A line projector has been long dreamed of for steering a robot from in front.

Autonomous navigation when walking for short distances has been highly prized for eating.  It's just been the real simple problem that tortures by a thousand cuts.

The cowarobot is the most popular robot suitcase.  It is not trivial.  It has 4 cameras in the handle for bearing & distance. It doesn't work in direct sunlight.  They don't use a bracelet for tracking.  The bracelet is for notifying when it has lost contact.  

The airwheel SR5 uses a bracelet for UWB tracking.  The UWB tracking is notably less accurate than machine vision but works in sunlight.  The DW1000 is the most famous UWB chip.  There is an arduino library for the DW1000 but it only computes distance from signal strength, not time of flight.  The general idea is the higher the bandwidth, the more precisely you can measure the time of flight of a packet.  Time of flight becomes possible in the 6Ghz range.

For all the vijeos teaching how to program neural networks & win programming contests, it's amazing how little anyone knows about how a robotic suitcase works.

There was once an idea for a leash, for either pulling it up hills or when the battery died.  The problem was the size leash it would take to transfer enough force to pull it from far enough away.  

If the application is just autonomous navigation when walking for short distances, there could be a smart leash.  It would measure axial tension to control speed & steer by detecting sideways tension.  It could be very light.  The trick is designing a small enough sensor which detects sideways & axial tension.

There are very large strain gauges for 1kg loads.

https://www.adafruit.com/product/4540

There are slightly smaller flex sensors for smaller loads.

https://www.adafruit.com/product/1070

The bare chip sensors found in bathroom scales are unobtanium.

Because of the size of strain gauges, there is more value in connecting the string to a hall effect joystick for steering. Measuring axial tension is a difficult problem.  The problem is the animal is not going to manetain a constant distance from the truck.  The ideal leash needs to be 2-4 meters with distances from 2-4 meters determining speed.  

 The leading idea is routing the string through the joystick to the tension sensor.  The leading tension sensor is a measuring tape spring with encoder.  It adjusts throttle depending on how much string has come out.  A UWB sensor could measure the length of string, but it would be redundant when the need to tension the string is factored in.

A spring loaded cable reel with encoder is the simplest idea but commercial ones over 1 meter are gigantic.  Farstening a 1m retractable segment to a fixed length string segment & passing it through the joystick would be difficult.

 Because of the low usage & low power, a brushed motor could tension the string, but it also has to be fast.  A sensored brushless motor would provide tension & encoding but require a motor driver & heat sink.   The l6234 is no longer made.

It might be easier to have the user hold a retractable string & the truck to just have the joystick, but it would entail a transmitter worn by the user.  There's still a user worn retractable string with a load cell on the joystick.

For testing, a toothbrush motor can create tension with 2V at 1.5A.  A large diameter brushless motor would be a long term solution.  The problem is the string isn't always under tension, so it's going to want to tangle.