Building a Robot in Steps
My nephew Krishna always go to Robogames with my son and I, along with his family. Krishna is tweleve and he really loves to drive radio controlled robots. This year for his birthday I promised I would help him make a combat robot he could drive in the Jr. Division. That's a one pound class (aka "ant-weight") they have at Robogames. My sister and her family live in San Francisco, so they don't have a great set up for building things. We figured we would try to make something whenever he got a chance to visit. That turned out to be last weekend, the weekend after his birthday. I wasn't really sure what kind of robot he wanted to make so to get ready I ordered a an ant-weight starter kit from the Robot Marketplace.
My sister came down Friday night from San Francisco and an Antweight Robot Kit from the Robot Marketplace arrived via UPS the same evening. I ordered the kit about a week and a half ahead, because I wasn't sure what Krishna wanted to build. I figured with the kit I had all the components I needed. And since I have a lot of motors, batteries and electronics around I figured I could improvise the rest. I thought I would get the kit with more time to spare, but it turned out that the standard motor of the Antweight kit-- which is a really good motor-- comes from Japan. With the Tsunami, it wasn't coming soon. I talked to them on the phone and they offered to substitute another set of motors. That allowed me to get it in time for Krishna's visit.
We ended up making the robot in about a day and a half. It would have been a day but we ended up making some changes that broke some stuff, that the extra half day went to fixing. I want to show what we did-- and how we did it-- not because it was so great but to show how possible it is to do this. We didn't have any tools that are different from what many people have in their garage or basement. We don't really have any special skill-- I am not engineer, a draftsman or a machinist. I'm kind of terrible at all those things but still I can have a good time making something like this. If you are reading this, you probably can too.
Conceptualization
When Krishna showed up we tried to draw the kind of robot he was thinking about making. I wanted to get Krishna to draw something because a simple hand drawing is a much better place to start then a description or components. There is a great guide on how to build an antweight robot on the forum for robot marketplace that among other things, discusses the trade offs of various robot designs.
He made a sketch of a wedge robot, with a vertical blade. At that point we had a shape in mind and the parts that needed to go into the robot. We could begin drawing shapes to make the shell.
Our plan was to make the robot by cutting and bending thin aluminum sheet. When you work with aluminum that way it is not that different then paper or cardboard, just stronger. In fact, my plan was to make a design in a simple cad program to use a pattern for cutting the aluminium. That pattern could be printed out on paper, cut out, and folded to make a mock-up of the robot shell.
Here you can see one of the patterns printed out.
Here is a version of it cut and folded into a paper prototype.
In this way we were able to try different shapes and see how the wheels, motor and battery fit within them. Things that were out of alignment or sized improperly were easy to see. The shape and layout changed a lot during this process and a lot of mistakes were avoided.
Manufacture
Once we had a paper pattern that we liked, I added dotted lines as a guide for a jig saw cut. Because I am using a hand jig saw, all the cuts have to be straight. There are also limitations on the type of shapes I can make. For example, it is really hard to cut a shape inside a pattern unless that shape is very large, because I would have to start with drill holes and I would need a lot of room to maneuver the saw blade. If you are working with tools as simple as this you have to think about the limitations in the design phase.
With the saw lines added, Krishna covered the back of the pattern with rubber cement and he pasted it to the aluminum sheet. Then we clamped the sheet to the worktable and put on safety glasses. Since Krishna isn't familiar with using the saw, I did most of the cutting for him to be safe. I let him try it a little.
After we had cut the pattern we took the piece and drilled holes into it where the screws were supposed to go. Screws were what we were using to hold the motors in position and attach the top to the bottom, so the holes had to be placed accurately. I used a little ¼ HP drill press I have in my garage, but on aluminum as light we were using (0.025") a rechargeable drill would also have worked.
In order to get the holes in the right place we drilled them while the pattern was still flat. After the holes were drilled we bent the sides along the dotted line of the pattern. Three sides of the top were bent at a right angle. The front side had a more gentle angle to create a slope. Of all the bad construction techniques I am using, the way I bend metal is probably among the worst. You can probably do a good job of bending aluminum by heating it and putting into a press brake. But I don't really know how to do that and I don't have the equipment. So what I do is just clamp one side to a steel plate and bend the other side with some groove joint pliers. I don't even have a metal a set of metal bending pliers. The results are pretty ugly, but serviceable. The edges and the sides are even, and the metal gets scuffed where the pliers clamp on.