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PostPosted: 12 Feb 2017, 11:02 
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I've seen lots of stats of how fast a table tennis ball can travel, but many are quite inaccurate because measurements are done at an angle to measuring sensor, and sensors can't take an instantaneous measurement, so they average over time.
So lets collect sources and theories in their discussion, to see if we can come to some consensus.

1. http://www.jayandwanda.com/tt/speed.html 70MPH ie 112km/h

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PostPosted: 12 Feb 2017, 13:15 
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In the past, I have done estimates using my cam corder film editor, using actual start and finish of ball. Then used online formula for calculation. The distance was estimated based on the table length.

I have calculated 69 mph

60-70 mph or 96-112 kph seams reasonable

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PostPosted: 12 Feb 2017, 15:33 
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That sounds very similar to the one above :up:

Did you calculate the speed at several intervals, to come up with a speed vs time curve, to estimate the initial speed?

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PostPosted: 12 Feb 2017, 21:02 
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haggisv wrote:
That sounds very similar to the one above :up:

Did you calculate the speed at several intervals, to come up with a speed vs time curve, to estimate the initial speed?


No

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PostPosted: 12 Feb 2017, 22:18 
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I can't believe this hasn't been done already many, many times in kinesiology labs all over the world by MSc or PhD students in Physical Education departments at Universities. I've personally heard of two studies involving table tennis at universities, with people known personally to me involved. It wouldn't take much more than a movie or video camera off to the side, shooting against a backdrop marked off with a pattern or grid. I'll betcha Butterfly has lots and lots of video. The only thing would be to find the published literature or theses - there's probably dozens done over the years. The papers will be in scientific journals, not in magazines or other sorts of media for public consumption. Butterfly's stuff probably never gets published.

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PostPosted: 13 Feb 2017, 02:10 
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LOOPOVER wrote:
In the past, I have done estimates using my cam corder film editor, using actual start and finish of ball. Then used online formula for calculation. The distance was estimated based on the table length.

I have calculated 69 mph

60-70 mph or 96-112 kph seams reasonable

Yes. Unfortunately if you are only using one camera you are prone to distortion from the lens. Even shooting at 50 fps I found the ball moved approx 9 inches during which time there was no image to capture. This is why the ball looks like a long sausage in the video below. That again builds inaccuracy in to the process so comparative speeds are the best you can hope for rather than absolute. You also have to define an area in the video in terms of calibrating the "length" measurement for tracking the distance the ball travels relative to speed. Get that measure even slightly wrong and it can make a big difference

Here's a quick and dirty example of what you can do - there are lot's of other possibilities our there too.



In this video, I've not showed you my first attempt at measuring the speed. The "line of calibration" was marginally off and it made 2-3mph difference in the serve alone. Not much when you look at one video of two shots but if I was testing 100's of rubbers on different blades, playing different shots, against different degrees of spin that 2-3mph would compromise the results significantly. Accuracy is essential if you want credibility along with consistency / continuity over many days shooting - either that or admit your results are comparative only.

iskandar taib wrote:
I can't believe this hasn't been done already many, many times in kinesiology labs all over the world by MSc or PhD students in Physical Education departments at Universities. I've personally heard of two studies involving table tennis at universities, with people known personally to me involved. It wouldn't take much more than a movie or video camera off to the side, shooting against a backdrop marked off with a pattern or grid. I'll betcha Butterfly has lots and lots of video. The only thing would be to find the published literature or theses - there's probably dozens done over the years. The papers will be in scientific journals, not in magazines or other sorts of media for public consumption. Butterfly's stuff probably never gets published. Iskandar


Yes they have and yes there are. Usually doppler radar is used in conjunction with high speed cameras. Just look at how baseball coverage can now track incoming ball speed and spin rates and outgoing ball speed and spin rates seamlessly. Trackman are involved with the baseball. I contacted them over a year ago asking them if their hardware could be used to calculate speed and spin rates for the table tennis - the answer was a flat no. There are different algorithms needed due to different ball sizes, weight etc. They also told me they had no intention of moving in the direction of table tennis at that time (probably not enough money in it for them).

