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cgeorg
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Roll

Post by cgeorg »

I have seen it posited on these boards that the roll phase occurs when axis tilt equals axis rotation. I cannot understand how a ball that has axis rotation greater than 0 (that is, the ball has rotational velocity in a different direction than its translational velocity) will not continue to hook. Can someone enlighten me?

I posted in this in the Mo & Friends forum, as opposed to Advice and Opinions, for a reason.
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Re: Roll

Post by Mo Pinel »

cgeorg wrote:I have seen it posited on these boards that the roll phase occurs when axis tilt equals axis rotation. I cannot understand how a ball that has axis rotation greater than 0 (that is, the ball has rotational velocity in a different direction than its translational velocity) will not continue to hook. Can someone enlighten me?

I posted in this in the Mo & Friends forum, as opposed to Advice and Opinions, for a reason.

I'll enlist the aid of purduepaul's physics training to answer this. But, I guarantee you it's true. I've confirmed it many times. Thanks for posting it here. We'll try not to disappoint.
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Re: Roll

Post by cgeorg »

Thank you Mo, I eagerly await Paul's response.
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Re: Roll

Post by MegaMav »

Paul has not been online in over 2 weeks.
Hes been a busy man.
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Re: Roll

Post by purduepaul »

All,

Yes I have been busy with spring coming and a new house, Mo is correct and tonight I will respond with a more thoughtout answer. Sorry if you thought I was dead but I have been lurking every morning as part of my daily routine.

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Re: Roll

Post by purduepaul »

Now that I am in beautiful, scenic La Crosse, WI. I have been thinking about your answer and here goes:

While a ball is going down the lane, it loses energy at an uneven rate. It loses very little energy during the skid phase, and most of it is lost during the hook phase of ball motion. The RG contours of the bowling ball will determine how fast and at what point a ball will lose energy during the roll of the ball down the lane. When axis tilt equals axis rotation, the hook phase of ball motion is stopped since the ball stops losing energy at its previous rate. Due to the axis migration of the ball and the RG contour the ball will lose energy at a very slow rate on a never ending lane, the ball will reach "roll out" where axis tilt and rotation equal zero, but this point very rarely happens during the course of motion. Hopefully this answers your question!

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Re: Roll

Post by cgeorg »

So, if I am reading this right, the ball path between "roll" (after the second transition - AR = AT) and roll out (AR = 0) is not perfectly linear, but not as curved as during the hook phase. Correct?

Does the intermediate differential of the ball contribute to this at all? e.g., will an undrilled symmetrical ball still exhibit these characteristics, since the RG paths will be circular rather than elliptical?

Also, a side note, I think you said "hook" when you meant "skid": It looses very little energy during the hook phase, and most of it during the hook phase of ball motion.
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Re: Roll

Post by kellytehuna »

The way I read that, is when Axis Rotation = Axis Tilt, the hook phase is complete. That is to say, all motion from that point on is LINEAR, not PARABOLIC. That being said, Axis Rotation and Axis Tilt will continue to decrease UNTIL they BOTH equal 0.
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Re: Roll

Post by Mo Pinel »

cgeorg wrote:So, if I am reading this right, the ball path between "roll" (after the second transition - AR = AT) and roll out (AR = 0) is not perfectly linear, but not as curved as during the hook phase. Correct? NOT TRUE! IT IS PERFECTLY LINEAR! THE GRAPHICAL ANALYSIS IS IN THE USBC BALL MOTION STUDY.

Does the intermediate differential of the ball contribute to this at all? e.g., will an undrilled symmetrical ball still exhibit these characteristics, since the RG paths will be circular rather than elliptical? NO ONE CARES ABOUT UNDRILLED BALLS, SO THE GRAPHICAL ANALYSIS HAS NEVER BEEN DONE. IT'S UNIMPORTANT!

Also, a side note, I think you said "hook" when you meant "skid": It looses very little energy during the SKID phase, and most of it during the hook phase of ball motion.
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Re: Roll

Post by MattCosta7 »

motion in the roll phase is linear, but not always on the path of the boards

This can be confusing visually, because we view it along the X plane, from the Y plane, a zth dimension higher, rather than looking from the z plane down onto the x and y
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Re: Roll

Post by purduepaul »

Mo Pinel wrote: IT'S ACCURATE NOW!
As Mo stated, yes the roll phase of ball motion is perfectly linear even when the ball is very slowly losing AR and AT after AR == AT.

ALL balls lose energy during the time they are rolling down the lane. If a ball "retains energy" , it will not slow down, and therefore not hook. Since we all like hook, the ball will NEVER "retain initial energy".

Drilled assymetrical cored balls generally reach the 2nd transition point sooner than drilled symmetrical cored balls. But both will still lose AR and AT very slowly after that due to the nature of drilled balls.
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Re: Roll

Post by cgeorg »

Mo Pinel wrote: NOT TRUE! IT IS PERFECTLY LINEAR! THE GRAPHICAL ANALYSIS IS IN THE USBC BALL MOTION STUDY.
Unfortunately, we don't have data from the USBC study as to the axis rotation and axis tilt at the various points on the lane, so it is an opinion that the ball had any AR or AT, or that they were equal, during that phase of motion in the study.

