JohnYandell
Hall of Fame
mbm,
Ha!
Ha!
The fast low bouncing version of the Bigservesofthands first serve
- Thread starter bigservesofthands
- Start date
bigservesofthands
Semi-Pro
The clip with the ball with 8 on it is not 10000 fps. It is 6000 fps. It clearly states that on the caption in the Peter Mcraw video.
I am not disputing that the racquet rotates on flat serves. If unchecked or for off center hits on the string bed where proper momentum transfer does not take place it rotates much faster than even intentional spin serves. It takes a lot of practice and skill to time the racquet that is rotating extremely fast to hit the ball with racquet face straight one and slightly inclined, dead center on the tennis ball and make contact at the dead spot near the tip of the racquet. The racquet tip velocity is likely more than 120 mph taking the rotation into account at the start of contact and likely slowed down to 90 mph or less after ball release. I am just marveling at the skill it took to hit that shot!
The ball certainly rolls in one direction and the racket rolls in the opposite direction in the Stosur serve clip. This is due to the gear effect. It has been studied for ball collisions including for tennis balls.
http://baseball.physics.illinois.edu/AJP-July07.pdf
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JohnYandell
Hall of Fame
I think we are both looking at a wall. You think it's blue. I think it's black.
Chas Tennis
G.O.A.T.
My claim for extra dwell time is for spin serves especially those that are hit out wide on both courts either through slice/top-slice/twist
Here is what I see for the Sony rx10 1000 fps serve:
It is a top slice serve. First frame is before contact. Second frame is contact albeit barely (which can be inferred from the fact that the shadow of the ball is partial and intersects the ball from our viewpoint). .................. The server has initiated ulnar deviation between frames four and five and the racquet head suddenly accelerates from it. When I serve traditional top slice serves, I go by both sight and feel and can feel the ball on the strings which is my trigger to initiate ulnar deviation. The ball is pushed by this ulnar deviation while getting embedded significantly more into the bed by frame five. ........................
........................................
There were several points that I don't agrees with in this post.
1) "Second frame is contact albeit barely (which can be inferred from the fact that the shadow of the ball is partial and intersects the ball from our viewpoint)"
I believe that the ball and shadow can be seen to touch but the ball and strings may not be in contact depending on the eye or camera viewing angle. I believe also that if the ball and shadow do not touch that the ball is separated from the strings. This can be checked with a tennis ball and racket in sunlight - walk around it and see how the ball and shadow behave when in contact and when not. I have not checked this out.
2) "The server has initiated ulnar deviation between frames four and five and the racquet head suddenly accelerates from it."
I don't believe that ulnar deviation can be observed in this way.
3) "When I serve traditional top slice serves, I go by both sight and feel and can feel the ball on the strings which is my trigger to initiate ulnar deviation."
Consider ball touches the strings. The ball is felt in the hand on the racket handle. Then nerve signals are sent to the brain. The brain uses that received signal to then send back nerve signals to activate ulna deviation muscles. I think the time required for the nerve signals to go from the hand to brain is longer than the time the ball is on the strings. Likewise, the time it takes for the muscle activation nerve signal (EMG? Signals & others?) to reach the forearm takes longer than the ball is on the strings. Look up the travel time of nerve signals.
On the other hand, it might also be possible to feel a shock through the bones faster than through the nerves. I have heard of that regarding running but not for tennis. That fast shock feel, if it is used, probably does not have the detailed feel of a nerve signal.
We do feel detailed nerve signals of impact after all strokes - how the ball impact felt on the racket. But I believe those feelings are received many milliseconds after the ball has left the strings for high pace strokes. These feelings might provide signature feel regarding the impact. These feelings are probably useful for training - by associating specific feelings with successful strokes. Trained by using trial and error - try motion, see stroke result, remember feeling that is associated. Repeat motion as best you can..... be a natural athlete....use feedback from high speed video?......
I don't recall seeing the two way measured transit times of nerve signals discussed for tennis strokes. Please post some references on nerve signal transit times and tennis strokes?
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JohnYandell
Hall of Fame
Jim has a point...
bigservesofthands
Semi-Pro
1. From the scales of the objects involved, the amount of shadow ball intersection, I cannot conceive of a light source (the sun) positioning that would cast that shadow with the ball not being in touch with the strings.
2. How else would you explain the sudden acceleration of the racquet head along the slice path and the corresponding forward motion of the ball? The racquet tip seems to have sped up at least 40 mph (0.73 inches/millisec) going by distance between strings as a measure.
3. Serving is clearly a learned response based on thousands of repetitions. The problem that our brain solves given enough practice, how much time before ulnar deviation should occur, so it happens during contact. For this our brain has learn to accurately track the falling ball and moving racquet head, keep time in the millisecond time scales, know what contact feels at such small scales so it reinforce/calibrate what has been learned. There is ample evidence in recent research that our brain can do all three.
