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-   -   Seriously about Twist serve (http://tt.tennis-warehouse.com/showthread.php?t=440128)

toly 09-14-2012 07:34 PM

Seriously About Twist Serve
 
Anatoly Antipin

Twist Serve


To create twist serve we have to brush a ball approximately from 8:00 to 2:00 o’clock, but above the ball’s equator. This kind of brushing motion creates topspin, sidespin, and spiralspin (gyrospin).

The spiral/gyro spin would be in clockwise direction causing the ball bounce deviation toward the right. The gyrospin motion rotates the ball about an axis pointing towards the target. That sort of spin is used to throw a gridiron football, but it has no effect on curvature of the ball through the air.

We can hit the ball above its equator if and only if the racquet face is tilted forward - slightly closed.

There is example of the racket motion around impact in case of twist serve.


Figure 1. The racquet’s movement around contact

The frame #2 is point of contact. The arm itself moves relatively slowly forward, to the right, and downward and practically doesn’t affect racquet brushing motions.

On the other hand, the wrist ulnar deviation rotates, very fast, the racquet upward and to the right almost perpendicular to the ball outgoing direction.

It seems, the wrist ulnar deviation produces the main contribution to the topspin, sidespin, and gyrospin. All others motions of the body (arm pronation, wrist flexion, and so on) create mostly translational motion of the ball.


Figure 2. The tilted forward racquet

The theta (ϴ) angle defines magnitude of the gyro and side spins.


Figure 3. Vector of the spin component along with its components

About fig.3 see also http://tt.tennis-warehouse.com/showthread.php?t=436086.

Assume that the racquet face tilted forward with theta angle (ϴ). Then gyrospin, sidespin, and topspin racquet's velocity components would be:

VGyrospin = VSpinHor*sin(ϴ) (1)

VSidespin = VSpinHor*cos(ϴ) (2)

VTopspin = VSpinVer (3)

The more we tilt the racquet face forward (increase ϴ), the more efficient would be gyrospin and less effective sidespin.

If ϴ =45° then VGyrospin = VSidespin , but I doubt that one can hit successful twist serve with so large theta angle.

Btw, topspin component isn’t affected by ϴ.

The theta angle also determines coordinates of the point of contact, see picture below.


Figure 4. The tilted forward racquet and ball’s equator

IMO ϴ should be less than 30° and thus point of contact would be next to ball’s equator, otherwise the ball goes into net.

LeeD 09-14-2012 07:37 PM

Too much conjecture. Just go out to the courts, toss above your head, strike the ball with the racket moving upwards, clear the net by 3', and the resultant twist serve bounces head high, opposite direction of the flight.

Raul_SJ 09-16-2012 05:54 AM

I will study this...

I am not clear on the "8 o'clock to 2 o'clock" brushing motion.
I am using that for a Topspin serve -- where the bounce is pretty much straight ahead.

NTRPolice 09-16-2012 05:57 AM

You also need to consider where you're serving from and where you're serving to. All the times ive hit this serve were on the deuce side serving down the middle.

I dont "try" to do this serve, but sometimes it just happens when im trying to serve a normal kick serve. I only realize ive hit this serve after I see the action on the ball (and usually the opponents getting all jammed up lol)

Roforot 09-16-2012 06:53 AM

Quote:

Originally Posted by toly (Post 6900345)
[b][size="4"] Anatoly Antipin


The more we tilt the racquet face forward (increase ϴ), the more efficient would be gyrospin and less effective sidespin.

If ϴ =45° then VGyrospin = VSidespin , but I doubt that one can hit successful twist serve with so large theta angle.

Btw, topspin component isn’t affected by ϴ.

The theta angle also determines coordinates of the point of contact, see picture below.


Figure 4. The tilted forward racquet

IMO ϴ should be less than 30° and thus point of contact would be next to ball’s equator, otherwise the ball goes into net.

I don't know about the math or physics, but I'm interested in trying out these ideas on the court. I can hit a twist serve, but I'd like to be able to mix it up and just hit a topspin serve so they don't get used to the sidespin. It sounds like tilting the racquet head forward should accomplish this.

