May 2009- What has eight legs, weighs 6 tons, is 23 ft. long, shakes the ground as it moves, scares little children and awes adults?

Give up? It’s the Walking Beast, a creation from sheet metal fabrication shop owner Martin Montesano.

An owner of a sheet-metal fabrication shop often has some unique hobbies, but Montesano’s is particularly extreme. In his free time, he built the giant Walking Beast in his Iron Clad Welding, Salem, Ore., shop.

The $50,000 beast took three years to build and is still being tweaked. It’s powered by a 454-cubic-in. Chevy V-8 with a modified Turbo 400 transmission, coupled to two Klune extreme underdrive planetary gear boxes and a modified Rockwell 2½-ton military axle to supply power to the leg crankshafts.

"I always had an interest in large scale robots," says Montesano. "There have been various small walking robots created, but there aren’t many large ones. So I decided I would create one. I researched various walking linkages while looking for mechanical ones because computer-controlled ones take a lot of years of testing and are quite complex and expensive. Once I found a mechanical system that worked, I started designing and building the machine.

"The Beast is all mechanical," he says. "It’s a whole series of pivot points and anchor joints. Basically, it’s a six-bar linkage that I’m using to move the legs."

The final drive ratio is 125 to 1. The legs are supported on a four-link system and use 56 pivot points and 114 bearings. A hydraulic A-frame lifts the machine, acting as a pivot point so the Beast can turn.

It can transport up to six passengers in its steel belly and two (including the driver) in the head. It has a step height of 41 in. and a stride of 5 ft., with a top speed of about 5 mph. It has eight legs, with all the metal cut from ¼-in. plate steel using a plasma cutter and then welded into a box frame.

Montesano used a CNC plasma cutter to cut the ¼-in. plates, bent the pieces on a press brake to produce the curves he needed and then MIG welded them into a box. At 8 ft., 4 in. wide and 11 ft. high, Montesano had to provide a ladder that’s mounted on the side to reach the passenger area.

"There were many challenges with the Walking Beast," says Montesano. "One of the big ones was building it to a size that I could transport. So I was limited by the Department of Transportation size constraints. I didn’t want to get a special permit to move it. The width became a big challenge for the length and height of the Beast. We had to have enough clearance between the legs and all the linkage.

"Initially I designed it so the two sides could be powered separately," he continues. "But there was too much twisting torque when it walked and turned. It just tried to bind its legs together rather than corner. So I came up with a hydraulic system that lifts the machine off the ground and rotates it to turn it.

"Another drawback in the design is the way the linkage works," he continues. "It takes a lot of power to initiate a step and then almost no power to move it through mid-stride. Then, as the legs come down, they accelerate, which makes it move pretty slow. Now I’ve come up with a coil spring design that I’m installing that will dampen how hard the legs will come down, and it will also help lift them up for the next step. This should make a smoother continuous walking cycle."

What does Montesano use the Beast for? He says, "It was mostly made as a toy to play around with different theories, but I do take it to festivals where we get a lot of attention." FFJ

Click here for a look at how the Walking Beast moves.