This is what I did on my very last spring. Thanks for adding the complete description here!

The Bittle documentation is here: https://bittle.petoi.com/ The "Board Configuration" page indicates the i2c library is here, https://github.com/jrowberg/i2cdevlib, in the "Arduino" folder.

Which version of IRremote are you using? It should be an older version, 2.6.1, rather than the latest. You can downgrade with Tools > Manage Libraries... That got my remote working.

@Rongzhong Li reloaded all software and now getting some movement! Woo hoo!

@Rongzhong Li another point is that when I turn it on it goes to the calibration pose. From the code it appears it should go to the rest pose, which I assume is with legs folded down to the floor.

@Rongzhong Li of course I entered the appropriate number of "Y"s at the prompt and uploaded the full sketch. My serial monitor is obviously working because I went through the calibration and saved settings. I know everything is wired properly because I can move every motor. The only skill that works is the return to the calibration state. It's as if the other skills are terminated shortly after starting to run. Before I really start reading your code, I thought you could point me to what would be causing that behavior. Otherwise there could be a problem with my board.

That was by far the most difficult part of the build. You need to push really hard to compress the spring completely and then shift it in. Not fun at all!