Limpinhitter 09-16-2012 06:54 AM

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toly 09-16-2012 07:31 AM

Quote:

Originally Posted by Raul_SJ (Post 6902334)
I will study this...

I am not clear on the "8 o'clock to 2 o'clock" brushing motion.
I am using that for a Topspin serve -- where the bounce is pretty much straight ahead.

When we hit topspin serve the theta angle is usually around zero degree ϴ =0°. Then, according to formulas (1), see post #1

VGyrospin = VSpinHor*sin(ϴ) = VSpinHor*sin(0°) = 0

So, the ball doesn’t bounce to the right.

Because of different magnitude of ϴ we can swing from 8:00 to 2:00 and produce different ball’s rotation. :confused:

spacediver 09-16-2012 07:50 AM

well done toly - your posts are becoming clearer. Only critique is that there was one sentence in there that was "borrowed" from an article by rod cross (about the gridiron football).

toly 09-16-2012 09:19 AM

Quote:

Originally Posted by spacediver (Post 6902494)
well done toly - your posts are becoming clearer. Only critique is that there was one sentence in there that was "borrowed" from an article by rod cross (about the gridiron football).

Thanks to you, I learned a lot about proper medical and tennis slangs.:)

Yes, I stole the Rod Cross sentence, because I know nothing about football and my English is still very poor.:(

toly 09-16-2012 09:31 AM

Quote:

Originally Posted by Roforot (Post 6902409)
I don't know about the math or physics, but I'm interested in trying out these ideas on the court. I can hit a twist serve, but I'd like to be able to mix it up and just hit a topspin serve so they don't get used to the sidespin. It sounds like tilting the racquet head forward should accomplish this.

Can you evaluate the theta angle when you hit decent twist serve? :confused:

Bowtiesarecool 09-16-2012 09:32 AM

It is my understanding that the kick serve bounces away as a result of how the ball deforms when hitting the ground at such a steep angle with heavy topspin. I have seen computer simulations of this effect, but can't remember where to find them.

toly 09-16-2012 10:46 AM

Quote:

Originally Posted by Bowtiesarecool (Post 6902667)
It is my understanding that the kick serve bounces away as a result of how the ball deforms when hitting the ground at such a steep angle with heavy topspin. I have seen computer simulations of this effect, but can't remember where to find them.

The gyrospin only causes the ball to jump to the right. For explanation see SystemicAnomaly posts in thread http://tt.tennis-warehouse.com/showthread.php?t=405281 :confused:

directionals 09-16-2012 03:52 PM

If the ball is struck at above the equator, then I don't understand why people say hit the ball from 8 o'clock to 2 o'clock. Shouldn't that be 10 o'clock to 2 o'clock then?

toly 09-16-2012 05:54 PM

Quote:

Originally Posted by directionals (Post 6903233)
If the ball is struck at above the equator, then I don't understand why people say hit the ball from 8 o'clock to 2 o'clock. Shouldn't that be 10 o'clock to 2 o'clock then?

If you brush the ball from 10 o’clock to 2 o’clock, angle theta would be around 30 degrees (ϴ = 30°) and this brush motion creates only horizontal component VSpinHor, see post #1, fig.3.

Topspin component of the racquet velocity will be zero, VTopspin = VSpinVer = 0. With tilted racquet (ϴ = 30°) and without topspin you definitely hit the ball into net.

There is simple approximate rule: For every degree of closed racquet face you have to swing the racquet the same degree upward. So, topspin component is very important for twist serve.

That’s why you have to swing from 8 o'clock to 2 o'clock. If ϴ is more 15° you maybe should brush the ball from 7 o'clock to 1 o'clock. :confused:

sureshs 09-16-2012 06:00 PM

Quote:

Originally Posted by directionals (Post 6903233)
If the ball is struck at above the equator, then I don't understand why people say hit the ball from 8 o'clock to 2 o'clock. Shouldn't that be 10 o'clock to 2 o'clock then?

I was also confused, then I realized he means 8 to 2 overall, but contacting the ball from 10 to 2. Before that the swing was in the air.

xFullCourtTenniSx 09-16-2012 06:19 PM

Quote:

Originally Posted by directionals (Post 6903233)
If the ball is struck at above the equator, then I don't understand why people say hit the ball from 8 o'clock to 2 o'clock. Shouldn't that be 10 o'clock to 2 o'clock then?

