Engineering Adventures: Final Project--Building the Frame!

Although the inner box itself was complete, there was still the pressing question of how to stabilize the linear gear columns it would be ascending. Initially, we were going to attach the columns directly to our outer box, and stuff tiny pieces of styrofoam between the columns and the sides of the box if necessary to ensure a tight fit. Although this plan allowed for a small amount of error, the box still had to be sized very precisely. We decided to build our box out of wood on the laser printer, and attach the sides to each other with sliding groves.

Columns attached directly to box

Here is a preliminary sketch of the box:

The idea having to size the box so precisely was very worrying, and I began doubting whether it was a plausible solution. But then Amon came to our rescue by suggesting that instead of the box, we make a frame to hold the columns in place. By doing so, the entire structure would be self-contained, and the outer box could become purely aesthetic. I was very happy with this plan, because it seemed like it would be far more successful than the wooden box, and would also allow much easier access to all of our mechanisms.

We decided that the frame, like the rest of the box, would be press-fit together. The press-fit dimensions we had used for the large stabilization arch could be reused for the frame, since it too required a very tight press-fit. (I had made the press-fit that held the inner box together slightly looser, in case it needed to be taken apart.) I wasn't sure how to securely attach the individual linear gear posts to the press-fit frame, but Lyn discovered that the way our gear posts had been built was very conducive to attaching to the frame (perhaps we had built them like that subconciously).

Room for Lego rod in the middle hole!

Lyn pointed out that we could slip a Lego rod though both the post's center hole and a hole in the Delrin frame, and attach it with little Lego stabilizers on either side.

The press-fit aspect of the frame was already dimensioned, but the length of the pieces and the placement of the holes was slightly difficult to measure. Lengthwise, the columns had to be spaced so that the gear trains would just fit--if they were just slightly too far apart, the round gears would not have enough grip on the linear gears to be able to climb. It took 3 Delrin iterations to get the size exactly right--in the first iteration, the holes were slightly too far apart. I also realized that the press fit protrusions/holes were backwards--since all of the pressure would be pushing out toward the shorter pieces, it would be better for them to have the protrusions, and the long side pieces have the holes. In the second iteration, the length of the long pieces was still slightly too long. The width of the frame was too long as well--the gears did not fit on their tracks.

Here is the process:

Press fit dimensions


2nd iteration--holes in the wrong place and slightly too long

Success!

Close up of success

We decided to print out a second frame, since just one didn't give us the support we needed. Throughout the iterations for the first frame, the laser printer had been giving us some trouble. Because some of the pieces were so long, there were some problems with warping that resulted in some of the press-fit dimensions being off. We had been forced to reprint some of the frame pieces because of this problem. Lyn suggested that instead of printing out multiple pieces at the same time, I print out just one at a time, and refocus the laser in between. This trick, along with some heavy tools to reduce warping, worked like a charm.

Slightly ghetto laser printing


Two frames

Fully assembled frame!

We also created a platform to fit between the two scissor mechanisms, for the creep's head to rest on. The top scissor pieces had to be able to open and close slightly, so we needed to create a top that would allow them to do so. Lyn gave us another great idea for this piece, and after some press-fit and delrin magic, this is what we produced: