world in which an abandoned suitcase, a box, or even a pile of rubble can
conceal an improvised explosive device (IED), bomb-disposal robots have become
essential. Many units in the field bristle with cameras, feedback devices and
processors. Such sophisticated robots offer a significant amount of capability
and autonomy, but their increasing complexity also drives up weight, size and
cost. As a result, organizations often have to share one system across several
To address this issue, Mechanical Mobile Platforms (MMPs), a
family of simplified, man-portable robots from The Machine Lab Inc. has been
developed to perform a range of surveillance and bomb disposal tasks at a price
point low enough for wide deployment. For the cost of a high-end system, which
can exceed several hundred thousand dollars, users can purchase nine or 10
MMPs. Powered by compact, economical, high-torque motors from the Faulhaber
group's value-added reseller Micromo, The Machine Lab's robots are making a
difference around the world.
Kick-Starting the Design
Machine Lab engineering team started out with one overarching principle: keep it simple. This required
an immediate trade-off. Instead of a robot that can perform 95 percent of all
possible tasks needed, an MMP might only handle 60 percent of the tasks. The
bottom line, as all engineers know, is that a solution doesn't need to be
perfect, it just needs to be adequate to the application at hand.
So, rather than focusing on building a single product, The Machine
Lab took the big picture approach and developed a modular design platform that
can be applied to a wide range of implementations. The basic line includes a
quartet of direct-drive MMPs ranging from a four-wheel model that can carry a 4
lb payload to a six-wheel model that can handle up to 30 lb. For loose terrain,
the company also offers two track-driven versions: a four-wheeled version and a
six-wheeled version. Here, too, the focus on simplicity came into play. Instead
of driving with all wheels, each of the track-driven MMPs sports two passive
wheels, providing savings in cost and weight without compromising performance.
The team avoided onboard processors and feedback devices, opting
instead for direct user control via wirelessly linked joysticks or switches.
The operator determines the path of the robot based on images transmitted by
the unit's wide-angle IR camera. The mobile platforms provide a zero-degree
turn radius and linear speeds as high as 6.0 ft/s. They range in size from 5 lb
and 11.5 x 11.2 inch to 40 lb and 29 x 19 inch, although custom versions can be
larger, such as the 1,500-lb unit built for clearing vegetation in mine fields.
Although cost control is important, a low price point would be
meaningless if a unit couldn't perform or failed after a few weeks in the
field. To obviate this issue, the foundation of each MMP consists of a rugged
aluminum chassis mounted on nylon wheels with rubber tires. Steel gears and
IP-rated motors help ensure survival.
"The robots we send to Afghanistan have to be pretty much IP62
weatherproof," says company president Zack Bieber. "They need to be able
to be washed down and they need to be able to resist the very fine, abrasive
dust that you find out there."Gripper
Perhaps the most
critical aspect of a bomb-disposal robot is the robot arm. Here, the
engineering team faced a number of challenges, particularly in the gripper and
wrist-rotation elements. To maximize the amount of payload a robot could handle
while ensuring stability, they had to minimize the weight of the arm. That
meant working with the lightest possible components. At the same time, those
components had to power the arm so that it could grip a wide variety of
materials and not only lift but rotate payloads as high as 40 lb.
One obvious way to get the torque required
was to gear down a high-speed motor, but that approach adds size and weight, as
well as complexity and cost. In keeping with the company's philosophy of
simplicity, The Machine Lab team decided to skip additional gearing in the
wrist rotator and look for a motor that provided enough muscle to do the job on
Size presented another constraint. The design required a motor
that would supply the required torque and still fit inside the 30-mm-diameter
tube of the robot arm.
"It was a very tight physical dimensional requirement," says
Bieber. "We picked the Micromo motor because of the power-to-weight ratio. It
was really the only one we could find that would fit our application."
The actual gripper design was a little trickier. The device needs
to operate slowly to provide operators with the precision movement they need to
handle explosive devices. At the same time, the grip needs to be fail-safe -
once an arm picks up an IED, it cannot drop it. To handle these requirements,
the design incorporates a gearmotor fitted with a planetary gearhead that
provides a 246:1 reduction ratio. An additional worm-drive gearbox resists act
driving, providing an additional 15:1 reduction ratio for a total of 3,690:1.
Although using multiple sets of gearing can increase torque, in practice,
stacking up gear reductions can actually rob the system of power. Using a motor
with a high-efficiency planetary gearhead provided the performance the design
Efficiency was another important design constraint. Running out of
power in a cell phone is merely annoying. Running out of power during the
disposal of an IED can cost lives. At every step the team focused on specifying
components for the most efficient possible design.
With the high-efficiency design used, the
units can deliver as much as an hour-and-a-half of constant operation on a
single charge from a 25V lithium ferrous phosphate battery pack that weighs
just 1.5 lb.
Above all, the most challenging aspect of the
gripper design was duty cycle, according to Bieber. The motors for the wrist
and gripper are specified to run 24 hours a day, but their actual duty cycle is
closer to 5 or 10 percent of that. During that time, however, they must
routinely perform to their limits and sometimes beyond.
"The types of tasks these robots have to do are all over the
place, and it's all dependent on the operator," he says. "So, if we say this
can only lift and rotate 5 lb, we know that the user may well end up trying to
grab a 20 lb object with it."
To eliminate overdriving or stalling the motors in those
situations, the design includes adjustable slip clutches on both the gripper
and wrist rotator.
So far, attention to detail has paid off. "We've got over 200
robots out in Afghanistan and surrounding countries, and probably another 50 to
80 out in law enforcement here in the U.S.," says Bieber. The company also
recently secured another U.S. Navy contract for 250 more robots.
Kristen Lewotsky is a technical writer for Micromo. For more information, go