The crux of the news about the latest partnership between Teknic, Inc., and the RIT electrical engineering
department in developing this advanced autonomous
humanoid robot called TigerBot lies in the challenges in
building the robot to the newest size specifications. “When
the size of the robot reaches above four feet — now
growing to 5’ 5” — the torque requirements change
dramatically because of the size and added material
weight,” says Ferat Sahin, Associate Professor, Electrical and
Microelectronics Engineering Department at RIT.
Since the force times the distance is the torque at a
given joint, when the robot is taller and the arms and legs
are longer, the torque requirements for the arms, legs, and
torso increase. To determine torque, RIT students working
on TigerBot implement it in Solid Works and simulate it in
Gazebo, attaching the weights of the links and parts, and
calculating the necessary torque at each joint. “We also put
probes on the links and took outputs for certain motions to
determine torque requirements,” commented Sahin. So, the
knee, for example, now requires 250 Newton meters of
As the size of the robot increases, the torque increases
in a non-linear fashion. “It is hard to do that with
reasonable gear ratios. We plan to use 1-to- 50 and 1-to-100
gear ratios,” said Sahin.
That means using higher quality motors and servos
with greater strength than is available among high-end
hobby servos. “The main limitation of high-end hobby
servos is their low torque rating. With higher quality
motors, you can come up with and use control profiles
based on human motion, as well,” Sahin explained.
RIT chose the ClearPath servo motors because they
meet the torque requirements without adding too much
additional weight themselves, plus are easy to use and
control thanks to ClearPath’s control algorithms. “They
come with a controller that is right next to the motor. The
embedded controller/control mechanism is better than that
of hobby servos because you can set up profiles, controlling
the motor with incremental changes or full angles. This all
happens internally. You simply have to send the proper
control signals to the controller,” Sahin pointed out.
Further, the new TigerBot requires high performance
gears so the robot can achieve the necessary torque. RIT is
looking at a couple of different kinds of gears: harmonic
and cycloidal. “We use harmonic gears from Harmonic
Drive. Their gears are ten times lighter than the cycloidal
gears, but you need to incorporate them and embed them
into the joints. This gives us freedom when designing the
joints. The torque is very close to that of the cycloidal gears,
but the backlash is greater,” Sahin said.
The cycloidal gears can handle very large torques, but
they weigh in at four kilograms so are heavy. “We are only
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The TigerBot project will continue to span many years as students enter and leave,
bringing the robot from its current state of development to the next stage, and finally
to the completed robot that will guide prospective students visiting the RIT campus
through its halls, introducing them to this educational institute.
Design, testing, and construction of TigerBot V are currently underway. This robot
will rise to new heights (literally, around five feet/five inches) and will gain new
capabilities on its way to maturity — just as RIT students accomplish new goals every