Discussion in 'Racquets' started by TW Staff, Feb 3, 2014.
The second video
I got the message
"this video is private"
Fortunately I'm playing the Babolat pure drive play...
Why is the power too low? Because you have some ego number in mind? The value of the number is how it changes in each session, not some relative scale. IMHO if the pros are 100 then 13 is probably accurate based on the vid. though I bet Zepp learns from these posts and inflates so the rec player "feels better".
I sent the videos to Zepp support and they wrote back that the values are way too low. I would prefer an absolute power figure being used. Zepp support told me that the sensor seems to be faulty and they would send me a new one.
But according to you, pros hit ten times harder than this:
See they ARE learning!
Maybe it is defective, but compared to this video, yes:
10x would be over the 100 power level but I think you can see the difference in the vids.
Certainly a twenty year old pro hits much harder than a 69 year old amateur. But do you understand what 10 times harder means? And no, I am not in a dick-measuring contest.
Well we are assuming some things, like that its some sort of linear progression. Maybe its some inverse logarithmic function or maybe its just tracking RHS and perhaps 7x (13 to 100 is about 7x)RHS doesnt lead to 7x ball velocity, etc.
Even if we knew I can't see how useful an absolute number would be, though the relative numbers between session or after starting new technics, weight training, etc. would have value.
Anyhow for 69 you are in great shape and you should market your secret.
How do you know whether it is really RHS?
There is a second option
220 kms per hour quoted for a competing vendor
220 kms per hour as a speed of an outgoing ball quoted as a max value for
a competing vendor
Babolat Team member
That is the problem: no information on how to interpret the metrics or how they are derived.
I still think there is a race to bring a product on the market (to get an early ROI for further development?) and immature products are coming out. Had I known, I would have waited 6 months... It was just the novelty effect that lured me...
Channels of communication
I believe some channels of communications should be open.
Chris Edwards is an excellent source of info-
he tried both sensors.
He is getting consistent power numbers for both sensors.
I have posted some questions for Chris Edwards in the section entitled
He responded to first three questions.
He promised a TW review shortly after March 17th (which is not very far away).
My experience with sensors as described above is limited to avionics.
I have checked that there are no Customer Reviews posted by TW US
for a Zepp Sensor.
I have looked for independent reviews of a Zepp sensors in Europe
and I cannot find them.
There is a manual for a Zepp sensor but it does NOT answer all of my questions.
There are tutorials as well.
I assume you know all tutorials already.
The max numbers for forehands from the ATP tour are in the range 100-124 mph
The link below
provides a list of publications on forehand.
The max numbers for forehands for elite Austrian players are below 60 mph,if my memory serves me well.
I have checked corresponding reviews for a Zepp golf sensor
There are three or four threads with a discussion about a Zepp sensor.
Please let me know which posts/threads of mine are of low technical quality and I will put an effort to improve them.
I don't, and I did use the word MAYBE a few times.
Do you know what it is really measuring?
Strongest forehand I got was 61. Strongest backhand was 63.
I clocked a 71 serve that was definitely an outlier.
BTW: the Zepp support team wrote me that:
The other issue I had was that I kept getting other user's data on the iPhone app instead of mine. This was finally resolved.
I should be getting a new Zepp sensor by midweek....
110 miles per hour?
110 miles per hour if I understand the max value issue correctly.
156 km/h racquet head speed... I'm not sure I serve that fast usually.
As I said my average power is well below 50 percent normally.
110 miles per hour
110 miles per hour was referring to an outgoing ball speed
Did you get your new sensor?
Did you get your new sensor?
Do you see any areas for improvement?
Do you see any areas to improve your serve?
Did you try to combine/cross reference your sensor data with videos of your strokes?
Arrives by Wednesday afternoon...
on the serve racquet head speed and swing speed are the same aren't they?
I've been mostly looking at the impact locator. I've seen some big improvements there. Also, I look at hitting more backhands and more topspin backhands. The one thing I don't care too much about is increasing my power... I'm very far from that unfortunately.
Two different enities
Two different entities are:
A racket head speed and an outgoing ball speed.
They are at the ratio 7 to 10 for forehand.
Probably a similar ratio for a serve.
Please let me know whether my explanation is clear enough
Please elaborate whether an impact locator improved your serve.
I do not understand the last sentence
I do not understand your last sentence.
Your power numbers for forehand are very good.
