Serve speed cage

[drakulie]

Guys, the speed trac measures speed in an area in front of it. In other words, if it is placed directly on the net, it will pick up the speed of the ball as it approaches the net>> Not directly at the net.

When mike and mav did testing of my serve speed measured against the radar on my vid, it was determined the speed trac was off by about 5-7 mph.

What I mean when I say "off", is if my serve speed would have been picked up as it left the racquet face (like they do in pro tournaments), as opposed to when it approached the net, my serve would have been 5-7 mph faster than what the speed trac measured.

jolly, good stuff!! Thanks for taking the time to do this. Much appreciated.

[drakulie]

Originally Posted by J011yroger

Maybe I could use a soccer goal?

I'm not exactly keen on the idea of serving into a chain fence from close range.

J

Put the speed trac behind the fence, and serve at the fence.

[fruitytennis1]

Originally Posted by fruitytennis1

Id say a 60 mph heavy topspin/kicker can prob hit the fence. Mabey add about 5 mph for a flat serve unless it hits the service line.

Im quoting myself... Well so this would be about correct if your talking about speed from the racquet face right???

[5263]

Originally Posted by Cindysphinx

How much difference does it make that Jolly is taller than I am? (I don't know this for a fact, but everyone is taller than I am!).

I would think that Karlovic's 33 mph serve would hit the fence, whereas Michael Chang would need a lot more mph.

Then again, I know nothing of science or physics or stuff like that.

yep, Cindy, those things matter.
That's where the common sense comes in with general rules of thumbs. you have to take the flyers out of the equation.

[canadave]

Originally Posted by J011yroger

I have a 2nd little baby tripod, and I was tempted to put the speed trac up on it, and make it exactly the hight of the net to try to cut out some angle error from the radar resting on the ground, but knowing me, on my very first serve I would hit the thing and that would be the end of that.

J

That might work, though, if you just secured the tripod to the net with some cord. That way if it gets hit, it doesn't get knocked over. The only way it'd be damaged is if you hit the gun itself and hit it so hard with the ball that you damaged its sensitive electronics

[canadave]

Or (in thinking about this further), would it not help to cut down the angle differential if you placed the speed gun on the ground, but back in the receiving court (perhaps around the service line, or even at the baseline?)

[drakulie]

^^^LOL. Don't try it. I did, and came extremely close to hitting the radar. Not worth it, IMO.

Here is a vid I took of the moment:

I placed the radar on the opposite side of the net (more than half way up) the service line:

http://www.youtube.com/watch?v=uvs1-q9ip5E

If I would have hit the radar, it would have surely smashed the poor thing.

Here is another one, although It didn't come as close to the first one:

http://www.youtube.com/watch?v=OjBOV9zsrps

Here is one I took, where I hit the camera. The camera was mounted on the fence, about 5 feet up. (fence, 23 feet from baseline): (luckily, the camera didn't break).

http://www.youtube.com/watch?v=FGWip2F_e7M

[5263]

Originally Posted by drakulie

^^^LOL. Don't try it. I did, and came extremely close to hitting the radar. Not worth it, IMO.

Here is a vid I took of the moment:

I placed the radar on the opposite side of the net (more than half way up) the service line:

http://www.youtube.com/watch?v=uvs1-q9ip5E

If I would have hit the radar, it would have surely smashed the poor thing.

Here is another one, although It didn't come as close to the first one:

http://www.youtube.com/watch?v=OjBOV9zsrps

Here is one I took, where I hit the camera. The camera was mounted on the fence, about 5 feet up. (fence, 23 feet from baseline): (luckily, the camera didn't break).

http://www.youtube.com/watch?v=FGWip2F_e7M

good stuff Drak.

[Cindysphinx]

Good grief.

As promised, I went out and tried to hit the back fence before the second bounce.

First, I paced off the distance of the back fence. It was the length of 21 size 9 Gel asics, so that sounds about right.

The court itself is an old, fairly smooth green court. The fence on these courts kind of keeps going well past the doubles alley, kind of bending away. Meaning that any serve hit to the corners has a very long way to travel before making it to the fence. There are two courts; the net on one of them is screwed up and is too high.

OK. I set up my hopper on the court with the too-high net because it was in the shade. After hitting some warm-up serves, I knew I was in deep trouble with this experiment. Most of my initial serves went into the net, probably because I was trying to hit them so hard and because the net was too high.

Of major concern was the fact that none of the serves that did go in were coming anywhere close to hitting the fence. Indeed, they seemed to be doing the opposite: staying very low.

I started troubleshooting. I changed my grip to be more Eastern FH. Nope. Grip change past Continental. Nope. More knee bend. Higher toss. Lower toss. Different toss location. More weight transfer. More slice. Serve from a singles position. Serve from a doubles position. Nope, nope, nope. Even balls that sailed well past the service line sometimes didn't make the fence on the second bounce.

