Last year, I built a turning head mechanism for a Bucky skull using a PVC frame. It worked out moderately well, but I had a couple issues with it. For one thing, while PVC pipe is fairly cheap, the connectors are not so cheap, and it took quite a few connectors to build the frame, so the resulting cost of the project was higher than I first anticipated. It wasn't outragious, but it was a factor. Second, the weight of the Bucky skull and the friction of PVC against PVC was enough to make it so that no servo I had could drive the mechanism. I had to go with a more powerful motor, which meant that I lost some control over the motor.
This year, I made an attempt to overcome both of these issues. My plan to deal with the first issue was to use a wood frame and only use PVC for the neck. For the second issue, instead of a Bucky skull, I used a wig head. This means I'll lose the ability to make it talk, but it is a lot lighter, which will make it easier for a servo to push it around. To reduce the friction of PVC on PVC, I am not having the PVC go through another piece of PVC. Instead, I took a very different approach.
The trick then became how to attach the hub to the PVC neck of the figure. What I came up with was to cut a piece of 2"x3" only slightly bigger than round part of what is now the top of the hub. I cut off a couple of the corners to make the piece of wood a little more round. I don't have the tools to do much more than that (I wonder if a hole saw would have worked for that). I drilled a hole through the center using a 7/8" spade bit. This hole served 2 purposes. It was the hole that the 1/2" PVC neck would go in, but it also was where the top of the bolt coming out of the top of the hub would go so that the block of wood would sit flat on the round part of the hub. I used a couple of #4-40 wood screws to attach the hub to the block of wood. The screws fit through the existing holes in the hub (the ones that the spokes originally went through) very nicely without any need to make the holes bigger.
That left only attaching the PVC neck to the block of wood. The 1/2" piece of PVC was slightly loose in the 7/8" hole, but it wasn't too far off. I would have liked to use Gorilla glue so that as it expanded, it would have filled in the gaps, but my Gorilla glue had dried up in the bottle, and I didn't want to buy more for this little project. Instead, I tried some epoxy that I had picked up from Harbor Freight a while back but had never used. At first, I mixed up way too little and didn't have enough to go all the way around, so I had to mix up some more. Once I got enough in there, it seemed to fill in the gaps. While I was holding it while the epoxy set, I made sure that I kept the PVC off the bottom of the hole, which was the bolt of the hub. I didn't want the epoxy getting on the bolt, since the wood block needed to rotate around the bolt. You don't want the wood block glued to the bolt, or it wouldn't rotate.
Next, I'll be putting chicken wire around the frame to give the body some shape and protect the mechanism. I'll probably show the end result of that in a future post.
Page last modified 03/15/2010