I finally make it to stand stably!

First I assumed that higher center of mass will be easier to control Whipbot's posture, analogy to make a broom stand on my palm (in my childhood, I realized higher, and heavier center of mass was easier...).

However in those case : when I mounted the battery on top of the bot, it wouldn't stand. I even prepared PID gain tuner by GUI slider indicator, but I couldn't reach to the optimal set of the gains.

I accidentally reached to stable gains when I changed battery mount points to lower of the bot. The bot became much calm and proof to a little noise such as being pushed by my finger.

But still it's not so robust since when I mounted another battery as a dummy weight, the bot easily fall down!  This experiment was conducted so that I can predict what will happen when I install other sensors and actuators to have the bot as a HOMEROBOT!

The reason why this bot is unstable in bigger payload, I think, is a low maximum rotation speed of the motor : 46 rpm at no load! To recover upright when the bot is tilted, it have to be accelerated to get inertial momentum, that means wheels are accelerating. But maximum rotation speed are low, so the period that acceleration can be applied is too short to recover the bot's posture.

Now I'm planning to replace current motors with high power motors!