Then I wondered if it could be the balls, because many of my hopper balls are ancient. I grabbed some newer balls out of my bag and opened a new can of balls, so now I was enduring the frustration of serving with just eight balls. I went over to the other court with the correct net and the blazing sun and tried again.

Oh, I was so close! I didn't count a ball as successful unless I was 100% certain it was in and I was certain the second bounce hadn't hit the ground first. Many balls were too close to be sure. I continued tinkering. I kept this up for just over an hour.

Finally, I isolated the variable that made the most difference: Focusing mostly on the racket drop, which produced a higher-bouncing ball.

I was just about to give up when *finally* one ball from the deuce court hit the T, kicked up and hit the fence.

I have two reactions.

First, I am not sure that this little experiment means I have a terrible, 33 mph serve. I hit a lot of serves today that I would be happy to serve on triple match point down against 4.0 players. Many would have produced poachable balls or defensive replies. Many of my balls had so much slice that they would cause geometry to work against me, especially if I was serving toward those deep fence corners. Or I would really nail one, but it wouldn't go down the T and instead would go well wide. Or they were the low skidding type that many opponents find difficult to attack.

Second, the exercise was valuable because I really got a chance to focus on exactly what my ball was doing and why. Usually, I practice either form (to fix some problem I have been having), or I work on placement.

So yes. I guess I can now say that I served a ball that hit the back wall before the second bounce. Someday I will decide if it was worth all the trouble.

[pabletion]

Originally Posted by 5263

(An Andy Roddick's 140mph serve...) It would cross the net in the 100-105 range and
be in the 8o range just after the bounce.

just guess in around 90 just before the bounce, as that is a short distance from the net.

Can someone proove this mathematically? Im sure some one in this forum has it. Somehow, a drop from 140mph to 90 before it touches the surface seems too much. Appreciate it!

[5263]

Originally Posted by pabletion

Can someone proove this mathematically? Im sure some one in this forum has it. Somehow, a drop from 140mph to 90 before it touches the surface seems too much. Appreciate it!

try checking this link and see what you think.

http://www.popularmechanics.com/outd...10.html?page=5

IMO it would suggest that Draks numbers were off far more than 5-7mph, that vid measurements came up with.
Not sure what the vid error introduced would be, but I'm sure MIke is. Frame count can be off, distance can be off, math error, etc.... plus there is the built in margin for error as well.
Maybe Mike can comment on his experience with this.

[5263]

Originally Posted by drakulie

Guys, the speed trac measures speed in an area in front of it. In other words, if it is placed directly on the net, it will pick up the speed of the ball as it approaches the net>> Not directly at the net.

Yes, ....but too not far out unless they have improved newer machines. It used to be out only about < 12'.
Do you have numbers for your radar's pick up area?
yes it will get you walking up from farther, but you are a big target and slow. The ball is very small, fast, and slowing quickly, all of which is a big challenge for the radar.

Your 82 on the receivers svc line should be well over 100 off the racket face.
Are you saying that it would only be an 87?

[Mike Cottrill]

Originally Posted by 5263

Not sure what the vid error introduced would be, but I'm sure MIke is. Frame count can be off, distance can be off, math error, etc.... plus there is the built in margin for error as well.
Maybe Mike can comment on his experience with this.

For best results to get max velocity from a radar gun, see this:
http://www.astroproducts.net/PDF/Sports_Radar/Tennis_Position_Instructions.pdf
If all your concerned with is consistency, then just place the radar gun in the same spot all the time.
Speed Cal and Video:
The main assumptions for the derivation of the formula for the speed calc:

1. The motion of the ball after the hit is only affected by the drag force of the air alone, which is assumed to be proportional to the square of the velocity. There is the obvious force of gravity, but being a vertical force, it doesn't significantly affect the calculation.
2. A V0 mph serve slows down to Vf mph over S feet. We need these numbers from some external source such as this website reporting a study done on Sampras' serve

From Video:
Example:
http://www.donthireddy.us/tennis/RoddickExample.html

The largest source of error is calculating the distance the ball travels from frame to ball contact and ball to surface contact.

From the example in the above link:
Here are speed readings with slightly different distance readings:

• 58.84’ == 139.04mph
• 58.50’ == 138.10mph
• 58.25’ == 137.41mph
• 58.00’ == 136.73mph

Notice the difference between 58.84’ and 58.50’ is only 4”.

That is why I suggested to J to use powder and string measuring from ground contact and where he made contact with the ball (that includes tying the sting to the face of the racquet and holding it up to were ball contact was made) to get an accurate distance measurement.

If the video is shot at 120/240 frames/fields per second or higher, the contact error times are not significant. At 30 or 60 frames/fields per second, the error goes up. The majority of the time, at slower frame rates the camera will not capture the impacts.

IMO, if a high frame rate is used and the distance is measured at the court, this will provide a more accurate max velocity reading than a radar gun; including what the ATP uses. I would like to see more data shared on shot spot. They should be able to calculate velocities from the footage they take.

