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How to measure rpm

Category: Electronics & Technics

How to measure rpm

rpm measurement

difficultyDifficulty: ★☆☆☆☆

timeTime: Less than 10 minutes

ScrapFrom scrap: ░░░░░░░░░░ 0%


One day before my next project I dumped on the table all of my motors and realized that I can not "approximately" choose from the fastest of them. After thinking for a few minutes, I found a great way to do this without the use of any special tools.


  • Motor
  • Duct tape

  • Computer
  • Microphone
  • Scissors

    How to measure rpm of a motor

  • Step 1

    Stick strip of tape length of about 10 mm to the spindle motor: wrap around the spindle 1 times and glue duct tape to itself.
    How to measure rpm

  • Step 2

    Do this as many times as needed
    How to measure rpm

  • Step 3

    Download and install Audacity, here is a link to sourceforge
    How to measure rpm

  • Step 4

    Plug a mic, press REC
    How to measure rpm

  • Step 5

    Connect the motor to a source of electricity
    How to measure rpm

  • Step 6

    Start the engine, bring a small distance to the microphone and a little trample rotating tape by finger to make a loud buzzing sound
    How to measure rpm

  • Step 7

    Press stop
    How to measure rpm

  • Step 8

    Where the chart has big crests, click, hold down the Ctrl key and spin the mouse wheel to zoom the chart.
    The chart clearly visible oscillation periods. Yes, it is the individual elements of what we heard "z-z-z-z-z-z"

  • Step 9

    Highlight one period, focusing on any element. I chose a lower peak.
    Tick "Duration"

    How to measure rpm

  • Step 10

    Analysis. Duration - the time (in seconds) for which the engine makes one turn. To find the rpm, it is necessary to divide 60 on duration, in other words:
    How to measure rpm

    And yet I know that this motor with this power supply produces 6000 rpm =)

ResultsResults and tips

  • I believe that this method is accurate enough
  • If the engine itself is noisy, it may complicate the task
(голосов: 1)

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  1. <

    6 November 2015 01:45

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    проще попросить аудасити построить спектр и навести курсор на пик
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  2. <

    24 January 2016 07:14

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    Thought you may be interested in the accuracy of your method. Tested a mabuchi RS-545SH. Mabuchi has an interactive app to model their motors. Here are the results:
    Voltage Mubuchi specs Audacity Results
    6V 2690 rpm 2650
    7V 3190 rpm 3157
    8V 3690 rpm 3529
    9V 4200 rpm 4090

    Pretty accurate!
    Dislike 0 Like