The secondary reason for designing this, other than I have a liking for small crazy robots, is to allow holding a bigger battery pack. My first Otto ran with no problem off an external power feed, even from a powerbank, but could not run off its internal 16340 battery. It would work with 2 servos attached, occasionally with 3, but never with 4. This holds a double 18650 battery shield. I will post a real photo rather than just renderings once I have finished painting the model. At the moment it is just a pile of PLA pieces.
Part designs are available at https://www.thingiverse.com/thing:4788924.