[5263]

Originally Posted by Mike Cottrill

IMO, if a high frame rate is used and the distance is measured at the court, this will provide a more accurate max velocity reading than a radar gun; including what the ATP uses. I would like to see more data shared on shot spot. They should be able to calculate velocities from the footage they take.

Great stuff Mike.
and nice link on that radar set up.

I've seen some stuff by hawk-eye but can't seem to find it again. They are able to pull speeds all along the flight of the ball.

I don't want to act like everyone is serving 155 mph out there, but there is this idea that a club player can't possibly hit 135, cause some pros don't do that, and that's just wrong.

Club players can often hit as big or bigger than many pro do in matches.
( sort of like how drive contest in golf hit longer than tour players.)
Club players don't have to hit their spots.
Club players don't have to win. (many of the bigger club servers I've known were not that tough to beat)
If pros don't win, you never hear about them long, no matter how fast they serve.
Club players don't often have a great all around game and can excel on focusing on the serve.
Club players have often been pitchers and QBs (or even tennis and volleyball) in early years.

I usually play with pretty good players, so I see lots of good serves. I also see lots of very avg serves and tons in-between.
I guess I'm just a glass half full kind of guy. I tend to focus on what CAN be done opposed to what is just some kind of average.
I believe you go where your focus is.

[drakulie]

Originally Posted by 5263

Yes, ....but too not far out unless they have improved newer machines. It used to be out only about < 12'.
Do you have numbers for your radar's pick up area?
yes it will get you walking up from farther, but you are a big target and slow. The ball is very small, fast, and slowing quickly, all of which is a big challenge for the radar.

Your 82 on the receivers svc line should be well over 100 off the racket face.
Are you saying that it would only be an 87?

No!! LOL. Sorry if I confused you.

The speed trac picks up the speed of the ball as it approaches the radar. Therefore, wherever you put it, there is a zone in front of it (can't remember off hand the measurement) where it will pick up the speed. I believe it is somewhere in the 10-15 foot range????

So, lets say I put the speed trac on the opposite baseline, which is 78 feet away from the baseline I'm serving from..... By the time the ball reaches about 10-15 feet in front of the radar, it will pick up the speed the ball is traveling at that point>>>> not the speed when it left the racquet, nor when it crossed the baseline.

1. My serve video where I hit a 108 mph serve, the radar was in front of the net facing me. So, it picked up the serve (108 mph) as it approached the radar. However, when Mike/Mav looked at the video and put in their formula, they concluded my serve was 5-7??? mph faster (at contact), than what the radar provided.

2. In this video, http://www.youtube.com/watch?v=uvs1-q9ip5E, the radar was placed on the other side of the net, and much further than my video with the 108 mph serve. As you could see, it registers a 92 mph ball approaching it. In this video: http://www.youtube.com/watch?v=OjBOV9zsrps, it resgisters the ball approaching it at 98 mph. However, being that the radar was further away from the contact point, explains why the ball was traveling slower than when I put the radar in front of the net, like in my 108 mph video.

3. In this video: http://www.youtube.com/watch?v=Uo4bk...eature=related, I placed the radar directly on the baseline, and it register a ball approaching it at 79 mph. Again, the speed seen here, is more likely the speed as it approached the opposite service line.

4. Lastly, the video seen here: http://www.youtube.com/watch?v=LKLUE...eature=related, on the back fence, which is 23 feet away from the baseline, resgisters the ball approaching at 43 mph, and most likely is the speed as it approached the baseline, not when it reached the fence.


Hope this all made sense.

[WildVolley]

Originally Posted by 5263

Great stuff Mike.

I've seen some stuff by hawk-eye but can't seem to find it again. They are able to pull speeds all along the flight of the ball.

Sometimes they animate a ball path (I think they call it shot tracker) and give a mph reading.

One of the most exciting things about shot spot is that it should allow detailed statistics on the professional game to be developed.

[Mike Cottrill]

Originally Posted by WildVolley

Sometimes they animate a ball path (I think they call it shot tracker) and give a mph reading.

One of the most exciting things about shot spot is that it should allow detailed statistics on the professional game to be developed.

Last few times I have seen Roddick on TV, it looks like he does not believe the machines..

[drakulie]

Originally Posted by Mike Cottrill

Last few times I have seen Roddick on TV, it looks like he does not believe the machines..

perhaps he should submit a video here at TW, in the 100 mph club thread, and have us take a look at it?

[5263]

Originally Posted by WildVolley

Sometimes they animate a ball path (I think they call it shot tracker) and give a mph reading.

One of the most exciting things about shot spot is that it should allow detailed statistics on the professional game to be developed.

I agree totally.

Drak,
So you agree your serves are in the 115 range, which would have been my estimate based on your different placement areas. right?

[drakulie]

^^^around that speed range. yes.

If I remember correctly, I actually hit a few the radar registered at 111-113, however, when I recorded the video, those serves were out, so I didn't include them.