A brief history of the Ultrasonic Following project, original records here:

Descriptive Blog Post About Ben Heck Project

I met Ben Heckendorn by winning a contest. After some discussion he invited me to collaborate on a project he'd being thinking about for awhile, luggage that follows you around, he called it Robot Luggage.  Several options were considered and I settled upon using ultrasonic time of flight differences as the operating principle. 

The system consisted of a Target, which contained an ultrasonic sender, and a Receiver, which contained two ultrasonic receivers (ears) spaced apart.  The time difference between receiving signals would give an Error value which could be used to close a loop and control the direction of the Luggage towards the Target.  

I was worried about an asynchronous setup between having rollover timers and missing signals on one or both ears so I decided to use a wireless link to start a measurement.  This was my first Arduino project which gave its own difficulties but in the end we had a working proof of concept that worked pretty well.

The system used Parallax PING sensors modified for send or receive only functionality, XBee for the ultrasonic link, and various power supplies and controllers for the robot.

The project garnered a lot of attention and even got a Hackaday Article of my blog post about my experience.  Over the years I've answered many questions in regards to this project, helping others replicate it, but it got harder as time went on because of our lack of documentation, the difficulty of the project,  and obsolescence of components we had used.

I've wanted to revisit the project and make an off the shelf system people could embed into their projects more easily and enlisted a few friends from a discord server I was part of.  I worked with Elliot to add the system above to his electronic wheelbarrow as proof of concept to start our new system, see the next log for his project