This post will be a fairly brief one – mostly it will go over process of attaching the legs to the main body of R2. As a refresher, the inside skeleton, sometimes referred to as the egg carton, frame of the robot has a thin skin wrapped around it. This skin is much, much too thin to support any real weight or force enacted upon it. So much so that later on I will actually use three layers rather than the standard two, just to make myself feel better about the general integrity of the body.
This is that skeleton from the side – you can see the grooves labled for where the bolts from the legs should go into the frame, with a center hole marked for electrical cables that will eventually run down to the motors in the feet:
At this point the body was a storage bin for other misc. bits and pieces, as well as some of the rolled up templates that had yet to be cut out. Once that was all together I wrapped a piece of plastic entirely around the frame, gluing it with the weld on to each of the exposed edges to ensure it properly held it’s shape.
With this layer on, it looks much nicer – now it’s clearly a trash bin!
I had to use plenty of painters tape to tack down the edges and for some time I applied pressure by hand as well. One thing that I noticed and you can see in the bottom of the picture is that the weld on, since it’s not a normal glue, but rather a solvent has left visible marks where it attached to the frame. Basically, the way it works is it dissolves the plastic, evaporates, and then the two pieces of melted plastic fuse together. It’s excellent insofar as it literally welds the plastic together creating extremely strong bonds, but as you can see in this example here, it also causes the plastic to distort if it’s too thin. Eventually to resolve this I will have to put an extra layer over this one to hide the blemishes.
Something important to note, that you’ve probably never realized, is that R2’s legs don’t attach directly to his body. In the above picture you can see the circular cut out where the legs will go, but what actually attaches there is known as a shoulder hub. This hub attaches on one side to R2 and on the other side to the body. I think the point of this piece in the original R2 was to give some place to distribute the forces incurred while driving and turning that was directly into the body/leg, and thus made him a little more durable. To create these hubs, I needed four circles cut out and glued into two circles each two layers thick per hub.
Each of the hubs then had a series of supporting struts glued to it in order to attach the two of them. This is critical to do well because as previously mentioned there will be a LOT of force applied to this piece. This was a VERY time consuming process, as it required my spending a significant amount of time sanding and trimming edges until they were able to glue the two sides together.
However, despite my best efforts, I still found that many of these pieces were either different heights or not level. So when I glued the opposite side on top of this one many of the joints required I shim them with pieces of scrap in order to create a solid contact. So after something like 6 hours of work sanding, trimming, shimming, and gluing I finally got bother of them together adequately and put the bolts in them to ensure everything lined up, which it mostly did, after a little adjusting to the angle of some of the drilled holes with the dremel.
Once those were together it meant I could attach them to the legs:
This ended up being a SIGNIFICANTLY more difficult task than it should have been. On the other side of the legs we have ribbing just like what was used to attach the two sides of the hubs together, and it turns out due to poor cutting on my part, and even worse drilling the bolts came out too close to the ribs in order to put the bolt on them and therefore I had to spend a lot of time at awkward angles sanding and dremeling and doing whatever I could to get them on. I don’t have a picture of them directly interfering but the below image makes it pretty clear how it could happen. The below picture also shows the strip of skin wrapped around the outside edge of the hubs, this was also a bit of a pain as I had to do a good job sanding the circles to make sure that they were, in fact, circles.