The vestibule-ocular reflex (https://en.wikipedia.org/wiki/Vestibulo–ocular_reflex) the fastest know reflex in our body and is able to track the ball and to some extent the racket at the millisecond time scales involved.
Here is a nice neuroscientist blog post that explains how we learn to keep time http://blog.brainfacts.org/2015/04/brain-mechanisms-of-skill-learning/#.V4SCVFdYy-8
Here is the relevant extract
Like people, rats are not very good at simply estimating short time durations. Instead the rats must figure out an indirect method for time measurement. Each rat in the study learned to perform a specific behavior sequence that lasted for approximately the desired time. With thousands of trials of training, each rat learned to improve its behavior pattern until it achieved the desired goal: measuring 0.7 seconds.
Here is current research that proves that one does not need to go deep into the brain for learned motor skills
http://www.cell.com/neuron/abstract/S0896-6273(15)00220-2?_returnURL=http://linkinghub.elsevier.com/retrieve/pii/S0896627315002202?showall=true
Here is recent publication that describes the newly discovered pathway for long term motor learning
http://www.pnas.org/content/112/11/3541
Here is another recent paper that describes the time scales involved in the initiation of the learned response.
http://bmcneurosci.biomedcentral.com/articles/10.1186/1471-2202-14-91
Here is the relevant extract if you want to skip reading the whole thing
It has been found that paired-pulse TMS applied over the primary motor cortex with an interstimulus interval of about 1.2 or 2.5 ms determines MEP facilitation in the hand muscles involved in subsequent movements. Also known as short intracortical facilitation (SICF), this effect seems to be partially due to interactions between I waves and is thought to take place in the motor cortex or upstream from the cortico-spinal neuron [23, 24, 25]. Cattaneo and colleagues demonstrated that there is an enhancement in the excitability of those inputs to the corticospinal neurons projecting from the motor cortex to the specific muscles to be used during grasping actions at least 600 ms before the movement itself takes place.
Here is recent research on how this plays out in practice for us tennis players http://mcgovern.mit.edu/news/news/m...ces-learning-new-skills-retaining-old-skills/
Here is the relevant extract
“That’s why an expert tennis player has to warm up for an hour before a match,” Ajemian says. The warm-up is not for their muscles, instead, the players need to recalibrate the neural networks that control different tennis strokes that are stored in the brain’s motor cortex.
However, skills such as riding a bicycle, which is not very similar to other common skills, are retained more easily. “Once you’ve learned something, if it doesn’t overlap or intersect with other skills, you will forget it but so slowly that it’s essentially permanent,” Ajemian says.
However, skills such as riding a bicycle, which is not very similar to other common skills, are retained more easily. “Once you’ve learned something, if it doesn’t overlap or intersect with other skills, you will forget it but so slowly that it’s essentially permanent,” Ajemian says.
I certainly need to do the recalibration to account for differences in ambient temperature/pressure, string tensions, balls being used ....
Yes I have started to incorporate high speed video into the mix. But given the lag and higher order areas of the brain involved in reasoning, I use it only for coarser grain corrections during non-training times. I do not have the luxury of somebody filming me or giving me real time feedback. Fine grain corrections happen on the practice court through trial and error and repetition of motions that have elicited the desired result or are trending in that direction.
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bigservesofthands
Semi-Pro
I will take it that comic relief is your contribution to the thread.
Chas Tennis
G.O.A.T.
Maybe this demo can clarify what it indicates when the ball and shadow appear to touch in videos and the ball is near contact.
1) Place a ball on the ground in sunlight. No matter where you view from, the ball and shadow always touch.
2) Place something small under the ball to raise the ball 1 inch above the ground. Close one eye. As you move your eye around, from most viewing angles the ball and shadow appear to touch. But you can also look under the ball so that the ball does not appear to touch the shadow.
Chas Tennis
G.O.A.T.
That is a great collection of references. Thanks.
bigservesofthands
Semi-Pro
There seems to be fairly good evidence out there that the ball indeed slides and slides significantly on the string bed. So much so that it has influenced the type of racquets we use today.
Here is an article for which you have contributed input for some parts
http://www.popularmechanics.com/adventure/sports/a2072/4221210/
Here is the relevant quote from that article that proves my point
On a 120-mph serve, the ball is in contact with the racquet strings for about 5 milliseconds, moving up to 5 in. laterally across the string plane, gathering spin.
Here is how this sliding influenced racket design
http://www.tennisindustrymag.com/articles/2006/01/the_inch_that_changed_tennis_f.html
Here is the relevant quotes that proves my points
Giving a player an extra inch of width allows the player to swing up at a steeper angle or faster or both. In that case the ball slides farther across the strings, so you really do need that extra inch.
