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Topic: How many SERVOS are possible with the ARDUINO? (Read 940 times) previous topic - next topic

Scored Bytes

Jun 10, 2006, 07:04 am Last Edit: Jun 10, 2006, 10:23 pm by Scored_Bytes Reason: 1
Hi there!

I´m workin´ on a project with the Arduino...and i´ve to control, i mean, six servos should move at the same time when i press a key(over serial send via Processing)...My problem is that five servos seem to be the magic border. When i write the code for six servos, none of the servos move. And the problem is not the Bytesize of the Program, its only 61...somethin´.

So my Question is how many SERVOS can i put on the ARDUINO? At the moment the are plugged at 5V.  Is that the problem? Or is more than 5 Servos impossible?

Perfect would be 11 Servos...

So i hope to find Answers

Thanks so far

sb

fritz

have you tested your script without the servos connected? Probably you've reached the maximum power level... how much mA do your servos need?

Peripheral_Hacker


P18F4550

In theory 12 but that would not be very effective, 9 is a more realistic number to get them to move smoothly, they need to be updated every 18ms, the pwm mark space is between .5ms and 2.5ms, center position being 1.5ms, so if we say the upper setting will be 2ms it's 18 / 2 = 9 servos, to get full swing 7 servos, i think this is how it's worked out, i've certainly had 7 servo's running on a pic before

donkahones

Are you signaling all of the servos from one pin or do they all have a dedicated signaling pin?

mem

I  run 12 Servos on a standard Arduino without problem, but they do need a separate power supply.

How are you connecting and powering the servos?

I posted a simple servo test sketch in this thread: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1268620031/3#3

You can use that sketch to command an individual servo or all servos.

mem

#6
Apr 21, 2010, 07:40 pm Last Edit: Apr 21, 2010, 07:41 pm by mem Reason: 1
Quote
9 is a more realistic number to get them to move smoothly, [glow]they need to be updated every 18ms [/glow]

P18F4550,  what is the basis for that statement?
I would be surprised if you could see any difference in movement between running 9 or 12 servos.

It is true that the servos may have a little less torque in the unlikely event that all 12 are being driven with 2ms pulses, but I have not seen any loss of smoothness of movement when 12 servos are driven.
have you?
 

P18F4550

mem,
i mean in movement, if they are stationary no there is no difference but if they are not updated every 18ms they get jittery, really it depends on the users individual code

mem

Quote
if they are not updated every 18ms they get jittery

That's not been my experience.

You can test this by changing the servo library so that all servos have a refresh period of 24  milliseconds and see if you can detect any more jitter or change in performance with the servos.

To do this, change the following constant in Servo.h to 24000
#define REFRESH_INTERVAL    20000

I would be interested to hear if you can detect a significant  difference.

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