24vdc geared drive motors (see below for specs)
(2) 6" Lawn mower wheels
Various bolts, nuts, screws, bushings (see below)
Cutting the Metal
The metal you want for George's frame is lightweight aluminum angle iron, like the stuff pictured below. I can be found and most hardware or building supply stores. Most pieces come in lengths of about 5 of 6 feet. Buy at least 5 feet. It doesn't have to be exactly like the stuff used in the prototype George; if it looks basically the same, it should work. Just make sure it is bent at a right angle, lightweight (but still relatively strong), and easy to cut.
You'll need to cut (2) 12 in. long pieces and (4) 13 in. long pieces. Use a hacksaw or band saw with a vice to cut the pieces; make the cuts as straight as possible! Now, take 2 of the 12" pieces and 2 of the 13" pieces, setting aside the other two 13" pieces. Without bolting them, arrange them into a rectangle with their corners overlapping where needed. It should look something like this:
Now, if your metal has pre-made holes, your job is a little easier. If not, use a slower-speed drill or drill press to drill four holes (I'm assuming you know how to drill metal). Put the holes where the X's are in the illustration above: one on each part that overlaps. Use bolts, washers, and nuts of whatever size the holes are to secure the rectangle together. Make sure they're snug. The photo below gives you the idea.
You should now have a basic rectangular frame, bolted together at the corners. Now remember those two extra 13" pieces of metal? They belong in the center of the frame. But first, you need the support caster.
Support Caster
The caster needed must be free-spinning, and tough yet lightweight. The prototype used a ball bearing caster about 4" high (that's the whole thing, not just the wheel). Look at the next two pictures:
The two extra pieces of metal are used both to secure the caster and strengthen the frame. Mount them down the center of the frame, the same way as the other pieces. They should be almost right next to each other, but you may have to adjust them to the width of your caster. Mount them and the caster as shown...
You should now have a rectangular frame, with two center beams and a support caster, all bolted together. This is the basic George frame. The following sections will show you how to add motors and drive wheels. Feel free to not follow this plan, though; if you have your own ideas for wheels and motors, use 'em!
Adding Motors
Obviously, George is pretty lifeless without motors. The kind we want are DC gear motors, either 12 or 24 volt. In the prototype George, we used surplus 24v, 140 RPM motors bought from All Electronics for about $12 each. (Check out our Resources section for more good motor sources!)
The motors must be geared to between 40 and 150 RPM; otherwise, they won't be powerful enough. Once you've found good motors, the hard part is mounting them. All motors are different in shape. some are round, others are square, others are just weird. Depending on your motor's shape, you'll need to come up with a good way to mount them securely. Browse your local hardware store for ideas! For now, I'll just show you how we mounted our motors on the prototype George.
Since our motors were round, we used a U-shaped pipe thingy to secure it. A picture's worth a thousand words:
Make sure the motors are mounted close to the front of the robot frame! This ensures that the 'bot will be stable, and also have a good turning radius.
Adding wheels
Motors aren't any good without wheels. George uses two drive wheels. Lawn mower wheels work great; get the 6" ones. Unless, of course, based on your motor mount and caster size, 6" is a bad size. Just try to get the frame level, and remember, bigger wheels mean faster robot. Attaching the wheels to your motor shafts is again a big problem, but not impossible!
You will probably need a reducing bushing to connect your small motor shaft to the big hole in your wheel. You have two options: buy or build. If you can find suitable bushings to buy, do it! you'll save yourself a lot of time. If not, you have to build. You can use wood, plastic, or metal; look around your hardware store again for ideas and help! You can use a set screw to secure everything. Below is a sample idea for making your own bushings.
You now have a robot "George" frame, complete with wheels and motors. It's ready for a remote control, computer brain, and sensors for a fully autonomous robot! Go to the Projects section for plans on adding these things and more!
E-mail the creators of George! Ben DeKraker is the main designer and programmer; Bob Potter is mechanics only. We appreciate your comments or questions!
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