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# How to measure rpm

Category: Electronics & Technics

## rpm measurement

Difficulty: ★☆☆☆☆

Time: Less than 10 minutes

From scrap: ░░░░░░░░░░ 0%

Preamble

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.

Materials

• Motor
• Duct tape
Tools

• 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.

• Step 2

Do this as many times as needed

• Step 3

• Step 4

Plug a mic, press REC

• Step 5

Connect the motor to a source of electricity

• 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

• Step 7

Press stop

• 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"

• 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:

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

Results and tips

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

1. <
##### fff

6 November 2015 01:45

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

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!
0