the side profile from the 3D rendered
model of the Vulture directly into an
Autodesk Inventor sketch and used this
as a guideline to outline the shape of the
torso. From there, I drew a chassis within
that shape and scaled it to the appropriate
size. This resulted in a fairly accurate
interpretation of the Vulture’s torso, though
I ultimately widened the torso a bit to
make room for the internal components.
Figure 4 shows the proposed model in
Inventor and Figure 5 shows the physical
manifestation.
I planned on mounting the weapons
directly to the torso and made sure to
include the standardized five-hole
Lynxmotion SES pattern so that I could
make use of their aluminum hub and
tubing system ( 3” segments). I bought
the Airsoft guns at a local Wal-Mart and
then performed some plastic surgery to
trim them down to the right size and
shape. I bent two Lynxmotion SES
U-brackets with a box brake so they
wrapped around the guns and provided
a means of mounting to the aluminum
hubs on the end of the weapon
mounts.
The torso itself sits on top of a
pan/tilt assembly built from two
RX- 28 Dynamixels, a hinge bracket,
and two side brackets. The legs of
the robot are connected to this
lower assembly using a
column of standoffs
between the hip yaw
servos and the lower pan
servo. An aluminum
plate in the center of
each column connection
provides additional
support. Figure 6 provides a
detailed close-up of this area.
This completes the construction
of the upper torso chassis.
Walking Gait
Figure 3
The walking gait is still a work in
progress; I have the feeling it will be a
continuously improving aspect of this
project. I started off using a static
gait with no IMU feedback based
entirely on Forward Kinematics (FK) via positional capture.
It is my goal that eventually Hagetaka will walk
using a dynamic gait with a fully implemented
balance and Inverse Kinematics (IK) engine. The
IK will take a considerable amount of time and
research with a 7DOF leg, so my next step will
be a FK based gait with IMU feedback for
pseudo-dynamic balance.
So, what makes this gait different from
that of standard bipeds? The standard gait
demonstrated by the majority of hobby
humanoid shifts the COG over the center of the
weight-bearing foot in order to lift its opposite leg
and take a step. This is a simple and fairly effective
way of getting around, however if you watch the
upper torso closely you will notice how much it
rocks side to side; fine for most uses, but when
a camera is being used to remotely pilot it
creates a considerable shaky-cam effect. This
problem is even more pronounced when
trying to ‘run and gun’ — a strategy which should
prove to be effective in Mech Warfare competition.
The walking gait used with the MicroRaptor
leg design helps to alleviate this problem; the
legs are brought underneath the torso and
steps are taken inline. The gait starts off with
both legs perpendicular to the ground, the
upper torso COG is then shifted to one side
enough so that the opposite leg can lift completely off of
Figure 4
60 SERVO 07.2009
Figure 5
