A kingdom for a wrist strap

A project log for Smart leash

Simple navigation for pet robots

lion mclionheadlion mclionhead 11/28/2022 at 19:070 Comments

The next need was a passive strap for the animal.  The trick is it must be small enough to pack on the robot.  It needs a stopper to keep from getting sucked into the spool.

1 option is just to have the animal hold something in his paw like a bolt or a ring.  A ring could go on a finger, but if the robot snags something, things could get ugly.  An elastic mane strap attached to the string by a plastic stopper could work but the mane straps are too small for a lion wrist.  It could go around a few fingers & provide enough stretching to avoid injury in the event of a snag.

Sideways offset

The next big wish is a sideways offset.  The simplest sideways offset involves changing the center angle of the pot.  The problem is the longer the leash, the bigger the sideways offset.  A more accurate offset requires computing a variable center angle from the leash distance & sideways distance.  The problem is this requires accurate knowledge of the pot angle & leash distance.

The pot only detects -50 to 50 deg before its voltage saturates.  Shorter leash distances would require a steeper angle until it saturated.  It wouldn't be steerable at shorter distances.

The sideways offset would be limited to real small amounts by the pot range.  This makes a fixed center angle less affected by leash distance.  A fixed center angle is a minimal place to get started.

There's no easy way to set the center angle remotely.  The paw controller could be reconfigured when the leash was on.  The steering stick is not a good way to adjust center angle.  The speed buttons could step the center angle with beeps indicating the current setting instead of speed offset.  The problem is if an animal is carrying the controller for center angle but not driving the throttle stick, it's going to flop around & interrupt the leash at random.  So the throttle & steering would have to be disabled when the leash was on.  

The other thing that would need to happen is a gain schedule for running speed.  That's another use for the speed buttons.  A new paw controller could be built just for leash mode, with buttons for setting gain schedule & center angle.  The parts are all end of life.  The mane need would be creating a new 900Mhz radio.  The bq51013 is end of life.  There's a good case for finally making a decent wireless charging alternative.  Old timers wouldn't think of Texas Instruments as being fabless, but apparently the BQ51013 went down with TSMC.

Center angle & gain schedule would initially be configured in the text file.

Failure modes

It just begs the question of whether there's any case it can run away when the leash is on.  The leading case is a hall effect sensor wire breaking after it's fully extended so it never detects a retraction.  It stays at full throttle.  There was 1 case where it didn't detect an extension, but so far no cases where it didn't detect a retraction.

Another failure mode is the leash becoming unbolted & deflecting steering randomly.

Finally, there's the paw controller bashing around in the container.  It could get powered on & erratically override the leash.

There's still more need to override the leash with the paw controller because the leash doesn't support reverse.