Give a 9-inch graphite racquet to a player today and the result would be some serious clipping of the frame every few shots
Here is a more conclusive paywalled study. But the conclusion and preview is available.Give a 9-inch graphite racquet to a player today and the result would be some serious clipping of the frame every few shots
http://link.springer.com/article/10.1007/BF02844026
Here is the relevant quote
At angles of incidence less than about 40° to the string plane, the ball slides across the strings during the whole bounce period. More commonly, the ball is incident at larger angles in which case the ball slides across the string plane for a short distance before gripping the strings. While the bottom of the ball remains at rest on the strings, the remainder of the ball continues to rotate for a short period, after which the ball suddenly releases its grip and the bottom of the ball slides backwards on the string plane.
This is pretty much how I described it earlier.
Here is most recent computer simulation data that describes the various stages of string bed and ball collision and how this is effecting string design/composition.
http://resource.ansys.com/staticass.../article/AA-V6-I2-The-Balls-in-Your-Court.pdf
Here is the relevant quote
The analysis showed that a tennis ball typically goes through three separate phases during an oblique impact: sliding, overspinning and rolling.
I use very low friction Wilson Revolve 17 gauge strings.
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JohnYandell
Hall of Fame
BSSH,
Yeah I don't agree with those quotes and they certainly aren't from me or my work. If you fire a ball at a clamped racket I have no idea what happens. I didn't go into our filming with any preconceptions but I can promise you that in live play nothing like that happens. You can subscribe to Tennisplayer for free for a month go into the interactive forum and find several super high speed clips of pro players that will show you what I saw.
Part of the problem may be with terminology. There is distension of the strings with the pocketing and some small rotation of the ball and it seems to "move" as the pocketing deepens around 3/8 of an inch as I said. But it simply can't slide a matter of inches because it is so deeply embedded.
As I said in a post above there is a clip floating somewhere on the TW site that shows all this. they just don't want me to post from my own site.
Yeah I don't agree with those quotes and they certainly aren't from me or my work. If you fire a ball at a clamped racket I have no idea what happens. I didn't go into our filming with any preconceptions but I can promise you that in live play nothing like that happens. You can subscribe to Tennisplayer for free for a month go into the interactive forum and find several super high speed clips of pro players that will show you what I saw.
Part of the problem may be with terminology. There is distension of the strings with the pocketing and some small rotation of the ball and it seems to "move" as the pocketing deepens around 3/8 of an inch as I said. But it simply can't slide a matter of inches because it is so deeply embedded.
As I said in a post above there is a clip floating somewhere on the TW site that shows all this. they just don't want me to post from my own site.
Chas Tennis
G.O.A.T.
I don't know the details of ball string interactions. There are many variables.
Often rackets are clamped when high speed video experiments are performed. In the high level serve, the racket is rotating rapidly about two rotation axes that, in my opinion, cannot not be simulated with a clamped racket. Also, high speed videos show very rapid racket rotations following off centerline hits. It has sometimes been said that the ball has left the racket before the racket can move. I don't accept that. I believe that the rotation of the racket from off centerline impacts may have a considerable effect on the forces on the ball. At this point, I don't believe that the simulations have covered off centerlinbe hits. This especially for a serve where if the ball hits to one side of centerline the racket rotates one way and on the other side of the centerline the other way. These off centerline hits then would add or subtract string speed to the ISR rotation in a non-simple way (rotation axes are different, etc.). Clamped rackets don't simulate the ISR of the serve or off centerline hits.
For your serves, a good approach is to first get all that your camera is capable of. See if you can get accurate enough estimates to support your views.
Do you have a camera with 240 fps? If you do close ups in bright sunlight and the motion blur is small, you may get some informative videos on your impacts.
240 fps with small motion blur most always gives
1) a frame before impact
2) a frame showing impact at a random time during impact
3) a frame after impact
Total time between 1) and 3): 8.6 milliseconds.
Back view and side view close-up and push the camera for all it's worth. Back views of impact have much smaller motion blur because the racket head and ball are moving away from the camera. This is critical information for stroke analysis, the killer application for high speed video.
Put into Kinovea and manually place markers to understand things as accurately as possible.
If the your camera has too much motion blur consider buying a used Casio F1, FH25 or FH100. They have shutter speed down to 1/40,000 sec. The current Casio Ex 100f has a shutter speed of 1/10,000 sec. A racket or ball at 100 MPH or 1760"/sec travels
1760"/sec X 1/10,000 sec = 0.176" = motion blur
You can see the advantage of a 1/40,000 sec shutter speed for 100 MPH objects.
Casio Fh100 with 240 fps and fast shutter.
Does your camera have a delayed trigger? I set mine to 10 seconds and then serve 2 or 3 times. Look along trajectory or perpendicular to the trajectory at ball impact.
ie don't prop your smartphone against the back fence on a towel.......
Often rackets are clamped when high speed video experiments are performed. In the high level serve, the racket is rotating rapidly about two rotation axes that, in my opinion, cannot not be simulated with a clamped racket. Also, high speed videos show very rapid racket rotations following off centerline hits. It has sometimes been said that the ball has left the racket before the racket can move. I don't accept that. I believe that the rotation of the racket from off centerline impacts may have a considerable effect on the forces on the ball. At this point, I don't believe that the simulations have covered off centerlinbe hits. This especially for a serve where if the ball hits to one side of centerline the racket rotates one way and on the other side of the centerline the other way. These off centerline hits then would add or subtract string speed to the ISR rotation in a non-simple way (rotation axes are different, etc.). Clamped rackets don't simulate the ISR of the serve or off centerline hits.
