Q: Will you explain how Seiko-chan's control technology differs from that of Seisaku-kun?
Yoshikawa: As in the case of Seisaku-kun, it combined an angular velocity sensor and a flywheel to maintain its balance between left and right. Seiko-chan detects its tilt to the right and left using the angular velocity sensor and applies rotational power to the flywheel housed in its chest using a motor to generate a counteraction that maintains its posture.
As for back to front tilting, which Seisaku-kun did not control, Seiko-chan detects its tilt using another angular velocity sensor and applies driving power to the unicycle in the same direction as the tilt to maintain its balance. This operation is on the same principle as an inverted pendulum.
When moving forward, the robot is controlled to keep bending forward at a certain angle. This gives forward drive power to the unicycle all the time. When moving backward, Seiko-chan bends backward. It can also track objects to its front, maintaining a certain distance, as it houses an ultrasonic distance measurement sensor under the flywheel. This function is aimed at reflecting the idea that "Seiko-chan likes to follow Seisaku-kun around."
Q: What part of the development did you find difficult?
Yoshikawa: It was really hard to pack all the components in its small chassis because the number of components increased compared with Seisaku-kun.
For example, Seisaku-kun only required one motor, which is capable of precise torque control, for its flywheel. Seiko-chan, on the other hand, required another motor to drive the unicycle in addition to the flywheel as it controls its balance in two axes. Just adding this extra motor and its motor amplifier occupied quite a bit of space inside.
We could have made the chassis bigger to accommodate an increased number of components, but the female employees who designed its external appearance didn't allow us to make Seiko-chan any fatter. As a result, we had to three-dimensionally install the substrates and electronic components. To tell the truth, some components were installed in her skirt.
Q: How are you planning to evolve Seiko-chan and Seisaku-kun from now?
Yoshikawa: As for Seiko-chan, we are aiming to enable it to make a turn and to climb up a hill. A feed-forward control that predicts the next action to be taken is essential to enable those motions.
When running up a hill, for example, the robot must detect the angle of the hill and raise its drive power compared with a flatland, even if its body angle remains the same.
To enable the robot to make a turn, we must set a trajectory and calculate its tilts and drive power in advance. As both Seisaku-kun and Seiko-chan have been operated almost entirely by feedback control, the level of difficulty will definitely increase.
Other than that, we had many requests from the children who participated in our visiting classes for Seisaku-kun to do things like...
"I want him to stand up the bicycle by himself when it falls over."
"I want him to do the kick-off riding*1."
"I want him to swim."
"I wish he could fly."
*1: The way to start riding a bike with one foot on a pedal and the other foot kicking the ground to gather speed.
My head aches when I think about adding new capabilities to meet the children's expectations while using Murata's key devices at the same time.