by David Geer
Contact the author at geercom@alltel.net
What is a DAGSI Wheg?
An adaptive wheel-leg robot!
Doctors Roger Quinn (engineering), Roy Ritzmann (biology), and colleagues
at the Case Western Reserve University (Case) collaborate in the
neuro-mechanical research of cockroaches. In 2001, their studies lead to
the birth of the Whegs (wheeled legs) robots, a product of the Case Center
for Biologically Inspired Robotics. Research (or, the Biorobotics Lab).
Alexander Boxerbaum developed
the DAGSI (Dayton Area
Graduate Studies Institute)
Whegs robot — named for the
Institute that funded the work — in
Dr. Quinn's Biorobotics Lab. It is the
largest and most recent robot in the
Whegs series. Its creators are in the
process of patenting its body flexion
joint, detailed below. One of the more
promising potential applications is
otherworld surface exploration.
The design of the Whegs robot —
which combines the utility of legged
transport to the wheel — has some
precedent in other robots, such as the
The DAGSI Whegs (wheeled-legs) robot
sporting six wheel-legs.
10 SERVO 03.2009
RHex and the PROLERO. While those
both each have a single leg per wheel,
Whegs have multiple legs per wheel
— typically three — as with the
DAGSI Whegs.
The PROLERO rotated its legged
wheels at an even, unchanging speed.
The body of the robot connected with
the terrain when the legs did not. This
is partially a function of having only
single legs. But, the RHex was
different. Because its wheels rotate
faster when the legs are not touching
the ground and the legs use an
alternating tripod gait (see sidebar),
the body remains in a reasonably
stable, level position compared with
the vertical motion of the PROLERO.
Both the PROLERO and RHex use
independent motors; one per each
of the six wheel-attached, leg-like
appendages. Each robot requires an
onboard control system for leg and
gait coordination. They both use skid
steering just like a bulldozer.
What is Different
About Whegs?
Whegs use a single motor which
drives all six wheels and all 18 legs
at a constant rate. "Running motors
at constant speed is more energy
efficient than cyclically accelerating
them as done in RHex," says Dr. Roger
D. Quinn, director of the CWRU
Biorobotics Lab. The single motor
design improves the power-to-weight
ratio over multi-motor designs because
the single motor platform scales well.
A mechanism of chains and
sprockets connect and drive them all in
a tripod gait. This is a crucial imitation
of the capabilities of the cockroach.
Whegs have the advantage that when
other legs lack traction, the system is
able to transfer power to the leg(s) with
traction to move the robot forward.
"Cockroaches change their gait
when they run on rugged terrain and
when they climb obstacles. Whegs
changes its gate passively without the
need for an active control system. It
has torsional (clock) springs in each
of the axles that permit its legs to
passively comply with the terrain,"
explains Quinn.
When a leg meets a larger
obstacle, the motor attempts to rotate
the wheel and leg. But, because the
load on the leg is bigger, the motor
instead winds the torsional spring in
the axle. The leg does not move at
this point. However, the other legs —
which have not met a large barrier —
continue to move. In this way, the