For your serves, a good approach is to first get all that your camera is capable of. See if you can get accurate enough estimates to support your views.
Do you have a camera with 240 fps? If you do close ups in bright sunlight and the motion blur is small, you may get some informative videos on your impacts.
240 fps with small motion blur most always gives
1) a frame before impact
2) a frame showing impact at a random time during impact
3) a frame after impact
Total time between 1) and 3): 8.6 milliseconds.
Back view and side view close-up and push the camera for all it's worth. Back views of impact have much smaller motion blur because the racket head and ball are moving away from the camera. This is critical information for stroke analysis, the killer application for high speed video.
Put into Kinovea and manually place markers to understand things as accurately as possible.
If the your camera has too much motion blur consider buying a used Casio F1, FH25 or FH100. They have shutter speed down to 1/40,000 sec. The current Casio Ex 100f has a shutter speed of 1/10,000 sec. A racket or ball at 100 MPH or 1760"/sec travels
1760"/sec X 1/10,000 sec = 0.176" = motion blur
You can see the advantage of a 1/40,000 sec shutter speed for 100 MPH objects.
Casio Fh100 with 240 fps and fast shutter.
Does your camera have a delayed trigger? I set mine to 10 seconds and then serve 2 or 3 times. Look along trajectory or perpendicular to the trajectory at ball impact.
ie don't prop your smartphone against the back fence on a towel.......
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JohnYandell
Hall of Fame
Chas,
Busy next few days but if I send you a couple of high speed clips that bear on all this, would you want to put them up?
Busy next few days but if I send you a couple of high speed clips that bear on all this, would you want to put them up?
Chas Tennis
G.O.A.T.
Yes, I can post them.
bigservesofthands
Semi-Pro
Here is a full access version of Rod Cross' paper
https://www.researchgate.net/public...tennis_ball_on_the_strings_of_a_tennis_racket
It does deal with hand held impacts as well not just clamped racquets. The paper claims the sliding happens for an even larger range of angles.
I believe that the ball does slide and for part of the time roll across the string before and after the embedding/pocketing , on oblique hits like spin serves. In some rare cases it might even skip across the bed embedding more than once like a rock skipping on water before it is finally pushed out.
Here is a close up animated gif of the rec kick serve that Chas posted.
The angle of incidence is very oblique. 10 degrees or less. The ball seems to slide across a large portion of the upper part of the string bed.
Thanks for providing Chas the clips to post. I look forward to studying them.
Thanks for the free trial suggestion. I might do the one month trial when I feel I have sufficient time to make use of that offer.
Chas Tennis
G.O.A.T.
Here is a full access version of Rod Cross' paper
https://www.researchgate.net/public...tennis_ball_on_the_strings_of_a_tennis_racket
It does deal with hand held impacts as well not just clamped racquets. The paper claims the sliding happens for an even larger range of angles.
I believe that the ball does slide and for part of the time roll across the string before and after the embedding/pocketing , on oblique hits like spin serves. In some rare cases it might even skip across the bed embedding more than once like a rock skipping on water before it is finally pushed out.
Here is a close up animated gif of the rec kick serve that Chas posted.
The angle of incidence is very oblique. 10 degrees or less. The ball seems to slide across a large portion of the upper part of the string bed.
Thanks for providing Chas the clips to post. I look forward to studying them.
Thanks for the free trial suggestion. I might do the one month trial when I feel I have sufficient time to make use of that offer.
I have placed red dots on the ball locations in Kinovea earlier. I'd like to see the red dot result for that video. If you wish to analyze that video I'd suggest trying Kinovea, it's fun but takes time especially when starting. I'll help.
I can't tell the position of the ball toward or away from the camera relative to the strings unless I'm seeing the squish. My first assumption is usually that it was in contact for 1 frame but for a moderate pace kick serve like that it could be two frames I don't know. I posted the video to show the image blur of the Casio FH100 and not to make any point using a video that is not good enough to show ball string contact.
Contact time is much clearer from the side. I have looked at a great number and believe one frame of contact is what I have seen nearly always. My Vimeo videos have many side views with fast shutters.
https://vimeo.com/user6237669/videos
I have made my arguments on interpreting videos and worked through your interpretations earlier, placing red dots and using shadows that happened to be there. The point is to be very uncertain when interpreting the videos. Approach suggested is to try other viewing angles that may better show what you want to observe.
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JohnYandell
Hall of Fame
Yeah I know Rod and have exchanged info and videos with him he's used in his work. But I think he has this wrong. That shot above shows one frame on the strings at most... maybe not even. At 3 milliseconds contact 240 frames is at the edge of seeable. Hopefully Chas will post the video I sent him.