I also know the ITTF are interested in this line apporach and they have commissioned research in this area

Study of Low Cost Doppler Sensors for Detecting the Spin on A Ping Pong Ball:
https://repository.ntu.edu.sg/handle/10 ... ?show=full
but the results to date highlight how difficult it is to do for table tennis and as far as I know it's not cost effective yet for the ITTF to even consider introducing.

And I've contacted other "golf swing analisis providers" but again, their maths is done for golf not table tennis which limits the use of their products and to be blunt, they hadn't even considered table tennis as a sport the application could be adapted for. Zepp do a tennis app (adaptation of their golf swing analyser - they are who I contacted) but their golf app is more for counting how many backhands and forehands you play and giving an idea of your service action rather than calculating actual spin and speed or angle of contact. I'm also not sure how it would cope with having to analysis multiple shot data from a very quick rally of say 6 shots in just a couple of seconds.

But this is definitely an area I am keen to explore further, no, it's definietely an area I wll explore further (probably need to be done in partnership as the cost, time and science involved is out of my reach) and I'll not just consider the measuring speed and spin either but that's for another day... My dream job :) = viewtopic.php?f=9&t=30841

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PostPosted: 13 Feb 2017, 11:56 
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I can see how a doppler radar can work out speed quite accurately, although the return signal must be very weak with such a small plastic ball. I'm not sure how they sense spin though...I would expect the additional speed of the surface, and the fact that the surface is so smooth, would make this return signal extremely weak. Using a ball with a pattern, and a very high speed camera, would seem a more appropriate choice.

The problem with using an averaging method for determining speed, would be that the speed drops off so dramatically at high speed due to the drag. The addition of spin would probably make this even worse. However, adding spin takes away from forward force on the ball, so I think it's quite safe to assume that the fastest ball will be one that's hit flat. So if we can measure the speed at many points during it's trajectory, and we know the relationship between drag force and speed, we should be able to estimate initial speed quite accurately.

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PostPosted: 13 Feb 2017, 15:26 
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While the flat-hit ball will have the fastest initial speed, the fastest USABLE balls in table tennis will be the ones with the most topspin, because they balls have to travel over the net and hit the table. The more topspin you can put on the ball the faster you can hit it and still have it hit the table. This is the basis behind the modern fast loop.

The reason why table tennis balls slow down so much is that they weigh so little, and have little momentum. Drag is proportional to the square of the speed, so increasing the force with which you hit the ball might increase the initial velocity but will not increase the velocity off the ball one foot away from the racket by nearly as much. It's a case of diminishing returns. Eventually you hit the ball hard enough to break it, and that's the limit of the initial speed you'll ever achieve. Don't know if anyone's strong enough to do this, but you could build a machine that can. Wonder what that Kuka robot can do.. :lol:

I guess now I know how they get those instant ball speed displays in tennis matches... :lol: I always suspected it had something to do with radar. Tennis balls are a lot larger than table tennis balls, of course, and have much larger radar cross-sections. You could also even build tennis balls with metallic, radar-reflective layers inside if you needed to. Doppler radar is, of course, how radar guns work (I never really thought about it before).

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PostPosted: 14 Feb 2017, 06:25 
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Re measuring the speed of tennis balls, I remember that at one stage they had some trace amount of metal added to them so that the speed could be measured via the radar doppler method. I suspect that with the advent of Hawkeye that it is now done via camera, given the touted accuracy of Hawkeye with respect to line calls, but I cannot confirm this.

Does this mean that in the absence of camera technology that the celluloid / poly material of the ball may need to be adulterated with the same for radar doppler speed determination?

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PostPosted: 14 Feb 2017, 07:12 
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They had a demo booth at one of the US National Championships with a robot and radar gun. Anyone could try their hand at smashing or looping to see the speed they achieved. Most of those I saw trying were the typical basement players with no technique and borrowed rackets and hitting 40 mph or so. I think the top speeds for that day were in the 50 to 60 mph range by some players with technique. I'm guessing 100 mph might be possible over a short distance with a freakishly fast blade and rubber and a person with a live arm.

Coming from a pressurized situation into a vacuum chamber the ball can travel at supersonic speed.


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