Walt Martin is kneeling, legs folded behind him, butt resting on his heels. “I’ve got to practice my yoga,” he says, clearly joking. Never mind that we’re in the cab of an 18-wheeler cruising through Colorado at 55 mph and Martin was, until a moment ago, the guy at the wheel. Maybe he was feeling cocky. After all the truck, outfitted with $30,000 worth of hardware and software from San Francisco startup Otto, had just hours before made the…