If you knew nothing about how to hit a kick serve, and I gave you this information (this thread) to teach you, how likely do you think you will be able to learn it? The answer is very unlikely.

People need simple cues and simple directions to do what they need to do, then let the body figure out the rest itself in a way that is comfortable.

If I told you 10 to 2, then you won't be aiming for much of a vertical factor in your swing. As a result, you will have trouble getting the ball over the net and getting the kick you want (especially when hitting the ball "above the equator").

If your kick serve has no kick to it, then returning the serve is about as difficult as returning a slice serve, it's not an issue unless you disguise both serves to look the same and vary your placement very well. It's the kick that makes it a problem. The "twist" just confuses inexperienced players and makes it look pretty.

TennisCJC 09-16-2012 07:06 PM

I think some of the information in your theory comes from this TWU article http://twu.tennis-warehouse.com/lear.../kickserve.php that supports more spin being generated if you strike the top of the ball. I have also seen other web instruction that you must get the racket head in front of the wrist to hit a good kick serve too and this supports your theory also.

I have an OK kick serve - not great - but I target the bottom inside and swing up to the top outside at almost a 45 degree angle thru the ball. I do try to keep the shoulders turn, swing more at the side fence and get the racket head through the ball - racket head slightly in front of wrist.

In reality, the racket probably does brush across the top of the ball as you indicate. Maybe contact the bottom or center but brushes across the top before the ball leaves the strings.

toly 09-17-2012 11:07 AM

To clarify the matter, there is one more example - Ryan Chung hits unreturned twits serve around 8:13
http://www.youtube.com/watch?v=nvGbQraZD98.

I extracted four frames from this video.


Figure 5. Ryan Chung's twist serve

Chung tosses the ball very far to the right. During contact the racquet is slightly closed and he hits the ball above its equator. This is really very complicated serve. :shock:

mightyrick 09-17-2012 11:27 AM

That is a great video clearly demonstrating the toss behind the head. Here is the link to the exact point in the video:

http://www.youtube.com/watch?v=nvGbQraZD98&t=8m08s

SystemicAnomaly 09-18-2012 04:17 AM

Quote:

Originally Posted by Bowtiesarecool (Post 6902667)
It is my understanding that the kick serve bounces away as a result of how the ball deforms when hitting the ground at such a steep angle with heavy topspin. I have seen computer simulations of this effect, but can't remember where to find them.

Are you talking about kick serves, in general, or specifically twist kicks? The term, kick serve, is somewhat generic/ambiguous. Some use the terms, kick serve & twist serve, as synonyms. Whereas others classify the twist serve as a specific type of kick serve. In this taxonomy, a kick serve is any serve with heavy topspin that kicks upward on the bounce. If the kick serve curves one way, in pre-bounce flight, and then kicks off in the opposite direction on the bounce then it qualifies as a twist serve. If the kick does not deviate appreciably left or right on the bounce then it would be a topspin kick (or a topspin-slice kick) serve.

Now the ball, on a twist serve, may very well deform a bit differently than it does on other types of serve. However, this is not really the underlying cause of the way bounces. The ball bounces the way it dues because of the way the ball interacts (rolls/skid/etc) with the ground. This interaction is influenced by the speed, the spins and trajectory on the ball prior to the bounce.

Note that (vertical-axis) sidespin does not directly affect the bounce (height or direction) according to physicist, Rod Cross. OTOH, horizontal-axis spins do have an effect on bounce height and direction. The most common of these is topspin and underspin. A ball that bounces off to the left or right, relative to the pre-bounce direction, indicates the presence of spiralspin as toly has indicated. This type of spin accounts for the left/right deviation seen on the bounce of a twist serve.

I've been talking about spiral spin for 4-5 years in these forums -- there are quite a few threads that discuss this type of spin. In his book, Technical Tennis, physicist Rod Cross refers to it as spiralspin, However, in his TWU article on kick serves, Rod refers it as gyrospin. It is sometimes aka Z-axis spin or longitudinal spin. Table tennis players refer to this spin type as corkscrew spin (or corkspin).

http://www.youtube.com/watch?v=Q8egU54BeyU


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