When I built the first version of the Stack-chan board, I wired the pins for small hobby servos driven by PWM, but since I was mainly using TTL serial servos, this support was only "just in case". The task of "developing a case and firmware to support PWM servos" was buried at the bottom of the backlog.
He was one of the first to modify my case and make an SG-90 version of the stackchan. He then submitted a pull request to my repository. (I found out later that this was his first pull request! I'm glad I could contribute to his great contribution to OSS.)
Since SG-90 servo motors are readily available and inexpensive, many other makers today use his case to build their Stack-chans.
He also gave me feedback on improving the board. The SG-90 does not have built-in speed control like serial servos, and it has a large peak current when changing angles rapidly. Therefore, the voltage drop sometimes caused the M5Stack to lose power. This voltage drop can be mitigated by connecting the battery to the 5V line via a diode.
After this, he created many applications using the SG-90 version of Stack-chan.
He created a "discomfort index meter" on the Stack-chan to cope with the hot Japanese summer. He demonstrated the use case of Stack-chan as a small indicator.
He also incorporated the Stack-chan into a quadruped robot. Since Stack-chan has a pan-tilt movement, it is also ideal for use cases in robot faces.
Last but not least, knowingly or unknowingly of the recent Stack-chan movement, M5Stack is also working on a small bipedal robot kit. Ahead of that, He is developing a robot that incorporates Stack-chan and adds our own bipedal capabilities.
Who will win the development race against the official M5Stack? We'll be keeping an eye on this one!