Chas Tennis
G.O.A.T.
Here is a 10,000 fps video of a Gulbis forehand impact.
For stop action single frame hold down the SHIFT KEY and use the ARROW KEYS.
For stop action single frame hold down the SHIFT KEY and use the ARROW KEYS.
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tennis_ocd
Hall of Fame
Perfect! One short vid is more than 4 pages of posts. Now can we get his left arm, albatross motion at 10,000 fps?
JohnYandell
Hall of Fame
OCD sure but 10,000 frames may not be enough to truly understand it.
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tennis_ocd
Hall of Fame
Still a beautiful backhand and what will always be the best 2:22 seconds of any pressor....
JohnYandell
Hall of Fame
This is a typical representation. It shows the pocketing and also the poly snap back. The ball embeds deeply and stays in the pocket with some minimal rotation within that pocket.
bigservesofthands
Semi-Pro
Thanks for posting Chas. John I assume you provided this video to Chas. Thanks for that.
Sorry for the delayed response. I was in-trasit, flying cross country to visit my sister's family on the East Coast.
This seems to be a fairly flat hit. The approach angle is not very oblique. The out going spin rate seems to be a quarter or less of the incoming spin rate.
There is not much torque on the ball either as the wrist (and by extension forearm) is not rolling forward much, close to contact.
I would expect a short dwell time and not much sliding on the string bed for such a hit. Even then it did slide/roll 2 full main string widths just based on very obvious embedding that is clearly visible.
I would argue that there is ball string contact for maybe half to a full main string width more if a more grazing initiation of the contact (which cannot be determined with accuracy at this video angle, but can be inferred by slowing down of incoming spin) and a slight amount of grazing at release (which can be inferred from the wobbly speed up of the opposite spin, while the ball is fully losing contact with the string bed), are both taken into account.
A best possible video from my perspective would be a 10000fps video of a twist serve, hit wide. Oblique hits with high outgoing spin would help as well.
Chas Tennis
G.O.A.T.
Here is the kind of video that you can easily achieve if you have 240 fps and a fast shutter speed as discussed for taking a video of whatever stroke you are interested in from the side.
http://tt.tennis-warehouse.com/inde...hands-first-serve.563286/page-4#post-10489863
See frame before impact, impact and frame after impact at end.
What might you expect to see?
http://tt.tennis-warehouse.com/inde...hands-first-serve.563286/page-4#post-10489863
See frame before impact, impact and frame after impact at end.
What might you expect to see?
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bigservesofthands
Semi-Pro
Here is an animated gif from the rx10 video where the ball is impacting much more obliquely and it plucks the main strings as it goes along. The initial ones less forcefully, the one it embeds into the most and then one more on its way out.
bigservesofthands
Semi-Pro
I am trying to figure out how to control shutter speed on the iPhone 6 plus for slow motion videos. The apis that Apple released provide a way to do so manually (and ISO levels too if needed) since iOS 8, got a bit better in iOS 9 and have more options in the upcoming iOS 10. There are apps in the app store that allow you to use them in their custom camera apps. However there does not seem to be an app out there that does slow motion (they all are either for still shots or regular video). I tried some clumsy experiments to use the regular Apple camera app in bright sunlight in that orientation. There is still a lot of motion blur. Less then indoors but enough to make it not very useful. The iPhone native camera apps automatic exposure settings don't work very well in that orientation. I will keep looking.
BTW I have a Mac. I don't have a Windows license to run a virtual version of it on my Mac. So I cannot run Kinovea, since it is Windows only. I don't intend to spend money on a Windows license just to run Kinovea.
JohnYandell
Hall of Fame
I think this clip pretty much settles the argument about "sliding." I will look for one of the serve. The point is that the way the ball flattens and embeds deeply in the strings is going to be similar in all hits--where you have enough frames to really see. The idea that the ball and the string bed somehow both keep their shape and that somehow a round ball rolls or "slides" across a flat string bed isn't what happens. The movement of the racket creates an illusion of sliding when you don't have enough information to really see.
BTW no matter how clear the iphone or how you control the frames it's still 240fps not enough to see anything about the impact--but great for strokes!
BTW no matter how clear the iphone or how you control the frames it's still 240fps not enough to see anything about the impact--but great for strokes!
bigservesofthands
Semi-Pro
You need both high resolution and high frame rate to tell what is going on. The one I posted above is from a well lit 1080p 1000fps clip. So it does give detail that the 480p 10000fps low light clip you provided is missing but at 10 times longer time scales. Given recent camera advances, we will hopefully have 10000fps and 1080p footage of string bed+ball contacts like these soon. That will answer a lot of questions beyond much doubt.
JohnYandell
Hall of Fame
As for the light it was outdoors at Indian Wells. The resolution is good enough to see every frame of ball string contact.
Chas Tennis
G.O.A.T.
Here is an animated gif from the rx10 video where the ball is impacting much more obliquely and it plucks the main strings as it goes along. The initial ones less forcefully, the one it embeds into the most and then one more on its way out.
