Although it's certainly not the first robot to take advantage of gyro sensors to maintain its balance, the MANOI AT01 robot from Kyosho turned out to be surprisingly stable. The robot uses Kondo servos and the RCB-3 controller board with 3 available analog servo inputs. The analog inputs can be used to add functionality to the robot with a number of different sensors.
Like most robots in this classification, sensors are add-on options and need to be ordered separately if owners want to take advantage of the performance enhancements. Thanks to Sugiura-san and the Sugiura Brothers, we were able to do a side by side comparison between a MANOI AT01 robot equipped with gyros and another robot without gyros. The video below clearly shows the performance improvement.
For comparison purposes, the Sugiura Family setup a KHR-2HV robot without the optional gyro sensors along side a MANOI AT01 equipped with two gyros. The KHR-2HV has a fairly similar construction but with lower power servos on an aluminum frame, and uses the RCB-3J controller, which is almost identical to the RCB-3.
Historically, the use of gyros with this class of humanoid robots started with the use of gyros designed for use in RC model airplanes and helicopters. The early gyro designs operated by intercepting and modifying the servo control signals sent from the robot controller. Typically they would apply a slight change to the pulse width being sent to the servo in order to compensate for the force the gyro was sensing.
That approach, which is still very popular today, had three limitations. First, since the servo control signal modification, either stretching or shrinking the pulse width, was done within the gyro sensor electronics, its application was typically limited to use with a single set of servos.
For example, for side to side motion, the robot builder had to decide whether the gyro should be put inline with either the set of hip servos or the ankle servos. They couldn't control both sets of servos at the same time. This was the cause of endless debates among robot builders over whether it was smarter to apply the correction to the upper or lower pairs of leg servos.
Second, the amount of signal adjustment was applied to both servos equally. There was no way to provide different amounts of gyro adjustment to different servos.
Third, since the gyros operated inline with the servos, it was often very difficult to turn them on and off. This became a big issue when the builder wanted to create new motion sequences. They would have to unplug the gyros in order to program the new movements they wanted to create, then plug them back in again to test. If you have big fingers, as we do, working in the close quarters and nest of wires plugged into the typical robot controller can quickly turn into an exercise in frustration.
To address these three limitations, recent robot controller designs have started to switch over to analog gyro sensors. This puts the controller literally into 'control' over how the inputs from the gyro sensors affect the robots servos. It means that robot builders can use the gyro inputs to modify the position of more than just one set of servos. In the side to side example, they can respond to a force by shifting both the hip and ankle sets of servos.
Moreover, the inputs can be scaled and modified under program control. And, when the builder wants to create a new motion sequence, they can turn the gyro inputs off or on. Pardon the pun, but it's a big step forward.
Here's a simple animation to illustrate the concept:
How effective is it really?
So that we could see for ourselves, the Sugiura Brothers demonstrated the two robots going through some typical moves - walking around, stopping and starting suddenly, punching, etc. In the video below you can see the robot without gyros is significantly less stable by the way it tends to rock back and forth, especially after a sudden stop.
Of course, the KHR-2HV can be equipped with analog gyro sensors as well, and would probably be able to achieve similar stability. The Hitec Robonova-1 robot also provides for similar gyro sensor input and control. Like MANOI AT01 and the Kondo robots, the Robonova-1 includes functionality in the robots software application to control multiple servos based on the gyro sensor inputs.
Sugiura's Dynamizer website (Japanese)
Sugiura Brothers website (Japanese)