I would love to see video of the throwbot using a 45 degree axis rotation, 45 degree axis tilt release. Would the ball hook? That would be data enough for me.
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Re: Roll

Post by MattCosta7 »

cgeorg wrote: Unfortunately, we don't have data from the USBC study as to the axis rotation and axis tilt at the various points on the lane, so it is an opinion that the ball had any AR or AT, or that they were equal, during that phase of motion in the study.

I would love to see video of the throwbot using a 45 degree axis rotation, 45 degree axis tilt release. Would the ball hook? That would be data enough for me.
The only problem therein would be that the axis rotation and tilt bleed at different rates through transition 1 and 2. So you would lose AR much faster than AT. They'ld only be identical at release, and after transition 2.

In the backend, once transition 2 completes (if it does, with that much tilt, balls don't always make it to transition 2), they would return to condition AR=AT, but will now be notably less than 45*, and I would assume that this degree would be dependant on condition, friction encountered and layout
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Re: Roll

Post by cgeorg »

The statement is that the roll phase begins when AR=AT, and that ball motion will be linear in the roll phase. If they are equal at the point of release, the ball should never hook.
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Re: Roll

Post by RevZiLLa »

My unscientific guess is that a ball released on a trajectory parallel to the gutter with equal axis rotation and tilt would move toward the left (for a right handed bowler) once it encounters friction after the skid phase because that axis rotation is pointed to the left.

If loss of axis tilt would tend to make the ball move right, the two effects could cancel each other if loss of axis tilt and rotation occur at the same rate after tilt=rotation.

This will be interesting to learn about!
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Re: Roll

Post by kellytehuna »

That would indeed be an interesting experiment, though I suspect it will travel dead straight! My wife has a lot of tilt and if she doesn't get around the ball enough (more axis rotation) she gets VERY little movement out of the ball.
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Re: Roll

Post by MattCosta7 »

From an utterly poor knowledge of flight simulators:

With many variations of Yaw and Roll, a plane will continue flying in a straight path, however with slight change in either, the plane will turn following the path of whichever is greater.

I would hypothesize that, the ball would not hook, because of this. The ball should maintain a linear path from wherever it encounters friction on the lane, to wherever it exits the lane, (as well as a linear path from the release through the oil to the friction, however these paths wont necessarily be the same) but this may not be necessarily parallel to the gutter due to frictional forces encounters. as well as the fact that roll doesn't require zero lateral motion, just a constant rate of change in postion. It will skid through the oil. Roll requires friction.

I define hook here to be a non-constant rate of change in ball position along the y axis (making the gutter the x axis). For every foot traveled in length (x), position on y is changing at a different rate in this period.

Roll, will be defined as a period of constant change in ball position along y.
For every foot traveled in length (x), the position on y changes at a constant rate.


I probably haven't expressed this perfectly, and most likely am way off base, but that would be my best interpretation of taking 3d rotational motions into a 2d plane. (I say 2d plane, because once the ball is on the lane, we assume the lane is flat, despite the fact that we know it isn't!)
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Re: Roll

Post by Mo Pinel »

cgeorg wrote: Unfortunately, we don't have data from the USBC study as to the axis rotation and axis tilt at the various points on the lane, so it is an opinion that the ball had any AR or AT, or that they were equal, during that phase of motion in the study.

I would love to see video of the throwbot using a 45 degree axis rotation, 45 degree axis tilt release. Would the ball hook? That would be data enough for me.

IT IS FACT, NOT OPINION! If you look at the axis rotation and tilt measuring chart, ALL the points where AR = AT are on the circumference of the chart. When the axis point goes the the edge (circumference) of the chart, AR = AT. The ball NO LONGER HOOKS once the axis point is there. You can do the work to check it out and report back to us, if you'd like. I've already seen it.
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Re: Roll

Post by purduepaul »

cgeorg wrote: Unfortunately, we don't have data from the USBC study as to the axis rotation and axis tilt at the various points on the lane, so it is an opinion that the ball had any AR or AT, or that they were equal, during that phase of motion in the study.

I would love to see video of the throwbot using a 45 degree axis rotation, 45 degree axis tilt release. Would the ball hook? That would be data enough for me.

I really do not like discussing hypotheticals, and just as a side note if you have 45 degrees of tilt...SEEK PROFESSIONAL COACHING! the greatest performance fit ever still couldnt help you since tilt delays ball reaction.

For arguements sake, no a ball with 45 degrees of tilt and rotation will not hook, will you see this on video anytime soon, no, however I put as an example for you. We know from practical experience that the guys with the longest hook zones with the same layout are ones with high axis rotation and low tilt. The more difference the longer the hook zone is. That is why bowlers with low axis rotation and axis tilt are hard to drill for in general and the layouts are very tempermental.

Once again, if you need to see everything on video to confirm it, please dont hold your breath to hold it. Believe Mo, he is right around 99.99% of the time.
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Re: Roll

Post by cgeorg »

I am going to digest this for a bit. One further question. Will a ball with more axis tilt than axis rotation hook?
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