In general the switched convertors work fine in range of inputs and the one in Hipi should be fine with either 12V or 7.5V input.
Agree we need to do something about adding battery support. Though in my experience with other robots it is much more convenient to just allow hot-swap of the batteries by including 2 battery connectors and using a pair of very low forward voltage Schottky diodes (I’m using Vishay’s V10P45S - but anything that is rated for 10A and at least 30V with as low forward voltage as possible is good):
This way you can use as many batteries as you want and charge them on a dedicated charger that will most likely be capable to provide much more charging current than any circuit we would be able to put inside the robot.
In that design there is also a LiPo voltage checker - but I think this is not necessary as we can implement a loop in the software that reads the voltage from the servos and issues warnings in case the battery drops below a threshold.
I agree about the mic input. The way I did it before was to split the processing in two parts (two Raspberry PIs): one in the head that covers the vision and audio, and one in the chest that covers the motor control (including the Dynamixel network) and the IMU. A big advantage with this approach is that the IMU is not affected by the head movement and does not need to be constantly adjusted with the head position. The two Raspberry PIs should both connect via WiFi (this is why Raspi 3 is so exiting, the WiFi is built in and no need to add a dongle that adds space) and using ROS. That being said I’m still far from having something that really works with ROS in this setup.
Now, back to the video/audio the simplest way is to use USB cameras with mic and let the Raspi in the head use the mic for sound processing. Should work fine with OpenCV. The even more interesting thing is that we might be able to process data from 2 cameras - also meaning 2 mics, so not only we will be able to receive vocal commands, but also identify the direction. Here is a picture of the head of the previous robot:
You see the microphones that I desoldered from the camera boards and moved them to the sides to improve the spatial recognition.