# Measuring rotational speed

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1. Mar 25, 2015

### Kariege

I'm planning on carrying out an investigation with a golf ball and projectiles. Is there any type of equipment/sensor that I can used to measure the rotational speed/angular velocity? I know a gun chronograph can be used to detect the velocity but what can I used to detect the angular velocity?

2. Mar 25, 2015

### Doug Huffman

High speed video of optical properties - like a unique mark.

3. Mar 25, 2015

### Quantum Defect

Something like a strobe/tachometer could work, but it might be tricky to do for a small moving object.

4. Mar 25, 2015

### Doug Huffman

Typical golf ball game speeds are 130 kph

5. Mar 25, 2015

### Kariege

I saw a non-contact laser tachometer. Is it able to detect the rotational speed instantaneously when the golf ball passes the laser? Or do I have to hold the laser into the moving golf ball for a period of time before it can detect the rotational speed?

Thanks

6. Mar 25, 2015

### Quantum Defect

I think that this will be difficult to do with something designed for working on cars. The ones I saw required affixing reflective material on the object -- I suspect that they are simply measuring the flashes of reflective light as a function of time to come up with the angular velocity.

With the golf ball, as @Doug Huffman noted, you have something small moving very rapidly across the field of view, possibly rotating around more than one axis, so the chances of having the relective bit come back into the frame is unlikely.

I suspect that fast video (as Doug noted) will work the best. I don't know what kind of equipment that the "Super Slo Mo Guys" use, but something along those lines might be able to track the rotational velocity as the golf ball leaves the tee.

7. Mar 25, 2015

### Kariege

I understand but here I think I'm just examining from a 2 dimensional view. So particularly I will look at backspin. But can I just hold the tachometer and point the laser to the ball and it's track? Can it detect the rotational speed in that way? I've seen the high speed video, they seem very pricy since the video camera should be around 1000fps, so I'm just trying to look for an alternative.

8. Mar 25, 2015

### A.T.

Some consumer cameras for ~300\$ can shot at 400-1200fps which should be enough for a golf ball. The resolution is low, but if you know exactly where the ball is, you can place the camera close enough to see the marks. You just need to catch the ball on two frames. Checkout the Nikon 1 for example, maybe some friends have it.

9. Mar 25, 2015

### Kariege

Ok I'll probably go out and ask for a camera rental then. Thanks everyone

10. Mar 26, 2015

### A.T.

These clips were shot with the Nikon 1 J1, so you know what to expect. Note that youtube re-encodes them, the original quality is somewhat better.

400FPS:

1200FPS:

11. Mar 26, 2015

### Kariege

nice, the 1200 fps looks just right with a sufficient resolution. First I thought it will be difficult with a 320x340 video. I'll go ask my friends if they have these kinds of camera with high speed capture soon.
Thanks a lot!

12. Mar 26, 2015

### A.T.

I would paint half of the golf ball black, to get the best 1D rotation reference. Also use as much light as possible, ideally direct sunlight.

Last edited: Mar 26, 2015
13. Mar 26, 2015