Why I Don't Trust The Speed Calculator


Here is the original video (HD) from when I was practicing raising my toss arm. As you can clearly see, the above is moderately gentle and there's more in the tank, also demonstrated by the fact the ball starts dropping into a standard 21" fence.

Out of curiosity I decided to check the speed serve calculator, because the serve felt good and it was right in the corner of the box .. almost! Magnified stills to come soon. I would like opinions using the speed calculator, for those willing to take the time. If you want to be more accurate and like risks, here is the full HD version:

Calculator: https://donthireddy.us/tennis/speed.html

I will post my results shortly, along with all stills featuring frame numbers and ball court contact positioning. I don't personally think it's as fast as the #'s I'm getting, hence my question.

Edit: I currently have a meniscus knee injury so really big leg drive is out for a while I'm afraid.
 
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Here are the stills:

Contact with court is actually about a ball wide and maybe a ball long (in this frame the ball is *about* to make contact with the ground).



Contact:


One frame after contact.


Ball court contact (the still above uses this frame):


One frame after court contact:
 

5263

G.O.A.T.
So nice serve around 100+mph. Not sure if in. What’s your question?
I think he is surprised the serve is that fast. Good rec servers don't realize they can often hit in the 100 range and the avg radar set up tends to bolster the idea everyone serves slower than they actually do. Radar is hard to set up for the fastest reading, making rec players feel slower. We also tend to think of our avg radar speed vs the top speed we see from tour Pros, which widens the gap even further in our minds. Granted, most pros serve significantly faster than most rec players, but not as much as most people think.....and some rec player can hit speeds right up there with the top pros....Sure it's rare, but it does happen.
 

ChaelAZ

Legend
I think he is surprised the serve is that fast. Good rec servers don't realize they can often hit in the 100 range and the avg radar set up tends to bolster the idea everyone serves slower than they actually do. Radar is hard to set up for the fastest reading, making rec players feel slower. We also tend to think of our avg radar speed vs the top speed we see from tour Pros, which widens the gap even further in our minds. Granted, most pros serve significantly faster than most rec players, but not as much as most people think.....and some rec player can hit speeds right up there with the top pros....Sure it's rare, but it does happen.

Agree. Looking at video serves seem a lot slower anyway, but I also think people put a 100 mph serve on a high pedestal, but many rec players can hit that mark. One thing for me though, I have used the video calculator and it always seems around 5 or so mph fast compared to my radar gun. Was just thinking about it and I will see if I can get out and shoot video with the radar and then we can use the video calc to see how close it can get. I think because I shoot higher fps (60 up to 240) I can get more accuracy. As @Digital Atheist mentions, shooting only 30fps, you don't have exact contact and bounce data like you would with the higher fps. That ceratinly make a huge difference. An example is if you set the video caculator to 30 fps and enter 14, you have a 103 mph serve. If you are actually off by just one frame and it is really 15, you are at 95 mph. In the same example, if you set the fps to 60 and enter 28 you are at a 103 mph serve, but at 29 you are at 99 mph. An so on at 120 fps, 56 is 102 mph and then 57 is 101 mph. So 30 fps frame measure leaves a bit to be desired. I mean general serving from 95 to 100 is still great no matter what the specifics, but there is a difference and one frame can be almost 10mph.

Anyway, it is a good serve in any case.
 
@Dragy: serve is definitely fractionally out. My question was seeking estimates on speed from others to compare with my own, since it seems to me the calculator is inflating the speed somewhat, even with very conservative input values.

I think he is surprised the serve is that fast.
Yes, this.

As @Digital Atheist mentions, shooting only 30fps, you don't have exact contact and bounce data like you would with the higher fps. That ceratinly make a huge difference.
I've made what I think are some very conservative estimations to allow for this and the output is still high.

Here are the numbers:
Edit: Frame 73 above is just prior to contact, so starting total frame count at that point gives a safe margin. Using frame advance and the court contact image above shows just how close the ball is to the ground, so I added another +0.3, and I think that is more than generous.

********************************

Total Frames @30fps = 13.3 (13.5)
Distance travelled = 59.7 feet (since the ball is a tickle long and the T is 60 feet but I don't land much inside the court, this also seems safe)
Initial speed = 108 (106.6) mph.

So the speed calculator gives 106mph using 13.5 frames and less than 60" travelled - very conservative input values - but somehow I think it's more like 101-102mph.

One thing for me though, I have used the video calculator and it always seems around 5 or so mph fast compared to my radar gun.
That seems to fit, I'm getting about 5 or 6 over what I thought it was. One day I will have to get a couple recorded with 95% effort and compare.

On a side note I'm curious what people think.
1. Do I still have a traditional trophy pause?
2. How far does the toss drop from peak height to contact? When I frame advance and compare, it's way more than it looks in the video.
 
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Demented

Rookie
I've used frame capture on my HD camera and a Playsight court at the same time. The video cap works just fine and lines up with Playsight. I'm not all that tall, 5'9 with fairly short arms and I can routinely serve at 102 with just my normal motion. The biggest my arm will support@age 36 is ~109-110. I think just about anyone with a good baseball style fluid motion can hit the 90's. I've tested some other various stuff before as well. With just my wrist/forearm/elbow driving the racket over my head(my arm is extended straight up while I toss it), I can flick the ball 78 mph. So the entire shoulder rotation, tricep extension and leg drive only adds 22 mph to my base power coming out of my forearm.
 
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