I’ve ditched the Arduino Uno and Adafruit motor shield, far too many limitations around power and pins. So now my robot is mostly done – using a bare ATMega328P and a single L293D H-bridge chip which I wrote a small library for.
I’ve solved the 7.4/6v/5v problem by feeding the 7.4v output from the 18650’s to a Mini DC/DC switching regulator that outputs 6V for the motors, and then a diode drops that to about 5.2v to feed the microcontroller, servo and H-bridge.
Its all on veroboard now and working quite well. I’m still waiting for the replacement chassis (and motor as one broke its connector off) but at least I don’t need to wait for a new motor shield, in fact I should have cancelled that 2nd order, they are crap. I’m also awaiting a better battery holder as the one I’ve got is spring-loaded and a bit of a tight fit for the protected NCR18650A’s.
Once I’ve got it fully built I’ll think about adding a laser pointer on the sensor “head unit” or ultrabright LED’s underneath, Fast & Furious style.