Can do? Well maybe can do

[Michael Wimble]

I haven't seen that anyone else is working towards the can do challenge,
but I've certainly made massive progress.

I've restudied my lecture on behavior trees, watched a lot of YouTube
videos, and looked at my existing behavior tree package that patrols the
house. With that, I wrote a fairly extensive 'fetch me a beer' tree. The
safety preconditions:

* Deal with the robot having fallen over.

* Deal with the robot tilting and approaching falling over.

* Deal with the battery critically discharged.

* Deal with the battery needing charging.

* Deal with the robot safety system having reported a serious problem
(discussed earlier).

Then the behavior tree selects the first of the suspected locations for
the beer and navigates to a pose near it. Later on I'll add other
locations to the database in case I've stashed hoards of beer in
multiple caches throughout my property. You can't take over the world if
you don't have your supply chains in place.

Then the OAK-D camera, which is about 5 feet off the floor is used to
attempt to find a can of beer with its wide-angle camera. The robot will
rotate in a full circle, if necessary, until it sees a can. Once found,
it makes a coarse navigation towards the can.

Then the gripper camera takes over to refine the robot's pose. The
gripper camera is a Pi Camera v3 mounted just above and behind the
gripper. The elevator is raised up until the Pi camera can see the can,
and then the gripper is positioned so the can is between the gripper
jaws ready to be grasped.

The can is grasped and visually verified to be in the gripper. The arm
is retracted and lowered near the robot; not all the way as that might
knock the can out of the gripper.

Finally, the robot navigates back to where it started, which would be
next to me.

I've added simulation for all the bits: the OAK-D camera, the Pi camera,
the gripper's vertical conveyor, the extender arm, the grasper, the
battery and the IMU.

I'm creating a GUI right now that allows me to run the behavior tree one
tick at a time. Between ticks I can set the tilt of the robot or the
battery voltage to simulate emergency situations. The GUI shows me the
position of the gripper motors. Rviz and gazebo, of course, show me all
the pretty pictures.

Not all of this is complete as of this moment, but it's moving along
quickly. When the simulation works well enough, I'll release the Kraken
on real hardware with real cans (of Coke Zero -- you don't want a drunk
ruling the world).

I don't have plans to open any doors to get at the beer at this
point--if I have time, I'll add that bit.

Once completed, of course, I'll get back to the real task of world
domination, backed up with use of the existing gripper hardware which
has a testicle twister as the end effector.