Engineered draw shots II

Engineered draw shots II

Post by John Lew » Tue, 02 Sep 1997 04:00:00


Thanks for your replies

Quote:
>Due to the hopeless server I subscribe to, it has taken quite a time for

me to read some of the replies to my original contribution where I
stated that the real secret to good quality draw shots was
acceleration through the ball.
Thank you for the feedback, and as some of you need reassurance,  Ill
take the argument a little further.
About 15 years ago, while a College Lecturer, I needed a project for
some Technician students who were required to produce a "design and
make" type piece of equipment as part of their course work.
As we had a billiard table 6 x 12 available I encouraged them to make
a device which would deliver a
cue in a piston like manner with a variety of differing  types of
action. The device produced relied on  the pendulum action of a
swinging weight, and had adjustments which enabled the cue to move
through long or short straight strokes.
When the device was set up, the students marked where the maximum
speed that the cue would hit the ball was, and then experimented with
ball placing, so that the ball could be hit with an accelerating blow,
by placing the ball before top speed was attained.  To cut a long
story short,
the results of their work more than confirm  what  I stated
originally,  that for a lengthy draw,
the ball is best struck with an acceleration. But I must add, that it
was possible to get draw shots with the cue positioned for maximum
speed,  but not as good as those where the cue was accelerating.
One  thing the lads did, which was interesting   was to take a short
piece of nylon about 2 inches long
by half inch dia., and machine a circular  groove across the centre at
right angles to the axis.
This was glued to an old cue, 2 inches from the tip, to  support  it
so that the centre of  the tip was exactly  half an inch above the
cloth.  This enabled  ***  strokes to be made through the ball
with a guaranteed strike height, and no ripped cloth.  The nylon was
allowed to rest on the cloth and slid safely during the stroke.  You
would have to try  this to believe how effective it is, but it looks
horrible
Incidentally, using THE METHOD for producing a draw, it is reasonably
easy to place the white ball on the green spot and***of the red
ball placed on the blue spot, into the middle pocket, without the red
rebounding of the top cushion, over the baulk line. It requires a very
long light stroke

Best regards,

 
 
 

Engineered draw shots II

Post by Ron Shepa » Wed, 03 Sep 1997 04:00:00

Quote:

>[...] The device produced relied on  the pendulum action of a
>swinging weight, and had adjustments which enabled the cue to move
>through long or short straight strokes.
>When the device was set up, the students marked where the maximum
>speed that the cue would hit the ball was, and then experimented with
>ball placing, so that the ball could be hit with an accelerating blow,
>by placing the ball before top speed was attained.  

I am curious about the details of this setup.  Was it entirely gravity
operated, no springs or anything else?  Was it only the stick weight that
was used for acceleration, or were other weights used too?  If there were
other weights, how were they attached to the stick?  

Here is the way I interprete your description of the experimental setup.
The maximum tangential stick acceleration (the corresponding force is
given by M*g*sin(theta), ignoring friction) will be maximized at the
beginning of the stroke, and the minimum acceleration will be at the
bottom.  Theta here is the angle of the pivot away from the equilibrium
position at the bottom.  However, this tangential motion has the
horizontal component that is determined by an additional cos(theta)
factor, so the horizontal acceleration of interest is given by
g*sin(theta)*cos(theta), which can be rewritten using trig addition
formulas as (1/2)*g*sin(2*theta), and this has a maximum at theta=45
degrees.  The velocity is the integral of this acceleration from the
starting angle to the final angle at the time of contact with the cue
ball; but a simpler way to determine the velocity is simply from the
difference of height of the stick center of mass from the starting angle
to the final angle.  Longer pivot arms will result in a larger stick
speed.

How was the stick speed measured?  How well did this speed agree with the
above simple analysis?

Quote:
>To cut a long
>story short,
>the results of their work more than confirm  what  I stated
>originally,  that for a lengthy draw,
>the ball is best struck with an acceleration.

How different was the stick angle and the contact point at this pivot
angle (45 degrees pivot angle for maximum acceleration, if the above is
correct) than at the bottom (0 degrees)?

Quote:
>But I must add, that it
>was possible to get draw shots with the cue positioned for maximum
>speed,  but not as good as those where the cue was accelerating.

Do you have any hypothesis on why this might have been observed?  It does
not agree with the simple physics model, so such an observed descrepency
would be very important in a classroom situation.  And, of course, in the
maximum draw situation, most pool players know that they must hit harder
for more draw, not softer, so it does not agree with practical experience
either.

$.02 -Ron Shepard