49 lines
1.9 KiB
Markdown
49 lines
1.9 KiB
Markdown
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# tacho
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Get the current number of degress of rotation.
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```sig
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motors.largeA.tacho()
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```
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The motors that come with your @boardname@ have a way to detect their own turning motion. They count the amount of motor rotation in degrees. The motor will count each degree of angle rotation up to 360 degrees for a full rotation. As the motor continues to turn, the _tacho_ count keeps adding up the degrees even past one full rotation. So, if the motor makes 3 complete rotations, the count will be 1080.
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The name _tacho_ comes from the first part of the word [tachometer](https://en.wikipedia.org/wiki/Tachometer) which is a device to measure how fast something is turning. The motor controller in the brick uses the tacho count to regulate the motor's speed.
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## ~hint
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**Measure RPM**
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A standard way to know how fast a motor is turning is by measuring its _revolutions per minute_ (rpm). One revolution is the same thing as a rotation, or one turn. How do you measure rpm? Well, here's a simple way:
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1. Record the current tacho count
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2. Run the motor for 60 seconds
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3. Get the tacho count again
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4. Subtract the first tacho count from the second one
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5. Divide that number by `360`
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## ~
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## Returns
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* a [number](/types/number) which is the total count of degrees of rotation that the motor has turned since it was first started or reset.
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## Example
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Run the motor connected to port **A** at half speed for 5 seconds. Display the number of full rotations on the screen.
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```blocks
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motors.largeA.setSpeed(50)
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loops.pause(5000)
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motors.largeA.stop()
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brick.showString("Motor rotations:", 1)
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brick.showNumber(motors.largeA.tacho() / 360, 3)
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motors.largeA.setSpeed(50)
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```
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## See also
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[angle](/reference/motors/motor/tacho), [speed](/reference/motors/motor/speed),
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[set regulated](/reference/motors/motor/set-regulated),
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[reset](/reference/motors/motor/reset), [clear counts](/reference/motors/motor/clear-counts)
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