"...The initial ones less forcefully, the one it embeds into the most and then one more on its way out."
The gif is hard to examine because the individual frames may not all be there and I don't know how to extract them.
From the original video, time between frames about 1 millisecond.
Frame #1. The blue line indicates the same string in every frame (see throat location). I believe that this is before any evidence of contact, ball approaching strings. Ball top edge 2 strings above blue string.
Frame #2. Ball top edge 1 string above blue string. The racket is rising rapidly. There is probably some movement of the blue string. String deflection 1st contact evidence.
Frame #3. Ball top even with blue string. Blue string straight - its contact over. String below blue string considerably deflected. Contact.
Frame #4. String below blue string straight. 2nd string below string possibly slightly deflected. Ball top position at blue string. Contact & ball squish.
Frame #5. Ball top position one string below blue string. Can't tell if there is contact any longer.
Frame #6. No string deflections. Is there any evidence of contact?
Frame #7. No sign of contact.
Frame #8. No sign of contact.
No evidence of contact in frames #1 & #5. If true, contact could have possibly ranged from as short as 2 milliseconds to as long as 4 milliseconds. From Frame #2 to #5 the top edge of the ball moves 2 stings from above the blue string to below the blue string. (relative to the rising racket).
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bigservesofthands
Semi-Pro
"...The initial ones less forcefully, the one it embeds into the most and then one more on its way out."
The gif is hard to examine because the individual frames may not all be there and I don't know how to extract them.
From the original video, time between frames about 1 millisecond.
Frame #1. The blue line indicates the same string in every frame (see throat location). I believe that this is before any evidence of contact, ball approaching strings. Ball top edge 2 strings above blue string.
Frame #2. Ball top edge 1 string above blue string. The racket is rising rapidly. There is probably some movement of the blue string. String deflection 1st contact evidence.
Frame #3. Ball top even with blue string. Blue string straight - its contact over. String below blue string considerably deflected. Contact.
Frame #4. String below blue string straight. 2nd string below string possibly slightly deflected. Ball top position at blue string. Contact & ball squish.
Frame #5. Ball top position one string below blue string. Can't tell if there is contact any longer.
Frame #6. No string deflections. Is there any evidence of contact?
Frame #7. No sign of contact.
Frame #8. No sign of contact.
No evidence of contact in frames #1 & #5. If true, contact could have possibly ranged from as short as 2 milliseconds to as long as 4 milliseconds. From Frame #2 to #5 the top edge of the ball moves 2 stings from above the blue string to below the blue string. (relative to the rising racket).
I examined the ball contact frames in high zoom before generating and posting the animated gif.
I don't think the bar for determining contact should be large deflections like in frame 2. A discernible deflection that is not present before and cannot be explained by anything other than contact should be good enough. Secondary keys like the changes in movement and spin of the ball should also be taken into account.
In high zoom I certainly see evidence of string deviation close to the ball and string edge on the string marked in blue and a slightly smaller deviation of the string above the string marked in blue, in frame 1 (likely start of the creation of the pocket).
Similarly under high zoom, I see contact all the way to the 6th string below the blue marked string in frame 5. The shadow of the let cord interferes with more clear distinction of the string below that. The deflection is more indicative of light pocketing (higher frame rates will indicate whether it is initiation or release of the pocketing).
So I believe that at least 8 main strings were involved in the contact that is being discussed. But the deflection of the two strings below the one marked in blue deviated the most (more than all others combined likely) and contributed most to the spin. The other six main strings did influence the result of the contact.
Hopefully 10000fps video at 1080p and above resolutions for these oblique contacts will be available soon. This will allow us to accurately see the location of first contact and pocket initiation and also the location of pocket release and loss of contact on the string bed. This will allow us to accurately determine how far the ball slid/rolled on the string bed.
Given the distances involved and how fast the racquet is moving you would need a camera very close to contact, filming at 1000fps+ side on, to incontrivertably discern air gap. It is likely that you will need the camera to be moving as well to keep the frame from obscuring the contact. Till that happens we are left with indirect inferences like I am doing above.
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Chas Tennis
G.O.A.T.
Here is a Kinovea video where the ball at maximum squish is indicated by a green ring. Forehand from Sony RX10 III video above.
This video is intended for single frame analysis. It has labels that only show in one frame. For single frame in Vimeo hold down the SHIFT key and use the ARROW KEYS.
Best to click Vimeo and go full screen so that the time bar does not block the collision. At full screen on my laptop, I can reduce the size with the touch pad and only the time bar shrinks. Same for ctrl KEY and "+" and "-" signs, time bar changes size but not full screen video.
1) You can see ball size and movement relative to a green ring that indicates the maximum ball squish. Once the green ring and other indicators are placed they do not move in the video frame, so they do not move with the racket. Use blue lines for ball location relative to the racket.
2) Blue lines were placed on the same crossed strings for the frames around impact. Use them for a ball to racket reference.
