is there any way I can measure my RPM?

Standaa

G.O.A.T.
I hit with a lot more topspin than the average player, so I wanted to see how much more the top pros have and compare it

also, do they get more spin on the ball simply because the hit harder?
 

jmnk

Hall of Fame
I hit with a lot more topspin than the average player, so I wanted to see how much more the top pros have and compare it

also, do they get more spin on the ball simply because the hit harder?
If you do not know how to measure RPM how do you know that you "hit with a lot more topspin than the average player"? And who is "average player"?
 

Chas Tennis

G.O.A.T.
If you view a ball as it goes away from the camera with a longer focal length lens you can see the print on the ball rotate. For example, view a served ball or forehand from behind. A smart phone with a wide angle lens may not work as well. ? You need one full rotation and some more to make sure you are seeing a rotation. 3600 RPM is 60 revolutions per second.

For this serve, I could see 4 ball rotations on my computer. The ball print on the Vimeo image was not as clear after Vimeo compression processing as the original video on my computer. Video in bright sunlight so that the camera's automatic exposure control will select a fast shutter speed and there will be less motion blur. With the ball going mostly away from the camera that also greatly reduces the amount of motion blur on the ball print. The camera is viewing along the ball's trajectory.

To do stop action hold the SHIFT KEY and press the ARROW KEYS. The print does not show well on this processed Vimeo video.
"High speed video close-up of a kick serve from a club player with a stronger serve. At 240 fps the lettering on the ball can be seen to rotate once every 4 frames. The spin rate is 60 rps or 3600 rpm."

In addition, you can mark up balls with a sharpie to make the marks show up better.
 
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SystemicAnomaly

Talk Tennis Guru
If you do not know how to measure RPM how do you know that you "hit with a lot more topspin than the average player"? And who is "average player"?
No doubt from observations of people he has played with and of other rec players he's seen. Don't necessarily need to actually measure RPM to conclude that you are hitting with a lot more topspin.
 

SystemicAnomaly

Talk Tennis Guru
after u hit the ball, look at it real hard and count how many times it spins in a second. this gives u rpm
Only if you multiply your count by 60. I prefer to count the total revolutions for a full minute. That way I don't need to do any math.

For greater precision, I will sometimes count how many times the ball spins in a full hour and then divide my count by 60.
 

Chas Tennis

G.O.A.T.
You observe one revolution (the print on the ball comes around and re-appears in the same spot one time). You count the number of frames necessary for that one revolution. (You probably will have to estimate a fraction of a revolution. For example, the ball rotated 1.1 revolutions in 4 frames.)

In the video of post #6, I showed the print came around to the same spot in 4 frames. (It does not show well in the Vimero compressed image, but the original shows the print). The frame rate was 240 fr/sec. The time between frames is 1/240 sec/fr.

Observation: the ball rotated one revolution in 4 frames or 1/60 sec
4 fr X 1/240 sec/fr = 4/240 sec
= 1/60 sec

In one second, the ball would have rotated 60 revolutions.

In one minute, the ball would have rotated 60 sec/min X 60 revolutions/sec = 3600 RPM.

Basically, the video camera records the location of objects in two or more frames. You can use those locations to indicate ball speed or spin rate. Spin rate is easier because you don't have to calibration the length scale. You just count frames for a given number of ball rotations.

To think about this hold a tennis ball in front of you and observe how the print looks as you move the ball away and the ball rotates.
 
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Chas Tennis

G.O.A.T.
Here is a more scientific effort to measure and discuss the spinning tennis ball. There may be another article by Cross for measuring ball spin somewhere.

Rod Cross article in the Tennis Warehouse learning center.

Note- if the ball goes away from the camera, as I described, the rolling shutter distortions won't be present because the ball does not move very fast in the frame of the camera.

More Tennis Warehouse articles.
 
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Chas Tennis

G.O.A.T.
To measure ball speed use the "undisputable method" - measure the time to travel a given distance. View in Youtube to hear sound.

I found the video interesting.
 
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