artist named Theo Jansen, who developed a mechanism
that did precisely what we wanted with such grace that it
was almost frightening. I encourage a quick Google search
for his name; you will find some truly amazing things.
A Jansen mechanism takes the rotation of a central
shaft and converts it into a straight line approximation
along the ground at the tip of a foot. It is well adapted for
walking machines because two legs can be attached at the
same rotation point on the shaft, producing a pair of legs
that move in sync. It also moves in a disturbingly organic
way, reminiscent of a horse. Unfortunately, rather little
information existed online at the time for this mechanism
and since the proportions of the individual linkages were
extremely important for it to function properly, we were
presented with the problem of determining the correct
ratios. This boiled down to watching youtube videos over
and over, while laying a ruler on the screen to measure
the legs as precisely as possible. Once we had a rough idea
as to how everything fit together, we broke out our free
student copy of Autodesk Inventor and attempted to model
the whole mechanism.
We actually got quite close! With a bit of tweaking, we
managed to get a pretty good approximation of a straight
line on the leg, so we built a miniature mockup of the
mechanism out of an old aluminum parking sign we found
on the side of the road. (Remember, cost-effectiveness is
important!) The motion looked quite good just rotating the
crank by hand. More presentations, more modeling on the
computer, and more research later we decided on the final
plan. The legs would be made from 1.5 x 0.5 x 0.0625
scrap rectangular steel tubing; the frame would be made
from 2x4 wood boards. As with every presentation up to
this point, we were met with skepticism. Why wood?
Wood is a better material than most people give it credit
for. It is flexible, light, strong, and cheap. It takes adhesives
well, it is easy to cut, and it’s not hard to find. Plus, we
figured the wood and metal together would keep with the
neo-Victorian theme we had conceived this project with in
the first place.
Eventually, we teamed up with Ecopeds — a San Jose
based manufacturer and distributor of electric scooters and
cycles. Bob met with us and was excited as we described
the scale of what we were trying to do. He essentially
funded the project and made it all possible. Check out
Ecopeds, they’re pretty cool!
Gotta give the shout out to
the sponsors you know.
So, our first semester was complete and our design
was basically set in stone at this point. Then came the hard
labor of actually fabricating and assembling the beast, and
the scale of it all became apparent. Nearly 200 feet of steel
tubing, 80 feet of 2x4 board, 120 bronze bearings, wires,
adhesives, woodscrews, and more would be needed to
actually get it all together. That and a bit of blood and
Hector cutting legs on a cold saw.
Daniel marks and centerpunches the legs.
Salvador cutting 2 x 4 beams for the frame.
SERVO 11.2009 55