Dr.Dave's 30 degree rule visualized

bbb said:
after you translate the link into English a pool player speaks
i believe it translate into
" a rolling-CB shot, over a wide range of cut angles, between a 1/4-ball hit (49 degree cut) and 3/4-ball hit (14 degree cut), the CB will deflect or carom off by very close to 30° (the “natural angle“) from its original direction after hitting the OB."
;)
Click to expand...
There's at least one pool book full of equations. I never saw how that could be put into practice.
 
bbb said:
after you translate the link into English a pool player speaks
i believe it translate into
" a rolling-CB shot, over a wide range of cut angles, between a 1/4-ball hit (49 degree cut) and 3/4-ball hit (14 degree cut), the CB will deflect or carom off by very close to 30° (the “natural angle“) from its original direction after hitting the OB."
;)
Click to expand...

Good summary! That sounds familiar. :geek:

For those interested, good "non math and physics" explanations and demonstration showing how useful this rule is can be found here:

 
nataddrho said:
Yes my thoughts too.

Possible product trajectory: synchronous infrared / ultraviolet strobe light and camera with appropriate lens filter, to use bright spots to target accurate Hough circle transform and ball identification, in real time.
Click to expand...
That's a clever thought! Although Kozoom can do it without any of that I'm guessing? Or they are actually using infrared light and camera in their 3-cushion games? haha
 
dr_dave said:
This system works fairly well only for full hits. For more info, including a demonstration, see:

Click to expand...
That's what I figured too, drawing out the diagram it says that the deflected angle theta is related to the approach angle phi via the following
sin(theta) = d/R (d = distance bewteen two centers of balls in the x direction, R = radius of ball)
sin(phi) = d/2R
So expanding sin (x) = x - x^3/3!, this gives the relation
theta = asin(2phi - phi^3/3), so it approximates the rolling CB carom angle as shown in the following diagram (red = front-of-ball prediction, blue = theoretical value). The approximation is fairly good (with 2 degree margin) from full-ball-hit to 3/4 ball hit.

1680641738273.png
 
dr_dave said:
Good summary! That sounds familiar. :geek:

For those interested, good "non math and physics" explanations and demonstration showing how useful this rule is can be found here:

Click to expand...
I really think that according to your own material this statement is wrong:

The 30° rule states that for a rolling-CB shot, over a wide range of cut angles, ... the CB will deflect or carom off by very close to 30° (the “natural angle“) from its original direction after hitting the OB.
Click to expand...

Why not say upfront:

The 30° rule states that for a SLOW rolling-CB shot...
Click to expand...

??

Also, in your 70 degree rule--for cuts thinner than 1/4 ball hits--you never mention speed. Is the 70 degree rule independent of speed?
 
7stud said:
I really think that according to your own material this statement is wrong:

Also, in your 70 degree rule--for cuts thinner than 1/4 ball hits--you never mention speed. Is the 70 degree rule independent of speed?
Click to expand...

All CB control principles (except a tangent-line stun shot) need to be adjusted for speed per the info and demonstrations here:

The 30 degree rule peace sign gives you the correct final angle, but you need to parallel shift your hand down the tangent line to predict the final direction properly, based on shot speed.
 
7stud said:
I really think that according to your own material this statement is wrong:
...
Click to expand...
A point that people often overlook is that the deflection angle is measured between two straight lines. The first is the path of the cue ball until it arrives at the object ball. The second straight line is the path of the cue ball after it finishes curving. The cue ball slides to the side various amounts depending on speed before it starts along its straight line. As you increase the speed the various final straight line paths are all parallel. They all form the same angle with the incoming path of the cue ball.

Another point that is often overlooked is that the natural rolling path for a half-ball hit is not 30 degrees. It is closer to 34. That can be very, very important if you are trying to place the cue ball very accurately. As shown in the graph above, and as bbb mentioned, the main point is that for fullnesses of hit on the object ball between about 1/4 and 3/4 the cue ball is deflected within five degrees of 30 degrees. But it is almost never exactly 30. (1/4 to 3/4 full is a range of cut angles from about 45 degrees to 15 degrees.)
 
Bob Jewett said:
A point that people often overlook is that the deflection angle is measured between two straight lines. The first is the path of the cue ball until it arrives at the object ball. The second straight line is the path of the cue ball after it finishes curving. The cue ball slides to the side various amounts depending on speed before it starts along its straight line. As you increase the speed the various final straight line paths are all parallel. They all form the same angle with the incoming path of the cue ball.

Another point that is often overlooked is that the natural rolling path for a half-ball hit is not 30 degrees. It is closer to 34. That can be very, very important if you are trying to place the cue ball very accurately. As shown in the graph above, and as bbb mentioned, the main point is that for fullnesses of hit on the object ball between about 1/4 and 3/4 the cue ball is deflected within five degrees of 30 degrees. But it is almost never exactly 30. (1/4 to 3/4 full is a range of cut angles from about 45 degrees to 15 degrees.)
Click to expand...

Excellent points. To be accurate with the 30 degree rule peace sign, one must shift down the tangent line appropriate amounts based on shot speed. And to be really accurate, one must learn three peace sign angles. The following video (starting at the 2:37 point) demonstrates how both things are applied at the table:

 
dr_dave said:
Excellent points. To be accurate with the 30 degree rule peace sign, one must shift down the tangent line appropriate amounts based on shot speed. And to be really accurate, one must learn three peace sign angles. The following video (starting at the 2:37 point) demonstrates how both things are applied at the table:

Click to expand...
I think another point to add is that the rolling CB carom angle, in particular 30 degree rule, is the same on any table conditions (slow/slick tables), so one only needs to judge when the curving of CB ends.
 
One ifandandbut I haven't seen discussed is the big ball. I used to love that thing because you could roll it anywhere with no particular stroke development. This was pre Simonis and it made slow cloth playable. I used it on 9 footers as well and the steeper drive through made angles more predictable. Funny, now that I think about it, there was little to no aiming difficulty transitioning from the Centennial Blue Circle. ( We called it the blue dot.) Wonder why that is. (?) And any tricks comparable to the peace sign? Besides skinnier?
 
Pubo said:
I think another point to add is that the rolling CB carom angle, in particular 30 degree rule, is the same on any table conditions (slow/slick tables), so one only needs to judge when the curving of CB ends.
Click to expand...
Yes, but the weight of the cue ball -- many are light -- has a significant effect on the follow angle. You might consider that a table condition.
 
You must log in or register to reply here.
Back
Top