Arduino Servo Libary, how many usec are 1 degree

Using Arduino Motors, Mechanics, Power and CNC
#1

Hi,

does anybody know, how many microsecond correlate with one degree? I just know, that 90 degree correlate with 1500 ms. But what correlate with 180 or 0 degree? I am interested in the data of the servo libary, not in the data of any servo.

Thanks for your help

Robert

#2

1000 microsec are 0 degree 2000 microsec are 180 degree

so 1000ms/180 =5,6 ms/degree

#3

Thanks you, that means, if I am working with a servo, where 0 degree are equal 600us and 180 degrees are equal 2400us I should work with us and not with degrees?

Robert

#4

yes writeMicroseconds()

instead of write()

#5

It probably depends on the particular servo you are using. Some servo may have an almost 2000us range of operation.

#6

Hi, You can learn a great deal very quickly by opening the library files and having a look around, in my case the libraries files are here -

C:\arduino-1.0-windows\arduino-1.0\libraries\Servo

Inside the directory you will generally find a .h file and a .cpp file, these are the source code files used to build the library.

Inside servo.h you will find the following limits have been set -

define MIN_PULSE_WIDTH 544 // the shortest pulse sent to a servo

define MAX_PULSE_WIDTH 2400 // the longest pulse sent to a servo

You could adjust these to give a wider range, but I would assume these are provided by the library creators to prevent damage to the vast majority of servos.

Inside the write function in servo.cpp you will find

value = map(value, 0, 180, SERVO_MIN(), SERVO_MAX());

So the range 0,180 is mapped to 544 to 2400 microseconds (unless you specifically set some other limits) which gives 10.31 uS per degree. I may have missed something so feel free to check and correct.

Duane B.

rcarduino.blogspot.com

#7

Using a bamboo skewer like below as a pointer to detect small movements, I've found that a standard servo has a ~5us dead band between discrete movements. That equates to only ~425 discrete positions in ~190 deg rotation.

#8

Hi Zoomkat,

Thats interesting and going slightly off topic, another reason why trying to measure an RC input to sub uS accuracy is something of a waste of time.

The other reason is this -

http://1.bp.blogspot.com/-Zi6qBbVC1WY/Tx2WLRS3jlI/AAAAAAAAAOA/i3sAqVLflvk/s1600/near.PNG

In my observation, the input signal varies by 40us for a constant input signal, the variation increases with distance and the nature of the built up environment around the transmitter receiver.

http://rcarduino.blogspot.com/2012/01/how-to-read-rc-receiver-with_20.html

Duane B.

#9