I do not know what a swing speed is
What strnings and which tension (ball park)?
I'm using rpm blast at 48 lbs. I think the Babolat sensors only measure the swing speed but don't give you a measure of the outgoing ball speed. I'm saying that because Babolat official says that string type/tension or lead tape won't affect the measurement. However, I don't know this for sure.
I'm wondering whether this topic should be discussed in a Babolat play thread and not here but I'll first answer the other questions you asked me. I already gave the answer to some of your questions in the Babolat play playtest thread btw.
When I wrote swing speed I meant outgoing ball speed. I am pretty sure the ratio is not the same for forehand and serve. On serve you hit a static ball that has no incoming speed.
I'm just not trying to hit harder or heavier balls. I've improved my consistency by hitting less off center shots. I discussed this in the Babolat play playtest thread. Mostly on my backhand and then on my forehand. I got some tips here on tt on how to do that btw.
i meant racquet head speed/outgoing ball speed. Sorry about that.
Not an official tester, but received my zepp. Have the testers got theirs yet?
So far one session. Seemed to collect accurate info. Not obvious since no minute by minute data similar to fitbit/jawbone app. At least start and end time would be nice. Also my session was recorded on a random day. Not sure how it's supposed to track date/time, but didn't work so far. Anyone have this happen?
Comfort-wise I didn't notice weight or impact to grip. I put it under my overgrip. Also I don't hold at the end of the grip.
* edit *
Resynced and the data includes more realistic power and duration and date!
A new thread entitled "sensors"
I will move some questions to to the thread entitled "sensors"
I will respond in the thread entitled "sensors"
I will respond in the thread entitled "sensors"
Zepp sensor finally works for me! Playing on clay courts in lugano
Gave very low figures, trained this week in dubai on hard courts
And now results are good: serve 62 average, 79 max. Forehand 50 average, 60 max, backhand: 42 average, 70 max, now
I wonder why does the surface make such
A big difference? If explainable. Zepp should add a parameter for surface type.
Hard surface and high temperature
Hard surface and high temperature did provide a higher speed of
an incoming ball (for forehand and backhand).
Don't think so. Played with 20 C in Lugano (indoors) and with 24 C (early morning in Dubai). Moreover, it was a slow hardcourt. Noticed no difference in speed. And anyway, it could not make a difference of a factor of 4.
Hard courts in Dubai
Hard courts in Dubai accumulate heat during the day.
Layer number 6 or number 5 is generally a rubber.
A quality and a weight of balls could matter as well
Even a difference between hard surface balls in Dubai and clay balls
in Lugano could matter
What does the Zepp sensor measure is the question? Swing? Impact?
If it matters that much, then these must be parameters to be entered when configuring the Zepp app.
The equation for momentum is: m(of tennis ball) x v(of tennis ball) + M(of racket) x V(of racket) = m x v' + M x V', v' and V' being the velocities after impact.
Newton: At impact - The force of the ball on the racket is equal and opposite to the force of the racket on the ball.
So: m (mass of tennis ball) x a (acceleration of tennis ball) = M (mass of tennis racket) x A (acceleration of racket)
a = v - v'
A = V - V'
The important factors are:
- swing speed of racket
- weight of racket
- speed of ball before impact
- weight of tennis ball
Apart from my problems with the surface, shouldn't a configuration parameter also include weight of the racket for more accurate measurement?
As I understand it:
The Zepp sensor has two acceleration sensors using piezoelectric effect to detect acceleration and gyro sensor: detects angular velocity using the coriolis force.
At impact with the ball, the racket rebounds slightly - this force can be calculated then from the resulting brief acceleration acceleration rebound value measured (and a default racket mass value).
The gyro sensor detects the direction of movement at impact, so it knows what type of spin applies.
Comparison with Sony
Sony limits usage of their sensor to four models.
To the best of my knowledge all four models have very close weights.
So in the case of Sony there is no issue-see your last sentence.
You may consider asking a Zepp support the question.
Once more i find a conversation very useful.
It provides an insight what sensors do well
The only thing to regret is that we did not do this analysis two months ago
I believe swing weight is an important parameter as well.
The only problem is that it does not enter in an obvious way equations
you posted above
Ball machines are recommended for testing sensors.
If a ball machine has multiple speeds comparing results from a slowest
to fastest gives some idea what a sensor can do for a given surface of courts
Separate names with a comma.