I am going to deconstruct the Mechanical Thrashing Torso in an attempt to provide some idea of how it was originally made. This is not going to be a step by step tutorial, as this project is several decades old, and frankly, I just don't remember what the steps were,
Someone once said a picture is worth a thousand words. It is time to put that to the test.
Stripped Down Spine Mechanism
This is an uncluttered view of the segmented vine. The full range of motion allowed by the mechanical stops can be demonstrated to full effect.
Here are a series of images demonstrating how the segmented joints come together. Pop rivets were used in assembling the joints because they're cheap and strong and will not rattle loose with use. A piece of steel tube, slightly longer than the width of the joint, provides the bearing surface upon which the joints pivot. 1/4-20 bolts and nuts secure the segments together without the need for lock nuts or Loc-Tite. Tightening the nuts and bolts down upon the ends of the steel tube insert was enough to keep everything from shaking apart during use. No lubrication was ever required either. Clanking and rattling was all part of the effect I was going for.
Rib Cage (front back and interior)
These images detail the rib cage. Extruded aluminum channel provides structure(sternum and backbone). Bolted to the aluminum are pieces of PVC pipe, and inserted into the pipe are segments of thick insulated electrical wire. This assembly of randomly found crap made a pretty satisfactory rib cage. Aside from the motor and batteries this is the heaviest part of the whole figure, which actually helped in getting the torso to convincingly flop around.
Motor, Mounting Plate, and Crank Arm
The drive motor is a 24 volt electric motor I bought surplus. I didn’t know what its specs were and I selected this motor on the basis that it was big and beefy. I was told that this particular motor was for an electric gate. Basically, a nice, hefty motor that is geared to operate slowly, say around 1 or 2 rotations a second, has a good amount of power. The motor is simply mounted to a piece of quarter inch thick aluminum plate which is attached to the base with a bracket.
The rotational movement of the motor is translated into the linear motion of the torso my means of a crank. As the crank rotates to its highest point the cables slacken, allowing the spinal column to slump forward, and when the crank rotates down to its lower position, the cables tighten up pulling the spine into an upright position.
In order to get enough leverage to move the torso, the cables need to be held away from the segmented spine. The drive cable pulls through holes in steel "L" brackets. A crude but effective set up. Eventually the stainless steel cable will saw through the softer metal brackets, but so far so good.
Cable Guide Breakage
Shown in this image is a point of failure an aluminum bracket that became over stressed when I was running the thrashing torso as fast as it could go. This is why some sort of speed control on the motor is a very good idea. This thing could tear itself apart pretty quickly if it was allowed to. Now I get to fix this.
Lower Cable Termination
This was a quick and dirty way of securing the loose ends of the cables and creating a mechanical connection. This is a small rope clamp I picked up at the hardware store with a piece of brass attached to it. The hole in the brass allows it to be connected to the drive motor cam.
Upper Cable Termination
Two separate cables run up the back and attach to the uppermost spine segment and the base of the skull. At the lower end both cables terminate together but are routed separately up the spine so that the torso and the head move independently of each other.
This image shows the upper cable terminations for both cables as well as the steel brackets serving as cable guides. There are much better ways of doing this but it got the job done.
Here is the torso with ribs removed so that the positioning of the cables is clearly seen. You can also see the cable that secures the jaw to the spine, causing the mouth to open when the spine goes erect. To operate correctly the cables required a bit of fine-tuning to get the lengths correct and the travel of the mechanism something close to what I wanted. Also shown is how the return springs were mounted, which cause the torso to tend to curl forward into a fetal position.
I allowed myself to get a little artsy-fartsy with the head. The skull is an electroformed copper shell. The copper was deposited a upon a wax sculpture coated with conductive paint. Once the layer of copper plate was thick enough I melted out the wax. That technique is called the lost wax technique. When I first heard of the lost wax technique I wondered how do you use a technique that's been lost. Yeah, pretty stupid. I attempted to plate over the copper with nickel but it didn't really turn out. It gave it a funky, industrial appearance, so I was happy with it. The eyes are 12 volt incandescent indicator lamps.