Calculating Your Effective Pivot Point.

dr_dave said:
Colin,

You might check out my March '08 article. It describes and illustrates the various "squerve" effects fairly well.

Regards,
Dave
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Thanks Dave,
That article clarified all the questions I had for Jim!

I knew swerve would be larger, due to increased elevation over the distance but hadn't though about the initial paths. Now I can see more clearly what Jim was refering to.

This will certainly come into play on certain shots where adjustments to my PPe will have to be made.

When hitting high CB and when hitting power draws and drag shots come to mind as shots I need to test more observantly. I have in fact noticed that on power draw shots with english there is a tendency to get too much squirt.

Something as simple as; when hitting high english increase adjustment by 30%. When hitting low draw english reduce adjustment by 30% might cover most of these shots pretty well.

Drag shots with english are rarely used, except perpaps for some safety play shots. I think most experienced players hit the CB in the middle height range as much as possible when playing english for position due to the fact that it is harder to judge the swerve when hitting higher or lower.

Anyway, I'll do some more testing and see what I come up with. It's good that these variations are being considered. It's already developed a system that I am finding to be much more reliable and predictive to what I was doing before.

Colin
 
What IS pivot point?

I sometimes believe that I am an ok player, but when people start to talk about squirt, pivot point, backhand english etc., I get lost...
 
dr_dave said:
Colin,
My first reaction to the formulas is that not many people will accept it because they will perceive it as too complex. I don't see any easy ways around this, unless a small set of "calibration shots" can be created to define a set of benchmark pivot lengths (and account for the given table conditions). Then every shot would fall somewhere between the benchmarks, making it easy for people to estimate (through judgment instead of calculation) a pivot length between the benchmarks pivots (e.g., the speed and distance for this shot are about halfway between these two benchmarks, so I'll split the difference on the pivot length).
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I'm hoping the video will make it easier for people to grasp this method and hopefully I can think up some benchmarks that act as easier introductions to the system.

One idea I've had is to produce a small ramp / stintmeter. It would measure cloth speed / slickness which should be proportional to the K factor. So all a person needs is to know thier own cue's natural pivot point and to roll the CB down the ramp. Refer to a chart and you've got your K value for those conditions.

At some time in the future it might be good to have some workshops and get instructors and more players up to scratch on the system. Hands on is the best way to learn. And when more players are using it, others will be keener to put in the effort to see what its all about.

Also, some people might not like changing their bridge length so much, and some people might prefer much shorter bridge lengths. A possible solution here is to use a combination of BHE and FHE with a fixed bridge length. So instead of varying the bridge length, one would instead change the amount they pivot with each hand. For a short pivot, you pivot just with the back hand. For a long pivot, you pivot just with the front end. For a pivot in between, you pivot partly with the back hand and the rest with the front hand. The only variable would be the percentage you pivot with one hand (e.g., pivot 25% with the back hand and the rest with the front hand). More food for thought.

Regards,
Dave
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I think it takes a bit of practice for players to learn:
1. Aiming while the bridge is being set at a specific distance.
2. Learning to stroke some shots at unusual bridge lengths.
3. Pivoting while keeping a perfectly still bridge hand.
4. Cueing straight after pivoting into an unusual body position or shifting the body after pivoting while keeping the bridge hand set.

But these are just a matter of coordination and a bit of practice I think. It only took me a few sessions to become quite comfortable doing this.

My shots nearly all range from 10 to 13 inch bridge length in play which would be pretty comfortable for most players. I'd prefer to be in the 12-15" which is probably close to what the predator 314 is. Or I might sand my cue down 0.5mm or so. The main reason for this is it would give me more room to swing on power shots that require being up near the natural pivot point. Another good option would be to have 2 cues with about 2-3 inches difference in their natural pivot points. On the extremes of being too short or too long, you could change cues.

Regarding FHE, my major concern with it is that it is hard to repeat accurately. It's hard enough keeping the bridge hand set during the pivot, let alone keeping the back hand in place during a front hand pivot. I just can't see FHE being highly systematizable, though it can be a good method to put a player into the ball park.

Colin
 
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hi guys - late the show as usual, but I'm really interested in the discussion here. I believe that this is extremely important work you're doing, and commend you on sharing it openly. By doing that, your work will only be improved and more refined.

I will spend more time in the next few days working with the numbers.

My first thought is how to "distribute" this information to a broader non-math audience. I'd like to eventually see if I can work out a way to present the calculation in a paper based slide chart. something like this or this
 
Patrick Johnson said:
I believe Jim must be saying that, although Coriolis predicts the final rolling angle of a CB hit higher to be less than the final rolling angle of a CB hit lower, a CB hit higher curves sooner than a CB hit lower.

Sorry if I got you wrong and confused things, Jim.

pj
chgo
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Not at all Patrick. As always, you have it right.

Jim
 
Colin Colenso said:
Jim,
Does this suggest 3 times more curve in the initial stages or for the total curve path.

I thought swerve was coming about mainly as a result of the coriolis masse' diagrams. I'm still don't understand this other source of swerve. Are they like vectoral components such that we can add them to coriolis type swerve forces.

Sorry if my questions are a bit strange, just trying to find a way to grasp this concept a bit better.

Colin
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Colin,

If you want to see how the rate of swerve and the final swerve angle are obtained in a quantitative way, or at least dissected into its components, I'll be happy to provide it. Of course, this can be found amongst Dr. Dave's technical articles, but you might want a non-vector treatment. However, it appears that Dr. Dave's BD article probably answered your questions to your satisfaction, so I'll cease and desist until further notice.

Just to note that the Coriolis masse is exactly the same, qualitatively, as the swerve that you've/we've been discussing. The only difference is the amount of it, as he was dealing with Masse shots (writ large). The math is the same.

And yes, hitting below center with english alters the rate of swerve (reduces it) compared to hitting along the central horizontal axis, but it's not as dramatic a difference as hitting above center. And although the rate is reduced, as both Patrick mentioned and Dr. Dave's article illustrates, the final swerve angle is greater at the point where the cueball reaches natural roll...a tortoise and hare sort of thing.

Thanks for your generous comment about the (5-V) thing. :)

Jim
 
Jal said:
Colin,

If you want to see how the rate of swerve and the final swerve angle are obtained in a quantitative way, or at least dissected into its components, I'll be happy to provide it. Of course, this can be found amongst Dr. Dave's technical articles, but you might want a non-vector treatment. However, it appears that Dr. Dave's BD article probably answered your questions to your satisfaction, so I'll cease and desist until further notice.

Just to note that the Coriolis masse is exactly the same, qualitatively, as the swerve that you've/we've been discussing. The only difference is the amount of it, as he was dealing with Masse shots (writ large). The math is the same.

And yes, hitting below center with english alters the rate of swerve (reduces it) compared to hitting along the central horizontal axis, but it's not as dramatic a difference as hitting above center. And although the rate is reduced, as both Patrick mentioned and Dr. Dave's article illustrates, the final swerve angle is greater at the point where the cueball reaches natural roll...a tortoise and hare sort of thing.

Thanks for your generous comment about the (5-V) thing. :)

Jim
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yw Jim.

I don't think I need the quantitative way now that I can visualize how the squerve curves differentiate. That should be all I need to collect usable data and to create some rule of thumb (if) rules. I doubt I can work it into the formula without making it overly confusing.

I'm just relieved after reading the part you wrote about swerving at 3 times the rate. I now know what that means and approx to what degree it affects the curves at different stages.

Colin
 
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