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Rock'em Sock'em Robots: Part 3
2024-03-15 | By Zach Hipps
License: General Public License
I'm making a version of the classic toy Rock ‘Em, Sock ‘Em Robots, but my version is life-sized! I'm using an air compressor to drive pneumatic cylinders for the punching arms. I'm also including some electronics that will detect the punches and keep track of who's winning. This is the third part of this series. I need to build a second robot, so I've 3D printed all of the pieces I used on the first robot, and I've cut all of the aluminum extrusion to build that second robot. Once I build the blue robot, I need to design a skeletal structure so that I can build out the torso of these robots, and then I think I'm going to try to wrap the skeletal structure in a thin layer of ABS plastic.
When I built the red robot, I needed to add a little bit more rigidity to the setup. So, I designed and prototyped a gusset piece out of wood, and it worked, but I think I want to make this out of metal. Since I don't have a way to do that here in my shop, I'm going to be using an online metal-cutting service. I added a little tab and I had them bend it to a 90-degree angle and that will make this part a lot stronger.
Now that I've got the aluminum gusset installed, I can start building the frame for the blue robot. But I didn’t get very far before I realized that I put the arms on backward! I was using the red robot as a reference to make sure I had all the parts in the right spot, and I put the arms facing the same direction as the red robot! These two robots are meant to have a boxing match, not start a conga line! I think I can take two screws off and lift it off and flip it around. Easy fix; now it's facing the right way.
I struggled to know exactly how far apart these robots needed to be spaced. I know that the chest pieces are probably going to stick out a little bit, and I want the punches to land in the middle of the chest, but I didn't have exact measurements, so I had to guesstimate. I may end up having to shift them a little bit either further apart or closer together, depending on how far they reach. I'll cross that bridge when I get there because there's no way of knowing at this point.
One thing that I noticed while assembling the blue robot's frame is that the shoulders and neck joints are a little bit flimsy, and the same problem existed on the red one. To fix that, I designed a bracket and installed it on the back of both robots. That made it a lot more rigid than it was before, and I think that it's going to hold up to those punches much better than what I had before.
The last thing that I need to do to get the blue robot in the same state as the red one is to route all of the pneumatic tubes. There are three pneumatic cylinders, and each cylinder gets two tubes. All of those tubes are routed to a central manifold. The central manifold has all of the solenoid valves, which control all of the movements of both robots.
I'm so relieved to have both robots in the same state. It's taken a lot to get here. Next on the list is to create the chest pieces. I went back and forth on how I was going to approach this. It's sort of a complex shape if you look at the original toy. There are a lot of contours, and it's something that I would need to sculpt out of foam or something, which is way outside of my comfort zone. I'm much more comfortable designing things that have square and predictable geometries. My first thought was to get a big sheet of rigid foam insulation, cut it into layers, stack those on top of each other, and sculpt out this shape. What I ended up doing was designing some skeleton pieces that would go inside and attach to the frame. Then I'm going to get a sheet of ABS plastic and wrap that on the outside like a skin. If you look at the 3D model, you'll see that I've designed these flat plates that slide up and down onto that center frame. I used the honeycomb pattern cut out to save weight. If you look closer at these plates, you can see that I have some bent metal tabs. This is how I'm going to attach the flexible ABS sheet to the skeleton pieces.
The skeleton pieces arrived, and I test-fit them onto the frame of the robot. They have a pretty tight tolerance. I have to twist them a little to make them easier to slide on. These skeleton pieces don't bolt to the frame itself, but they do bolt to each other, and the tolerance is tight enough that I think that should be rigid enough. If it turns out that they need to be bolted to the frame, I'll figure out some way to do that. I'm going to go ahead and cut some short aluminum extrusion to bolt these skeleton pieces together. I've got a big sheet of ABS plastic, and the idea is to attach full sheets to the robot, wrap the skin around it, and cut holes where the neck needs to go. When I tried that, however, the results were disastrous. It doesn’t look right, and things aren’t wrapping around the right way. When I look at these, it's pretty obvious why… These skeleton plates are made up of two different sizes. The inner one is a much larger diameter than the outer one. In order to wrap a piece of skin around, it needs to be a sort of conical shape. Of course, the first thing I do is measure the circumference of the smaller part and then the circumference of the larger part, and I enter that into the cone formula to create a flat pattern template. When I wrap this together, it sort of makes a truncated cone, but the problem is that the skeleton plates are not perfect circles, so this pattern did not work at all.
I decided to go with an iterative process. I get some large pieces of paper and begin taping them to this shape and cut away the excess, and I slowly refine the pattern over and over from shape to shape until I get something that is pretty close. Then, I used the pattern and cut a piece out of the ABS sheet, and I was surprised at how well it fits. There are some minor adjustments that I need to make, so I wrote down some notes before cutting out the final piece. Fortunately, the left and the right-hand sides are just mirror images of each other, so I can flip the template upside down and cut the other pieces out of the plastic. I used a bandsaw to cut these pieces out, and now I have all four pieces that are ready to attach to the skeleton pieces.
The next piece that I need to make is the front breastplate piece, and it's got these ridges that go back and forth, kind of like a mountain top. One of the reasons I chose to use ABS plastic is because it's a thermoplastic. So theoretically, I should be able to heat this plastic and make it conform to these contours, and to do that, I thought I would just use a typical heat gun. It has plenty of power to heat a piece of plastic sheet, so I tried it on a little test piece, and it works pretty well. I went ahead and started on the full-size piece, but it didn't work as well as I had hoped. It started to warp a little bit. I remembered that I had watched a video about bending plastic from David Picciuto on his YouTube channel “Make Something.” I'm going to use one of the techniques that I learned from that video. I bought a cheap single-burner hot plate from Walmart and removed the heating element and straightened it out. A heating element like this solves the problem I had earlier with the heat gun, which just blasts too much heat and it's not very focused. The heating element, on the other hand, is going to apply heat just where I need it and not anywhere else, and that's going to be the key to success.
I stepped away from this project for about 6 weeks while I worked on other projects. I ran into so many problems trying to bend this plastic using the heating element from the hot plate, and it just turned out horrible. It doesn't look good. It's not what I was going after. The plastic is kind of wavy. There's a lot of extra bumps in here that I don't like the look of, so I think I need to recognize when it's time to throw in the towel and move in a different direction. I think this process is really interesting and I think it would work with a single bend but trying to get a series of bends to line up exactly where they needed to, it just didn't work out. At this point, I think I'm going to backtrack and call this a failure and remove all of the ABS plastic. Instead, I'll design some shell pieces that I can print using my 3D printer. I printed all of the parts on the 3D printer, and they look awesome. I can already tell that this is going to turn out way better than the sheets of ABS plastic. The only downside is that this is a lot of surface area to cover, so I have to break the prints into smaller pieces to fit onto the printer’s bed. It took so much trial and error to get to this point, and honestly, it was mostly “error,” but I think it was worth the effort. Stay tuned for part 4 where I finish them and do some fighting!
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