3) Label for ball spin and reversal.
4) The video was taken with the camera panning to the right rapidly. The effect of panning is indicated by the yellow and red crosses in the center on the frame. The crosses indicate the location of a white reference mark on the wall as the camera pans. The camera panning has to be considered for the most accurate location measurements.
5) Frame Count is indicated. Each frame is 1/960 sec apart, 1.04 milliseconds. Close to 1 millisecond per frame.
This video is intended for single frame analysis. It has labels that only show in one frame. For single frame in Vimeo hold down the SHIFT key and use the ARROW KEYS.
Best to click Vimeo and go full screen so that the time bar does not block the collision. At full screen on my laptop, I can reduce the size with the touch pad and only the time bar shrinks. Same for ctrl KEY and "+" and "-" signs, time bar changes size but not full screen video.
1) You can see ball size and movement relative to a green ring that indicates the maximum ball squish. Once the green ring and other indicators are placed they do not move in the video frame, so they do not move with the racket. Use blue lines for ball location relative to the racket.
2) Blue lines were placed on the same crossed strings for the frames around impact. Use them for a ball to racket reference.
3) Label for ball spin and reversal.
4) The video was taken with the camera panning to the right rapidly. The effect of panning is indicated by the yellow and red crosses in the center on the frame. The crosses indicate the location of a white reference mark on the wall as the camera pans. The camera panning has to be considered for the most accurate location measurements.
5) Frame Count is indicated. Each frame is 1/960 sec apart, 1.04 milliseconds. Close to 1 millisecond per frame.
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bigservesofthands
Semi-Pro
As I predicted technology is catching up and footage is showing up in the public domain.
This is one of the best super slow motion high resolution kick serve videos that is available in the public domain at the moment (shot on a phantom).
Raonic's starting around 0:10.
Here is the ball string bed interaction
I highlight the slow down on first contact which is at the top right of the racket. This is followed by pocketing, sliding/rolling and then eventual ejection/acceleration of the ball from the top left. The ball is in contact with the string bed for more than half the width of the top half of racket. You can see it more clearly than in the gif above by zooming into to the video on a good monitor. Don't have time to generate a zoomed in high resolution gif.
So yes size of the racket does matter for modern strokes. You cannot hit effective modern kick serves with old style rackets with small heads. You would be clipping the frame often on them. This is as I had predicted based on what I feel when I serve a couple of years ago and backed by research available at that time. Now there is visual proof as I had predicted.
Chas Tennis
G.O.A.T.
I think that serve is probably a slice serve. See also the black marker on the ball and estimate the spin axis direction.
I can't tell if the ball is in contact with the strings from that camera view. The ball has a velocity component toward the camera (poorly shown) and a component to the right (well shown). For example, similar uncertainty, if a pencil is pointed directly toward you can you see how long the pencil is?
I can't tell if the ball is in contact with the strings from that camera view. The ball has a velocity component toward the camera (poorly shown) and a component to the right (well shown). For example, similar uncertainty, if a pencil is pointed directly toward you can you see how long the pencil is?
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J011yroger
Talk Tennis Guru
J
FiReFTW
Legend
J
The elegance of a balerina dancer right there.
J011yroger
Talk Tennis Guru
rogerroger917
Hall of Fame
Superstar!!!
J
Chas Tennis
G.O.A.T.
Pictures appear to be from the 3rd video of the OP.
3th serve video from OP.
This is a technique where the racket face faces the sky but the serve is not a Waiter's Tray serve. This serve uses ISR but more to rotate the upper arm while it is more horizontal than for a high elvel serve and also there is still an angle at the elbow. The face of the racket appears different as it approaches the ball as it must because it never was 'edge on' to the ball as for the checkpoint for the high level serve.
I believe that Bigservesofthands is getting very heavy pace with this technique. The ball is probably launched at a lower height and bounces lower. He appears to be tilted forward at impact. The ball appears to hit the backscreen hard and may still be rising. ? Proof to me that other techniques may develop high pace. BSSH claimed a measurement for one of his techniques of 131 MPH. I can believe that is possible. ?
(Pace can be verified by videoing the trajectory from the side with any known video frame rate. I've posted the technique.)
The high level serve uses both swinging motions and a distinct rotation (ISR) and the results of both of those motions appear in the racket rotations seen at impact. I have posted the video many times and discussed both rotations. This would not be the case for the above OP serve.
I believe, but do not know, that if pace is produced by two major racket motions, instead of just one, that control of the racket face may be more accurate and consistent. BSSH appears to get nearly all pace from closing the racket face at impact - as the video indicates. The high level serve gets its pace from both 1) closing the racket face plus 2) ISR rotation at impact, then the high level serve will be more reliable in my opinion. The problem for BSSH would be controlling the high & low of the trajectory, hitting the net or going long. He probably would have an advantage in controlling the side-to-side placement of the serve.
High level serve showing both closing & ISR rotation at impact as the racket moves forward.
