PLANTRACO SPIDER: Currently under construction. It is designed around an existing infra-red remote-controlled tank and incorporates an injection molded leg with living hing joints so that four of the links are a single piece of polypropylene.
ELECTRIC STEAM SPIDER II (ESSII): Uses the same design for the linkages as the Steam Spider II with electric components from an RC tank instead of a boiler. A small video camera and polycarbonate componets are planned.
CRABFU'S STEAM SPIDER: Designed in collaboration with Crabfu and powered by a small steam engine. The initial sketches have four leg pairs and differentially steered. It will be approximately 20 inches long and constructed of sheet metal that is cut and folded. The left and right sides will be independent and a large central gear will drive both cranks. The center portion of the frame will be removable to compensate for various sizes and styles of boilers, steam engines, and mounting points. Fabrication will be outsourced.
This prototype is made of layers of 1/8" polycarbonate layered and held together with small rods that go all the way through the body. Openings for the motors, stepped gears, links, and shafts are built into the layers. Several of the pivot points rely entirely on a 2-dimensional version of a ball and socket joint cut into the pieces.
A single square crankshaft drives all three sets of legs. Disks are connected to this shaft and off center by the length of the crank arm. This can be seen in the pictures and video. The disk increases the overall space required by the crank and lowers the ground clearance but simplifies the drive train and assembly.
The three sets of legs are all identical with the middle set rotated backwards. All of the connecting pieces were built symmetrically front to back with the crank shaft at the center.
An inherent question is "how fast can it go?". The specific answer is determined by the size, materials, design, efficiency of the power train, and the amount of power applied. The "poly speed" video shows a single leg unit attached to a power drill. The manufacturer's maximum rating is 800 RPM. Each cycle of the crank translates to two 1.75 inch steps of the legs yielding roughly 2.5 miles per hour. This model can handle more.
This was the first powered prototype. It moved the concept well beyond theoretical. It had a stride length of 4 inches and easily handled carpet or grass. The 2-inch step height enabled it to step onto a 2 by 6 with little effort.