Tennis Warehouse: Zepp Tennis Sensor Playtest

julian

Hall of Fame
The lowest position of a vertical drop

What I don't get is that apparently some users are happy with their 3D serve trajectories, whereas mine are often off the mark. Sometimes OK, sometimes way off, and I do not have any great variance in my stroke...
The lowest location of a vertical drop of your post number 314 could be improved/"lowered"
assuming that the picture/snapshot provided by Zepp is "correct"
Your video indicates that it is NOT.
My post is not a criticism of your serve.
 

julian

Hall of Fame
Hidden assumptions

I believe there are 3 hidden assumptions in the 3D serve analysis:
Location of a tossed ball at a contact (probably a straight up toss)
A velocity of a tossed ball (small comparing to a racket head speed)
A small value of spin for a tossed ball.
 
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julian

Hall of Fame
Another thread

What I don't get is that apparently some users are happy with their 3D serve trajectories, whereas mine are often off the mark. Sometimes OK, sometimes way off, and I do not have any great variance in my stroke...
See as well another thread untitled
"Succesful and unsuccessful tennis serve" in the section
Tennis Tips/instruction
 

julian

Hall of Fame
Apex

What I don't get is that apparently some users are happy with their 3D serve trajectories, whereas mine are often off the mark. Sometimes OK, sometimes way off, and I do not have any great variance in my stroke...
Your apex should be compared with an apex of other Zepp users
 

julian

Hall of Fame
Two serves-2 tosses

What I don't get is that apparently some users are happy with their 3D serve trajectories, whereas mine are often off the mark. Sometimes OK, sometimes way off, and I do not have any great variance in my stroke...

Say you "have" two serves A and B.
The first serve A was successful.
You toss a ball for the serve B.
Say the toss B is lower by 2-3 inches from some reasons.
How do you adjust your vertical drop to get the serve B in?
Obviously you "shorten" your vertical drop/nadir or you increase the speed of the racket to make-up for a lower toss.
Which parts of a body are utilized to accommodate that?
Obviously the elbow is one
 
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gzhpcu

Professional
Julian, that is not my question you are remarking on. I asked why some persons are happy with the 3D trajectory, whereas I am not.
 

julian

Hall of Fame
Units and definition

Don't understand the question... is it rhetorical? :confused:
There are two points made by others previously:
The tracking mode provides dimensionless numbers.
3 D provides numbers with dimensions
The tracking mode does NOT provide the definition of power.
The 3D mode talks about the racket head speed.
Do we compare apples with apples?
 

gzhpcu

Professional
There are two points made by others previously:
The tracking mode provides dimensionless numbers.
3 D provides numbers with dimensions
The tracking mode does NOT provide the definition of power.
The 3D mode talks about the racket head speed.
Do we compare apples with apples?
Julian, I am not talking about figures. I am talking about the graphic in the 3D serve...
 

julian

Hall of Fame
TW review

Yeah, but not details about tracking mode figures, 3D serve mode trajectories stats, nothing... I would like to hear users comment on these points and if they find the results satisfactory, not trivial stuff like the mount and the bluetooth synch...

TW is preparing a review.
You may request some answers,I think
 

julian

Hall of Fame
I am getting some feedback from my students

Yeah, but not details about tracking mode figures, 3D serve mode trajectories stats, nothing... I would like to hear users comment on these points and if they find the results satisfactory, not trivial stuff like the mount and the bluetooth synch...
I am getting some feedback from my students.
Basically zepp gives a contact point too low.
 
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julian

Hall of Fame
How do you know that a trajectory is "bad"?

Yeah, but not details about tracking mode figures, 3D serve mode trajectories stats, nothing... I would like to hear users comment on these points and if they find the results satisfactory, not trivial stuff like the mount and the bluetooth synch...

I have a question for you:
how do you know that a given 3 D trajectory is "bad"?
There are obviously 2 cases:
1. A good quality video is available to compare with
2.there is no video
My question is serious
Switching gears a bit.
A clean trajectory is presented in
http://www.youtube.com/watch?v=lPBM-hE1Dhw
I have only a backhand trajectory
 
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julian

Hall of Fame
For gzhpcu

Hi,
Say that you have a red line.
Say that the red line is almost vertical.
Is it correct to assume that the northern end of the red line
corresponds to an earlier time?
 

gzhpcu

Professional
I have a question for you:
how do you know that a given 3 D trajectory is "bad"?
There are obviously 2 cases:
1. A good quality video is available to compare with
2.there is no video
My question is serious
Switching gears a bit.
A clean trajectory is presented in
http://www.youtube.com/watch?v=lPBM-hE1Dhw
I have only a backhand trajectory
A given trajectory is bad when portions of the trajectory go off the screen, or the trajectory does not go above the head...
 

gzhpcu

Professional
Hi,
Say that you have a red line.
Say that the red line is almost vertical.
Is it correct to assume that the northern end of the red line
corresponds to an earlier time?

The line (actually the form is a quadrilateral, filled in with red) represents the inclination of the racket. Since the trajectory goes forward, the upper corner point and the lower corner with the connecting line is the start time for impact.
 

julian

Hall of Fame
Your vertical drop

A given trajectory is bad when portions of the trajectory go off the screen, or the trajectory does not go above the head...
Where is a vertical drop in your post 314 ?
Please see my e-mail
 
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julian

Hall of Fame
Zenith and nadir of the video should be reproduced

A given trajectory is bad when portions of the trajectory go off the screen, or the trajectory does not go above the head...

