The good news is that Roamer has run for quite a while, with never a failure to find the charging station. Like a turtle, Roamer has wound up with wheels off the ground a few times (I think I know how to solve that issue).
The bad news is that running for many hours takes a toll on little dc motors--shall we say failure?
There are no brushes in these little motors, merely little "fingers" that wear out rather quickly.
A dc motor with genuine brushes would probably last longer--but a robot that buzzes around twelve to fourteen hours a day is going to strain a brushed motor.
I'm testing a stepper motor to see if that might provide the reliability I want. A companion robot needs to run a long time without serious maintenance. I have more work to do.