Do you believe that the racket motions shown in this serve video are true for high level serve impacts?
3th serve video from OP.
This is a technique where the racket face faces the sky but the serve is not a Waiter's Tray serve. This serve uses ISR but more to rotate the upper arm while it is more horizontal than for a high elvel serve and also there is still an angle at the elbow. The face of the racket appears different as it approaches the ball as it must because it never was 'edge on' to the ball as for the checkpoint for the high level serve.
I believe that Bigservesofthands is getting very heavy pace with this technique. The ball is probably launched at a lower height and bounces lower. He appears to be tilted forward at impact. The ball appears to hit the backscreen hard and may still be rising. ? Proof to me that other techniques may develop high pace. BSSH claimed a measurement for one of his techniques of 131 MPH. I can believe that is possible. ?
(Pace can be verified by videoing the trajectory from the side with any known video frame rate. I've posted the technique.)
The high level serve uses both swinging motions and a distinct rotation (ISR) and the results of both of those motions appear in the racket rotations seen at impact. I have posted the video many times and discussed both rotations. This would not be the case for the above OP serve.
I believe, but do not know, that if pace is produced by two major racket motions, instead of just one, that control of the racket face may be more accurate and consistent. BSSH appears to get nearly all pace from closing the racket face at impact - as the video indicates. The high level serve gets its pace from both 1) closing the racket face plus 2) ISR rotation at impact, then the high level serve will be more reliable in my opinion. The problem for BSSH would be controlling the high & low of the trajectory, hitting the net or going long. He probably would have an advantage in controlling the side-to-side placement of the serve.
High level serve showing both closing & ISR rotation at impact as the racket moves forward.
Do you believe that the racket motions shown in this serve video are true for high level serve impacts?
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Tennisanity
Legend
As I predicted technology is catching up and footage is showing up in the public domain.
This is one of the best super slow motion high resolution kick serve videos that is available in the public domain at the moment (shot on a phantom).
Raonic's starting around 0:10.
Here is the ball string bed interaction
I highlight the slow down on first contact which is at the top right of the racket. This is followed by pocketing, sliding/rolling and then eventual ejection/acceleration of the ball from the top left. The ball is in contact with the string bed for more than half the width of the top half of racket. You can see it more clearly than in the gif above by zooming into to the video on a good monitor. Don't have time to generate a zoomed in high resolution gif.
So yes size of the racket does matter for modern strokes. You cannot hit effective modern kick serves with old style rackets with small heads. You would be clipping the frame often on them. This is as I had predicted based on what I feel when I serve a couple of years ago and backed by research available at that time. Now there is visual proof as I had predicted.
Doesn't look like that to me. It looks as if the ball comes in and goes out from the same top right, I think you'd see that from another angle.
Stefan Edberg's main weapon was the kick serve. He used 85 in racquets for the most part, if I'm not wrong. If you're saying that amateurs are better off serving kick serves with bigger head racquets, that's one thing. However, to categorically state that you cannot hit effective modern kick serves with old style racquets with small heads doesn't seem correct.
coolschreiber
Hall of Fame
As I predicted technology is catching up and footage is showing up in the public domain.
This is one of the best super slow motion high resolution kick serve videos that is available in the public domain at the moment (shot on a phantom).
Raonic's starting around 0:10.
Here is the ball string bed interaction
I highlight the slow down on first contact which is at the top right of the racket. This is followed by pocketing, sliding/rolling and then eventual ejection/acceleration of the ball from the top left. The ball is in contact with the string bed for more than half the width of the top half of racket. You can see it more clearly than in the gif above by zooming into to the video on a good monitor. Don't have time to generate a zoomed in high resolution gif.
So yes size of the racket does matter for modern strokes. You cannot hit effective modern kick serves with old style rackets with small heads. You would be clipping the frame often on them. This is as I had predicted based on what I feel when I serve a couple of years ago and backed by research available at that time. Now there is visual proof as I had predicted.
PoPo!!!!!! You're back!!!! This clown show just got back on the road everyone.
mbm0912
Hall of Fame
poetry in motion
J
Raul_SJ
G.O.A.T.
He is in that position right around when the ball has bounced in the service box; still time to recover.
It's okay as long as you are balanced and able to recover for the return, which it looks like he is.
He is not really moving laterally much; mainly spinning.
Wander
Hall of Fame
BSSH talks a lot of unsubstantiated crap like balls pocketing multiple times during high top spin strokes and this hokum about the ball sliding and rolling on the stringbed for 10-15cm. Of course this is not actually true.
The problem is that oftentimes his weird theories are mixed with real scientific stuff, and he seems very serious about studying tennis strokes. But his perception of what's going on at contact point is suspect at best.
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JohnYandell
Hall of Fame
More than suspect!
sredna42
Hall of Fame
MasturB
Legend
J
Might be better suited for throwing a cricket ball. Or playing jai alai.
rogerroger917
Hall of Fame
Pomo is the new era of tennis.
