When the frame rate of a video matches the speed of a particular part, the effect is the same as using a strobe light. In the video, that part freezes.
Since the frame rate of a video can be adjusted, this effect can be used to determine the rotational speed of a part.
The smartphone must support slow-motion video recording (filming at a high frame rate). This is the case for all smartphones starting with iPhone 5S. The range is as follows:
• 0.5—240 Hz (30—14400 RPM), for all phones from iPhone 6 onward
• 0.5—120 Hz (30—7200 RPM), for iPhone 5S
THE HERTZ (Hz) VALUE IS MORE ACCURATE THAN THE REVOLUTIONS PER MINUTE (RPM) VALUE, SINCE REVOLUTIONS PER MINUTE ARE CALCULATED FROM HERTZ AND ROUNDING IS DONE.
To get a clear image, good lighting is important. The clarity of the image is controlled by the exposure of the video (exposure time and light sensitivity (ISO)). If the exposure time is reduced, the image will increase in clarity, but brightness will lower. To increase the brightness, you need to raise the camera's light sensitivity (ISO), but then the amount of noise increases. You also need to manually adjust the focus of the camera.
Videos can be captured using the iOS "Screen Recording" function.
It is possible to choose a video format that has the best quality, but has a significantly lower maximum frame rate. The difference between the formats is clearly visible only when using the digital zoom. Also, when using a format with better quality, the Rolling Shutter effect is stronger. Therefore, the best quality format can be used at speeds less than about 1000 rpm.
You can turn on hints for easier observation of changes in rotation speed. Hints show how to change the frame rate (decrease or increase) depending on the direction of rotation of the mark. The hints are selected manually, but then you do not need to remember this information. The hints are relevant for frequencies close to the rotation frequency. If the direction of rotation of the impeller is known, hints can be selected in advance. The arrow showing the direction of rotation of the impeller must correspond to the "+" button.
The video tachometer measures the rotational speed in exactly the same way a stroboscopic tachometer would.
• Minor changes in text design.
Ratings and Reviews
Doesn’t Use / Damage Flaslight
The explanation (by the developer) is pretty geeky, but the the idea is sound, and works!! (Note: the iPhone flashlight seems fairly durable, but one of the other actual strobes burned out a reviewer’s phone flashlight, which is the only camera flash!)
So: no use of flashlight except nice and steady light, as designed, to illuminate the rotating object.
Works and easy to use
The only good general purpose RPM measurement application I was able to use without any hassle.
Be careful as half the RPM and 2X can give the illusion of video frequency match. You’ll have to pay to measure in single digit accuracy.
We used it to check the tachometer in our airplane. It worked great. Found the tachometer needs recalibrated.
Developer Response ,
Thank you for your feedback!
You've probably seen my videos of helicopter. It would be nice to have similar videos of airplanes.
It would be great if you could make a video recording of the screen during the measurements and send the video to me. But after calibrating the tachometer :)
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- Dmitriy Kharutskiy
- 8.5 MB
- Requires iOS 10.0 or later.
- iPod touch
- Requires iOS 10.0 or later.
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- © 2019 Dmitriy Kharutskiy
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