[[projects:projects]]:[[robots]]

====== billiards ======

photo of billiards table
  - identify balls, pockets, rails
  - re-project to perfect rectangle

billiards-playing robot, with drone for eyes<br/>
  * drone launches from robot, parks above the center of the table

step 1, drone and laptop
  *   draw table on laptop, by tracing edges from the camera
  *  interpolate for camera angle to get rectangular table
  *  allow for drift if the camera moves
  *  identify balls and pockets
  *  draw lines between cue ball, object ball, pocket
  *  do for each object ball
  *  choose the most obtuse angle

step 2,
  *  identify the cue, signal when it is aimed correctly

step 3
  *  build robot that can shoot a que stroke
  *  move in a rectangle around the table
  *  retract wheels and drop into solid stance
  *  gently place a hand on the table
  *  fine-tune the aim based on drone video
  *  deliver a straight stroke at specified speed

step 4
  *  add strategy, speed, position of balls after the shot, plan three shots ahead

Library of photos of billiards tables in various stages of the game

Software to detect rails, pockets, balls, cue ball, cue.

AR billiards
  * Cameras detect cue and cue action
  * Detect balls, pocket, rails
  * Reproduce the table in the viewscreen
  * Draw ghostball and lines
  * Advise easiest shot
  * Advise proper aim and speed
  * Beep when aimed correctly
  * Negative feedback for tip right or left, backend right or left, too fast, too slow

===== Physics =====

==== side-spin, "english" ====

**Squirt** - deflection on the cue ball when using side spin. Right English squirts to the left. Direction is fixed at the moment of the cue strike.  Degree of squirt depends on the flex of the cue.  A stiff expensive cue can have minimal squirt.

**Swerve** - after squirt, cue ball swerves back the other way. Degree of swerve increased by elevating the back of the cue.  The point along the shot line where swerve begins depends on pace, and also on the cloth.  More pace, the farther along before the swerve begins. With enough pace, swerve is eliminated.

Ergo. Hit on the right \\
Fast pace, QB goes to the left (squirt > swerve) \\
Slow pace, QB goes to the right (swerve > squirt) \\

There is a pace at which the QB squirts to the left but bounces off the rail back to the cue tip.

**Back-hand English** - cancels squirt, depending on cue's pivot length.
https://youtu.be/5T3ai0SM1aw

**Throw** - deflection on the object ball \\
two types:
  * Cut-induced throw 
  * Spin-induced throw 

The cue ball clings to the object ball for a fraction of a second throwing it off the line.

Chalk mark on the cue ball at point of contact increases throw. \\
Spit on the cue ball at point of contact decreases throw.

**Gearing** is the amount of outside English that exactly compensates for the throw.

At wider angles (greater than 20°) increased speed reduces the amount of throw.

Questions
  * Topspin, bring cue up, Ronnie O'Sullivan?
  * Mental game, start strong, then fade?