Zenith and nadir of a video/your video should be reproduced at least
approximately.
My statement is much stronger than yours.
The shape of your backswing taken from the video is different than one produced by a trajectory of Zepp.
There is a list of other parameters which can be compared between a video and trajectory
(see
J Appl Biomech. 2013 Oct;29(5):573-82. Epub 2012 Dec 27.
The effect of age on discrete kinematics of the elite female tennis serve.
Whiteside D1, Elliott B, Lay B, Reid M.)
 
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julian

Hall of Fame
May I try again?

The line (actually the form is a quadrilateral, filled in with red) represents the inclination of the racket. Since the trajectory goes forward, the upper corner point and the lower corner with the connecting line is the start time for impact.
There 4 corners/vortices
They do correspond to 4 different frames.
Which corner/frame is the last ? timewise?
 

julian

Hall of Fame
I goofed

I don't think that you read the whole thing exactly. The article I referenced is in regards to pitching, not batting.

Zepp uses this same sensor for a baseball hitting app I believe.

John

I goofed. It is one of problems with Internet.
You asked the question:
"Isn't what they are doing basically the same thing?"
I have thought that "they" meant Zepp.
I have said that implicitly what you have said in your last sentence above AND I added
that Zepp for baseball is solving easier problem than Zepp for tennis.
No harm done.
Sorry
 
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julian

Hall of Fame
A racket should go "down" after the contact

A given trajectory is bad when portions of the trajectory go off the screen, or the trajectory does not go above the head...

A racket should go down after a contact
Post number 265 violates the principle stated above.
Post number 268 is very borderline,even for a kick serve
 
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julian

Hall of Fame
Trophy position is very shallow

Next question: how come they don't notice that it does not make sense?
The trophy position of the trajectory in question is very shallow.
In another words a vertical drop is very shallow.
Please let me expand on this one.

It is not obvious whether :
1. a player has a very shallow vertical drop.

OR

2.the player does not have a shallow vertical drop but a trajectory produced by a sensor
suggests that a vertical drop is shallow.

The distinction is important because we have to define what is tested:
1.the technique of the player in question
OR
2.technology producing trajectories.

Just to make sure that I am explained myself clearly:
I am not over critical of Zepp.
I am trying to get focused on one given subject of a conversation.

Switching gears a bit:
For comparison please see the video of Serena.
Please click "loading part" and "the acceleration part" of

http://www.dartfish.tv/Player.aspx?CR=p611c91651m2149588&CL=1
 
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kimguroo

Legend
Now I have pro mount problem like other users.
Zepp device is just not staying with pro mount. It flies several times during playing...
 

julian

Hall of Fame
Federer

When you jump, you do not jump and hit the ball on the way coming down...
https://www.youtube.com/watch?v=x83QWTDggN4
You jump up towards the toss...
Let me make couple of trivial remarks:
There are 3 principles "used"by Federer:
1.a contact point is as close as possible to a highest point of his/video trajectory

2.a head speed of a racket is maximal around a contact point

3.a vertical drop of a racket provides a significant contribution to a head speed of a racket

My understanding of coaching is that items 1 and 3 should be implemented,
say for high performance juniors.

If I would use a Zepp sensor I have to be sure that a sensor is somehow in sync with me/ coach.
My humble opinion is that we are not at this stage yet.

I understand that item number 3 is kind of trivial.
Basically if a coach is not satisfied with a speed of a ball pro produced he/she may try to
work on "increasing" the vertical drop.

Post number 268 demonstrates the case when a contact is too early.
Once more it is not obvious whether it is a player or Zepp
The racket should go down in post number 268 after a contact,
at least I teach this way.
 
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gzhpcu

Professional
How can they show such a trajectory? Don't they have tennis player testers to interpret the information generated? :confused:
 

julian

Hall of Fame
Please see my E-mail

Julian, do you have a Zepp sensor? If not, recommend you get one for hands on experience...

Please see my E-mail.
I have multiple problems with understanding trajectories.
I understand videos better.
I appreciate your feedback.
 
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gzhpcu

Professional
Please see my E-mail.
I have multiple problems with understanding trajectories.
I understand videos better.
I appreciate your feedback.
I prefer videos actually, but sometimes for a quick look (not video replacement), I would like the Zepp info (if only it worked...)

I also wonder if the size of the stationary figure is not misleading at times, and if it is sized according to the configuration parameter of player height entered in the Zepp application...
 

julian

Hall of Fame
size of the stationary figure

I prefer videos actually, but sometimes for a quick look (not video replacement), I would like the Zepp info (if only it worked...)

I also wonder if the size of the stationary figure is not misleading at times, and if it is sized according to the configuration parameter of player height entered in the Zepp application...
You are probably right in your last sentence.
However it maybe one of two issues.
The second issue in your post 265 is that it looks like a racket goes UP after the contact.
I do not think it can happen in realistic serves
 

gzhpcu

Professional
You are probably right in your last sentence.
However it maybe one of two issues.
The second issue in your post 265 is that it looks like a racket goes UP after the contact.
I do not think it can happen in realistic serves
Maybe it was a bad serve. To really check, one should video the session and then check the serves with the Zepp sensor...
Or hit a serve, check it right away on the video, check it right away on the Zepp app.
 
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kiki

Banned
Another Led Zepp thread!!!
Oh God...they are so sensitive musicians they have a sensor named after them!!!
 

gzhpcu

Professional
So, I got the new version. Here is the "improved" 3D serve feature:

cGPVxCJK.jpg


How can they get it so wrong??
 
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