Loki Crosses the
Pond — Part 1
by Alan Marconett
I first became interested in bipeds when I ran across a
Robotics website by David Buckley in the U.K. One of
David’s bots was called Loki. I thought I recognized the
name. Loki is the Norse god of trickery, mischief, and
change; and a major character in Norse mythology. Then I
remembered, in the TV series Star Gate SG-1, Loki is an Asgard!
Ifound David’s pictures of Loki with exaggerated postures
quite amusing! Although I was already deeply involved
in another robotic project — a hexapod I named Shelob
(the giant spider from Lord of the Rings) — I was taken
by the antics of Loki walking and posturing. I had to
build one!
I began to entertain the idea of designing and building
my own Loki. David’s Loki has what looks like aluminum
legs and feet. I couldn’t figure out a simple way to solder or
weld the leg and feet parts together. I later found out that
the original Loki’s legs were made of painted aircraft-type
plywood. Since I prefer working with metal, I hit upon the
idea of making the parts out of PCB (printed circuit board)
material. Double-sided PCB stock is fairly easy to cut, and
easy to soft-solder together with a simple soldering iron. I
was hooked on another bot project!
Cutting Loki deck parts on CNC'd Sherline Mill. A paper template
guides the clamp setup and verifies proper tool path.
50 SERVO 06.2008
Design
After a few hours on a CAD package, I had designed a
body, the legs, and the feet parts to be CNC milled out of
PCB material. I got the rough dimensions from eyeballing
David’s pictures. My body would be a little wider, due to
the PIC “QwikFlash” controller board I planned on using.
This additional width would lead to my initial failure, as
you’ll read.
Loki walks by lifting one foot up and over the other.
Many biped robots accomplish walking by shifting the
body weight to keep the CG (center of gravity) within the
landed foot. Not so with Loki, whose feet are quite big,
with toes extending towards each other, passing the CG
of the bot, and actually overlapping. So, Loki is able to lift
up a foot and hold it up as long as desired. This can lead
to some outrageous postures, and is exactly what drew
me to Loki!
Remember I mentioned that my first attempt was a
Cutting Loki deck parts on CNC'd Sherline Mill.
